Vegetation formations and associations of the zonobiomes along the

29
Plant Ecology 129: 29–47, 1997.
c 1997 Kluwer Academic Publishers. Printed in Belgium.
Vegetation formations and associations of the zonobiomes along the North
American Pacific coast: from northern California to Alaska
M. Peinado1 , F. Alcaraz2 , J. L. Aguirre1 & J.M.a . Martı́nez-Parras3
;
1
Departamento de Biologı́a Vegetal, Universidad de Alcalá de Henares, E-28871 Alcalá de Henares, Madrid,
Spain. E-Mail: [email protected]; 2 Departamento de Biologı́a Vegetal. Facultad de Biologı́a. E-33600
Murcia, Spain; 3 I. B. Luca de Tena. C/ Pirineos s/n. E-41005 Sevilla, Spain; Author for correspondence
Received 24 October 1995; accepted in revised form 26 July 1996
Key words: Bioclimatology, Biogeography, North America, Pacific coast, Phytosociology, Plant associations,
Vegetation formations, Zonobiomes.
Abstract
This phytosociological study, carried out according to the Braun–Blanquet method and supported by cluster analysis,
describes Walter’s zonobiomes along the North American Pacific coast between the California–Oregon state border
and Alaska (USA), including some interior zones of British Columbia and the Yukon Territory (Canada). Twenty
two floristic associations are identified and each is characterized by a unique floristic combination, a distinctive
geographical range and particular bioclimatic or edaphic conditions.
Introduction
Survey area
Walter (1985) divided the geo-biosphere into nine zonobiomes, each one being a large and climatically uniform environment characterized by distinctive zonal vegetation. Peinado et al. (1994a) described the
climax associations that characterize the zonobiomes
between the southern tip of the Baja California Peninsula (22 530 N) and approximately the California–
Oregon state border (42 N). By means of phytosociological relevés and field data taken between 1989
and 1992, the relations among zonobiomes, associations, bioclimatic belts, ombrotypes and physiognomical formations thriving in that latitudinal range were
described in that article. A sketch of these relations is
shown in Table 1.
Between 1992 and 1994 we carried out new
phytosociological campaigns from northern California
to Alaska, and registered 1156 new phytosociological
relevés, 254 of which are now employed to analyze climax vegetation, describe dominant plant associations,
and delimit zonobiomes, bioclimatic belts and ombrotypes between the northern border of the already surveyed area and the latitude 64 N in Alaska.
Except for some inland zones (see below) the surveyed
area (Figure 1) stretches from 41 to 61 along the
Northern American coast between sea level and the
summit line of the mountain ranges of the northern
part of the Pacific Border System (Brouillet & Whestone 1993). Two parallel belts of mountains dominate
the area. In the north, the Chugach and Saint Elias
Mountains of Alaska and the Insular Mountains of
the islands of Queen Charlotte and Vancouver, constitute a seaward fringe of peaks. To the south, the
Coast Ranges between northern California and Oregon (the Klamath and the Siskiyou) and Washington
(including the Olympics) dominate the outer coastal
topography. Throughout coastal British Columbia, the
surveyed area stretches from sea level up to the summit
line of the Coast Range, which separates it from the
drier regions of the east. From the Fraser River Valley, in southeast British Columbia, southwards, across
Washington and Oregon, the Cascades define the eastern boundary. Between the Coast Ranges and the Cascades, the fertile but drier Puget Basin and Willamette
Valley are formed.
Code
CY
CE
YU
ID
AM
BE
RO
AE
DU
CA
LO
CA
GAR
LIT
UM
OXA
PC1
SIT
OXA
PC2
LAR
THU
ENG
GYM
LUP
GLA
LYC
TSU
ANE
LAT
NEO
PGM
NAN
RUB
LAM
Association
Zonobiome
Bioclimatic belt
Formation
Ombroclimate
Antigono leptopi-Cyrtocarpetum edulis
Cercidio praecocis-Prosopidetum palmeri
Yucco validae-Fouquierietum diguetii
Agavo cerulatae-Idrietum columnaris
Ambrosio chenopodifoliae-Larreetum tridentatae
Bergerocacto emoryi-Agavetum shawii
Roso minutifoliae-Aesculetum parryi
Fraxino angustifoliae-Aesculetum parryi
Malosmo laurinae-Quercetum dumosae
Calystegio intermediae-Ceanothetum megacarpi
Lonicero denudatae-Quercetum agrifoliae
Ceanothus pumilus-Calocedrus decurrens
Arbutus menziesii-Quercus garryana
Arbutus menziesii-Lithocarpus densiflorus
Umbellularia californica-Quercus agrifolia
Oxalis oregana-Sequoia sempervirens sub. Lonicera interrupta
Rhododendron macrophyllum-Pinus contorta
Polystichum munitum-Picea sitchensis
Oxalis oregana-Sequoia sempervirens sub. Tsuga heterophylla
Cryptogramma acrostichoides-Pinus contorta
Thuja plicata-Larix occidentalis
Thuja plicata-Tsuga heterophylla
Picea engelmannii-Abies amabilis
Gymnocarpium dryopteris-Abies amabilis
Lupinus subalpinus-Abies lasiocarpa
Picea glauca x engelmannii-Abies lasiocarpa
Lycopodium annotinum-Picea sitchensis
Abies amabilis-Tsuga mertensiana
Anemone multifida-Picea glauca
Pinus latifolia-Picea glauca
Betula neoalaskana-Picea glauca
Picea glauca-Picea mariana
Betula nana-Picea glauca
Rubus chamaemorus-Picea mariana
Larix laricina-Picea mariana
II
III
Thermotropical
Hiemilignosa
Siccideserta
Semiarid
Arid
Semiarid
Mesotropical
III–IV
Inframediterranean
Durifruticeta-Siccideserta
IV
Thermomediterranean
Durifruticeta
Semiarid-Dry
Durisilva
Aciculisilva
Durisilva
Mesomediterranean
IV–V
V
VII
Mesomediterranean,
Colline, Montane
Colline
Montane
Aciculisilva-Durisilva
Aciculisilva
Dry-Subhumid
Subhumid
Humid
Subhumid-Humid
Humid-Perhumid
Subhumid-Humid
Humid-Perhumid
Uppermontane
Humid
Perhumid
Humid-Perhumid
Perhumid
Subalpine
Humid
Mesoboreal
Perhumid
Dry
Meso-Supraboreal
Supraboreal
Humid
Dry-Subhumid
Dry
Dry-Subhumid
Subhumid
30
Table 1. Sketch of the relations among associations, zonobiomes, ombrotypes, bioclimatic belts and formations along the northern Pacific coast. Associations marked with
were described in Peinado et al. (1994a)
31
Figure 1. Situation of the surveyed area.
The surveyed area stretched inland in only two
cases: (a) in the southwestern part of the Yukon Territory and neighbouring Alaska, the summit line of the
Pacific Northwest System was crossed to take relevés
of the boreal forest, which occurs in the lee of the
Chugach and Saint Elias Mountains and reaches its
western coastal limit near Anchorage (Alaska). This
inland area stretched between Whitehorse (Yukon Territory) and Fairbanks (Alaska), mainly following the
Dalton and Alaska highways; and, (b) the Clearwater
National Forest in Idaho and Montana (114–117 W)
was also surveyed to take relevés from the easternmost
penetrations of the Pacific montane forest.
The area stretches from approximately 41 300 N in
California to Denali National Park in Alaska (64 N).
In longitude it reaches its western limit on the Kenai
o
Peninsula, at approximately 152 W, while the easterno
most relevés were taken at 115 W in British Columbia
and Montana; however, most of the relevés (194) were
taken between the Pacific coast and the Pacific Border
System windward slopes.
The geology is extremely complex and forms a
mosaic of many different rock types. However acidic
soils predominate, since a huge granitic batholit dominates the geology of the mainland coastal mountains
northward from the North Cascades to Alaska. In any
case, climate becomes the strongest factor conditioning plant growth so that the influence of rock types
becomes less important: thick, acidic, organic layers can develop over all kinds of rocks. Under a very
oceanic influence, regardless of the geologic origins of
the soils, stunted forests become common, primarily
because of the huge amount of rainfall that leaches soil
components.
Inland, in the lee of the British Columbia Coastal
Ranges and in the Yukon, the whole area was heavily
glaciated at least once during the Quaternary (Hughes
et al. 1969). The glaciers altered the surface, building
smoothed plateaus, mountains and valleys; the bedrock is often overlain by glacial, fluvial or lacustrine
deposits; in late glacial times water draining off wasting ice deposited large sheets of infertile sand that now
form extensive dunes supporting Pinus contorta var.
latifolia communities. Permafrost is a common feature
in most of this area.
