I TA L I A N H A B I TAT S
Mountain peat bogs
9
Italian habitats
Italian Ministry of the Environment and Territory Protection / Ministero dell’Ambiente e della Tutela del Territorio
Friuli Museum of Natural History / Museo Friulano di Storia Naturale · Comune di Udine
I TA L I A N H A B I TAT S
Scientific coordinators
Alessandro Minelli · Sandro Ruffo · Fabio Stoch
Editorial committee
Aldo Cosentino · Alessandro La Posta · Carlo Morandini · Giuseppe Muscio
"Mountain peat bogs · Relicts of biodiversity in acid waters"
edited by Alessandro Minelli
Texts
Francesco Bracco · Augusto Gentilli · Alessandro Minelli · Margherita Solari · F abio Stoch · Roberto
Venanzoni
English translation
Alison Garside · Gabriel Walton
Illustrations
Roberto Zanella
Graphic design
Furio Colman
Photographs
Nevio Agostini 134 · Archive of Museo Friulano di Storia Naturale 17/2, 36, 46, 52/3, 139 · Archive of
Museo Friulano di Storia Naturale (Maria M. Giovannelli) 74/1, 74/2, 77, 126/2 · Archive of Museo Friulano
di Storia Naturale (Gianfranco Tomasin) 78/1, 78/2, 81 · Archive of Museo Friulano di Storia Naturale
(Ettore Tomasi) 10, 15, 31/1, 31/2, 37/1, 50/2, 51, 52/1, 52/2, 53/1, 53/2, 115, 124, 126/1, 127, 129/1,
129/2, 133, 138 · Mauro Arzillo,16, 101 · Stefano Bossi 82, 83 · Paolo Fontana 72 · Claudio Furlan 86, 87 ·
Luca Lapini 90, 91, 92, 95, 97, 98, 99, 100, 107, 108, 110, 113, 143 · Giuseppe Muscio 30/3, 34, 39/2,
60, 73, 75, 102, 140, 144 · Ivo Pecile 54, 64, 85, 93, 96 · Paolo Paolucci 88, 104, 105/1, 105/2, 106/1,
106/2, 109, 111, 112 · Provincia Autonoma di Trento (Renato Perini) 19 · Roberto Parodi 103 ·
Margherita Solari 25, 43, 141, 142, 147 · Fabio Stoch 62/2, 63, 69 · Roberto Venanzoni 6, 8, 11, 13, 14,
17/1, 18, 22, 23, 24, 26, 28, 29, 30/1, 30/2, 31/3, 35, 37/2, 39/1, 41, 42, 48, 49, 50/1, 55, 114, 116, 117,
118, 121, 122, 123, 128, 132, 136, 137 · Adriano Zanetti 125 · Roberto Zucchini 44/1, 44/2, 47, 62/1, 66,
67, 70, 71, 84, 120, 145, 146
Mountain peat bogs
Relicts of biodiversity in acid waters
©2004 Museo Friulano di Storia Naturale, Udine, Italy
All rights reserved.
No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form, or
by any means, without the prior permission in writing of the publishers.
ISBN 88 88192 17 4
ISSN 1724-6539
Cover photo: Scichizza peat bog in eastern Alps (photo by G. Muscio)
M I N I S T E R O D E L L’ A M B I E N T E E D E L L A T U T E L A D E L T E R R I T O R I O
M U S E O F R I U L A N O D I S T O R I A N AT U R A L E · C O M U N E D I U D I N E
Italian habitats
Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Francesco Bracco · Roberto Venanzoni
Vegetation of peat bogs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Francesco Bracco · Roberto Venanzoni
1
Caves and
karstic
phenomena
2
Springs and
spring
watercourses
3
Woodlands
of the Po
Plain
4
Sand dunes
and beaches
5
Mountain
streams
Aquatic invertebrates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Fabio Stoch
Terrestrial invertebrates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Alessandro Minelli
Vertebrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Augusto Gentilli
6
The
Mediterranean
maquis
7
Sea cliffs and
rocky
coastlines
8
Brackish
coastal lakes
9
Mountain
peat bogs
10
Realms of
snow and ice
Conservation and management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Francesco Bracco · Fabio Stoch · Alessandro Minelli · Roberto Venanzoni
Teaching suggestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
Margherita Solari
Select bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
11
Pools,
ponds and
marshland
12
Arid
meadows
13
Rocky slopes
and screes
14
High-altitude
lakes
15
Beech
forests of the
Apennines
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
List of species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
7
Introduction
FRANCESCO BRACCO · ROBERTO VENANZONI
Peat bogs are wetland environments in areas with excess water, either near
lakes and riversides, or on flat areas and slopes over which a fine film of water
flows. The vegetation is mainly composed of hygrophilous species (sphagnum,
mosses, sedges, and grasses) which, when they die, form the organic deposit
known as peat. The term used to indicate a peat bog, in the Latin languages, is
closely related to the word peat itself, so that: its literal meaning is a place
where peat comes from or is produced. The significance refers to geologicalmineralogical characteristics, without taking into account the biological
component of this ecosystem, which is extremely interesting from the point of
view of natural history.
In the Nordic languages, in countries where peat bogs are more widespread,
the corresponding words have different roots and become moor, moos, mire,
bog, fen, etc.. These terms, with the addition of adjectives describing the
various types, are now consolidated in the scientific terminology of the sector.
ITALIAN
FRENCH
SPANISH
GERMAN
ENGLISH
TORBIERA
TOURBIÈRE
TURBERA (TRAMPAL)
MOOR
MIRE
TORBIERA ALTA
HAUT-MARAIS,
TOURBIÈRE BOMBÉE
TURBERA ALTA
TURBERA ABOMBADA
HOCHMOOR
RAISED BOG
TORBIERA BASSA
TORBIERA PIANA
BAS-MARAIS
TURBERA BAJA
TURBERA PLANA
NIEDERMOOR
FEN
TORBIERA CLIMATICA MARAIS RECOUVRANT
TURBERA CLIMÁTICA
DECKENMOOR
TURBERA DE RECUBRIMIENTO DECKEN-HOCHMOOR
BLANKET BOG
BLANKET MOSS
TORBIERA DI
TRANSIZIONE
MARAIS DE TRANSITION
TURBERA DE TRANSICIÓN
ÜBERGANGSMOOR
TRANSITION BOG
AGGALLATO
MARAIS FLOTTANT
MARAIS TREMBLANT
TURBERA FLOTANTE
SCHWINGRASEN
SCHWINGMOOR
FLOATING MAT
TREMBLING BOG
CUMULI DI SFAGNI
BUTTES À SPHAIGNES
ABOMBAMIENTO
MAMELÓN
BULTEN
HUMMOCK
In the geological or pedological sense, a peat bog is defined as an environment
in which the accumulation of peat reaches a depth of at least 30 cm;, which,
when dried, loses approximately 30% water; and which, excluding minerals,
contains 30-35% pure carbon. Peat therefore retains up to 8-9 times its dry
Basin with peat bog area on slopes of Mont Blanc (Val d’Aosta)
■ Distribution
8
Palù Marcia peat bog in Trentino
Peat bogs are typical in areas where, owing to temperate climate and specific
hydrological and edaphic factors, organic matter produced by plants (mainly
bryophytes, but also grasses, sedges and others) does not decompose but
accumulates, forming peat. This phenomenon gives rise to the natural silting
process of water basins.
In Europe, peat bogs tend to become rarer moving from north to south, and are
found on both low ground and mountains, i.e., in areas where forests generally
represent the natural plant community, in the absence of modifications by
humans (potential vegetation).
In Italy, peat bogs are mainly found in the Alps and northern Apennines, and
diminish drastically moving southwards down the peninsula, progressively
reducing to tiny sphagnum moss populations. The region with the highest
density of peat bogs in Italy is Trentino Alto Adige (South Tyrol) (an autonomous
weight in water; and, with its considerable organic matter content, it has a high
calorific value when dried of between 3,000 and 5,000 Kcal/kg.
A peat bog is considered “active” if peat accumulation is ongoing, and “dead”
if this process has been interrupted.
The floral species and quite highly specialised types of vegetation types
present (bio-indicators) allow the various types of peat bog to be classified
according to their ecological and genetic characteristics, without the need to
use the complex system of classification which involves detailed chemical and
stratigraphical analyses.
For the natural - and therefore conservation - aspects discussed in this volume,
the concept of peat bog refers to the geo-botanical rather than the geopedological sense. In fact, in defining these habitats, EEC Directive 92/43
makes reference to precise terms deriving from the characterisation of their
vegetation, described according to the phytosociological method.
The environments in question are the habitats called active raised bog (habitat
7110), limestone bogs with Cladium mariscus and Carex davalliana (habitat
7210), Alpine pioneer formations of Caricion bicoloris atrofuscae (habitat 7240)
and wooded peat bogs (habitat 91D0). This book describes the natural aspects
of mountain peat bogs, although in some cases species growing in loweraltitude bogs are also mentioned.
Conventional phytosociological nomenclature is used, such as association,
alliance, etc., as well as taxonomic and systematic biology terms. Where
possible, the common names of plants are also given.
Peat bog distribution in Europe: darker areas have many; yellow areas contain none
9
10
Great fen sedge (Cladium mariscus)
region, also called the South Tyrol): in
the province of Bolzano alone, more
than 700 sites have been counted with
typical peat bogs and peaty
environments of interest to naturalists,
although. There is no lack of examples
in other Alpine regions. In these areas,
peat bogs are found from the uplands
to Alpine level, and are at their best in
Floating island formed of sphagnum in Posta
the sub-Alpine, where there are some
Fibreno lake (Latium)
rare examples of boreal pine woods
with sphagnum mosses.
Further south, many damp peaty environments are found in the Ligurian
Apennines and around Modena. The survival of the Sibolla peat bog in Tuscany
is worth mentioning - a rare example, especially considering that it developed
practically at sea level. In these regions, the type of peat bog begins to differ
from the Alpine model, and the plant communities that grow there are limited to
sphagnum moss colonies and relict communities of broad-leaved cotton grass
(Eriophorum latifolium) and Davall’s sedge (Carex davalliana), covering only a
few dozen square metres.
Proceeding even further south, in central-southern Italy, the Campotosto peat
bogs disappeared after the construction of a hydroelectric dam, but the floating
island formed of Sphagnum palustre on the lake at Posta Fibreno is worthy of
mention. The last examples of any interest are the fens in Calabria, in the Sila
and Aspromonte mountains, the existence of which is due to siliceous
substrate and high altitude.
Examples of peat bogs on the islands of Sardinia and Sicily are limited to
extremely rare sites on the Madonie and Monte Limbara. They represent the
southernmost limit of this type of mid-European vegetation, and are thus of
enormous biogeographical and biological value.
One plant typical of peat bogs is great fen sedge (Cladium mariscus). Moving
southwards, this species tends to form two types of community. The first group
retains the characteristics of mid-European peat bog phytocenoses, and is
distributed from Alpine and pre-Alpine spring belts and on the shores of the
large inland lakes in the north and central-south as far as Lake Monticchio in
Basilicata. The second group includes phytocenoses characterised by plant
species of more Mediterranean biogeographical type and moderately
halophilous (i.e., having a preference for salt), and are therefore found near
coastal lakes.
11
12
Peat formation
The essential element of a peat bog is
the green and reddish-brown carpet of
mosses and sphagnum, between a few
centimetres and several metres deep,
the bottom of which may be several
centuries old at the bottom. The blanket
of sphagnum grows on the surface,
while the underlying part dies and
accumulates, slowly forming peat.
The debris of a forest - branches, leaves,
etc. - is broken down and converted into
humus through the action of bacteria,
fungi and other decomposers. However,
the layer of living sphagnum can radically
alter the chemical characteristics of the
environment in which it grows, causing
strong acidification. Sphagnum can
absorb large numbers of cations and
release as many hydrogen ions - an
exceedingly useful characteristic in these
habitats which have few mineral
nutrients. Because of this characteristic,
sphagnum mosses have been used as
bio-purifying organisms. As peat layers
form, organic acids are also produced,
e.g., tannic acid, brown in colour. This
comes from the growth of bacteria and
is assisted by two contributory
conditions: low temperature, due to the
cool microclimate of these
environments, and abundant water,
which prevents contact between dead
organic matter and the air. The result is,
in essence, that the decomposition of
organic matter is blocked.
Over time, the deeper layer of dead
sphagnum becomes compressed
by its own weight, and no further
breakdown occurs. Instead, the surface
blanket is renewed each growing
season above the underlying dead
layers and, as a consequence, the
overall structure gradually rises.
Under the microscope, the intimate
Francesco Bracco · Roberto Venanzoni
nature of peat reveals itself as a dense
mesh of dead molecules, both large and
small, which can retain huge amounts of
water. This means that the sphagnum
layer can rise above the water-table level
and, absorbing like a sponge, can retain
water from atmospheric precipitation
over a long period, guaranteeing a water
supply to the young sphagnum plants
during their growing season.
13
■ Geomorphology
14
Peat bogs occur where various soil morphologies ensure the presence of
water - on the floor of alluvial valleys, on flat summits and plateaux, slopes
with flowing water, close to springs, etc..
The larger peat bogs are usually in valley bottoms or on the edge of lakes,
including many small lakes in cirques or morainic dykes at high altitude, and
near the lakes resulting from large-scale glacial excavations like Lake Iseo or
Lake Maggiore in the pre-Alps. They also occur in the morainic and intermorainic pools of foothill cirques.
In small lake basins, where silting by peaty vegetation on the edges is not yet
complete, a residual pool remains in the centre, called the “eye” of the peat
bog.
In many cases, especially in upland areas, localised marsh flora can be found
over extremely limited areas: enormous spaces are not necessary, and it is
often enough to stroll through the woods to find, in the small hollows
containing springs and alongside streams, delightful glades populated by
mosses forming tiny carpets and small hummocks where the main species of
the typical flora of these environments are concentrated.
