ALPINE PLANTS AT THE
EQUATOR
– Giants and Dwarfs
John and Hilary Birks
INTRODUCTION
Why is Africa so enigmatic to biologists?
What is the geological history of Africa?
How does one identify East African alpine plants?
How rich is the East African alpine flora?
What are the main vegetation types?
How did we come to be in East Africa?
BALE MOUNTAINS, ETHIOPIA
Bale Mountains National Park
Flora
MOUNT KENYA
Vegetation zones
Climate
Flora
How do alpine plants survive such extreme conditions?
AMBOSELI NATIONAL PARK
POTENTIAL THREATS TO EAST AFRICAN ALPINE FLORA
CONCLUSIONS
INTRODUCTION
Why is Africa so enigmatic to
biologists?
An enigmatic continent to biologists in several ways
1. One of the most homogenous continents. Bestknown plants and animals occur in the four
major zones that stretch from the western
shores to the eastern shores. Desert, savannah,
forest, and uplands of east and south.
2. Plants and animals in these four zones have
wide natural ranges and represent 75% of
Africa’s biota.
3. Remaining 25% of rare and/or very localised
species in biodiversity ‘hotspots’ and centres of
endemism (e.g. western Cape, eastern Cape,
Drakensberg, Namaqualand, Simien and Bale
Mountains in Ethiopia, Mounts Elgon, Kenya,
Meru, Kilimanjaro, and Ruwenzori centred around
the equator in east Africa).
4. Has a staggering diversity in centres of
endemism. Much to be discovered taxonomically.
5. Several botanical curiosities – Welwitschia,
Adansonia digitata (baobab), giant Senecio, giant
Lobelia.
6. Remarkable fauna (birds, fish, mammals, etc).
7. Long human presence, mainly low disturbance
until recently.
What is the geological history of Africa?
Africa is the largest fragment of Gondwanaland. After
nearly 200 million years of stability, between 270 and
200 million years ago, it started to drift apart.
Unlike other parts of Gondwana, Africa maintained a
relatively stable position on the globe and hence had
a relatively stable climate.
Main geomorphic features are
vast alluvial basins and plains
and complex system of rivers
and streams – Nile, Zaïre, Niger,
Zambezi – and the Great
Rift Valleys.
Kingdon 1990
Great Rift Valleys – largest, longest, and most
conspicuous feature of their kind on Earth.
3500 miles long from
the Afar Depression in
the Horn of Africa to
the mouth of the
Zambezi river in
Mozambique
Ranges from salt flats
at 175 m below sealevel to 5895 m
(Kilimanjaro)
Great Rift Valleys are
visible from outer
space
Pavitt 2001
Middle-Late Tertiary – extensive uplift and
subsequent rifting and subsidence 22, 6, and 2.5
million years ago. Created Great Rift Valleys of East
and central Africa, the upthrust block of Ruwenzori
(5109 m) in Uganda, and the Ethiopian Dome.
Uplifted faces split along their axes to form rift valleys
about 40 km wide on average.
Along the rifts, many volcanoes
– Elgon, Aberdare, Kenya,
Kilimanjaro, Meru
Kingdon 1990
Western Rift
Eastern Rift
Pavitt
2001
Largest highlands of Ethiopia are a plateau of
Miocene and Oligocene lava flows subsequently
broken up by the
formation of the
Abyssinian (=Ethiopian)
Rift.
Simien Mountains in
north (4543 m) and
Bale Mountains
(4400 m) in south.
Largest continuous
alpine area in Africa.
Pavitt
2001
Glaciers exist today on Ruwenzori, Mt Kenya, and
Kilimanjaro, but are in rapid retreat and decay at
present.
Quaternary glaciations saw major expansion of
these glaciers, plus glaciers on Mt Elgon and the
Bale Mountains. Abundant evidence of freeze-thaw
and solifluction activities today on Mt Kenya and
Bale Mountains.
How does one identify East African
alpine plants?
Ethiopia – not too bad. About 5800 species, 21%
endemic, about 500 alpines.
8 volumes finished in 2006
2003
2004
(847 species of bird (3.6% endemic), 242 mammals (12.8%))
Ethiopia is proud of its
endemic plants.
Published by Ethiopian
Tourist Commission
1995.
Also partly supported
Flora of Ethiopia and
Eritrea. One of the few
East African countries
with a complete,
modern flora (well, not
quite complete!)