The Pacific coast of North America has a maritime climate, characterized by wet mild winters, cool
relatively dry summers, and a long frost free season.
During all seasons the prevailing westerly winds are
moisture-laden from the passage over relatively warm
seas. In winter, the land is colder than the ocean, and
often there are precipitations along the coastal lowlands. However, in the southern part of the study area,
mainly between northern California and southern British Columbia, the land along the coast is warmer than
the ocean during the summer and, consequently, when
the wind reaches the low coastal area, there is little or
no precipitation.
So, from northern California to coastal Alaska there
are two great macroclimates: temperature (with relatively wet summers) and mediterranean (with dry summers). The first prevails over most of the territory,
32
while the second occurs from northern California to
southern Oregon up to approximately 40circ300 on the
coast and 43 150 inland (Peinado et al. 1994a, b; Delgadillo 1995). Although some climatic diagrams from
Oregon, Washington and, even Vancouver (cf. Walter
& Lieth 1975; Walter 1985; Franklin 1988), show typically mediterranean curves, cryptoprecipitations from
the summer fogs supply an additional amount of unrecorded water of up to 200 mm (Ruth 1954; Azevedo
& Morgan 1974), and extended periods of cloudiness
and fog often greatly reduce evaporation.
Besides these prevailing macroclimates, topography is the most important feature governing precipitation patterns. The Pacific Mountain System stretches
like a great stone wall from central coastal Alaska to
the southern border of the surveyed area (and, in fact,
on to Baja California), presenting an effective barrier
to the moisture-laden westerly winds. Rainfall records
from stations along a west-to-coast transect at 52 300
show this pattern. Bella Bella, a station situated on a
coastal island, received an average annual precipitation
of 2700 mm. Ocean Falls, on the mainland and about
24 km from the shoreline, receives 4400 mm. Bella
Coola, situated at the bottom of a fiord, about 65 km
inland, receives 1550 mm. Kleena Kleene, in the leeward of the Coast Range, averages only 355 mm per
year.
Mean annual precipitation west of the mountain
axis generally ranges from 800–1000 mm for the driest
stations of northern California and southern Oregon
(Major 1988; Franklin & Dyrness 1988) to 3400 along
the coastal plains and windward slopes of northern
Oregon, Washington (Waring & Franklin 1979; Franklin & Dyrness 1988), British Columbia (Krajina 1965;
Brooke et al. 1969) and Alaska (Hultén 1968; Viereck
& Little 1991). Everywhere, 75–85% of the precipitation occurs between October and March. Near the
coast and at sea level the mean annual temperatures
( C) ranges from 14.5 at San Francisco, 11.5 at Crescent City (California), 10.6 at Quinault (Washington)
to 6.5 at Sitka (Alaska).
The climate changes in the lee of the coastal mountains, which are responsible for the drier climate that
occurs in some surveyed valleys, such as the Willamette Valley and other interior valleys of southwestern Oregon, and the Puget Trough in Washington. Annual precipitation (mm) means for some stations situated in these areas are: Medford, Oregon,
497; Grant Pass Oregon, 767; Salem, Oregon, 767;
Greenwater, Washington, 1487; Elwha Ranger Sta-
tion, Washington, 1431 and Sequim, Washington, 418
(Franklin & Dyrness 1988).
A zone of highly continental boreal climate occupies the lee of the coastal range in northwestern British Columbia, southwestern Yukon and the interior
of Alaska (Elliott-Fisk 1988; Brouillet & Whetstone
1993). The climate is very continental, the summers
are short but relatively warm (temperatures may reach
above 30 C ), the winters are long, extremely cold
(temperatures below ,40 C are common and the coldest month averages below ,25 C ) and dry; annual
temperature fluctuations exceed 40 C and at some
sites can vary seasonally by almost 90 C (Oechel
& Lawrence 1985). Although precipitation is light
(150–300 mm per year in interior Alaska), evaporation is low and permafrost forms an underground
layer so that bogs and wet areas are common. Mean
annual precipitation (mm) ranges from 250 at Whitehorse on the southeast of the surveyed boreal area,
to 630 at Homer (Alaska) on the boundary between
temperate and boreal climates. Precipitation minimums (190 mm) have been recorded in the Ruby Range
Ecoregion (Oswald & Senyk 1977).
According to the climatic classification into macrobioclimates (Rivas-Martı́nez et al. 1993 modified by
Rivas-Martı́nez 1994) that we used in the previous article on more southern Pacific coast zonobiomes, the
following bioclimatic belts and rainfall types or ombrotypes can be recognized in this northern study area:
1. Mediterranean macrobioclimate (Zonobiome IV):
Bioclimatic belt: Mesomediterranean.
Ombrotypes: Subhumid, humid and perhumid.
2. Temperate macrobioclimate (Zonobiome V):
Bioclimatic belts: Colline, montane and subalpine.
Ombrotypes: Perhumid and humid.
3. Boreal climate (Zonobiome VIII):
Bioclimatic belts: Mesoboreal and supraboreal.
Ombrotypes: Dry and subhumid.
Materials and methods
Field work was carried out between 1992 and 1994.
1156 phytosociological relevés were registered in sites
selected on the basis of physiognomy, structure and
species dominance. Relevés were taken in every kind of
plant community, from forests to grasslands. Depend-
33
ing on the community, plot sizes vary from 200 m2
(forests) to 2 m2 (grasslands). For each relevé, cover/abundance data of all vascular species were recorded using the Braun-Blanquet (1979) scale. Following the process described in Kent & Coker (1992) the
relevés were arranged by means of tabular sorting and
rearrangement of both relevés and species. In this way
several synthetic tables grouping homogeneous relevés
were obtained. Further bibliographic research, mainly
using different survey books on the vegetation of the
territory (Franklin 1988; Franklin & Dyrness 1988;
Elliott-Fisk 1988; Peet 1988; Lausi & Nimis 1991),
allowed us to conclude that 232 of our relevés corresponded to vegetation types that could be considered as
zonal climax communities. These relevés were used in
numerical analysis.
For the numerical analysis the cover/abundance values on the scale of Braun-Blanquet were transformed
into the 1–9 ordinal scale of van der Maarel (1979). The
clustering was carried out with the program SYN-TAX
5.0 (Podani 1993), starting with a matrix that included
every plant (471 taxa) recorded in the relevés together
with their respective coverage indices. The classification was made using Euclidean distance with a average
linkage clustering method of similarity.
The resulting classification allowed us to distinguish fourteen main vegetation groups. With the goal of
identifying the floristical composition of these groups,
a synthetic phytosociological table was elaborated by
scoring species in percentage or constancy classes,
according to Braun-Blanquet’s scale as modified by
Géhu & Rivas-Martı́nez (1982). A more detailed
phytosociological analysis based on a careful study
of the relevés, including studies on the distributional
ranges of each species, and on the available climatological, edaphological and topographical data, allowed
us to identify eight new associations, which had not
been separated in the numerical analysis. Locations of
relevés (measured with Global Position System) can
be obtained from M. Peinado upon request.
Plant nomenclature follows Kartestz (1994).
Results
The cluster diagram is shown in Figure 2. This initial
relevé classification separated fourteen groups. The
subsequent classic phytosociological analysis separated eight additional groups. Table 2 shows the floristical composition of these twenty two groups by scoring
species in percentage classes. To limit the size of this
table, only those taxa reaching indices III, IV or V in
at least one group have been listed, but the complete
table can be obtained from M. Peinado upon request.
The synthetic table joins these groups or floristical associations into four great types: Type I, enclosing associations in which some mediterranean genera (such as Ceanothus, Calocedrus, Quercus, Lithocarpus, Arbutus) are dominant; Type II, enclosing
associations dominated by taxa belonging to the Vancouveran floristic element (Takhtajan 1986; McLaughlin 1989); this type is constituted by the coniferous
forest found on coastal lowlands between Oregon and
southeastern Alaska; Type III, enclosing two associations dominated by conifers occurring in mountainous
zones near the coast from Oregon to British Columbia,
as well as at sea level but in the lower latitudes of the
Alaskan coast; finally, Type IV encloses three groups
which are dominated by conifers of the genus Picea
and deciduous trees that occur in the boreal zone.
Discussion of results
Three large physiognomical formations or forest zones
that have already been recognized in the surveyed area,
can be related with our four types: mixed evergreen
forest (Type I), Pacific coast coniferous forest (Types
II and III) and boreal forest or taiga (Type IV). These
tree formations seem to correspond to Walter’s zonobiomes IV (Sclerophyllous forest), V (Oceanic, temperate forest) and VIII (Boreal forest), respectively.