Peat bog area near Madonna di Campiglio (Trentino)
Alpine tarn at Bordaglia, with peat bogs (Julian Alps, Friuli)
15
16
■ Ecology and development
Most peat bogs, on the basis of their origin and overall morphology, belong to
two main types. Peat deposits may be flattened, as in the fens (submerged or
partly submerged), the existence of which is linked to the water-table (this is
why they are also known as soligenous mires). The peaty deposit tends instead
to build a convex ridge in raised bogs, which develop above the water-table
level, are clear of groundwater and can therefore only evolve by depending on
rainwater (ombrogenous bogs).
In It is obvious that, in this case, the climate must ensure a certain continuity of
meteoric water supply. High temperatures which bring about long, dry, hot
summers are not the case here: rather, moderate temperatures which are more
favourable for plant growth, especially for sphagnum mosses. This is why peat
bogs are widespread in areas with temperate oceanic climates bordering the
Atlantic. In Italy, these particular conditions occur mainly in hilly regions and in
the pre-Alpine belt, due to the higher rainfall in the mountains and lower
temperature due to altitude.
In reality, between the two extremes of ombrogenous raised bogs and
soligenous fens, many transitional situations exist, which depend mainly on the
Mountain peat bog with cotton grass (Val Dolce, Friuli)
relationships between the influence of
the water-table and water supply from
rainfall alone, the amount of nutrients in
the water, the type of geological
substrate, and other minor factors.
A third type of peat bog also exists,
known as transitional or mosaic,
characterised by an irregular profile
and the presence, on the flooded peat
level, of many alternating hollows and
small hummocks and floating masses
of vegetation (floating meadowlands)
formed of sphagnum mosses or the
roots and rhizomes of higher plants
such as various species of sedges
(Carex), Rannoch rush (Scheuchzeria
palustris) and others.
The formation of a peat bog, either
raised or fen, or an area with marsh
vegetation, is due to two general
processes of opposite significance:
silting up, and the creation of
marshland.
Silting up involves gradual colonisation
by vegetation, which, from the edges,
progressively invades the body of
water towards the centre. Marshland
results from the colonisation of
sometimes vast, previously dry and
then flooded areas (e.g., river valleys).
Edaphic,
geomorphological
and
climatic conditions then allow the
vegetation which will form the fen,
raised, or transitional bog to develop.
There have been various attempts to
group, express and classify the
complex processes of peat bog
formation and explain them within a
single theory, and all of them must in
17
Rannoch rush (Scheuchzeria palustris)
Davall’s sedge (Carex davalliana)
18
An archaeological archive
Peat bogs can also serve as important
testimonies to the presence of man,
whose remains are as well preserved as
plant debris. The peculiar environmental
conditions favour the preservation of all
materials resistant to the weak acids
buried in peaty sediments. For example,
the keratinised parts of animals (skin,
hairs, claws) which have escaped
superficial degradation processes, may
be preserved for a very long time in the
deeper layers of the bog.
The blanket of sphagnum is sterile
underneath because of the absence of
bacteria. This fact has long been known
and, indeed, during the First World War,
this type of peat was sometimes even
Fiavè bog (Trentino)
Francesco Bracco · Roberto Venanzoni
used as a wad for emergency medical
dressings.
For the same reason, peat bogs are
often sites of enormous archaeological
interest in which, between the peat
layers, the presence of humans in the
distant past can be traced. In the Fiavè
peat bog (Trentino), remains of lake
dwellings have been found constructed
on piles (known as palafittes) dating
from 2100-2000 B.C. and from 14001300 B.C., when today’s peat bog was
still a barrage lake of glacial origin.
Even more fascinating finds are
mummified human bodies, such as
Tollund Man (ca. 400 B.C.) found in
Denmark in 1950, and Grauballe Man,
discovered close by in 1952. Both
belong to the era defined by
anthropologists as that of the “peat bog
men”, and human remains dating from
the Iron Age have regularly been found
in the peat bogs of north-western
Europe, especially in Denmark and
Germany.
The remains, amazingly well-preserved,
of these distant ancestors of ours have
provided much information on such
details as the clothes they were wearing
when they died and their last meal,
thus providing clues to their level of
civilisation and type of diet.
Their deaths, often violent, have been
interpreted as ritualistic.
Fiavè palafittes (Trentino)
Grauballe Man, for instance, had traces
of hallucinogenic mushrooms in his
stomach and Tollund Man had a rope
round his neck and so may have been a
human sacrifice, or a criminal
condemned to death.
In England, there have been significant
finds in peat bogs from Roman times.
In particular, the period when the legions
defended the border that marked the
most northerly expansion of the Roman
Empire is well documented. Sandals,
utensils, coins, tablets engraved with
correspondence, and many other finds
from Roman camps and settlements
have enriched our otherwise meagre
archaeological knowledge of these areas.
19
20
~12 000 years ago
~11 000 years ago
~10 000 years ago
~8 000 years ago
~4 500 years ago
~2 600 years ago
~2 000 years ago
today
1. clayey-silty
substrate
2. peat bog
with phragmites
3. peat bog
with Caricetum
4. peat bog
with alder
5. peat bog
with birch
6. peat bog
with pine
7. high, ancient
peat bog
8. high, recent
peat bog
Simplified model of development of a peat bog from the end of the last Ice Age until today in Alpine areas
some way be compared with individual ecological processes. In this section, an
attempt is made to demonstrate the major stages with sufficient clarity.
In 1908, Weber proposed, as the basic phenomena for the formation of a peat
bog, a succession of phases during which an aquatic environment, silts up as
follows:
- lake mud (aquatic phase)
- peaty mud (lentic phase)
- peat from reeds (Phragmites australis) and sedges (telmatic phase or peat
formation)
- shrubs and alder woods (Alnus glutinosa) (amphibian phase)
- birch (Betula) and pine (Pinus) woods (terrestrial phase)
- peat from Rannoch rush (Scheuchzeria palustris), sedges (Carex) and mosses
(telmatic phase). This phase (see figure) is commonly attributed to the time
interval between 3000 and 80 B.C..
- sphagnum peat (semi-terrestrial phase).
Climatic changes (an increase in humidity), the scarcity of nutrients and a
reduction in pH, also caused by sphagnum mosses, prevented the
development and renewal of tree species and gave rise to the luxuriant growth
of the raised sphagnum bog. This period is indicated as beginning in 800 B.C..
In ecological terms, these phases correspond to different plant growth
conditions in relation to the water level.
In the aquatic phase, the macrophytic and bryophytic communities are absent,
and the deposition of organic matter is due to the activity of phytoplankton
suspended in the water. The lentic phase corresponds to the appearance of
communities of floating plants, or ones rooted in deep water.
The telmatic phase implies the existence of species and/or plant communities
that can build up peat deposits at water level or just below. In the semiterrestrial phase, species and/or plant communities root above the water level,
although they may be submerged seasonally. Peat deposits formed of the not
yet decomposed remains of roots and aerial plant parts therefore accumulate
above water level.
The terrestrial phase marks the appearance of species and/or communities
which are adapted to deeper water-table levels and which cannot tolerate
flooding. With less water and therefore in less conservative conditions for soil
organic matter, new peat deposits can only accumulate slowly.
Weber was also the first scientist to observe that the blanket of peat formed of
sphagnum mosses, called accrual, is above the water-table level, and that the
zone of contact is recognisable and forms a horizontal boundary (called
“Grenzhorizont” in German); in many cases, this level has been dated.
21
Vegetation of peat bogs
FRANCESCO BRACCO · ROBERTO VENANZONI
■ Raised bogs
In Italy, there are very few ombrotrophic
peat bogs compared with the other
types.
They are also called minerotrophic,
because their development is influenced
by the mineral load dissolved in the
groundwater. There are many more of
Totes Moss peat bog (South Tyrol)
transitional or ombrominerotrophic type.
Ombrogenous bogs, which develop
entirely dependent on rainwater and are called raised bogs, are extremely rare,
and always small. They are mainly found at high altitudes on the southern
slopes of the Alps. In Europe, raised bogs are more common in northern and
western regions which are strongly influenced by the Atlantic Ocean; in the
more continental areas of central and Alpine Europe, they are represented only
by relicts. As already mentioned, their water supply does not come from the
water-table, but depends exclusively on rainwater, as does their nutrient supply.
In fact, because water of meteoric origin (rain or snow) lacks mineral nutrients,
the only nutrient supply for plants comes from wind-borne dust and the small
amount of nitrogen in ammoniac form deposited by rain. For this reason, raised
bogs are classified as extremely oligotrophic and dystrophic habitats, i.e., poor
in nutrients and rich in humic acids; and ombrotrophic.
A typical raised bog is formed of an accumulation of sphagnum moss which is
raised above the water-table level and includes the following: a slightly convex
summit, its borders, or rand, and a trough, termed lagg, which forms at ground
level and defines the rand laterally. The convex surface of the raised bog is not
smooth but tends to have hummocks, hollows, and small channels which
converge into the lagg. The lagg, depending on the size of the bog, may allow
a small stream to form, which encircles the raised area of the sphagnum
carpet, collecting excess water not trapped by the sphagnum.
Outside this frontier represented by the lagg, forest flora or fen vegetation
Marsh helleborine (Epipactis palustris)
23
24
thrive, as they are in contact with both
groundwater and the stream water,
which contains more nutrients. The
flora around a raised bog therefore has
mesotrophic characteristics, unlike the
strictly oligotrophic vegetation of the
bog itself. The top of a raised bog is
treeless: the seeds of tree species are
able to germinate, but the seedlings
cannot easily establish themselves
because of the acid environment and
scarcity of nutrients. The viability of a
Sphagnum hummock
peat bog is expressed by its capacity
to grow upwards, causing the crown to rise and the sides to become
increasingly steep. This growth mechanism is recorded in the peat deposit, the
structure showing alternating thick layers of lighter peat and thin layers of
darker peat, which have been affected more by conversion and humification.
This alternation is the result of a process called cyclic regeneration, and is due
to the different ways peat forms in the hollows, where organic matter is
produced more rapidly and preserved more completely, and on the
hummocks, where dead material is deposited in a drier environment and is
more subject to decomposition and conversion.
Vegetation profile of Pezzabosco peat bog (Trentino)
25
Peat bogs are often surrounded by trees and are subject to invasion by shrubs
1. Abietetum albae
2. Sphagno-Piceetum
3. Sphagnetum magellanici
4. Sphagnetum magellanici with Carex rostrata
5. Sphagnetum magellanici with Scheuchzeria palustris and Rhynchosporetum albae
6. Carex rostrata and Menyanthes trifoliata at pool edge
7. Eriophoro-Trichophoretum caespitosi
8. Molinietum
9. Mesobromion
9
1
2
3
4
4
5
4
5
6
4
6
8
5
4
7
26
Sphagnum hummocks
Sphagnum spp (genus Sphagnum) are
bryophytes so, in terms of
organisational level and complexity,
they are similar to what are commonly
called mosses.
These plant organisms play a specific
role in peat bogs. The huge volume of
organic material they gradually build up
is converted into peat, which influences
and characterises the living conditions
offered by the bog itself to other
organisms, both plant and animal.
Within the class of mosses, sphagnum
mosses are an isolated group
comprising the single genus
Sphagnum. This encompasses more
than 200 species, 24 of which were
recorded in this country by
Cortini Pedrotti in the very recent
Italian Moss Flora.
Sphagnum mosses are a uniform group
which have been well described in
terms of anatomy and morphology.
The general aspect of a sphagnum
blanket is that of a flat carpet or a
dense, uniform system of cushions and
hummocks, due to the enormous
number of individual stems clustered
extremely close together.
An individual sphagnum is made up of
a tiny slim erect stem, which only has
rhizoids during its earliest growth
stages; no trace remains afterwards.
The stem bears tufts of short lateral
branches at regular intervals. Some of
these, known as patent branches, are
perpendicular to the stem, others are
reflected, i.e., close to the stem and
facing downwards; at the apex, many
ramifications are gathered together in a
compact rosette.
In some cases, sphagnum mosses,
which generally appear green, may vary
in colour from brown to bright red,
Francesco Bracco · Roberto Venanzoni
1000 x
owing to the presence of pigments in
the cell walls.
The stem has no xylem conduits, the
centre being occupied by a cordon of
parenchymal cells enclosed within a
lignified cylinder; at the periphery is the
hyaloderm, formed of a variable
number of layers of dead cells, either
empty and intercommunicating, or
open to the exterior through pores.
These parenchymal cells, called
hyalocysts, have thick walls reinforced
by spiral thickenings which allow them
to remain open. Hyalocysts can
therefore absorb water through
capillarity and permit the sphagnum to
remain soaked in water even above the
level of the water-table that permeates
the substrate.
Both stem and branches have tiny
leaves (only a few millimetres long),
uniform in shape and lacking median
nerves. Stem leaves tend to have a
different outline from those on the
various types of branches: the former
may be flat and spatulate, whereas the
latter are concave, carinate, and tend to
curl inwards at the tip. Reflected
branches often have elongated leaves
with a less curled tip than those on the
patent branches.
The leaves are formed of a single cell
layer with two different types of cell
elements. Solitary hyalocysts are
inserted regularly in the mesh of a
regular reticulum formed of much finer
and more brightly coloured living cells.
These cells, called chlorocysts, appear
green because of the presence in them
of chloroplasts.
The hyalocysts in the leaflets and stem
allow the sphagnum plants to absorb
and store an amount of water
approximately 20-25 times their dry
weight; the lack of rhizoids is therefore
largely compensated by the hyalocysts,
which act as systems of water and
nutrient uptake.
In sphagnum mosses, the growth of an
individual takes many years. One
branch at the stem apex grows each
year, assuming the form and functions
of the stem, thus continuing its growth
upwards. As it lengthens, the lower
sections of sphagnum die off, and this
mechanism also vegetatively multiplies
the individuals, separating the branches
that have progressively grown from the
same stem, which then become
independent organisms.