Kenya – much more difficult as there is no complete
flora and the lowland flora is very rich. Total number
not known. When the Flora of Tropical East Africa
(1952-?) is complete (maybe not until 2050!), may
be 10,000 species – who knows? Best to stick to
alpines (about 500)!
1987
1994
1957
How rich is the East African alpine flora?
Alpine flora is not overwhelmingly rich
In 11 days (sometimes with 11-12 hours of travel)
saw 212 species
Compositae
49 Liliaceae
6
Cruciferae
5
Rosaceae
15 Gentianaceae
6
Boraginaceae
5
Leguminosae 12 Scrophulariaceae 6
Ferns
4
Lobeliaceae
11 Ericaceae
5
Iridaceae
4
Labiatae
9
5
Caryophyllaceae
3
Balsaminaceae
Rest were 1 or 2 species in 42 other families
A great place if you like Compositae, Rosaceae
(especially Alchemilla), and Leguminosae (especially
small Trifolium)!
Recent expeditions in alpine areas
Yunnan, 2009
Tien Shan, 2008
Qinghai, 2006
Tibet, 2005
Bhutan, 2002
Sichuan, 2001
Days No. species
24
1085
14
560
11
473
22
802
14
520
16
380
Species/day
45
40
43
37
37
24
Central Patagonia, 2006
North Patagonia, 2005
23
16
493
497
21
31
Tasmania/SE Australia, 2008
New Zealand, 2003
15
16
340
352
23
22
Eastern Cape, 2009
E Africa, 2007
Drakensberg, 2002
12
11
15
612
212
702
51
19
47
Oregon & N California, 2004
15
584
39
On a species per field-day basis, E Africa is the poorest and
Drakensberg and the Eastern Cape the richest alpine areas we have
visited in the last 9 years! Africa is a continent of contrasts.
What are the main vegetation types?
Mainly dry savannah,
some moist
savannah, and alpine
areas
Parallels patterns in
mean annual rainfall
Kingdon 1990
How did we come to be in East Africa?
Went on Alpine Garden
Society expedition in
September-October 2007
to Bale Mountains of
Ethiopia and Mt Kenya in
the Eastern Rift Valley.
Led by John Grimshaw
and Harry Jans.
Saw some of the amazing
Afro-alpine flora and
fauna and some of the
rich sub-alpine, montane,
and lowland flora.
Hedberg
1997
Photo: Harry Jans
BALE MOUNTAINS, ETHIOPIA
Introduction
1. Addis Ababa to Lake Ziway
and Shashemene. Stay at
Wendo Genet (9 hrs driving)
2. Wendo Genet to Goba (11.5
hrs driving)
3. Goba to Bale Mountains S
4. Goba to Bale Mountains N
5. Bale (Tullu Dimtu, 4400 m)
6. Goba to Wendo Genet (12)
7. Wendo Genet to Debre Zeit
8. Addis Ababa to Nairobi (air)
1:2,000,000
Rift Valley mainly agricultural areas (tef, Eragrostis
tef) with some remnant Acacia tortilis savannah
(1500-1800 m). Above this, a series of altitudinal
vegetation zones on the two sides of the Bale
Mountains
Miehe & Miehe 1994
Ethiopia uses the Coptic calendar, so we have had
two Millennium celebrations!
Bale Mountains National Park
Bale Mountains National Park created in 1971. Highest
proportion of animal endemicity of any terrestrial
habitat in world, plus 27 endemic flowering plants.
Largest continuous upland area above 3000 m in
Africa.
Ethiopian wolf
(Canis simensis)
Road sign
Anubis baboon (Papio anubis)
Large area and isolation give rise to high endemism
Ethiopian wolf (Canis simensis)
Lobelia rhynchopetalum
Henry Lamb
Giant mole-rat
(Tachyoryctes
macrocephalus)
Rouget's rail
(Rougetius rougetii),
Mountain nyala or gedemsa
(Tragelaphus buxtoni
Afro-montane forest of Podocarpus falcatus,
Juniperus procera, and Olea capensis to ~ 2700 m
Then Hagenia abyssinica and Hypericum revolutum
become dominant
Ericaceous belt and Afro-alpine zone above 3800 m.
Much of the Afro-montane forest is disturbed with
forest clearance, banana (Ensete venticosum
or Musa ensete) and khat (Catha edulis)
plantations, and agroforestry
‘cultural landscape’.
Bale Mountains lie between 6°40’ and 7°10’N. Consist
of Miocene basalt and trachyte lavas overlying Mesozoic
marine sediments.