Type I, Mediterranean associations
Mixed evergreen forest (Sawyer et al. 1988; Franklin 1988: Franklin & Dyrness 1988; Barbour &
Christensen 1993) is the classic broad sclerophyll
forest formation described by Cooper (1922) that was
ecologically studied in the well-known work by Whittaker (1960). This forest type has a rather dense,
species-rich overstory of sclerophyll, hardwoods and
needle-leaf evergreen trees. In northern California and
southern Oregon common associates are Arbutus menziesii, Calocedrus decurrens, Lithocarpus densiflorus,
Pseudotsuga menziesii var. menziesii, Quercus chrysolepis, Q. kelloggii, and Umbellularia californica (Barbour 1988; Sawyer et al. 1988).
The Arbutus menziesii-Lithocarpus densiflorus
association is a dense forest (cover up to 100%), dominated by a closed canopy up to 35 m in height, constituted by Arbutus menziesii, Lithocarpus densiflor-
34
Table 2. Frequency of taxa in the sampled associations. Frequency is shown in percentage classes: V
21–40%, I 1–20%
=
= species occurring in 81–100% of the plots, IV = 61–80%, III = 41–60%, II =
Association
Number of relevés
CAL
n=10
GAR
n=14
LIT
n=10
OXA
n=16
PC1
n=5
PC2
n=3
THU
n=30
LAR
n=9
GYM
n=6
ENG
n=7
TSU
n=3
SIT
n=19
LYC
n=12
LUP
n=7
GLA
n=7
NEO
n=9
ANE
n=9
LAT
n=6
NAN
n=8
PGM
n=7
RUB
n=12
LAM
n=12
Type I: Mediterranean taxa
Ceanothus prostratus ssp. pumilus
Pinus jeffreyi
Calocedrus decurrens
Eriophyllum lanatum var. achillaeoides
Hordeum jubatum
Achillea millefolium var. occidentalis
Aspidotis densa
Elymus arizonicus
Quercus kelloggii
Quercus garryana
Taxicodendron diversilobum
Arbutus menziesii
Ceanothus integerrimus
Pinus ponderosa var. ponderosa
Lithocarpus densiflorus
Quercus chrysolepis
Lonicera hispidula var. vacillans
Ceanothus vestitus var. hookeri
Sequoia sempervirens
Umbellularia californica
Scrophularia californica var. californica
Stachys bullata
Cytisus scoparius
Garrya elliptica
Myrica californica
V
V
V
IV
IV
III
III
III
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II
III
I
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III
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V
V
V
V
IV
III
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II
III
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II
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V
V
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V
IV
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III
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II
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V
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III
III
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IV
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Types II and III: Temperate taxa
Pinus contorta var. contorta
Amelanchier utahensis
Thuja plicata
Vaccinium membranaceum
Paxistima myrsinites
Larix occidentalis
Mahonia aquifolium
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Abies grandis
Amelanchier alnifolia
Spiraea betulifolia var. lucida
Symphoricarpos var. albus
Holodiscus discolor
Chimaphila umbellata ssp. occidentalis
Pinus ponderosa var. scopulorum
Acer glabrum
Abies amabilis
Clintonia uniflora
Menziesia ferruginea
Valeriana sitkensis
Picea engelmannii
Ribes lacustre
Streptopus roseus var. roseus
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.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
II
II
.
.
.
.
.
.
.
.
.
I
.
I
.
I
II
.
I
.
I
I
.
.
I
I
IV
IV
IV
IV
IV
IV
III
III
.
III
.
.
.
.
.
.
I
I
.
.
I
.
.
V
V
IV
IV
.
.
.
.
.
II
.
.
.
.
.
V
III
III
II
V
III
III
.
.
.
.
.
.
.
.
V
IV
V
IV
.
.
II
.
.
.
.
.
I
.
I
.
II
II
.
.
I
.
.
.
.
.
.
.
.
.
.
.
IV
.
.
.
.
.
.
.
.
.
I
.
I
.
.
I
II
.
I
.
.
.
.
.
.
.
.
I
.
II
III
.
.
II
I
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Table 2. Continued
Association
Number of relevés
CAL
n=10
GAR
n=14
LIT
n=10
OXA
n=16
PC1
n=5
PC2
n=3
THU
n=30
LAR
n=9
GYM
n=6
ENG
n=7
TSU
n=3
SIT
n=19
LYC
n=12
LUP
n=7
GLA
n=7
NEO
n=9
ANE
n=9
LAT
n=6
NAN
n=8
PGM
n=7
RUB
n=12
LAM
n=12
Lonicera involucrata
Chamaecyparis nootkatensis
Tsuga mertensiana
Dryopteris dilatata
Picea x lutzii
Abies lasiocarpa
Lupinus arcticus ssp. subalpinus
Pedicularis racemosa
Ribes acerifolium
Luzula glabrata var. hitchcockii
Picea glauca x engelmannii
Sorbus sitchensis var. sitchensis
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
I
I
.
I
.
.
.
.
.
.
.
.
I
.
.
.
.
.
.
.
.
.
.
II
.
.
II
.
.
.
I
.
.
.
.
II
III
.
.
.
.
.
.
.
.
.
.
III
.
IV
IV
.
.
.
II
.
.
.
.
.
I
.
.
II
.
.
.
.
.
.
.
.
.
.
V
IV
II
.
.
.
.
.
.
I
I
I
II
.
.
V
V
III
III
III
.
II
I
.
.
II
.
V
.
.
.
.
V
IV
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Types I, II and III: shared taxa
Pseudotsuga menziesii var. menziesii
Elymus glaucus
Trientalis borealis ssp. latifolia
Vaccinium ovatum
Polystichum munitum
Rubus parviflorus var. parviflorus
Oxalis oregana
Rubus vitifolius
Trillium ovatum
Corylus cornuta var. californica
Acer macrophyllum
Maianthemum racemosum ssp. amplexicaule
II
I
.
.
.
.
.
.
.
.
.
.
V
III
I
.
.
.
.
.
.
II
I
.
V
I
III
III
.
I
.
.
.
II
I
.
III
I
II
V
V
IV
IV
III
III
III
III
III
III
.
.
IV
.
.
.
.
.
.
.
.
V
II
.
.
II
II
.
.
.
.
.
.
V
.
I
I
IV
I
I
I
I
I
II
I
V
I
.
.
.
IV
.
I
I
.
.
.
III
.
.
I
I
I
.
I
I
.
.
I
I
.
.
.
.
III
.
.
.
.
.
.
II
.
.
.
II
.
.
.
.
.
.
.
III
.
.
.
IV
.
II
I
I
.
I
I
.
.
I
.
.
.
.
.
.
.
.
.
I
.
.
.
.
I
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Pteridium aquilinum var. pubescens
Rhododendron macrophyllum
Gaultheria shallon
Tsuga heterophylla
Mahonia nervosa
Rosa gymnocarpa
Maianthemum racemosum ssp. racemosum
Maianthemum stellatum
Tiarella trifoliata var. trifoliata
Picea sitchensis
Blechnum spicant
Maianthemum dilatatum
Alnus rubra
.
.
.
.
.
.
.
I
.
.
.
.
.
I
.
.
.
.
.
I
.
.
.
.
.
.
III
I
I
.
I
.
I
.
.
.
.
.
.
I
I
II
II
I
II
.
.
.
I
I
I
I
IV
IV
I
.
.
.
.
.
.
II
.
.
.
II
.
V
.
.
II
.
.
.
.
.
.
II
I
I
II
V
III
II
I
I
I
.
I
I
II
II
.
.
II
I
IV
III
III
.
.
.
.
II
I
.
.
V
.
.
I
I
I
.
II
I
II
.
.
.
III
.
.
III
.
III
.
I
.
I
.
.
.
II
.
.
II
II
II
.
.
.
.
.
.
II
IV
.
.
.
II
III
V
III
III
III
.
.
.
.
.
.
.
.
II
IV
.
.
.
.
.
.
.
.
.
I
.
.
.
.
.
.
.
.
.
III
.
.
I
.
III
.
.
.
I
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Boreal taxa
Betula neoalaskana
Picea glauca
Mertensia paniculata var. paniculata
Rosa acicularis ssp. sayi
Ribes triste
Anemone multifida
Salix brachycarpa
Galium boreale
Abies bifolia
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
V
V
III
III
III
.
.
.
.
.
V
II
II
.
III
III
II
.
.
V
I
III
.
I
II
IV
III
.
V
II
.
.
.
.
II
.
.
V
I
I
I
.
.
.
.
.
I
I
II
.
.
I
.
.
.
I
II
II
I
.
.
.
.