Short ramifications in the apical rosette
bear the archegonia and antheridia, i.e.,
organs producing female and male
gametes, respectively. The latter,
flagellar antherozoids, produced by the
antheridia, fecundate the single egg cell
27
28
■ Vegetation of transitional and high-altitude peat bogs
Sphagnum hummocks
produced by each archegonium. The
zygote forms the spore apparatus,
raised by an elongated axis named
pseudopodium. This is tipped by a
round capsule attached to an
expanded foot. The spores form
within the capsule and, when ripe,
due to the high pressure of the liquid
inside, are actively expelled through
the operculum.
Spores germinate in the presence of
fungi with which mycorrhizal
symbiosis develops. The result is a
brief filamentous juvenile phase
(protonema), which then grows to
form a small lobed thallus with
numerous rhizoids. From this, the new
individual develops, assuming the
form and organisation described
above.
Sphagnum mosses may become an
important component of
environments in which the water
tends to be acid (pH <6.5). In these
conditions, depending on species,
they behave like hydrophytes (i.e.,
rooted and growing under water,
forming floating masses of
vegetation) or hygrophilous plants
(growing in wet or damp soil).
Sphagnum mosses, as well as
preferring acid waters, also avoid
those in which large amounts of
mineral salts and nutrients are
dissolved. Both conditions, acidity
and lack of nutrients, are to some
extent maintained by the sphagnum
mosses themselves, as they can
secrete organic acids and also
adsorb the cations circulating on their
membranes. However, the efficiency
of these mechanisms is limited by the
fact that acid secretions are
produced only by plants living where
there is plenty of sunlight, while
adsorption capacity is fairly modest.
Therefore, where waters have high
mineral contents, sphagnum mosses
die and leave room for colonisation
by other plants.
The vegetation colonising this particular environment is not homogeneous and
is characterised, as already seen, by a complex mosaic of hollows and
hummocks. The depressions in the surface of the bog are colonised by
sphagnum mosses such as Sphagnum cuspidatum which hold more
groundwater and which, together with other species, constitute the transitional
bog. The hummocks, which may vary in diameter from a few centimetres to
several metres, are mainly composed of other species of sphagnum such as S.
medium (= S. magellanicum), typically red in colour, and S. rubellum. A few
higher plants also grow here, including cotton grass (Eriophorum vaginatum),
small cranberry (Vaccinium microcarpum), cranberry (V. oxyccocus), northern
bilberry (V. uliginosum), bog rosemary (Andromeda polifolia) and common
sundew (Drosera rotundifolia). As the sphagnum mosses gradually grow, the
hummocks become larger and, in particular, reach a critical height. At this
point, maintenance of the water balance is hindered, so that the sphagnum
mosses are reduced in vitality and the peat decomposes, allowing colonisation
by mosses, lichens and heather (Calluna vulgaris).
The latter species, thanks to the mycorrhizae in its roots (fungal hyphae which
live in symbiosis with the plant and amplify its absorbent capacity) are able to
live on these extremely acidic and nutrient-poor substrates, forming low
shrubs, i.e., true heath.
Cranberry (Vaccinium oxycoccus) immersed in a mat of sphagnum
29
30
Bog rosemary (Andromeda polifolia)
Bottle sedge (Carex rostrata)
Sundew (Drosera sp.)
Vegetation of sphagnum bogs,
shrubby sphagnum bogs and peat
woods (Sphagnion medii, VaccinioPiceion). Spagnetum magellanici is the
most typical association, and is usually
a deep, continuous layer of sphagnum
forming an undulating carpet emerging
from the basic bog level. Typical
common bryophytic species are
Sphagnum medium, S. rubellum and
the moss Aulacomnium palustre,
together with other species like S.
capillifolium and S. tenellum.
The higher plants include small
cranberry, few-flowered sedge (Carex
pauciflora), cotton grass and various
sundews (Drosera rotundifolia, D.
longifolia). In higher areas, where the
peat becomes degraded, we find small
shrubs like heather and cowberry
(Vaccinium vitis-idaea), together with
various species of moss, including
Polytrichum strictum.
On the slopes, or edges, where the
sphagnum layer is thinner, the
Eriophoro-Trichophoretum
caespitosum association is found,
identified by dominating tufted bulrush
(Trichophorum caespitosum ssp.
caespitosum), cotton grass, Alpine
bulrush (Trichophorum alpinum) and
sphagnum mosses like S. flexuosum
and S. compactum.
On the sphagnum carpet, shrubs may
grow, and some species of conifer or
broadleaf trees like downy birch
(Betulla pubescens), Scots pine (Pinus
sylvestris) and mountain pine (Pinus
mugo s.l.) may locally dominate.
The most common association is Pinus
mugo-Sphagnetum, characterised by
the typical bryophytic species of
sphagnum carpets in raised bogs, such
as Sphagnum medium, S. rubellum
and S. fuscum, and by flowering plants
such as mountain pine, downy birch,
cotton grass, small cranberry, etc..
Vaccinio uliginosi-Betuletum pubescentis is a rare association only found
in a very few peat bogs in Trentino-Alto
Adige (South Tyrol). Sphagnum birch
woods only grow very sporadically, and
their presence in Italy, at the
southernmost limit of their range, is of
enormous phytogeographical and
biogeographical interest. These forestry
communities are little known, and the
species from which they take their
name present problems of a systematic
and biogeographical nature. Northern
bilberry is actually a species typical of
wooded raised bogs, and its presence
in Italy is by no means a certainty, since
this species is often confused with
Vaccinium gaultheroides; similarly, the
presence of downy birch (Betula
pubescens) in Italy is doubtful, because
it appears to be replaced by
Carpathian birch (Betula carpatica ssp.
carpatica).
The spruce forest (or red fir, Picea
excelsa) and sphagnum (Sphagnum
girgensohnii-Piceetum) association
grows on the outer edges of the peat
bog lagg, forming a very narrow belt,
e.g., Pazzabosco bog (Trentino).
This vegetation is characterised by
Sphagnum girgensohnii and S. palustre
31
Cowberry (Vaccinium vitis-idaea)
Alpine bulrush (Trichophorum alpinum)
Vaccinium gaultherioides
Peat bogs as palynological archives
Peat bogs are of botanical interest from
two different viewpoints. In the first
place, they host many quite rare plant
species of great phytogeographical
interest. Secondly, they provide a
unique chance to learn about the plant
landscape of past epochs.
Peat bogs offer almost perfect
conditions for the preservation of plant
remains, which make it possible to
identify the basic characteristics of the
vegetation in the surrounding area
during its entire existence. This natural
archive of floral successions is provided
by the nature of the plant remains
trapped in the layers of peat and the
sedimentary conditions produced by the
bog itself, which create an environment
with high preservation properties.
The plant materials are mostly pollen
grains, the characteristics of which
make them a good vector of precious
information. The outer wall of a pollen
grain has two layers, the inner or intine,
and external or exine which is, in turn,
complex.
Of key importance in the latter are
sporopollenins, very stable chemical
compounds which can only be broken
down in oxidising environments. The
exine also has a very variable
appearance, with grains, striae, spinules
and reticular sculpturing, and areas of
grain opening in the form of grooves or
pores of different patterns.
This creates an enormous variety of
pollen types which can be distinguished
morphologically under the microscope
as belonging with certainty to families,
genera, or even to individual species of
angiosperms and gymnosperms. Pollen
grains therefore represent clearly
identifiable evidence of plant species
which can be preserved for a very long
Francesco Bracco · Roberto Venanzoni
DEPTH
32
scots pine
oak, lime, elm
spruce
beech
1m
~ 6000 years ago
~ 10000 years ago
2m
3m
POLLEN
25%
50%
75%
100%
Example of a pollen diagram
Pine, lime and beech pollen (x 2000)
time in suitable environments, such as
peat deposits.
Conditions of anoxia occur here, due to
the very high water content (up to 95%)
and the presence of easily oxidised
substances, such as humic acids and
their derivatives. These conditions are
accentuated by the consumption of
oxygen by decomposing organisms and
the much lower speed of diffusion of the
gas itself through the waterlogged peaty
sediments. In these conditions, all
materials resistant to weak acids, for
example cutinised plant parts (leaf
epidermis, hairs), which have not
decomposed on the surface are
preserved for a very long time, once they
are enclosed within the peaty sediment.
This process is particularly efficient in
preserving pollen grain exines and can
guarantee their reliability as evidence of
past flora.
Pollen, at least in the case of many
anemochorous (wind-pollinated) plants,
is produced in great quantities that are
widely dispersed over the surrounding
area. This does not happen with the
macro-fossils of plants which, unlike
pollens, can thus only provide a
circumstantial but strictly local record of
the vegetation cover in the past, and
species preferring dry environments
are drastically under-represented or
entirely absent.
The easy diffusion of pollen allows its
successful dispersal over the territory
and particularly on peat bogs, which act
as efficient traps and preserve the grains
inside the peat.
Another important factor is that the
waters percolating through the
accumulated peat impede any vertical
movement of pollens deposited.
This means that pollens can be linked
unambiguously to their deposition level,
so that the succession of layers forms
an accurate record of the floral history of
the surrounding area.
If the pollen of an anemochorous
species is not found in the peat
sediments of a given period, it is very
likely that it did not grow in the
surrounding area.
Fossil pollens also allow a statistical
record to be built up of the palaeoflora
on a territorial scale, as all wind-borne
pollens are produced in considerable
quantities ad, if considered fairly
uniformly distributed, can become
trapped in peat sediments.
Naturally, interpreting quantitative
results is a complex task and must
take into account many complicating
factors which can recur to a greater or
lesser extent.
Not all anemochorous plants produce
identical amounts of pollen during
flowering, and not all pollen grains are
preserved in the same way. There may
also be local effects, e.g., if individuals
of an anemochorous species grow
immediately adjacent to the peat bog,
they may have dropped their flowers
directly onto the peat, thus drastically
33
34
Peat bogs as palynological archives
Peat bogs can preserve pollen from surrounding trees
affecting the pollen load.
The efficiency of pollen air transport,
which ensures its dispersal, means
that pollen may also arrive from other,
perhaps remote areas.
This happens in mountain peat bogs
affected by the transit of ascending air
currents, which transport pollen
upwards from lower-altitude
vegetation belts.
It is obvious that a quantitative
reconstruction of flora cannot take into
account species which are
autogamous (with self-pollinating
mechanisms) or entomophilous
(insect-pollinating), for which to
presume that abundant pollen is
produced and uniformly distributed in
space is not valid.
But they may act as indicator species
of particular ecological and floral
situations; nothing can be deduced
from their absence.
The most frequently recurring species
in pollen samples isolated from the
peat matrix using complicated
laboratory techniques, are those of
shrub and forest formations. These
include pine (Pinus), spruce (Picea),
poplar (Populus), birch (Betula), alder
(Alnus), beech (Fagus), hornbeam
(Carpinus), lime (Tilia), elm (Ulmus), oak
(Quercus), ash (Fraxinus), willow (Salix)
and hazel (Corylus).
Interpretation of pollens from
herbaceous species is more complex.
These include the gramineae (grasses),
which are important as they may mark
the transformation of the floral
landscape by man creating clearings
for pastures and growing arable crops
in areas previously covered by forests.
Pollen analysis of peat deposits has
been particularly important for
interpreting the climatic and floral
situations in the Quaternary era, in
relation both to post-glacial variations
in the plant landscape and a
description of Pleistocene vegetation
in glacial and inter-glacial periods.
and mosses such as Plagiothecium
undulatum and Ptilium crista-castrensis.
Nature-wise, these are impoverished
aspects of a boreal association found
on the Alps as relicts of extreme
importance in terms of biodiversity
protection. Another forest phytocenosis,
Bazzanio-Piceetum, only occurs in a
very few sites in Trentino-Alto Adige.
The last tree association of peat bogs
is the pine-wood of Scots pine and
molinia or moor grass (MoliniaPinetum), which grows on peaty soils
with vegetation typical of raised bogs.
Guide species, among the grasses, are
moor grass (Molinia caerulea) and,
among the trees, Scots pine.
living sphagnum
35
Area of flooded peat bog
floating mat
peat
substrate
lake-bed sediments
Origin of a floating island
36
Heaths
The heaths (Ericaceae) are a large
plant family, spread throughout the
world, many species of which are
characteristic of mountain peat bog
flora. They are generally shrubs with a
definite preference for acid soils.
Difficulties in nutrient uptake are
overcome by the mycorrhizae, i.e.,
complex symbioses with fungi that live
on the plant’s root system.
The heaths comprise almost 3000
species, grouped into about 170
genera.
Those growing in acid peat bogs are
all dwarf shrubs, with branches trailing
on the ground, and small, often
coriaceous leaves.
The low pH of peat bogs also attracts
some species commonly found in
other habitats with highly acid soils;
for example, heather (Calluna vulgaris),
or species growing in coniferous
forests or on upland moors, i.e., those
of the genera Rhododendron and
Vaccinium. The most common and
widespread are bilberry (Vaccinium
myrtillus), cowberry (V. vitis-idaea) and
V. gaultherioides.
Three other much rarer species of
these heath allies also grow in acid
mountain bogs. Two of them, small
cranberry (V. microcarpum) and
cranberry (V. oxycoccos), are dwarf
shrubs with thin creeping stems and
flowers with fused down-turned petals
forming a corolla tube.
In Italy, both species are distributed in
the Alps, in the acid peat bogs of the
mountain and sub-Alpine belts.
The third species is bilberry (V.
myrtillus), which at one time was
believed to be widespread on
meadows, moors, scrubland and also
peat bogs.