35
36
Table 2. Continued
Association
Number of relevés
CAL
n=10
GAR
n=14
LIT
n=10
OXA
n=16
PC1
n=5
PC2
n=3
THU
n=30
LAR
n=9
GYM
n=6
ENG
n=7
TSU
n=3
SIT
n=19
LYC
n=12
LUP
n=7
GLA
n=7
NEO
n=9
ANE
n=9
LAT
n=6
NAN
n=8
PGM
n=7
RUB
n=12
LAM
n=12
Betula nana
Arctostaphylos rubra
Potentilla fruticosa
Salix myrtilifolia var. myrtilifolia
Salix reticulata ssp. reticulata
Ledum groenlandicum
Salix glauca var. acutifolia
Picea mariana
Rubus chamaemorus
Equisetum sylvaticum
Salix arbusculoides
Agrostis exarata
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
II
.
.
II
.
I
.
III
.
II
.
I
I
.
.
.
.
.
II
I
.
.
.
II
.
.
.
.
.
.
V
IV
IV
III
III
IV
III
.
.
II
.
I
III
III
III
III
II
V
V
V
II
.
II
I
III
II
II
II
.
V
III
V
IV
III
II
.
IV
II
I
I
.
V
III
V
III
IV
III
III
Types II, III y IV: shared taxa
Arctostaphylos uva-ursi
Pinus contorta var. latifolia
Betula papyrifera
.
.
.
.
.
.
.
.
.
.
.
.
III
.
.
II
.
.
I
.
.
III
V
IV
.
.
.
.
III
.
.
.
.
.
.
.
.
.
III
III
II
.
.
II
.
II
.
.
IV
.
.
IV
V
.
I
.
.
I
.
.
.
.
I
.
.
III
Shepherdia canadensis
Aralia nudicaulis
Cornus canadensis
Gymnocarpium dryopteris
Oploplanax horridum
Lycopodium annotinum
Orthilia secunda
Pyrola chlorantha
Rosa woodsii
Vaccinium ovalifolium
Rubus pedatus
Athyrium filix-femina ssp. cyclosurum
Viburnum edule
Equisetum arvense
Epilobium angustifolium
Populus balsamifera ssp. balsamifera
Streptopus amplexifolius
Alnus viridis ssp. sinuata
Linnaea borealis ssp. longiflora
Populus tremuloides
Empetrum nigrum ssp. hermaphroditum
Geocaulon lividum
Vaccinium vitis-idaea
Vaccinium uliginosum
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
I
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
I
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
II
.
.
.
.
.
.
.
.
.
.
.
II
.
.
.
.
.
.
I
I
I
I
.
.
.
.
I
I
I
I
.
.
.
.
I
II
.
.
.
.
.
III
III
I
.
II
.
.
.
.
.
.
.
.
.
.
.
.
.
IV
II
.
.
.
II
.
I
V
III
III
I
.
.
.
.
II
II
.
.
.
.
II
.
I
.
.
.
.
.
.
III
V
V
I
V
IV
III
III
.
III
I
III
.
II
II
.
I
II
I
.
I
.
.
.
.
IV
IV
II
.
II
.
.
.
II
II
.
.
.
.
.
.
IV
.
.
.
.
.
.
.
II
II
II
.
.
I
.
I
II
II
I
.
.
.
.
.
I
.
.
.
.
.
.
.
V
V
III
IV
II
.
.
III
IV
I
I
II
I
I
II
.
I
I
II
.
II
I
I
.
II
I
.
.
.
.
.
.
.
.
I
.
I
.
I
I
I
.
.
.
.
.
.
I
V
IV
III
III
III
II
I
.
V
III
III
.
.
.
I
I
II
I
I
I
.
.
II
II
IV
III
II
III
I
.
.
II
II
III
V
IV
III
III
III
III
III
II
I
II
.
.
III
.
.
.
.
.
II
I
I
.
.
.
I
.
II
I
.
.
III
II
.
II
I
.
II
.
I
.
.
.
II
II
.
.
.
.
I
I
II
.
.
.
V
IV
.
III
.
.
II
.
II
.
.
I
I
.
.
.
.
.
.
III
II
.
.
.
II
I
V
IV
IV
III
.
.
.
.
.
.
.
.
.
.
.
.
.
II
I
.
.
I
.
I
.
III
V
V
.
.
II
.
.
II
I
.
.
.
I
.
.
II
I
.
.
I
.
.
IV
III
V
V
I
.
II
.
.
.
.
.
.
.
.
.
I
I
I
.
.
II
.
I
III
IV
V
IV
37
Figure 2. SYN-TAX classification of 232 relevés, using all the vascular taxa included in them (471). N
group.
us and Quercus chrysolepis; this canopy is towered
by scattered individuals of Pseudotsuga menziesii var.
menziesii that form an overstorey up to 65 m high. The
association appears in the Klamath and Siskiyou mountains on the coast of northern California and southern
Oregon. This area, whose climate data correspond to
the mesomediterranean belt under a humid ombroclimate, is roughly coincidental with that of the redwood
association (Oxalis oregana-Sequoia sempervirens;
see below); the Arbutus menziesii-Lithocarpus densiflorus association is essentially a redwood border forest
occurring chiefly on sunny or leeward slopes, which
receive less summer fog than the slopes with redwood
forest. In fact, both Whittaker (1960) in the Siskiyou
and Klamath, and Griffin (1988) in northern California
refer a tan oak-madrone forest (L. densiflorus-A. menziesii) that substitutes redwood forests inland according to a decreasing-humidity gradient. This ecological role is similar to that played by the Umbellularia
californica-Quercus agrifolia association southwards,
between Humboldt and Monterey counties (Peinado
et al. 1994a).
=number of relevés clustered in each
Thus, physiognomically, ecologically and floristically the Arbutus menziesii-Lithocarpus densiflorus
association is closely related to other associations
described in the area: Klamath Mountain mixed
evergreen forests (Whittaker 1960; Barbour 1988),
black oak-madrone forest (Cooper 1922; Mason 1947)
and Pseudotsuga-sclerophyll type (Franklin & Dyrness 1988); the Lithocarpus-Arbutus-Quercus forest
described by Griffin (1988) is only partially related
to the Arbutus menziesii-Lithocarpus densiflorus association, because Griffin’s description includes some
southern oak forests (from Humboldt County southward) belonging to the above-mentioned Umbellularia
californica-Quercus agrifolia association.
The SYN-TAX program grouped the Arbutus
menziesii-Quercus garryana association near the Arbutus menziesii-Lithocarpus densiflorus association. The
former is dominated by a more or less closed canopy
of deciduous (Quercus garryana, Q. kelloggii, Corylus
californica) and evergreen trees (Quercus chrysolepis,
Arbutus menziesii, Umbellularia californica), towered
by several conifers (Pinus ponderosa var. ponderosa, Calocedrus decurrens, Pseudotsuga menziesii
38
var. menziesii), which, together with the lack of
Lithocarpus densiflorus, are an outstanding difference
in comparison to the Arbutus menziesii-Lithocarpus
densiflorus association. However, the many shrubs,
vines and forbs in the understorey shared by both associations provoked their close grouping.
When plotted on a map of site locations, the relevés
of this association are circumscribed to the valley bottoms and lowlands enclosed by the Cascade Range on
the east and the Coast Ranges or Siskiyou Mountains
on the west. Except for the boreal ares, these valleys
are the warmest and driest regions of the surveyed
area because they are in the rainshadow of the coastal
mountains. In this area several communities with Quercus garryana, Q. kelloggii and conifers have already
been described; the Arbutus menziesii-Quercus garryana association is closely related to some of them: the
Quercus and coniferous forests of the interior valleys
of western Oregon (Franklin & Dyrness 1988); the oak
woodland (Whittaker 1960); the black oak forest type
(Waring 1969); some of the northern oak woodland
of Griffin (1988), and most of the Oregon oak forests
(Küchler 1988).
A third association included into Type I is the Oxalis oregana-Sequoia sempervirens already described
by us (Peinado et al. 1944a) as grouping redwood
(Sequoia sempervirens) forests. An interesting problem is the changing clustering of this association; in
the present cluster it is grouped into the mediterranean
type; however, using the same sixteen relevés, and
also employing Euclidean distance as a measure of
similarity, our previous cluster (Peinado et al. 1994a)
grouped it with the temperate forest now included in
Type II. The question is whether redwoods belong to
the mediterranean zonobiome (Type I) or to the temperate zonobiome (Type II). Even though the climate
diagrams from stations in the redwood range are mediterranean, there is a water surplus from the summer
fogs that equilibrates the evapotranspiration losses.
An answer to the question can be given from a
floristical viewpoint. When the species linked to the
redwoods are plotted on a map it is revealed that the distribution areas of none of the associated species completely coincides with that of Sequoia sempervirens.