Francesco Bracco · Roberto Venanzoni
Heather (Calluna vulgaris)
Nowadays, these plants are
considered to belong to V.
gaultherioides, a smaller diploid
species. Northern bilberry constitutes
a different stirps, tetraploid and visibly
larger, quite rare in Italy and with a
much more local distribution,
exclusively in high-altitude, acid peat
bogs.
Another extremely rare heath that
grows in the sphagnum mats of acid
peat bogs is bog rosemary
(Andromeda polifolia). This is also a
small shrub, but the branches are
erect and the alternating leaves, unlike
those of Vaccinium, have a linearlanceolate blade.
Lastly, belonging however to the
separate Empetraceae family, is
crowberry (Empetrum nigrum). This
again is a small shrub, with upright or
erect branches, small elliptical leaves,
unisexual flowers and a corolla with
separate petals.
Non-woody flora of the hollows of
floating mats with or without
sphagnum (Rynchosporion albae).
Typical
associations
of
these
environments are Rynchosporetum
albae, Caricetum limosae and, in some
less acidic situations, also ScorpidioCaricetum limosae. As well as the
species which give their name to these
plant communities, white beak-sedge
(Rhyncospora alba) and bog sedge
(Carex limosa), the rare rannoch rush and
a rare pteridophyte, marsh clubmoss
(Lepidotis inundata), may locally be
abundant. These species, present in the
hollows and rooting in the peat, also
colonise the lowest submerged parts of
the sphagnum carpet. In transitional
bogs, a typical association of the
floating mats is Caricetum lasiocarpae.
This is a compact carpet of sphagnum
including Sphagnum recurvum, S.
palustre and S. teres, in which
herbaceous plants are distributed with
varying levels of dominance.
The guide species of the association,
slender sedge (Carex lasiocarpa), being
taller, with narrow leaves slightly curled
at the tips, emerges above the shorter
grasses like white beak-sedge and bog
sedge. More conspicuous residents are
oblong-leaved
sundew
(Drosera
intermedia), marsh violet (Viola palustris)
and marsh cinquefoil (Potentilla
palustris). When the bog is richer in
calcium and other alkalis, mosses are
plentiful (Drepanocladus, Scorpidium,
and others), and flowering plants such
as Carex dioica and Cladium mariscus.
37
White beak-sedge (Rhyncospora alba)
Slender sedge (Carex lasiocarpa)
■ Fens
38
Availability of nutrients (nitrogen content)
2%
Simplified diagram of distribution of
vegetation depending on nutrient availability
and acidity.
OLIGOTROPHIC
acid oligotrophic peat-bogs
From top to bottom, optimal conditions for:
a) vegetation of a raised bog;
b) vegetation of transition bogs and flat
neutral-alkaline peat bogs;
c) marsh vegetation of tall sedges,
reed beds, marsh and riparian woods.
a
3%
low transitional peat bog
low alkaline peat bog
MESOTROPHIC
acid low peat bog
b
4.9%
EUTROPHIC
eutrophic peat bog
c
10%
2,5
pH
3,5
ACID
4,8
6,4
8,0
NEUTRAL
ALKALINE
Low-lying peaty areas (or fens) are
associated with definite climatic
conditions, their development being
determined by the water-table. They
are produced by the silting-up of lakes
or slow-flowing watercourses, or on
slopes, in spring areas, etc. The
nutrients carried by the flowing waters
and the depth of the water-table
determine the composition of the flora
Fen with cotton grass, Apennines
responsible for the silting process and
therefore also the type of peat that is
deposited on the bed of the fen. Apart
from pioneering stages, during which
organic matter (gyttja) accumulates on
the bed of the basin, true peat begins
to form when the roots and rhizomes of
herbaceous species, such as marsh
reeds, cattails (Typha latifolia, T.
angustifolia) and tall sedges like tufted
sedge (Carex elata), lesser pond sedge
(C. acutiformis), greater pond sedge (C.
riparia), etc., begin to accumulate.
Common reed (Phragmites australis)
These species, abundant and
dominating the landscape, constitute
the species-poor vegetation of the riparian belts of reed-beds (Phragmitetum
australis, Typhetum angustifolia, etc.) and tall sedges (Caricetum elatae,
Caricetum gracilis, Caricetum acutiformis, etc.).
Within this aquatic environment, the production of organic matter is high
enough, compared with the mineralisation caused by decomposition of
organisms, to form organogenic deposits on the bottom and, especially, close
to the edges, where this process is particularly fast. This allows reed-beds and
meadows of tall sedges to become established.
These plant formations, by means of organic matter production and the
accumulation of their organic remains, raise the ground level and form a belt of
more consolidated silt which moves outwards in the direction of open water.
At the same time, hydrophytes and reed-bed vegetation gradually colonise the
39
40
Grasses of mountain peat bogs
The flora of mountain peat bogs
includes many sedges or Cyperaceae, a
family whose species often play a
dominant role in the vegetation,
characterising it physiognomically and
thus acting as markers defining the
plant communities present. It is a family
of usually perennial, grass-like, nonwoody monocotyledons (i.e., related to
common grasses) which includes
approximately 90 genera and 4000
species. It has cosmopolitan
distribution, although the family is
particularly well represented in
temperate-moist areas and sub-Arctic
regions. The Italian flora includes a
couple of hundred species classified
into some twenty genera. They grow in
many different environments (meadows
and pastures, forests and cliffs), but
most species are hygrophytic, marsh or
peat bog plants.
In order to give a general picture of the
Cyperaceae, while sacrificing some
exceptions, they usually have rhizomes
or underground stolons from which
above-ground, unbranched, solid stems
grow, with basal leaves and no nodes.
The leaves have a linear blade with a
decurrent sheath on the stem, usually
closed, and most often without a ligule.
While the general bearing and
appearance of the leaves are very
similar to those of the gramineae, they
are distinguished by various
characteristics, in particular the
triangular stem section and tristichous
(three-row) arrangement of the leaves.
The flowers are usually inconspicuous,
with a simple involucre reduced to
scales or bristles; there are two or three
stamens and the ovary is superior, with
two or three stigmata which show the
number of carpels. Individual flowers
Francesco Bracco · Roberto Venanzoni
are generally borne inside spikelets.
There may also occasionally be a single
spikelet at the stem apex, but more
often the spikelets are gathered
together in larger inflorescences to form
a simple or compound spike, in a
capitulum, or with lateral elongated
branches as long as the main axis or
longer. Each spikelet is made up of an
axis bearing a variable number of
flowers, each positioned at the axil of a
glume. There may also be sterile
glumes, i.e., without flowers at the apex
or base of the spikelet. The whole
spikelet is borne on the axil of a bract.
The most important Cyperaceae in peat
bog flora are the sedges sensu stricto
(genus Carex), cotton grasses (genus
Eriophorum), bulrushes (genus
Trichophorum), beak-sedges (genus
Rhynchospora), spike-rushes (genus
Eleocharis), flat sedge (Blysmus
compressus) and great fen sedge
(Cladium mariscus).
Within the genus Carex 2000 species
have been described, of which about
120 grow in Italy. A good many of these,
around 30 species, grow in mountain
peat bogs, which are often their
exclusive habitat. Some are very rare:
e.g. bristle sedge (C. microglochin),
few-flowered sedge (C. pauciflora),
flea sedge (C. pulicaris), lesser tussock
sedge (C. diandra), peat sedge
(C. heleonastes), C. juncella, closeheaded Alpine sedge (C. norvegica), club
sedge (C. buxbaumii), Hartman’s sedge
(C. hartmanii) tawny sedge (C. hostiana)
and slender sedge (C. lasiocarpa).
Some species are infrequent, e.g.,
dioecious sedge (C. doica), downyfruited sedge (C. tomentosa), bog sedge
(C. limosa) and poor sedge (C. irrigua).
Others, such as Davall’s sedge
(C. davalliana), silvery sedge (C.
canescens), C. stellulata, C. fusca,
carnation sedge (C. panicea), yellow
sedge (C. flava; sensu stricto), longstalked yellow sedge (C. lepidocarpa),
Oeder’s sedge (C. oederi), bottle sedge
(C. rostrata) and tufted sedge (C. elata),
are more common, at least in northern
Italy.
All the species in this genus have
unisexual flowers in single flower
spikelets gathered in uni- or bisexual
ears. The ovary, which later becomes
the fruit, is enclosed in an involucre
called the utricle, with an apical opening
from which two or three stamens
protrude. Between the leaf blade and
the sheath is a ligule, and this is an
exception to the general characters of
the family. The various species may
form carpets, if they have elongated
underground stolons, or compact
dome-shaped clumps, which give the
vegetation cover its characteristic
undulating appearance.
A much less numerous genus is that of
the cotton grasses, which are one of the
most obvious signs of the presence of a
peat bog. When the fruit ripens, the six
bristles which make up the involucre of
the flower and surround the ovary,
lengthen greatly and, as a result, the
spikelets take on the appearance of
white tufts of cotton, up to 4 cm long,
which give the plant and all the
vegetation an unmistakable appearance.
Species in mountain peat bogs include
Scheuchzer’s cotton grass (Eriophorum
scheuchzeri) and the rarer harestail
cotton grass (E. vaginatum), with a
solitary terminal spikelet. Narrow-leaved
cotton grass (E. angustifolium) and
broad-leaved cotton grass (E. latifolium)
have more spikelets at the stem apex.
Trichophorum bulrushes, like cotton
grasses, have involucre bristles
sometimes up to 2 cm long in Alpine
bulrush (Trichophorum alpinum), while
they are shorter and less obvious in
tufted bulrush (T. caespitosum). Both are
low species (less than 20 cm high), but
differ in that only the more common
latter species forms typically rounded
clumps.
A much more important genus is
Rhyncospora, with about 200 species
worldwide. Only two of them grow in
Italy, white beak-sedge (Rhyncospora
alba) and brown beak-sedge (R. fusca),
which differ in the colour of their
spikelets: whitish in the former and
reddish-brown in the latter. They are
small herbaceous shrubs, with spikelets
gathered in terminal and sometimes
axillary glomerules. Both species are
extremely rare in Italy.
Broad-leaved cotton grass (Eriophorum latifolium)
41
42
new areas which are subtracted from the body of water. In particular edaphic
and climatic conditions, this belt may be formed of a sphagnum blanket
(transitional bog).
The raised ground, due to the production of peat from marsh reeds or sedges,
allows colonisation by tree species, and marsh woodland gradually develops.
With the addition of branches and leaves, this completes the phases of silting
up of the water body and the formation of peat. In these conditions, the
availability of acid substances is generally low, and this enhances the chemical
reactions of reduction and fermentation which lead to the formation of marsh
gas (methane) and the presence of sulphides dissolved in the water. The latter
react with iron compounds and, together with the abundant humic substances
in fen soil, give it its dark colour.
As the soils of neutral-basophilous fens are usually rich in lime and nutrients
and have a pH from neutral-alkaline to slightly acid, when drained and
cultivated, they can produce high yields when used as mown water-meadows.
The water-meadows and marsh vegetation found today in these landscapes
are to be considered as secondary semi-natural formations, derived mostly
from the felling of marsh woodland, and this fact must be taken into account in
the sphere of management and conservation. As already mentioned, in front of
the silted area created by the succession of vegetation belts, floating mats of
vegetation, also called “trembling bogs”, can be found. In eutrophic conditions
(i.e., high nitrogen and phosphate availability), these are composed of reedbeds and great fen sedge growing on the mesh formed by their own rhizomes
and, in more oligotrophic situations (i.e., minimal nutrient availability in the
water) by carpets of sphagnum, known as transitional bogs.
These carpets are formed of sphagnum species such as Sphagnum
cuspidatum and S. recurvum which, with the accumulation of plant parts, give
rise to true sphagnum peat. In this floating sphagnum mat, higher plants also
grow, like bog sedge, white beak-sedge and narrow-leaved cotton grass
(Eriophorum angustifolium), as well as more ubiquitous species like bottle
sedge (Carex rostrata), bogbean (Menyanthes trifoliata), marsh cinquefoil, etc..
Within this context, the permanence of fen vegetation and the tendency to form
plant alliances typical of raised peat bogs may create an interesting mosaic, the
vegetational elements of fen, raised and transitional bogs all endowing the area
with high local biodiversity. Fens are also widespread on slopes and spring
environments.
Wetland area used as mown water-meadow
Iridescence from hydrocarbons (marsh gases)
43
44
Carnivorous plants
Francesco Bracco · Roberto Venanzoni
Although the biological phenomenon of
carnivorous plants is spectacular, their
rigorous definition is not always simple.
A carnivorous plant must be able to
absorb nutrients from dead animals
coming into contact with its outer
surface and obtain an advantage in
terms of increased growth, probability of
survival and reproductive efficiency (e.g.,
pollen and/or seed production). It must
also have some type of adaptation for
the attraction, capture and digestion of
prey, which requires substantial
commitment of resources. In reality, as
often happens, the boundary line
between carnivorous plants and others
is not quite so finely drawn. The
carnivore is a complex syndrome, and
has appeared more than once during
evolution in groups of very different plant
organisms, i.e., it is not a single event.
Exotic genera such as Brocchinia and
Catopsis (of the Bromeliaceae, the
pineapple family), Paepalanthus
(Eriocaulaceae), Craniolaria, Ibicella,
Martynia and Proboscidea
(Martyniaceae) show borderline
behaviour, in that they capture small
animals by trapping them on the
viscous secretions of their leaves, but
there is no proof that they secrete
digestive enzymes.
Other plants with viscous leaves (e.g.,
Drosera) capture small animals that
they are unable to digest; but larger
insects (hemipterans of the reduviid
family), which cross the leaf surface to
reach this food, leave their faeces on
the leaves which are then absorbed by
the plant. In the same way, the bacterial
flora in the remains of the captured
animal can contribute to digestion by
Common butterwort (Pinguicula vulgaris)
Alpine butterwort (Pinguicula alpina)
co-operating with the plant’s enzymes
or substituting them completely.