Most of the associated species overlap into the redwood area and extend broadly beyond. Some of them
extend northward into British Columbia and, even, as
far as Alaska; some southward along the coast to Baja
California; and some species only reach the neighbouring North Coast Range or the Sierra Nevada-Cascades
axis.
Most of the floristic assemblage associated with
redwoods can be divided into two groups; the northern group, closely related to the Vancouveran floristic
element (Takhtajan 1986; McLaughlin 1989; Peinado
et al. 1994b), and the southern group, linked to the
Californian floristic element (Raven 1988; Peinado et
al. 1994b). These groups support two floristical and
climatic subassociations (Peinado et al. 1994a): (a) the
Lonicera hispidula subassociation, of the mesomediterranean belt, supported by many Californian elements; and (b) the Tsuga heterophylla subassociation,
of the colline belt, differentiated by some Vancouveran elements. This floristically intermediate composition between temperate and mediterranean is the origin
of the difference in grouping of the Oxalis oreganaSequoia sempervirens associations in the two clusters.
As discussed below, this intermediate floristical composition also agrees with Walter’s map (1986: Figure
2) where coastal northwestern California is drawn as a
zonoecotone between both zonobiomes.
The fourth association included in mediterranean
Type I is the Ceanothus pumilus-Calocedrus decurrens association, but the Euclidean distance shows a
clear separation from its neighbouring associations.
Physiognomically, this association looks like a very
open forest (tree cover <50%) whose dominant species
(Calocedrus decurrens and Pinus jeffreyi) show poor
growth and short height; the understorey is dominated
by flat cushions of Ceanothus pumilus and the openings
are occupied by a perennial herbaceous assemblage
that gives a characteristic sparse and xerophytic appearance. Among these herbaceous undergrowth many serpentine species are found: Achillea millefolium var.
occidentalis, Calochortus howellii, Aspidotis densa,
Eriophyllum lanatum var. achillaeoides, Horkelia sericata, Cirsium cymosum, Melica geyeri, etc. Almost all
these are endemic to the Siskiyou and Klamath Mountains (Whittaker 1960).
Whittaker (1960), White (1971) and Franklin &
Dyrness (1988) described the climax community on
serpentine soils at low elevations in the Siskiyou and
Klamath Mountains as an open grassland savannah
with scattered Pinus jeffreyi and Calocedrus decurrens,
with a floristical composition that is very similar to
that of the Ceanothus pumilus-Calocedrus decurrens
association.
Mediterranean evergreen forests (including our
Type I) occupy a latitudinal fringe between 31 N,
the southern limit of the thermomediterranean belt
(Peinado et al. 1994a), to 43 150 where, as discussed
below, the temperate associations of zonobiome V
39
begin to constitute the climax vegetation. In this entire
area, the climax vegetation on lowlands chiefly corresponds to sclerophyllous ecosystems, but in its northern
limit – i.e. in the southern portion of the area surveyed here – there is a transitional zone in which two
great ecoclimatic regions (Mediterranean and Temperate) overlap and, in fact, Walter described this area
as zonoecotone IV–V. The southernmost limit of this
transitional area was situated at Salmon Creek, California (35 480 N; Peinado et al. 1994a); from there northwards the zonoecotone stretches to southern Oregon
changing in latitude inland. On the coast, the transition is gradual due to the moderating effect of the
ocean, and roughly coincides with the area of the redwoods (Oxalis oregana-Sequoia sempervirens association) that occupy a narrow coastal fringe (between
35 480 , at Salmon Creek, California, and 42 50 , at
Chetco River, Oregon), which is seldom wider than
30 km (Zinke 1988). Redwoods settle on northern or
ocean-exposed slopes where the fog effect is ecologically important; and are replaced on sunny or leeward
slopes by more drought-tolerant associations dominated by some evergreens (Umbellularia californica,
Arbutus menziesii, Lithocarpus densiflorus) and some
Quercus (Q. agrifolia southward, Q. chrysolepis everywhere, and the deciduous Q. garryana and kelloggii
northward).
Inland, the northern border between zonobiomes
IV and V is sharper and reaches higher latitudes: the
climax vegetation in the Roseburg Valley, and in the
basins of the Mackenzie and Umpkua rivers clearly
belongs to zonobiome V; the northernmost interior limit of the mediterranean zonobiome can be established
at 43 150 N (Delgadillo 1995).
Types II and III, Temperate associations
The most conspicuous feature of the temperate associations belonging to Types II and III is the dominance of
conifers: Abies amabilis, A. grandis, Larix occidentalis, Picea sitchensis, Pinus contorta, Thuja plicata and
Tsuga heterophylla, all long considered typical constituents of the temperate Pacific Coniferous Forest or
Pacific Northwest Forest. Type II groups associations
whose dominant trees and associated flora are generally regarded as montane species occurring on lowlands and low and middle height mountain slopes. Type
III groups associations characterized by the presence
of subalpine species and the constancy, and sometimes
dominance, of Tsuga mertensiana and Chamaecyparis
nootkatensis, the most typical subalpine trees of the
surveyed area.
The group labelled as PCO in the cluster dendrogram is not a true ecological or biogeographical unit,
but an assemblage of two edaphic associations that are
both dominated by Pinus contorta. P. contorta, the
lodgepole pine of western North America, is diversified into three taxa, which, in addition to the several
morphological features pointed out by Kral (1993),
also play different ecological or successional roles.
P. contorta var. murrayana is a typical oromediterranean tree (Delgadillo 1995); P. contorta var. latifolia
is essentially a montane and mesoboreal variety, whose
geographical area roughly coincides with the northern
sector of the Rocky Mountains; finally, P. contorta var.
contorta is the variety adapted to the lowest altitudes,
and grows on sites with microclimates and substrates
that discourage other trees. In the surveyed area this
variety occurs in two very specific places: (a) seashore, on sandy soils and, frequently, under salt spray
influence; and (b) rocky places, over poorly-developed
soils, built from dunite, a kind of rock which weathers
into serpentine.
Floristical composition is different in the two
P. contorta var. contorta associations (Table 2); the
first, Rhododendron macrophyllum-Pinus contorta,
corresponds to some coast-dune forests described from
northern California (Vogl et al. 1988) to Washington (Franklin & Dyrness 1988). The Cryptogramma
acrostichoides-Pinus contorta association is a very
open pine forest, dominated by three conifers (P. contorta var. contorta, Pseudotsuga menziesii var. menziesii and Thuja plicata), which show poor growth
(about 7–10 m tall and 10 cm diameter at breast height),
and thrive on dunite outcrops situated within the area
of the montane forests belonging to the Thuja plicataTsuga heterophylla association. The Cryptogramma
acrostichoides-Pinus contorta association is not a climax association but an edaphoxerophilous community,
which we only found in southern British Columbia;
however, it could be related to some P. contorta var.
contorta forests described by Larson (in Franklin &
Dyrness 1988). The dunite habitat of P. contorta var.
contorta have also been referred by Mathews (1990)
in the Cascades.
The Thuja plicata-Larix occidentalis association is
the easternmost inland penetration of the Vancouveran
element. It is a relictual detached portion of the Pacific
Northwest Forest, centred on the storm track of the
Westerlies (Daubenmire 1978), occurring as far east
as the continental divide at Clearwater National Forest
40
between Idaho and Montana, and in southern British
Columbia. This association is very well characterized
by the presence and dominance of several conifers:
Larix occidentalis, Pinus ponderosa var. scopulorum,
P. contorta var. latifolia and Abies grandis. It is closely
related to some montane associations described by
Daubenmire (1952) in eastern Washington and northern Idaho, as well as to the Tsuga heterophylla zone
on the eastern slopes of the Cascade Range described
by Franklin & Dyrness 1988).
From northern California (as far south as Caspar,
Mendocino County, 39 270 N, where it thrives at the
mouths of streams and in low valleys facing the ocean),
but chiefly from southern Oregon to the Gulf of Alaska,
forests of Sitka spruce (Picea sitchensis) characterize a
long narrow band adjacent to the Pacific ocean, where
maritime influences are maximum, the temperature is
cool and there is high precipitation and frequent fogs.
The Picea sitchensis band is generally only a few kilometers wide, except where it penetrates inland along
river valleys, or where the coastal plain is unusually
broad, as happens on the west side of the Olympic
Mountains. Additionally, the Sitka spruce forest usually thrives up to 150 m in elevation but may reach up
to 600 m where mountains are very close to the ocean.
In the numerical analysis Sitka spruce forests
were separated into two associations that we call
Polystichum munitum-Picea sitchensis and Lycopodium annotinum-Picea sitchensis associations. The first
association groups relevés taken from northern California to approximately Glacier Bay National Park in
southeastern Alaska, while the second encloses those
relevés taken from that point northward to the sea-level
timberline of P. sitchensis on the westernmost Kenai
Peninsula.
The Polystichum munitum-Picea sitchensis association is characterized by several montane species,
with western hemlock (Tsuga heterophylla), western
cedar (Thuja plicata) and Sitka spruce being the most
common trees. Douglas fir (Pseudotsuga menziesii var.
menziesii) is common and sometimes co-dominant,
but its range does not extend northwards much beyond 53 N, and it characterizes the southern stands
of the Polystichum munitum-Picea sitchensis association in British Columbia, Washington and Oregon. In
northern California, Sitka spruce becomes confined
to the immediate coastal zone, forming salt spraytolerant pure stands often protecting the adjacent redwood forest that replaces them inland (Zinkle 1988).
The range of the Polystichum munitum-Picea
sitchensis association lies in the area with the highest
precipitation in western North America: 5600 mm have
been recorded on the coast in some places in Alaska
(Viereck & Little 1991), and British Columbia (Krajina
1965; Pojar & MacKinnon 1994), as well as on the
Blue Glacier of the Olympic Mountains in Washington
(Fonda & Bliss 1969).
The Polystichum munitum-Picea sitchensis association thrives near the coast within the montane belt
with perhumid ombroclimate, and it corresponds to
several forest types described by Scott (1962), Krajina
(1965), Franklin (1988), Franklin & Dyrness (1988)
and Archibold (1995). The denomination perhumid
rain forest or temperate rain forest are used for these
montane forests, while the subalpine Lycopodium
annotinum-Picea sitchensis association has been called
a subpolar rain forest (Pojar & MacKinnon 1994).
Since the northernmost areas occupied by the
Polystichum munitum-Picea sitchensis association are
largely inaccessible, the northern limit of its range cannot be determined exactly; the transitional ecotone with
the subalpine Lycopodium annotinum-Picea sitchensis
association should lie somewhere between Glacier Bay
and the Malaspina Glacier (between 59–60 N).
SYN-TAX clustered 34 relevés within a group that
we have named Thuja plicata-Tsuga heterophylla association to reflect the dominance in most of the relevés
of western cedar and mountain hemlock. In fact, this
association is a complex of several climax forests of
the montane belt of western Washington and Oregon [Franklin & Dyrness’ (1988) Tsuga heterophylla
zone] and southern British Columbia [Krajina’s (1965)
coastal western hemlock subzone] which constitute
the classic forest with climax of Tsuga heterophylla
and Thuja plicata and subclimax of Pseudotsuga menziesii var. menziesii (Weaver & Clements 1938; Cooper
1957).
The range of the Thuja plicata-Tsuga heterophylla
association complex climatically overlaps the montane
belt with humid climate; when precipitation increases
(perhumid ombroclimate) it is replaced by two associations: Polystichum munitum-Picea sitchensis towards
the coast (lower horizon of the montane belt), and
Gymnocarpium dryopteris-Abies amabilis at higher
altitudes (upper horizon). Transitions between those
associations are frequent and difficult to map, so the
Picea sitchensis and the Abies amabilis zones have
often been considered as variants or subzones of the
Tsuga heterophylla zone, a point of view supported
by Scott (1962) and Krajina (1965) but not shared by
Franklin & Dyrness (1988).
41
Owing to the broad range of the Thuja plicataTsuga heterophylla, many floristical variants can be
distinguished on the basis of seral or edaphic changes.
Some of these variants have been described by Krajina
(1965), Brooke et al. (1969) and Franklin & Dyrness (1988). We recognize the following variants:
(a) Gaultheria shallon-Pseudotsuga menziesii variant,
characterizing the drier, generally southern, forests;
(b) Rubus spectabilis-Alnus rubra variant in disturbed
forests, mainly along talus, tracks and roads; (c) Epilobium angustifolium variant on clearings opened
by cuts; (d) Thuja plicata variant, in wet habitats,
chiefly along stream banks or alluvial habitats, where
there is permanent seepage and gleyed soils occur;
(e) Lysichiton americanum variant, in little depressions
where water stagnates.
Forests with Abies amabilis as co-dominant (16
relevés) were separated by SYN-TAX into two groups;
one of them, formed by only three relevés, was
included near the subalpine associations, while the
second was placed near the montane associations. This
separation responds to their floristic composition, a
mixture of montane and subalpine species as corresponds to the transitional habitat of the Abies amabilis forests, which form an altitudinal subzone lying
between the temperate mesophytic Tsuga heterophylla
zone of the lowlands and the subalpine Tsuga mertensiana zone (Krajina 1965; Brooke et al. 1969; Fonda
& Bliss 1969; Franklin 1988; Franklin and Dyrness
1988).
The small group of three relevés closely corresponds to the Abies amabilis-Tsuga mertensiana
described by Brooke et al. (1969), later labelled Tsuga
mertensiana-Abies amabilis community (Douglas
1972). The main floristic feature of this subalpine
association is, in addition to the lack of the montane elements Tsuga heterophylla and Thuja plicata,
the presence of the subalpine species Tsuga mertensiana, Chamaecyparis nootkatensis and Vaccinium deliciosum.
On the contrary, in the other thirteen Abies amabilis relevés, these subalpine elements are lacking,
while montane Tsuga heterophylla is a conspicuous codominant. Two associations can be distinguished. Six
relevés from the North Cascades, the Olympic Mountains and the coastal mountains of British Columbia
constitute the Gymnocarpium dryopteris-Abies amabilis association, floristically related to the Abies
amabilis-Tsuga heterophylla community (Fonda &
Bliss 1969). This association forms an altitudinal
fringe above the zone of Thuja plicata-Tsuga hetero-
phylla and below the zone of Abies amabilis-Tsuga
mertensiana.
The other seven relevés come from central British Columbia, between Bowron Lake Provincial Park
(53 ) and Meziadin Junction (56); Picea engelmannii var. engelmannii is the co-dominant (Picea
engelmannii-Abies amabilis association). This spruce
is a montane and subalpine taxon (Taylor 1993), found
from northern Mexico to British Columbia, which –
according to our available bibliographical data – had
never been reported in coexistence with Abies amabilis.
The combination Picea engelmannii-Abies amabilisLycopodium annotinum (together with Pinus contorta
var. latifolia on disturbed and burned sites) seems to
be an outstanding feature of the interior montane belt
in that latitudinal fringe.
Although A. amabilis is considered a coastal species (Hunt 1993; Pojar & MacKinnon 1994) our easternmost relevé was taken about 625 km in a straight line
from the Pacific shoreline. Its presence so far inland
can be satisfactory explained by the latitudinal fringe
in which it occurs being one of the migratory paths
for humid Pacific air masses (Brouillet & Whestone
1993) and, thus, subjected to the strong influences of
the eastwards moving westerlies, which provoke maximum interchange between plants of the oceanic and
continental climates (Daubenmire 1978). This zone
is where the continental species Abies lasiocarpa and
Picea engelmannii penetrate westward into oceanic climates. Our westernmost relevés of the Picea glauca engelmannii-Abies lasiocarpa (see below) come from
this zone and were taken only 125 kilometers from the
Pacific shoreline.
The presence of the Abies amabilis-dominated
associations forming an altitudinal horizon or fringe
above the typical montane belt of the Thuja plicataTsuga heterophylla association, and under the typical subalpine parkland with Tsuga mertensiana and
Chamaecyparis nootkatensis, could be related to temperature and precipitation. Warmer temperatures on
lower slopes limit Abies amabilis growth, and thus their
community types occur at higher elevations (Fonda
& Bliss 1969). Abies amabilis-dominated zones are
wetter and cooler than the adjacent Thuja plicataTsuga heterophylla zone, and receive considerably
more snow, much of which accumulates in winter
snowpacks as deep as 1 to 3 meters (Brooke et al.
1965: Arno & Hammerly 1984). The precipitation
increase, together with the lower temperatures this
association endures, provoke podsolization of the soils,
a phenomenon that seldom or never appears under the
42
Thuja plicata-Tsuga heterophylla association (Franklin & Dyrness 1988). In terms of bioclimatic belt
and ombrotype the A. amabilis-dominated associations
mainly thrive in the higher horizon of the montane belt,
under perhumid ombroclimate. An exception is the
Abies amabilis-Tsuga mertensiana association which
thrives in the subalpine belt, also under a perhumid
ombroclimate, but in very oceanic climate conditions.
One of the most characteristic plant communities
of the subalpine belt from the Rocky Mountains (Peet
1988) westward to the leeward slopes of the Pacific
Border System (Fonda & Bliss 1969; Daubenmire
1978; Pojar & MacKinnon 1994) are forests dominated
by spruces and subalpine firs that have received different names: Rocky Mountain Abies lasiocarpa-Picea
engelmannii forest (Oosting 1956), Engelmann sprucesubalpine fir zone (Krajina 1965), Abies lasiocarpa
zone (Franklin & Dyrness 1988) and Merriam’s Hudsonian Life zone (Barret 1962).