The extremely common shepherd’s
purse (Capsella bursa-pastoris), often
found along roadsides and on waste
ground in Italy, is seldom thought of as
a carnivorous plant. However, its seeds,
during germination, are surrounded by
a layer of mucus which can capture
and digest soil nematodes, protozoa
and bacteria.
There are more than 600 species of
carnivorous plants in the strict sense,
belonging to the following families of
dicotyledons: Sarraceniaceae (with the
genera Sarracenia, Heliamphora,
Darlingtonia), Nepenthaceae
(Nepenthes), Droseraceae (Drosera,
Dionaea, Aldrovanda, Byblis,
Drosophyllum), Dioncophyllaceae
(Triphyophyllum), Passifloraceae
(Passiflora), Cephalotaceae (Cephalotus)
and Lentibulariaceae (Genlisea,
Pinguicula, Utricularia).
Of this list, the last genus is the most
numerous: the bladderworts
(Utricularia). It includes about one-third
of all carnivorous species, and is
followed by the Drosera (with more than
150 species), Nepenthes and Pinguicula
(each with dozens of different species).
In general, these plants grow in well-lit,
damp environments with extremely few
available nutrients. The soil is usually
acid; less frequent (mainly Pinguicula) is
colonisation of calcareous soils, which
are in any case nutrient-poor. In these
conditions, carnivorous plants obtain
mainly nitrogen from the tiny animals
they trap as prey, but there is some
experimental evidence that they also
benefit from other nutrients, particularly
sulphur and phosphorus. Having
predatory habits, which we tend to
consider a prerogative of animals,
carnivorous plants are basically
autotrophic, i.e., capable of
constructing the complex organic
molecules of which they are made,
starting from very simple substances.
They can also survive successfully
without capturing anything. However,
the substances deriving from
carnivorism give them the chance
effectively to increase their growth, and
augment flower and seed numbers, thus
improving their reproductive
possibilities.
Carnivorous plants have various
trapping devices:
- drop-traps: the pitchers of Nepenthes,
Sarracenia, etc.
- sticky traps: the leaves of Drosera,
Pinguicula, etc.
- springs: the leaves of Dionaea,
Aldrovanda etc.
- suction traps: the bladders of
Utricularia and Genlisea.
Some of these devices use movements
of plant parts (Drosera leaves,
Utricularia bladders, Dionaea leaves,
etc.) and specific attractions like nectar
secretions, coloured patches and shiny
drops. Tissues also exist for secreting
enzymes, such as protease, esterase
and acid phosphatase, which can
digest the prey.
The biological strategy of carnivorism is
not an optimal solution for plants:
although a new source of nutrients is
exploited, the complex set of
adaptations required (nectar secretion,
mucilage and enzymes, management of
active movements) impose a metabolic
expenditure which, in itself fairly low,
involves a considerable reduction in the
photosynthetic capacity required for
reinvestment in leaf structures. This
45
46
Carnivorous plants
explains why these plants are restricted
to extreme environments with little
competition and a need for nutritional
compensation.
In Italian mountain peat bogs, the three
genera of carnivorous plants present,
indicate the evolution of two major
groups of dicotyledon angiosperms, the
Rosidae and the Asteridae: the former
include sundews (Drosera), the latter
butterworts (Pinguicula) and
bladderworts (Utricularia).
Three species of Drosera are recorded
in Italy, and the two which are
particularly associated with the flora of
mountain sphagnum peat bogs are
common sundew (Drosera rotundifolia)
and long-leaved sundew (D. anglica).
Long-leaved sundew is interpreted as a
fixed, widespread hybrid between
common sundew and a species absent
in Italy (D. linearis). The two mountain
peat bog sundews are both small (10-20
cm), with a basal rosette of leaves and a
slim erect flower stalk. This is most
often hairless, and bears a small
number of flowers with five white petals.
Common sundew has leaves with a
rounded-reniform blade and a long slim
leaf-stalk which keeps it anchored to
the soil; long-leaved sundew has slim
leaf blades, up to ten times longer than
their width and kept erect. The trap is
composed of tentacles on the leaves,
characteristically red, with a shiny drop
of sticky secretion at the apex. These
tentacles are capable of movement
triggered by a mechanical stimulus (two
inputs within a minute), which causes
them to bend as both sides of the
tentacles extend. Slower movements,
which may also involve folding the
whole blade around the prey, are
triggered by chemical stimuli. Oblong-
Francesco Bracco · Roberto Venanzoni
leaved sundew (Drosera intermedia) also
grows in peat bogs and is distinguished
by its leaves with elliptical blades
gradually decreasing along the long
leaf-stalk. The appearance is therefore
effectively “intermediate” between the
two previous species.
There are more species of butterworts
than sundews in Italy, and systematic
study has led very recently to the
description of species new to science.
Many species of butterworts are
characteristic of damp calcareous
rocks, but at least two also grow on
acid soils and therefore also in peat
bogs: common butterwort (Pinguicula
vulgaris) and southern butterwort (P.
leptoceras). The former is distributed
throughout Europe; the latter grows on
the Alps, Jura and northern Apennines.
Both have a compact basal rosette of
Common sundew (Drosera rotundifolia)
pale green elongated oval leaves with
inrolled margins. The upper surface is
sticky and shiny and forms the trap for
capturing small prey. The flower stems
are hairless, glandulous, and up to 1015 cm tall. The flower at the apex has a
conspicuous irregular bilabiate corolla
with five divisions and a long spur. In
common butterwort, the corolla is violet;
in southern butterwort, it is usually a
patchy white and pale violet.
The last of the carnivorous plants is
bladderwort. This is not part of
emergent peat bog vegetation, but
grows in aquatic environments close by.
It is a plant with a slim branched stalk
that bears leaves divided into linear
segments. It grows under water, with
just the erect undivided stalk, which
bears the terminal inflorescence,
emerging.
The two most typical species of peat
bog environments, lesser bladderwort
(Utricularia minor) and intermediate
bladderwort (U. intermedia) have leaf
dimorphism: as well as the green
photosynthesising leaves, immersed in
the water, there are also colourless
leaves, similarly divided, which sink into
the sediment on the bottom. The flower
in both species has a small bilabiate
corolla, with a yellowish-white spur with
darker veins. The leaf bladders are the
traps used for capturing minute aquatic
animals like microscopic crustaceans. In
lesser bladderwort, they also appear on
the green leaves, but in intermediate
bladderwort they tend to be only on the
branches bearing the colourless leaves
used for anchoring the plant to the
bottom. The bladders, 1-2 mm in
diameter, act as suction traps and have
an operculum surrounded by sensitive
hairs. When the bladders are closed,
internal hydrostatic pressure is
maintained lower than that of the
surrounding water by systems of active
transport which expel chlorine ions, with
which sodium ions and water are
associated. Mechanical stimulation of
the sensitive hairs, within 10-15
milliseconds, causes the operculum to
open, and a fast current of water enters,
sucking the animal which had touched
the hairs into the bladder. The
operculum then closes, imprisoning the
prey, which is digested by enzymes
freed by the secreting hairs on the
internal surface of the bladder.
Contemporarily with digestion, the
above-mentioned active transport
processes also occur, reducing
hydrostatic pressure inside the bladder
and thereby preparing it for the next
hapless victim.
Lesser bladderwort (Utricularia minor)
47
■ Vegetation of mountain fens
48
Fen vegetation is mainly meadow flora forming part of the Caricion davallianae
association, characterised by dominant species like Davall’s sedge, black bogrush (Schoenus nigricans), the rare brown bog-rush (S. ferrugineus), fewflowered spike-rush (Eleocharis quinqueflora) and blunt-flowered rush (Juncus
subnodulosus) which, growing at relatively high altitudes, may also move
downwards as far as the springs on the plains.
Together with these small-sized species, great fen sedge is also often found,
forming plant communities in bogs or even floating mats, growing in front of
the reed-beds, in open water, and contributing greatly to the silting up of lakes
or springs.
Peat bogs, important but often small habitats, require special protection
A slightly sunken meadow in the mountains, occupied by a peat bog
49
50
Geobotanical aspects of flora
Francesco Bracco · Roberto Venanzoni
A well-known characteristic of the flora
of aquatic and marsh environments is
the prevalence of species with wide
geographical distribution, explained by
the unifying conditions of water in even
greatly varying climatic conditions.
In peat bogs, this is true of bryophytes;
the geographic distribution of higher
plants has different connotations.
Peat bog flora has abundant species
with geographical distribution over the
colder climatic areas. These are plants
found in the cold belts of the Eurasian
continent and corresponding areas of
boreal America (circumboreal
distribution).
Some of the most conspicuous and
easily identified species in peat bogs marsh violet (Viola palustris), marsh
cinquefoil (Potentills palustris) and
bogbean (Menyanthes trifoliata) - have
this phytogeographical distribution. The
two most typical representatives of peat
bog carnivorous flora are also in this
category, like common sundew (Drosera
rotundifolia) and the less frequent longleaved sundew (D. anglica) (more fully
described on pages 44-47).
Many sedges, such as lesser tussock
sedge, club sedge, slender sedge, bog
sedge and bottle sedge, are similar.
Three-flowered rush (Juncus triglumis),
heath rush (J. squarrosus) and marsh
clubmoss (Lepidotis inundata) swell the
numbers of the large contingent of
circumboreal species even further.
A second important phytogeographical
category is formed of plants mainly
found in the Arctic belt and, further
south, only in high-altitude mountain
sites (Arctic-Alpine species).
This is a typical example of disjointed
distribution, i.e., territories too far apart
for the plants to spread by means of
their usual dispersal mechanisms.
Thread rush (Juncus filiformis) has this
type of distribution, together with
various species of the genus Carex. The
following are some rare examples:
bristle sedge, few-flowered sedge,
capitate sedge, Carex juncella, and
close-headed Alpine sedge.
An even more unique
phytogeographical situation is that of
plants which, with similar distribution
types to the above, are today found
only in restricted, fragmented sites on
Bogbean (Menyanthes trifoliata)
Cotton grass (Eriophorum vaginatum)
Marsh violet (Viola palustris)
the mountains of southern Europe.
These are “glacial relicts”, i.e., coldclimate species which spread during
the Ice Ages and, following post-glacial
warming, now only remain on sites in
southern Europe with particularly cool
microclimates and little competition,
like mountain peat bogs.
Some of the more typical plants of
marsh flora belong to this category:
Rannoch rush (Scheuchzeria palustris),
Scheuchzer’s cotton grass (Eriophorum
scheuchzeri), peat sedge (Carex
heleonastes), bog rosemary
(Andromeda polifolia), crowberry
(Empetrum nigrum), cranberry
(Vaccinium oxycoccos), small cranberry
(Vaccinium microcarpum) and the rare
dwarf birch (Betula nana).
51
52
Grass of Parnassus (Parnassia palustris)
Birdseye primrose (Primula farinosa)
Broad-leaved cotton grass (Eriophorum latifolium)
Other rare species of flora are marsh
helleborine
(Epipactis
palustris),
dioecious sedge (Carex dioica), flat
sedge (Blysmus compressus), grass of
Parnassus
(Parnassia
palustris),
Tofield’s asphodel (Tofieldia calyculata),
marsh
arrow-grass
(Triglochin
palustre), birdseye primrose (Primula
farinosa), broad-leaved cotton grass
(Eriophorum latifolium) and carnation
sedge (Carex panicea).
Amongst the more representative
vegetation is the Caricetum-davallianae
association, dominated by small
clumps of Davall’s sedge, sometimes
associated with marsh horsetail
(Equisetum palustre), grass of
Parnassus and carnation sedge. This
vegetational type is sensitive to
variations in water level caused, for
example, by artificial drainage, which
favours the entry of water-meadow
species like marsh valerian (Valeriana
dioica) and especially moor grass, large
clumps of which then tend to cover and
replace all the fen species.
The Schoenetum nigricantis association
is found in Alpine regions on more
thermophilous sites with hot summers
and at sub-mountain or even lower
altitudes. It is characterised by a few
plants of the Caricion davallianae
alliance and, among associated
species, an abundance of species of
the order Molinietalia, such as moor
grass, devilsbit scabious (Succisa
pratensis) and yellow loosestrife
(Lysmachia vulgaris) and the vegetation
of marsh reed-beds (Phragmites-
Magnocaricetea), such as marsh reed,
marsh sedge, etc..
From the ecological point of view, this
vegetation represents a primary
succession stage of silting in sites with
“hard” water and wide, flat banks,
where
the
Cladietum
marisci
association (further from the banks)
and water-meadows of moor grass
(closer in) find optimal conditions.
Black bog-rush also appears in
Mediterranean regions, where it grows
not only in wet carbonate-rich soils, but
also tolerates chlorine and sulphates,
constituting thereby sub-halophilous
associations, i.e., in waters with very
little salt.
Instead, the Primulo-Schoenetum
ferruginei association is the typical
vegetation of fens with waters rich in
dissolved limestone in Alpine regions,
especially on more continental sites at
sub-mountain and mountain altitudes.
The flora is characterised by prevailing
black bog-rush and a strong
contingent of species typical of the
Caricion davallianae alliance and
higher plants, including birdseye
primrose, tawny sedge (Carex hostiana)
and Davall’s sedge, Tofield’s asphodel,
etc.. Associated species mainly arrive
from fertile mown meadows (MolinioArrhenatheretea class).
Ecologically, it belongs to the set of
associations which appear during
silting of sloping and spring sites, with
running water rich in lime but
oligotrophic, i.e., extremely poor in
nutrients.
53
Marsh horsetail (Equisetum palustre)
Yellow loosestrife (Lysimachia vulgaris)
Aquatic invertebrates
FABIO STOCH
A great deal has been written on the
aquatic fauna of central and northern
Europe. Many detailed studies in the
United Kingdom, the Netherlands and
Belgium have revealed fairly low
numbers of species, but very specific
in relation to the environmental
characteristics described in the
preceding chapters of this book.