Though this widespread subalpine area has classically been denominated the Picea engelmannii Province
(Daubenmire 1978), and A. lasiocarpa considered the
unique co-dominant subalpine fir, spruces scored in
our relevés north of the 54 parallel show a mixture P. engelmannii and P. glauca features, probably reflecting the regular hybridization between both
spruces in sympatric areas (Taylor 1993). Following Taylor’s nomenclature, these intermediate spruces
should be broadly named P. glauca, but they have
been named Picea glauca engelmannii in this article. The situation of Abies lasiocarpa through central
British Columbia and northern Washington is similar, because many of the specimens show intermediate features with the Rocky Mountain subalpine fir
A. bifolia and they would best be classified as A. bifolia lasiocarpa (Hunt 1993). In this article they are
included as A. lasiocarpa.
All our relevés with this subalpine fir were clustered
into a single group, in which at least two associations can be distinguished. Southern relevés, from
the Olympic Mountains, North Cascades and southern British Columbia (including subalpine forests in
Tweedmuir Park, at 52 ), are characterize by the
presence of Lupinus arcticus ssp. subalpinus and
the absence of spruces. They constitute the Lupinus
subalpinus-Abies lasiocarpa association corresponding to the Abies lasiocarpa type (Fonda & Bliss 1969)
found on the drier inland south-facing ridges where it
replaces the Abies amabilis-Tsuga mertensiana association. Ecological variants or subassociations can be
differentiated. Stands of A. lasiocarpa-Pinus albicaul-
is form parklands at higher elevations and correlate
with the Pinus albicaulis-Abies lasiocarpa association
(Daubenmire & Daubenmire 1968). In wetter areas,
combinations of A. amabilis and T. mertensiana are
found with subalpine fir. Finally, a variant of Arctostaphylos uva-ursi-Juniperus montana thrives on drier
soils, chiefly on wind-exposed ridges and steep slopes.
The second association, Picea glauca engelmannii-Abies lasiocarpa, is spread throughout
central and northern British Columbia. Besides the typical subalpine subassociation, there is another montane subassociation; relevés north of Meziadin Junction
(56 ) have several montane taxa, such as Athyrium
filix-femina ssp. cyclosurum, Gymnocarpium dryopteris and Tsuga heterophylla, which are characteristic
of the Tsuga heterophylla subassociation that replaces
northward the Picea glauca-Abies amabilis association
within the upper horizon of the montane belt.
Finally, Abies lasiocarpa forms timberlines or
krummholzs in some mountain passes across the
coastal mountains between British Columbia and
Alaska, i.e. White Pass, Skagway Pass or Juneau.
These communities are physiognomically characterized by dwarf firs (1.5–2 m height), dominant over a
dense carpet of prostrate shrubs: Salix arctica, S. stolonifera, Rubus arcticus, Empetrum nigrum, Cassiope
mertensiana and others. Picea glauca is absent, and
P. sitchensis and T. mertensiana may occur on western
slopes, where the snow influence is greater. An unusual
combination of Abies lasiocarpa and Sitka spruce can
be seen east of Skagway; with the rise in altitude these
forests give way progressively to timberlines of both
species together with T. mertensiana at 1000 meters,
in White Pass.
The last group included in Type III is the Lycopodium annotinum-Picea sitchensis, whose relevés were
taken in the western slopes of the Alaska coastal mountains, from the Panhandle to the forest limit situated as
far west as the Kenai Peninsula. This association correlates with the westernmost forests of the coastal Sitka
spruce-hemlock zone (Viereck & Little 1991) and the
subpolar rainforest (Pojar & MacKinnon 1994). The
area has an oceanic climate with moderately warm
summers, a growing season of 120–180 days, and moderately cold winters in which most annual precipitation
occurs (Viereck & Little 1991).
Such a climate has been considered as oceanic boreal (Brouillet & Whestone 1993), but, on the
basis of climax vegetation and climatological features,
the coastal area where this association lives must be
included in the temperate macroclimate. Climatologic-
43
al conditions regulating boreal ecosystems are diverse
(Larsen 1980) but most authors agree in considering
at least these conditions: (a) the area has to be north
of the average location of the arctic front during the
winter (Bryson & Hare 1974; Hare & Hay 1974), and
included within the permafrost range (Brown 1970;
Oechel & Lawrence 1985); (b) in boreal areas, precipitation occurs more frequently in the summer (Oechel
& Lawrence 1985; Elliott-Fisk 1988); (c) daily and
annual temperature fluctuations must be extreme and
the growing season must be less than 120 days (Hopkins 1959; Walter 1985). These climatological conditions are found inland of the summit line of the Alaskan
coastal ranges, but never on the ocean-facing slopes of
the surveyed area.
From a floristic point of view, Table 2 reveals that,
except for those species with a wide range, there is a
clear separation between the Type IV boreal forests and
the Lycopodium annotinum-Picea sitchensis association. Instead, floristic relations with temperate forests
are outstanding, both at the dominant level (Picea
sitchensis, Tsuga mertensiana) and at the understorey
level (Menziesia ferruginea, Oploplanax horridum,
Gymnocarpium dryopteris, etc.). The co-dominance of
T. mertensiana clearly includes this association among
temperate subalpine forests.
Within the Lycopodium annotinum-Picea sitchensis association a Betula kenaica subassociation can
be distinguished in grouping relevés from the coastal
stands of the Kenai Peninsula; Betula papyrifera var.
kenaica and Picea lutzii, a hybrid between P. sitchensis and P. glauca, are differential species.
Type IV, Boreal associations
Type IV encloses relevés characterized by the dominance of trees and shrubs considered as typical elements
of the boreal forest. Across North America the boreal
forest is dominated by two trees, Picea glauca and
Picea mariana, which have very similar ranges but
occupy different habitats (Oechel & Lawrence 1985;
Elliott-Fisk 1988). P. glauca is generally assumed to
be more mesophytic than P. mariana: it grows best
on nutrient-rich, permafrost-free, well-drained soils
(Brunisols or Podsols). P. mariana is confined to poorly
drained soils; poor drainage is mostly due to ground
ice, so that the presence of P. mariana is generally
linked to permafrost and to its associated Cryosols
(Carleton & Maycok 1980).
Despite this ecological difference, P. glauca also
forms forests on Cryosols (Douglas 1974; Lausi &
Nimis 1991), and these forests are characterized by
an underwood similar to that of the P. mariana muskeg: Betula nana, Ledum groenlandicum, Rubus
chamaemorus, Potentilla fruticosa, Arctostaphylos
rubra, Vaccinium uliginosum, among others. P. glauca
forests with this floristical composition occur on northfacing slopes, at higher altitudes and near the northern
distributional limit of the species, i.e. in the supraboreal belt. P. glauca stands from lower altitudes and
in the southern limit of the boreal forest (mesoboreal
forest), typically lack these understorey species.
SYN-TAX divided the boreal relevés into three
groups, one dominated by P. mariana, and two by
P. glauca. However, the more detailed phytosociological analysis allowed us to distinguish several subgroups (Table 2).
Relevés dominated by P. glauca were numerically
separated into two groups, which – when plotted on
a map of site locations – correlated with precipitation and temperature patterns. The first and smallest
group (Betula neoalaskana-Picea glauca association)
corresponds to the zone with higher precipitations and
temperatures, i.e. to forests stretching over the relatively warm basins of the Susitna and Matanuska rivers
(Alaska), an extensive coastal plain almost completely
open to the ocean influence from winds through Cook
Inlet. The presence of some temperate, hygrophilous,
and relatively termophilous, taxa such as Gymnocarpium dryopteris, Athyrium filix-femina ssp. cyclosurum, Alnus viridis ssp. sinuata, Streptopus amplexifolius, Cornus canadensis and Lycopodium annotinum
is the differential feature of this association. Its area
is permafrost-free and receives more precipitation than
any other in the boreal part of the surveyed area; in
terms of bioclimatic classification, it corresponds to
the mesoboreal belt with subhumid ombroclimate.
The second and largest group of P. glauca separated by SYN-TAX clustered relevés from the lee of
the Wrangell-St. Elias Mountains, a rainshadow area
whose annual precipitation average oscillates between
190 mm on lowlands and 625 mm on mountains
(Oswald & Senyk 1977). It can be divided into three
subgroups or floristic-ecological associations. The
first, Betula nana-Picea glauca, encloses the supraboreal forests, recorded on the leeward slopes (between
700–1200 m) of these mountains; its shrubby underwood clearly reveals the existence of frozen ground
and correlates it with the Picea glauca-Salix glauca
community (Douglas 1974) and the Picea glaucaRhytidium rugosum community described in the same
are over winter frozen Brunisols (Lausi & Nimis 1991).
44
Relevés from Kluane Lake and Whitehorse were
grouped together into a second subgroup that we call
Anemone multifida-Picea glauca association. The area
between Kluane Lake and Whitehorse is included in the
Ruby Range Ecoregion, the driest zone of the southern Yukon (Oswald & Senyk 1977). Lausi & Nimis
(1991) described the Picea glauca-Hypnum procerrimum community in this xeric-continental area as the climax vegetation on sandy Brunisols derived from loess
deposits. Its floristical and structural composition, an
open or closed forest with P. glauca dominant over an
underwood in which Shepherdia canadensis, Anemone
multifida and Arctostaphylos uva-ursi stand out, correlates with the Anemone multifida-Picea glauca association. The dominance of Populus tremuloides on two
relevés indicates the successional, post-fire role of this
tree in boreal ecosystems (Youngblood 1955).
The third group dominated by P. glauca (Pinus
latifolia-Picea glauca) is characterized by the codominance of Pinus contorta var. latifolia. Relevés
of this association come from the Cassiar Mountains
in the north of British Columbia, and from Whitehorse
area in the south of the Yukon Territory, corresponding
to the southernmost occurrences of the boreal forest.
Lausi & Nimis (1991) have described a Pinus contortaHylocomium splendens community in this area, whose
structure (an open mixed forest of P. glauca-P. latifolia) and floristical composition approximate it to the
Pinus latifolia-Picea glauca association.
Thirty one relevés dominated by P. mariana were
clustered by SYN-TAX into a group. However, the
phytosociological analysis distinguishes at least three
associations. The Picea glauca-Picea mariana association corresponds to the transitional forests between
the woods in the depressions provoked by the permafrost (Rubus chamaemorus-Picea mariana) and the
forest of the Betula nana-Picea glauca association.
Picea mariana muskegs with a similar ecological
role have been described by Lausi & Nimis (1991)
on the Yukon’s Cryosols and named Picea marianaLedum palustre community (equivalent to the Rubus
chamaemorus-Picea mariana association) and Picea
mariana-Ledum groenlandicum community (equivalent to the Picea glauca-Picea mariana).
Lastly, the Larix laricina-Picea mariana association is an open mixed forest, co-dominated by Larix
laricina and P. mariana, which grows on the Fluvisols
of the Tanana River. L. laricina is considered a typical
species of the interior Alaskan wetlands (Barbour &
Christensen 1993; Archibold 1995).
Conclusions
The phytosociological study carried out with the 254
relevés taken along the Pacific drainage basin between
northern California and Alaska has revealed:
(1) The landscape of the surveyed area is dominated
by three large physiognomical formations, which correspond to three zonal macroclimates and zonobiomes: Mixed Evergreen Forest (Mediterranean macroclimate; zonobiome IV), Pacific Coniferous Forest
(Temperate macroclimate; zonobiome V) and Boreal
Forest (Boreal macroclimate; zonobiome VIII).
(2) The mediterranean macroclimate stretches from the
southern border of the surveyed area (41 300 N) to
42 50 along the coast and 43 150 inland. It is substituted northward by the temperate macroclimate, which
stretches along the Pacific coast, mainly on the windward slopes of the mountains of the Pacific Border
System, north to the Alaskan timberline on the Kenai
Peninsula.
(3) In the coast of northern California and southern
Oregon there is a broad ecotone between mediterranean and temperate formations, the former setting on
sunny or leeward slopes, the latter thriving on northern or ocean-exposed slopes where the fog effect is
ecologically important. The most typical transitional association is the redwood forest (Oxalis oreganaSequoia sempervirens), whose floristical composition
is intermediate between mediterranean and temperate
elements. This ecotone is a northern extension of the
one already detected by us between 35 480 and 40
(Peinado et al. 1994a) and was drawn by Walter (1986)
as zonoecotone IV–V.
(4) The boreal macroclimate appears in the lee of
the British Columbia coastal mountains approximately
north of 58 N. Its presence is detected by the appearance of the Picea glauca forest and the Picea mariana
muskegs. It stretches, always to the leeward of the
Pacific Border System, over most of the interior areas
of British Columbia, the Yukon Territory and Alaska.
Although Walter (1986) mapped the boreal zonobiome
VIII as the potential vegetation for most of the southeastern Alaskan coast, the Sitka-spruce forests of that
area have a floristical composition that closely approximates that of the temperate zonobiome V.
45
(5) The sixteen floristic zonal associations that have
been found, some of which had already been identified
by other botanists, occupy large geographical zones
and thrive under specific bioclimatic patterns of temperature (bioclimatic belts) and precipitation (ombrotypes). Another seven azonal associations have been
identified, most of which are linked to edaphic factors
such as serpentines, dunites, permafrost and sandy
dunes.
(6)The following zonobiomes and major plant associations exist in the surveyed area:
Zonobiome IV
Mesomediterranean belt: Spreads northwards from the
southern border of the surveyed area to 42 50 along
the coast (north of 40 300 occurs mainly in a topographic mosaic with colline forests) and 43 150 inland.
The major zonal associations are: Oxalis oreganaSequoia sempervirens subassociation with Lonicera
hispidula (coastal; perhumid); Arbutus menziesiiLithocarpus densiflorus (coastal; humid); and Arbutus menziesii-Quercus garryana (inland; subhumidhumid). Azonal associations are: Ceanothus pumilusCalocedrus decurrens (serpentines); Rhododendron
macrophyllum-Pinus contorta (coastal, sandy dunes);
and Polystichum munitum-Picea sitchensis (coastal,
under salt spray influence).
Zonobiome V
Colline belt: Exclusively coastal, it spreads between
40300 and 4250 . The only zonal association is
the Oxalis oregana-Sequoia sempervirens subassociation with Tsuga heterophylla, and the azonal associations Rhododendron macrophyllum-Pinus contorta
and Polystichum munitum-Picea sitchensis are also
present.
Montane belt: Beginning at 42 50 in the coast and at
43 150 inland, it spreads northwards along the coast to
at least 60 , where it is replaced by the subalpine belt.
Zonal associations are: Polystichum munitum-Picea
sitchensis (lower horizon; perhumid; with oceanic
influence); Thuja plicata-Tsuga heterophylla (humidperhumid), Gymnocarpium dryopteris-Abies amabilis (upper horizon of the southern coastal mountains;
perhumid); Thuja plicata-Larix occidentalis (relictual in the track of the Westerlies; perhumid); and
Picea engelmannii-Abies amabilis (upper horizon of
the interior mountains of British Columbia situated
in the track of the Westerlies; perhumid). Azonal associations: Rhododendron macrophyllum-Pinus
contorta (coastal, sandy dunes) and Cryptogramma
acrostichoides-Pinus contorta (dunites).
Subalpine belt: Subalpine forests form the highest
forest belt of the temperate mountains and constitute the climax vegetation along the Alaskan coast
north of 59–60. Zonal associations are: Lycopodium annotinum-Picea sitchensis (coastal with oceanic influence; perhumid); Abies amabilis-Tsuga mertensiana (mountains with oceanic influence; perhumid); Lupinus subalpinus-Abies lasiocarpa (southern mountains, from the Cascades to southern British
Columbia; humid); and Picea glauca engelmanniiAbies lasiocarpa (mountains of central and northern
British Columbia; humid).
Zonobiome VIII
Plant communities with boreal influence begin to
appear as far south as 58 in interior British Columbia
and spread northwards in the lee of the Pacific coastal
mountains. The boreal forests only reach the coast
on the lee of the Kenai Peninsula. Zonal associations
are: Betula neoalaskana-Picea glauca (mesoboreal;
subhumid); Betula nana-Picea glauca (supraboreal;
dry); Anemone multifida-Picea glauca (occurs in the
Ruby Range; mesoboreal; dry); Pinus latifolia-Picea
glauca (southern limit of the boreal forest; mesoboreal;
dry). Azonal associations: Rubus chamaemorus-Picea
mariana (Cryosols with permanent permafrost), Picea
glauca-Picea mariana (Cryosols with winter permafrost) and Larix laricina-Picea mariana (Fluvisols).
Acknowledgements
This work has been supported with grants from the
Subdirección General de Promoción de la Investigación del Ministerio de Educación y Ciencia (PR94090 and PR94-094) and DGICYT (Research Project
PB94-0359). We thank C. F. Warren from the UAH
Instituto de Ciencias de la Educación for her linguistic
assistance. We also thank two anonymous referees for
comments that improved this paper. Part of the research
was carried out during a four-month stay at Rancho
Santa Ana Botanic Garden, Claremont, California.
46
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