Significant impetus to knowledge on
peat bogs was given by the Telma
Project, financed by UNESCO in the
Detail of a sphagnum hummock
1960’s and 70’s, which aimed at
drawing up a conservation plan for the
peat bogs of Northern Europe, as well as the recent Habitat Directive of the
Nature 2000 project, which has considerably increased our knowledge of these
habitats in Europe over the last ten years.
Despite the interest and peculiarities of these environments, this abundance of
foreign literature contrasts with the paucity of Italian faunal and ecological
studies, which are more or less limited to the Alpine peat bogs. While the
number and size of peat bogs do fall from north to south - until they become
sporadic in southern Italy and on the islands - it is undeniable that this rarity
corresponds to increased interest in these biotopes, which become small
“islands” of biodiversity and are thus at greater risk of disappearing.
Our knowledge of the aquatic invertebrates of Alpine peat bogs is mainly due to
research by Giorgio Marcuzzi and colleagues (University of Padova), which
began after the war and continued sporadically for the next thirty years or so.
These studies were recently resumed as part of the monitoring of “sites of
European interest” (a category of protected areas to which most remaining
Alpine peat bogs belong) in Trentino-Alto Adige and Friuli Venezia Giulia; there
is still very little information on peat bogs in the Apennines and on the larger
Italian islands.
Damselfly nymph (Ischnura elegans)
55
■ Invertebrate life in sphagnum bogs
The main peculiarities which may be observed in the distribution of aquatic
invertebrates in peat bogs depend on whether sphagnum moss and allied
species are present or not. Despite the fact that these plants mainly
characterise high-altitude peat bogs and require a certain level of acidity, some
species also form carpets in the fens. Although detailed studies are lacking, we
do know that the fauna does not differ significantly from one bog to another,
probably because the same habitat parameters can be applied.
Studies, mostly conducted on Northern European peat bogs, have
demonstrated that their environmental mosaic allows colonisation by aquatic
populations made up of organisms small enough to live on the surface of the
thin film of water present in the hollows of leaves and, lower down, in water
trapped by sphagnum.
These micro-organisms generally tolerate specific physico-chemical conditions
which, amongst other things, may vary widely in both space (e.g., from the top
to the bottom of the sphagnum bank) and time (often even over a period of only
24 hours). Temperature, light, amount of water trapped, dissolved oxygen and
acidity (expressed in pH) are all factors which drastically affect the presence of
invertebrates.
10
surface of hummock
0
5
2
0
surface of
hummock
DEPTH (cm)
HEIGHT OF SURFACE (CM)
56
11.30 h
-5
4
6
18.30 h
-10
8
16.00 h
-15
16
18
20
22
24
TEMERATURE (°C)
Daily summer temperature variations in surface
layers of a sphagnum carpet
10
25
50
75
100
LIGHT INTENSITY (arbitrary unit of meas.)
Variations in light intensity beneath surface of a
sphagnum cushion
The surface temperature of a carpet of sphagnum varies greatly during the day,
due to season, rainfall, wind, and the shadiness of the site. There may be a
marked temperature gradient (up to 8-10 °C in summer) in the upper 10 cm of
the sphagnum, which is a poor heat conductor; the temperature tends to
stabilise in the deeper layers. In the evening, the surface cools down faster than
the underlying layers, thereby inverting the gradient.
There may also be marked differences in temperature between different areas
of the bog, particularly between the hummocks and pools of water. This
temperature difference affects species distribution in the bog, especially
species living in cold water, which form an important part of the population.
Light intensity also decreases rapidly from the surface towards the inside of a
sphagnum hummock, thereby limiting the presence of photosynthetic microorganisms (mainly micro-algae: desmids, diatoms, flagellates of the genus
Euglena; see pp. 58-59) and their predators to the top few centimetres of the
surface layer.
The concentration of dissolved oxygen varies with luminosity, which depends
on the photosynthetic activity of both sphagnum cells and micro-algae. The
presence of decomposers (bacteria and fungi) also drastically reduces the
amount of oxygen in a sphagnum carpet and in the sediment: anoxia is usually
reached 20 cm below the surface, so there are no invertebrates
at this depth.
However, one of the most important factors is
undoubtedly the amount of water retained by the
sphagnum; a small shallow pool and a sphagnum cushion
generally offer very different microhabitats, usually hosting
different fauna. The micro-fauna that can be obtained
simply by squeezing a bank of sphagnum – usually
protozoans, rotifers, nematodes, oligochaetes, gastrotrichs
(see drawing), harpacticoid copepods, hydrophilid and
hydraenid beetles, and dipteran larvae – is very different
from that obtained by filtering the water from the pools
(where hydrozoans, cyclopoid copepods, dytiscid
beetles and water bugs dominate).
The presence of most aquatic species is also limited by
the acidity level: a pH lower than 6.5 is common in
Italian peat bogs, while less than 4 is unusual. This
acidity allows acidophilic species of invertebrates
common in Italian peat bogs and those of Northern
Europe to thrive.
57
58
Microscopic forms of life among peat bog hummocks
If carefully examined in detail, peat bog
hummocks reveal their complex, threedimensional structure. The interweaving
of tiny leaves creates a mosaic of microhabitats which are revealed in all their
complexity when observed under a
magnifying-glass or a microscope. This
complexity gives rise to the hypothesis
that, the larger the carpeting hummocks,
the smaller the organisms which can
inhabit it. A microscopic protozoan will
perceive a peat bog hummock as an
immense labyrinth, far more complex and
vast than a copepod or a nematode
would find it. Still less space would be
available through the eyes of a beetle,
and an amphibian would not find the
habitat suitable at all.
This phenomenon is due to what
ecologists call the “fractal structure” of
the habitat. Since inhabitable space
expands with the decreasing dimensions
of the animals which live in it, microorganisms are clearly much more
numerous here than other invertebrates.
This is why hummocks have such a rich,
diversified microflora and microfauna.
Studies on British peat bogs show that
they contain more than 300 species of
microscopie algae, protozoa and rotifers,
whereas all the rest of the fauna treated in
this volume do not exceed more than
about 100 species.
The most common microscopic algae are
the Desmidiaceae, with several dozen
species in peat bogs. Many belong to the
genus Closterium and are sometimes
exclusive to peat bog waters. Each
individual is composed of a single cell
divided into two symmetrical halves – a
feature which makes them immediately
recognisable. They vary in size from a
hundredth of a millimetre to slightly more
than a millimetre. One explanation for
their considerable numbers is that peat
bog hummocks increase the acidity of the
water they hold by means of ion
exchange: with falling pH, the availability
of free carbon dioxide increases, and this
helps photosynthetic algae to flourish.
Also abundant in this environment are
diatoms, which can be collected in great
numbers simply by squeezing a handful
of vegetation. Diatoms are often even
Fabio Stoch
more numerous than desmids, but fewer
species are found, above all in acid
lcoations. Diatoms are unicellular
organisms protected by a siliceous
covering of complex structure - a feature
which makes them particularly attractive
to watch under the microscope.
As well as diatoms and desmids, there
are great numbers of other
photosynthetic micro-organisms, such as
cyanobacteria (blue algae),
Chrysophyceae, and phytoflagellates.
Among the latter are cells of
Chlamydomonas, of which one species,
C. acidophila, may reach densities of
more than 50,000 cells/sq.cm. in the peat
bogs of northern Europe. But perhaps the
most incredible micro-organisms which
live in this peculiar habitat are the
thecamoebae and heliozoa. The former
construct a theca, or “house”, around the
single cell of their bodies, consisting of a
transparent secretion to which minute
mineral or organic particles stick, creating
splendid, variegated figures, mainly
bottle-shaped, which have - quite rightly made these animals famous among
microscope enthusiasts. Their “houses”,
are rarely longer than one-tenth of a
millimetre. Still more incredible are the
heliozoa, such as Actinophrys sol, from
whose rounded, single-celled bodies
irradiate long pseudopods, making these
minute creatures look like tiny suns.
Lastly, among the protozoa in peat bogs,
are abundant ciliates, with bodies
covered with minute cilia, or threads,
which beat rhythmically and
synchronously together, allowing the
organism to propel itself through the
water, sometimes very quickly.
Microscopic observations of a handful of
material from a peat bog will reveal plenty
of species - a tiny world of creatures
teeming in a single drop of water.
To conclude this brief review of the
microscopic world, we must recall
several multicellular micro-organisms
which are often abundant: many species
of rotifers, gastrotrichs and tardigrades.
The latter, which climb like minute sloths
up the sphagnum stems, are perhaps the
most curious animals which inhabit this
tiny world.
c
c
a
d
a
b
b
Various thecae of thecamoebae (a, b, c) and Phacus phytoflagellates (d)
Desmids: Netrium (a), Hanthidium (b), Closterium (c)
59
■ Peat bog invertebrates
60
Flooded part of a peat bog in Tarvisio Forest area (Friuli Venezia Giulia)
The specific environmental characteristics of raised bogs and sphagnum
carpets mean that they can host interesting acidophilic species, presumably
glacial relicts, which often have boreal-alpine geographical distribution (see
pp. 76-77). These are species that live in both in Northern Europe and in on
the Alps, and sometimes even further south down the Apennines, where they
remain only on some relict sites. This category includes some species of
harpacticoid copepods, chironomid midges and beetles.
Much better known in Italy, fens without sphagnum host less specific fauna,
not dissimilar to that of other wetlands of the same kind, as these are usually
environments of fairly recent origin, with eutrophic water (i.e., rich in
nutrients), alkaline or only slightly acid, subject to brusque variations in
environmental parameters, and the aquatic invertebrate fauna is usually
species-poor.
Detailed studies of peat bogs in north-eastern Italy (Trentino, Veneto and
Friuli Venezia Giulia) have recorded less than one hundred species of aquatic
invertebrates on average for each biotype. In these habitats, the taxonomic
groups with the most species are nematodes, followed by copepod
crustaceans, insects (mainly coleopters and dipterans, with rare mayflies,
dragonflies, stoneflies and water bugs) and molluscs; the other groups have
few species.
Zoogeographical studies of some of these bogs have demonstrated that the
dominant species are cosmopolitan or sub-cosmopolitan (i.e., species with a
very wide geographical distribution in all or most continents), Holarctic (i.e.,
widely distributed in the northern hemisphere: North America and EuropeAsia) or Palaearctic (Europe-Asia alone). The remaining species are all
widespread in Europe, although (obviously in relation to the microclimate of
these areas) Mediterranean species are insignificant.
Among the aquatic invertebrates studied so far, there are no endemic
species, i.e., those with restricted distribution (e.g., exclusive to Italy or a
small part of its territory). The explanation for this is probably the fairly recent
nature of their colonisation, which must certainly have begun during the postglacial period, i.e., in the last 10,000 years.
Among the many taxonomic groups found in Italian peat bogs, only the major
ones are mentioned here, omitting species with wide ecological tolerance
which colonise the habitats of peat bogs and ponds, wetlands, streams and
lake-sides, but focussing on peat-loving species or those of particular
importance to Italian biogeography.
61
62
Cnidarians. Hydras are extremely
common in Italian peat bogs. These
small predatory polyps feed on other
minute invertebrates, such as dipteran
larvae, crustaceans (cladocerans,
copepods) and sometimes even young
newts and newt larvae. One of the
species, Hydra hadleyi, reported in a fen
in the Veneto, had previously only been
described in North America; it has never
since been found in Italy. This fact, as
well as its absence from the species
Polyp of genus Hydra
checklist of Italian fauna, is presumably
due to the almost complete lack of
attention that these invertebrates have received in faunal studies in this country.
Nematodes. The nematodes populating Italian peat bogs are well-known as
regards Alpine biotopes, where these organisms are often by far the dominant
taxonomic group. As well as species living between the roots of plants,
generally widespread and of great ecological importance, both freshwater and
terrestrial species, i.e., also present in wet soils, are found in Italian peat bogs.
They always have wide geographical distribution, and are at times locally
abundant, such as Plectus parietinus, Rhabdolaimus terrestris, Monhystera
filiformis and Paractinolaimus macrolaimus.
A study conducted on the Veneto peat bogs showed that nematodes are found
in debris on the beds of pools or
floating on the surface. Peat bog
nematodes have widely varying feeding
habits, and may be bacteriophages,
phytophages, predators or parasites.
Oligochaetes
Oligochaetes.
Although
always
present in Italian peat bogs, these
organisms are represented by a few
common widespread species which
live in many freshwater environments
(streams, pools, ponds). Lumbriculus
variegatus and Elsiniella tetraedra are
among the most abundant.
Molluscs. Although extremely rare or absent in acidic peat bogs, as the
calcium carbonate in their shells is soluble in acid, many species of molluscs
are well-represented in fens and alkaline bogs. They often have great ecological
importance, and sometimes are locally so abundant as to be worth mentioning:
Lymnaea peregra, Galba truncatula, Gyraulus albus, Bithynia tentaculata and
Valvata cristata are among the most common. Bivalves, which bury themselves
in the sediment on the bottom of pools, include Sphaerium corneum, as well as
many species of the genus Pisidium, such as P. casertanum, P. subtruncatum,
P. obtusale and P. nitidum.
Cladocerans. Very frequent in pools, these too are generally represented by
species of great ecological importance, such as Simocephalus exspinosus, S.
vetulus, Cerioaphnia pulchella, Alona affinis and A. quadrangularis, to quote
only a few. The recent finding of a species new to Italian fauna is of interest: A.
rustica, collected by squeezing mosses in a peat bog in Val d’Aosta.
Copepods. In Italian peat bogs, these
crustaceans are represented by two
different orders, cyclopoids and
harpacticoids. Cyclopoid copepods
frequent all sizes of pools, where they
can be found in very large numbers.
The most abundant species are
usually widespread, predators like
Megacyclops viridis, Macrocyclops
albidus and Diacyclops bicuspidatus,
and
the
phytophages
and/or
detritivores Paracyclops fimbratus,
Harpacticoid copepod (Bryocamptus)
Eucyclops serrulatus, Thermocyclops
dybowskii and Tropocyclops prasinus.
The most common species in high-altitude peta bogs is Acanthocyclops
vernalis, widespread in Europe, which may reach an altitude of 2800 m on
the Alps.
Next to these large-sized species (large, for copepods, means 0.7-1.8 mm
long), there are also some small species of specialised cyclopoids (just over
half a millimetre long) living among mosses, sphagnum and peat debris. Among
these, Diacyclops languidus and D. hypnicola, occasionally also found in
subterranean waters, are characteristic of peat bogs in the Alps, Apennines and
central and northern Europe.
63
Harpacticoid copepods, as well as a few commonplace species (like
Canthocamptus staphylinus and Attheyella crassa) which live in pools, include
species that live in sediment, amidst sphagnum, inside moss cushions and
even in waterlogged soil. The most common of these are Bryocamptus
pygmaeus, Epactophanes richardi and Phyllognathopus viguieri. Other species
are extremely interesting, as they live only in peat bogs and interstitial mountain
habitats, such as B. veidovskji, Elaphoidella gracilis, Moraria mrazeki, M. alpina,
Maraenobiotus veidovskji and Hypocamptus brehmi. The last four in particular
may be boreo-alpine species, but their taxonomy and distribution is still under
study.
64
Hydracari (Water mites). Information on water mites in Italian peat bogs is still
fragmentary. These interesting arachnids, with a complex life-cycle including
ectoparasitic juvenile stages living on various species of aquatic insects, are
tiny predators (a few millimetres long) and fairly frequent in Alpine and Apennine
peat bogs. They include the genera Panisus and Protzia, widespread in Alpine
biotopes with slow-moving waters, and Arrenurus (Megaluracarus) cylindratus,
in central Italian peat bogs.
Ephemopterans and plecopterans. In Italy, there are no mayflies exclusive to
peat bogs. Studies in Alpine and pre-Alpine peat bogs have more than once
recorded nymphs of Cloeon dipterum, a ubiquitous species that frequents still
waters, like pools and ponds, where they almost always form monospecific
populations. Where the water in the bog changes more frequently, as well as in
the rivulets that sometimes originate from C. dipterum is replaced by other
species, such as Centroptilum luteolum and Habrophlebia lauta, which require
more highly oxygenated water.
Also stoneflies, the aquatic nymphs of which prefer well-oxygenated flowing
waters, are very rare in peat bogs: the only species found often are those of the
genus Nemoura, like N. cinerea and N. sinuata.
Ischnura elegans
Odonates. The larvae of dragonflies and damselflies are predators at the top
of the food-chain in peat bog pools, where they are very frequent. During the
early stages their diet includes micro-crustaceans (copepods, cladocerans)
and small insect larvae; the later aquatic stages feed on larger invertebrates,
as well as tadpoles and young newts. For the ecological role they play, much
importance is also given to several species of odonates as bio-indicators of
these environments, and they have considerable importance as species of
European interest in the Habitat Directive.
65
66
The most frequent species in Italian peat bogs are Ischnura elegans and
Aeshna juncea. Rarer species include Somatochlora alpetris, A. caerulea and
Leucorrhinia pectoralis. The latter is listed in the appendix of the Habitat
Directive and is reported from Alpine peat bogs in north-eastern Italy and in
the Sebino peat bogs at Lago d’Iseo.
The smallest European damselfly, Nehalennia speciosa, is recorded from a few
sites in north-eastern Italy.
Water bugs. Very common in both raised peat bogs and fens, peat bog
heteropterans (water bugs) are, with few exceptions, predators which feed on
micro-crustaceans, the larvae of aquatic insects, and small insects that have
accidentally fallen into the water.
Water bugs are one of the most constant components of aquatic invertebrate
populations in peat bogs, although no species is particularly associated with
this type of habitat. They mainly live in the larger pools: both species which
can swim (belonging for instance to the genera Notonecta maculata and
Naucoris cimicoides) and ones which live on the surface of the water (like
Gerris and Velia) move by exploiting surface tension.
Beetles. There are many families of aquatic coleoptera (beetles) in peat bogs;
each one has specific food preferences and a characteristic lifestyle.
The haliplids include phytophagous species, which feed mainly on filamentous
algae; they are fairly good swimmers and common in peat bog pools. They are
aquatic both as larvae and adults, and the most widespread species in these
habitats is Haliplus ruficollis.
The gyrinids are predatory beetles. Their larvae hide among the bottom debris,
but adults live on the surface, where sometimes hundreds of them may be seen
milling about on the water. This specific lifestyle also corresponds to the
particular morphology of their eyes, which are compound, neatly divided into
two sections. When the insect swims on the surface, the upper part of its eyes
is above water, while the lower part is partly submerged, allowing the animal to
spot prey either above or below the water surface. The most surprising
specialisation is found in the legs: the front pair have been modified into organs
which, being spatula-shaped, are suited both to catching prey and ideal for
moving on the water. The other four legs are completely transformed into
flattened bristly swimming organs. One of the most frequent species in peat
bogs is Gyrinus paykulli.
Notonecta maculata
Ilyoris cimicoides
67
68
Dytiscids are predators of between a few millimetres and more than three
centimetres long; able swimmers, they also frequent pools and areas of open
water. They are aquatic during both larval stages and as adults. Many species
gather in Italian peat bogs, although none is exclusive to this habitat. Those
most closely associated with peat bogs are Bidessus grossepunctatus,
Hydroporus melanarius, H. tristis, Agabus congener, Ilybius aenescens and
Graphoderus austriacus. The more common and locally abundant species, but
of great ecological importance, include Copelatus haemorrhoidalis, Hydroporus
memnonius, Agabus bipustulatus, Hydaticus seminiger and, among the larger
ones, Dytiscus marginalis, which prey on large insect and amphibian larvae and
tadpoles. Hydraenids, a family of small or tiny black beetles (sometimes less
than 2 mm), are also frequent. They are found among debris, and, in sphagnum
carpets and streams (genera Ochthebius, Hydraena, Haenydra and Limnebius).
They are all scrapers which feed on the micro-algae and fungal patina forming
on submerged debris. Aquatic only as adults, the larvae are found in the wet
soil on the edges of peat bogs.
Very frequent in peat bogs are members of the family of the helophorids, small
dark beetles easily recognised by their lengthwise-grooved pronotum. They are
represented by numerous species, difficult to identify, of the genus Helophorus.
They are omnivores which mainly live in sphagnum carpets, where they nest
between fronds or detritus; they are only aquatic as adults.
The best represented beetle family in peat bogs is that of the hydrophilids,
aquatic both as larvae (during which stage they are predators) and adults (when
they are usually phytophages or detritivores). This family includes both benthic
and riparian species, belonging to numerous genera (the most frequent are
Berosus, Helochares, Enochrus, Anacaena, Limnoxenus, Hydrobius and
Laccobius, the last one with many species). Representatives of Laccobius and
Anacaena live not only among detritus, but are also frequent in carpets of moss
and sphagnum, where they are easily captured by pressing the surface with
one hand: the beetles are thus squeezed to the surface and are easy to spot
moving about, hampered by the water.
Very similar to hydrophilids and with the same lifestyle are the spheridiids, of
which Coelostoma orbiculare is one of the most typical components of peat
bog fauna. Once again, this is a beetle of great ecological importance, found in
all types of still water (pools, ponds, marshes).
Some species of the dryopid family are also frequent in peat bogs. These
beetles populate the edges, clumps of Carex spp. and sphagnum hummocks,
where they feed on micro-algae and decomposing plant material. The eggs are
deposited in rotting debris and the larvae develop in the same environment.
Characteristic of marshes and peat bogs are Dryops doderoi, present on the
Apennines and on the islands, D. anglicanus in northern Italy, and D. similaris,
which is widespread.
Lastly, bog debris hosts the larvae of the scirtids (genera Cyphon and Scirtes in
particular), which are detritivores. The adults become terrestrial and live on
shrubs and grasses, sometimes a long way from water.
Caddis-flies. Unlike the other taxonomic groups just mentioned, the
trichoptera fauna (caddis-fly) is much better known in the peat bogs in the
Apennines than in the Alps, having been studied by researchers of the
University of Perugia. Trichoptera frequent mainly pools and rivulets, only a few
species being found in sphagnum. Most caddis-fly larvae living in peat bogs,
with rare exceptions, construct a cocoon of tiny twigs and bits of wood, dead
leaves and debrisdetritus (sometimes the shells of gastropods) held together by
silken threads. These animals are detritivores, cutting up and fragmenting
dead leaves and other organic debris at the bottom of the pools, thereby
contributing towards the breakdown of organic matter. Only some species,
usually living in stretches of flowing water, do not construct cocoons and are
predators: they usually require a gravelly or stony substrate and are therefore
only to be found in marginal habitats, such as the rivulets that form
downstream from raised bogs.
Among the more frequent although not exclusive species are those of the
Caddis-fly larva of the family Sericostomatidae
69
genera L. lunatus, L. borealis, Microptema, Plectrocnemia, Sericostoma,
Stenophylax and, among those without cocoons, the many species of
Rhyacophila, such as R. dorsalis, R. intermedia and R. orobica.
70
Caddis-fly larva cocoon of the family Limnephilidae
Dipterans. Excluding the Culicidae
(mosquitoes) and the Chironomidae
(midges), almost nothing is known
about dipterans in Italian peat bogs,
although their larvae populate all sorts
of micro-habitats. These include the
families of the Ceratopogonidae (biting
midges), Psychodidae (moth flies),
Tipulidae and Limoniidae (crane flies),
Rhagionidae (snipe flies),Tabanidae
(horse flies), Stratiomyidae (soldier
flies) and Syrphidae (hover flies).
Chironomidae larvae inhabit all peat
bog micro-habitats, where both
detritivorous and predatory species are
found, the latter prevailing, belonging
to the tanypodine family. Some species
Mosquito larva
were considered true tyrphobiont
components, i.e., exclusive to these environments; nowadays they tend to be
considered tyrphophile, i.e., species preferring the peat bog environment but
not exclusive to it. Presumably their distribution is limited not so much by the
structure of the peat bog habitat, but by an acid pH, which may also occur in
other environments (dystrophic lakes, moderately polluted waters). Many
peat-loving species are reported from Alpine peat bogs. Of particular note are
Acamptocladius reissi (recently reported from Trentino-Alto Adige),
Schineriella schineri (an extremely rare species, with only three known sites in
Europe, one of which is in Italy), Labrundinia longipalpis (the only European
species of a genus which is numerous in South America, known also as a subfossil in the Lago di Nemi, near Rome). Species of the genus Psectrocladius,
like P. platypus and P. oligosaetus, are also sometimes abundant. Lastly,
Telmatopelopia nemorum is found frequently in peat bogs and woodland
pools (prevalently in alder woods).
Various species of mosquito larvae live in peat bog pools, such as Aedes
vexans, which filter fine organic debris suspended in the water. These
dipterans only live in still water, avoiding even weak currents.
71
Terrestrial invertebrates
ALESSANDRO MINELLI
The terrestrial invertebrates populating
Italian mountain peat bogs are neither
rich in species nor adequately known.
There are various reasons for the faunal
poverty of these environments.
Mainly responsible are the difficult,
selective topography and microclimatic
conditions discussed in previous
chapters. Secondly, almost all peat
bogs are not very big, and thus
represent “islands” that are too small to
sustain sufficiently numerous and
Few flowers grow on peat bogs
therefore viable populations of many
species for unlimited periods. There are
also more specific reasons. One is the dominance of plants like sphagnum
mosses, and bryophytes in general, which - for reasons which are still unclear are of practically no interest as food to almost all phytophagous insects. Another
reason why very few terrestrial invertebrates frequent peat bog vegetation is the
scarcity of flowers offering pollen, and, more importantly, nectar. This latter
situation is why some Lepidoptera, although finding food plants in a peat bog
(especially Vaccinium species) for their larvae to eat, are forced as adults to seek
food further away, in plant communities with more flowers.
There are therefore very few tyrphobiont species, i.e., those closely associated
with these habitats with peaty soil, and also few peat-loving species, which are
commonly but not exclusively found here. There are also many species of
insects and other invertebrates which are often or occasionally found, but
which gravitate towards other types of vegetation in areas around peat bogs.
Although the latter species are not listed here, it is important to take them into
account, because, in terms of biodiversity, they may represent the largest
proportion of fauna counted in a peat bog, and their presence highlights the
incessant and often massive flux of organisms between different ecosystems,
despite all our conceptual schematisation.
Grasshopper Roeseliana roeseli
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74
Euconulus fulvus
Cochlicopa lubrica
Terrestrial molluscs. The peat bog environment is one of the most inhospitable
for terrestrial molluscs, especially when plant communities grow on acid soils.
The problem is obviously more dramatic for molluscs with shells, which require
the availability of calcium carbonate. Nor is the vegetation amongst the most
appetising for these species, given the prevalence of bryophytes (seldom used
by animals, as mentioned above) and sedges, with hard scrawny leaves.
In mountain peat bogs, practically only euryecious species are to be found those which tolerate wide variations in their environment. They are more
frequent in water-meadows or leaf litter in woods, and of tiny dimensions, such
as the genera Carychium, Cochlicopa, Nesovitrea, Punctum and Euconulus. In
terms of diet, this fauna belongs to the phyto-saprophage category rather than
that of phytophages in the strict sense. The population is slightly more varied
where the substrate surrounding the peat bog is calcareous; genera include
Vallonia, Columella, Vitrea and Vertigo. The latter genus is mainly represented
by Vertigo antivertigo and V. angustior, whereas two extremely rare species, V.
genesii and V. geyeri, are listed in Annex II of the Habitat Directive.
Further away from the water, where the strictly acid nature of peat bog soil and
its perennial moisture content diminish, hygrophilous and calciphilous mountain
species can be added, such as the helicid Arianta arbustorum, the clausiliid
Macrogastra plicatula, the slug Arion subfuscus, and the curious representatives
of the genera Vitrinobrachium and Semilimax, with their rudimentary shells. The
latter two genera include species with a distribution limited to the Alps. Among
the other terrestrial molluscs found in peat bogs, the most interesting species
from the zoogeographical point of view are Nesovitrea hammonis and N.
petronella, both with a boreo-alpine distribution (see pp. 76-77).
Spiders and Phalangida. The most
important predators among mountain
peat bog invertebrates are without any
doubt the spiders. There are almost
always many species, usually
hygrophiles, which weave their webs
amongst
the
vegetation
(e.g.,
representatives of the families of the
Theridiidae, Liniphyidae, Araneidae,
Dictynidae and many Tetragnathidae),
hunt by lying in ambush (Thomisidae,
or crab spiders), or else stalk their
Araneus diadematus
victims on the ground or between
plants (Lycosidae, Clubionidae and
Salticidae). The traps constructed by spiders of various families differ widely in
appearance. Among the lower vegetation, in particular, “awnings” of nonviscous silk built by the tiny representatives of the linifiids abound. The circular
traps characteristic of the Araneida more often require the support of taller and
more robust plants.
There is much documentation available regarding spiders of central European
peat bogs, where up to fifty species of these predatory invertebrates may be
present in the different facies of the peat bog.
Instead, knowledge of the spiders of Italian mountain peat bogs is entirely
fragmentary. Some recent data are available on the related group of phalangiids
or harvestmen, but only for medium-altitude bogs. There are many species also
in this case, but none are specific to peat bog habitats.
Orthoptera. The biomass of phytophage insects in peat bogs, as in many other
terrestrial ecosystems, is represented for the most part by the Orthoptera
(which also include zoophagous species), as well as by Lepidoptera larvae
(caterpillars). Among other plant users, the largest component is made up of
the Hemiptera (mainly shieldbugs, cicadas and aphids), which are sap suckers.
There are few species of Orthoptera found in mountain peat bogs, but this the
short list does include some specialists. Some of them, like Xiphidion dorsalis,
Roeseliana roeseli, R. azami minor, Chrysochraon dispar and C. beybienkoi, lay
their eggs on marsh plants, thanks to their long ovipositor in the shape of a slim
sword. The distribution of some of these species in Italy is very limited or
localised. R. roeseli, for example, is confined to sites on the Eastern Alps, and
replaced on the Western Alps by R. azami minor; whereas C. beybienkoi is only
75
76
Glaciations and boreal-alpine species
The distribution area occupied by a
species on our planet is only partly
explained by the ecological
requirements of that species. It may be
absent from many areas which might
appear potentially suitable - a fact which
is often verified after the introduction of
a plant or animal into an area where it
did not previously occur naturally.
As well as ecology, distribution areas
are also the product of history: a history
of climatic variations, migrations, local
extinctions and re-colonisations. In
other words, distribution areas are not
immutable; on the contrary, they may be
modified greatly and also quickly,
especially during periods of intense
climatic change.
This is what happened over a large part
of Europe during the alternating Ice Ages
and inter-glacial eras of the Quaternary
epoch. During the coldest periods,
advancing glaciers drove fauna and flora
increasingly further south, as far as the
natural geographic barriers (especially
mountains and seas) would allow. For
many species therefore, the large
Mediterranean peninsulas (Iberian
Peninsula, Italy, the Balkans)
represented areas of refuge where
animals and plants could survive during
the periods of maximum glaciation and
from which, later, they once again
departed for fresh colonisation of central
and northern Europe.
The biogeographic barriers of our
continent are formed of high rugged
mountain ranges, from the Pyrenees in
the west, over the Alps and the Balkan
reliefs, as far as Anatolia: a system of
mountain chains roughly aligned along
the earth’s parallels which block the
northward re-colonisation routes taken in
post-glacial times by species which had
survived the most severe glaciations.
At high altitudes on these mountains,
especially the Alps, many populations
have thus remained stranded and,
instead of following the lines of longitude
from the Mediterranean regions towards
the heart of Europe, returned along the
valleys and southern slopes of the
mountains as the glaciers gradually
retreated. As the icecap melted, plants
and animals began to benefit from a
more favourable climate.
On occasions, starting from the same
southern refuge area, a migration began
which divided along the way, giving rise
on the one hand to populations which
settled above the treeline on the Alps,
and others (of the same species) which
continued their journey as far as
Scandinavia, without settling in Central
Europe. These were species well
adapted to life in cold environments
(peri-glacial and similar), whose
distribution area was thus split into two,
separated by great distances in between:
a northern distribution area, usually
bordering the Scandinavian peninsula,
and a southern one, corresponding to a
tract or tracts of the Alps.
The animal and plant species with this
type of distribution area are called
boreo-alpine. Slight variations on the
theme may involve additional fragments
of distribution - for example on the
Scottish mountains or the highest
summits of the Apennines in Abruzzo but their origin is always the same, i.e.,
the climatic events of the last Ice Age
and subsequent post-glacial period.
They are therefore distribution areas
which formed in fairly recent times, over
the last ten thousand years or so.
Such a limited time interval has not
been long enough, in general, for the
Alessandro Minelli
Alpine and Scandinavian populations to
have developed a sufficient level of
genetic divergence to be considered
distinct species.
Animal species with a boreo-alpine
distribution (or boreal-montane if the
southern section of the distribution area
is not limited to the Alps) live in “cold”
habitats like mountain peat bogs. These
include the gastropod molluscs
Nesovitrea hammonis and N. petronella,
the staphylinid beetle Euscnecosum
tenue, the nitidulid beetle Epuraea
placida, and some tenthredinid wasps
of the genus Dolerus.
Example of Nesovitrea and, below, boreal-alpine
distribution of Nesovitrea petronella
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ones differs, because the presence of normal wings is not always accompanied
by normal development of the muscles for their movement. Most individuals of
Ph. diligens are in any case brachypterous.
Another species in mountain peat bogs is Pterostichus rhaeticus which, despite
having wings, is flightless. It is occasionally found in sphagnum bogs, where a
very similar species which usually prefers warmer sites may also sometimes be
found: Pt. nigrita.
Loricera pilicomis (with Holarctic distribution), Europhilus gracilis (EuropeanSiberian) and Agonum atrum (European) should also be mentioned. In marginal
reed-beds, species like Oodes helopioides and Odacantha melanura are
frequent, more typical of lower altitudes and habitats without sphagnum
mosses.
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Phonias diligens
Pterostichus rhaeticus
to be found on the Sila mountains in the south. For C. dispar, only very old
reports exist for Alto Adige (South Tyrol) and this species may even now be
extinct in Italy.
In some high-altitude peat bogs species typical of Alpine meadows can also be
found, such as Kisella alpina, which colonises Rhododendron bushes on the
remains of ant-hills a few centimetres above the water-soaked ground of small
peat bogs in the South Tyrol.
There are also some species of the genera Gryllotalpa, Tetrix and Xya, as well
as Stetophyma grossum, Parapleurus alliaceus and more generalist species like
Poecilimon ornatus, Xiphidion discolor, Tettigonia cantans, T. viridissima and
Metrioptera brachyptera.
Carabid beetles. The most prestigious member of this important family of
predators is Agonum ericeti, which lives in mountain peat bogs. This is a peatloving species for which there are old reports from locations in Trentino but no
recent accounts anywhere in Italy.
The most significant species is therefore Phonias diligens. This is a peat-loving
species with Eurasian distribution, which ventures southwards in Italy as far as
the Ligurian Apennines. It reproduces in spring and the larvae develop over the
summer.
Like the other Carabidae, especially of the pterostichine tribe, it has wing
polymorphism. In other words, wing development may differ, within the same
species or even in a single population: there are mactropterous individuals, with
normally developed wings, and brachypterous individuals, with short wings.
The latter, naturally, do not fly, whereas the flying ability of the macropterous
Staphylinid beetles. These long-bodied (often extremely long) coleopterans
have a short wing-case that leaves part of the abdomen bare, and are one of
the best represented groups of terrestrial invertebrates in
mountain peat bogs. Three habitat types are home to
different communities of staphylinids.
Acylophorus glaberrimus (see drawing) and Atanygnathus
terminalis are characteristic of (but not exclusive to) true
sphagnum peat bogs. The former is found in Italy in
medium-altitude bogs, but also in fens, while the latter,
more sporadic, has also been reported in the area around
Bressanone. Also rarely found in sphagnum bogs is
Tetartopeus sphagnetorum.
In fens with short herbaceous vegetation, the most
characteristic species is the small Atheta (Philhygra)
fallaciosa, joined by the congeners A. graminicola, Boreophilia
eremita, Gabrius trossulus, Gymnusa brevicollis, Oxypoda islandica,
Philonthus corvinus, Quedius boopoides, Q. fulvicollis, Stenus bifoveolatus, S.
crassus and S. fulvicornis. The members of the last genus are easily recognised
by their large protruding eyes and mobile lower lip, or “mask”, which can
suddenly be thrust out to pounce on prey, in a similar way to that of the young
aquatic stages of damselflies and dragonflies.
At higher altitudes, above 2000 m, the most frequent staphylinid beetle is
Euscnecosum tenue, with boreo-alpine distribution. Where the water only
moves sluggishly, Gnypeta coerulea, Olophrum consimile, Philonthus coracion
and Quedius unicolor are also found among mosses and at the base of
herbaceous plants. Evidence of this community has also been found in sub-
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fossil Holocene peat accumulated close to glaciers in the
Swiss Alps.
On flowers, Eusphalerum minutum (see drawing) may be
found, represented by that sub-family of the omaliines in
which the wing-cases are normally much longer than is
generally found in staphylinid beetles.
Where there are many taller herbaceous plants, i.e., tall
sedges in reed-beds - which, although more
characteristic of the Veneto plain in Italy, are still to be
found in the mountains - the community with staphylinid
beetles appears to be richer. In particular, Erichsonius
cinerascens, Myllaena intermedia and Schistoglossa
viduata are abundant, and are joined by Atheta (Philhygra) elongata,
A. (Ph.) volans, A. (Ph.) parca, Calodera ligula, C. parca, Cryptobium fracticorne,
C. collare, Euaesthetus ruficapillus, Lathrobium impressum, L. brunnipes, L.
magistrettiorum, L. rufipenne, Myllaena minuta, Paederus melanurus,
Philonthus nigrita, Ph. fumarius, Staphylinus erythropterus, Stenus argo, S.
juno, S. phyllobates, S. trivialis, Tachyporus transversalis, Tetartopeus
paeninsularum and T. terminatus.
The microhabitats most frequented by this fauna are large clumps of sedge,
especially those of Carex elata, which guarantee less exposure to predators
and environmental fluctuations. If the water level rises, this fauna tends to climb
up the plants, although many species are capable of moving on the water
surface without any risk. Stenus in particular, has two pairs of glands next to the
anus which open and produce chemical substances (terpenes): excreted in tiny
amounts, these can abruptly lower the surface tension of the water, giving the
insect a rapid forward thrust.
For many of these species, the geographical distribution gravitates round
central Europe, the sites in northern Italy being the southern extremes of an
often discontinuous distribution area. In other cases, the Italian species are
vicariants of other phylogenetically and ecologically similar species which live
north of the Alps.
preferences of L. nigerrimus are quite
unusual: it does not feed on terrestrial
plants like its many congeners, but
attacks an aquatic plant, bladderwort.
Other representative beetle families
are the cryptophagid Telmatophilus
typhae, found on the flowers of Typha
and Sparganium, in the seeds of which
the larvae develop; the kateretids
Kateretes pedicularis and K. pusillus,
both found on sedges, and the
nitidulid Epuraea placida, a sub-Alpine
Plateumaris sericea
alpine mountain species with boreoalpine distribution which spends its life under the bark of pine trees, including
those growing in peat bogs, where it probably feeds on fungal hyphae.
Other beetles. The vast family of the Chrysomelidae, or leaf beetles, is mainly
represented in mountain peat bogs by species typical of the surrounding plant
communities, such as some species of the donaciine tribe (Donacia,
Plateumaris) which live on semi-submerged and riparian phanerogams. The
small Longitarsus nigerrimus can also be found, often associated with the
above-mentioned rove beetle Tetartopeus sphagnetorum. The diet
Ants. The ant populations of peat bogs are determined by the nature of the
soils, in which the mineral component is almost or totally absent. Therefore,
ants, including the most common, which nest only in mineral substrats, such as
many representatives of the genera Lasius, Camponotus and Formica, are
excluded. Instead, edaphic conditions are favourable to colonisation by
Myrmica and Leptothorax.
Tenthredinid wasps. The adults of this vast family of Hymenoptera look like
wasps, but without the characteristic “waist”, i.e., the extreme narrowing at
the base of the abdomen. The adults often visit flowers, whereas the larvae,
similar to caterpillars, usually feed on leaves. Some species of tenthredinids
with a boreo-montane geographical distribution in wet environments,
including peat bogs, belong to the genus Dolerus. Their larvae develop mainly
on grasses, sedges and rushes. Some of them can grow by feeding on
horsetails, plants fairly unappetising to the other animals. The adults of these
tenthredinids start to fly quite early in spring, when the willows, on which they
feed, are in flower.
The entire life-cycle of Amauronematus (various species, all rare, which may be
found in peat bogs) and Pontania is passed on willows, and give rise to the
formation of the characteristic galls on willow leaves, including dwarf species at
higher altitudes. Amauronematus includes many species living in the boreal and
sub-arctic regions of Europe, Asia and North America, so that the presence of
some species in the Alps should be interpreted as a bio-climatic relict.
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