Boulder fields and till ridges indicate the former
presence of 30 km2 ice-cap around the highest point,
Tullu Dimtu (4400 m). Also valley glaciers on northfacing slopes.
Mean annual temperature at 3170 m is 11.8°C.
Mean minimum temperature of coldest month is 0.6°C.
Frost is common above 4000 m.
Rainfall is seasonal with the bulk falling between JulySept. Increases with altitude (1061 mm at 3500 m).
Sparsely populated by humans but disturbance by
cutting, burning, and grazing has greatly increased in
last 30 years. Fire is a major ecological factor.
Vegetation history (Umer et al. 2007) extends back to
about 17000 years ago at 3950 m.
Late-glacial open herb vegetation After 4500 BP, Afro-montane
Early-Mid Holocene Ericaceae belt Podocarpus-Juniperus forests
developed due to cooler and drier
extended higher than today
conditions
Podocarpus later declined
Little pollen evidence for human impact but Afromontane vegetation is changing due to increased
human activity in recent years.
1983
1996
Nievergelt et al. 1998
Changes in Afro-alpine vegetation of giant Lobelia
rhynchopetalum
1974
1996
Natural spatial or cyclic dynamics between Lobelia and
grasses or due to changes in small mammal (e.g. giant
mole-rat) densities?
Nievergelt et al. 1998
Major vegetation types
1. Afro-montane rainforest
and human derivatives
2. Upper montane forests of
Hagenia and Hypericum
3. Ericaceous belt (Erica
arborea, E. trimeria)
4. Afro-alpine heaths
(Helichrysum, Alchemilla,
Lobelia rhynchopetalum)
Umer et al. 2007
Miehe & Miehe 1994
Travel in the Bale Mountains
Difficult!
Famous for its giant Lobelia, L. rhynchopetalum
Pachycaul plant
From von Rüppell 1840
Mabberley 1976
Flora
Surprisingly varied with a range of alpine
vegetation types and a wide range of plant sizes
(<1 cm to 3 m tall)
Lobelia, Helichrysum, Senecio, Trifolium, Alchemilla
Erica, Kniphofia
Arabis, Sagina, Cardamine
Swertia (Gentianaceae) – centre of its richness
MOUNT KENYA
Introduction
Mt Kenya 5195 m
Second highest African
mountain
Lies very near equator (16
km)
First climbed by Halford
McKinder in 1899, an
Oxford geography student
“because at that time most
people would have no use
for a geographer who was
not an adventurer and
explorer”. Revolutionised
teaching of geography
Hedberg
1997
Flew to Nairobi
Drove to Naro Moru
River Lodge and stayed
one night
Trekked from Park
Entrance (2440 m) to
Meteorological Station
Hut (3048 m) where we
spent one night
Climbed to MacKinder’s
Hut (4205 m) through
the ‘vertical bog’!
2 nights at MacKinder’s
Hut and forced down by
bad weather and
extreme cold
1:920,000
Appropriate title!
William, our trek
leader
Classical biological area for plants and animals
1948
1957
1967
1995
Great scope for ‘resurvey’ type work
Mt Kenya hyrax, Procavia johnstonii var. mackinderi
First climbed 13 September 1899
Halford MacKinder
Boy & Allan 1988
MacKinder on summit,
13 September 1899
Allan 1988
MacKinder’s Hut
4205 m altitude
Inside
without heating.
-4°C outside and
just above
freezing inside!
Photo: Roger Farrows
Vegetation Zones
Climbed western side:
zonation like south
side
- montane forest
- bamboo zone
- Hagenia zone
- Erica zone
- alpine zone
Coe 1967
Alpine zone begins about 3300 m,
nival zone about 4500 m
Dendrosenecio
keniodendron
Grow very slowly
About 2 cm in 20 yr
2 m tall plants 100 yrs+
(Hedberg 1969)
Alpine zone, Mt Kenya, October 6th 2007
Climate
On equator and at high altitudes (4000 m or more).
Very different from other mountains at higher
latitudes.
No seasonal differences on the equator (2°C
maximum range) but strong diurnal variations (20°C
January-February; 12°C July-August).
Frost occurs most nights and day temperatures may
be moderately high. Temperature may change 10°C
in 30 minutes. Mean temperature is 0°C at an
altitude of 4750 m. Rarely ever below -12°C.
“Winter every night, summer every day”
(Hedberg 1957)
Plant growth must therefore withstand
• night frosts
• rapid heating by intense radiation
• frost-heave and solifluction
Precipitation – two main rainfall periods April-May
and November-December (October in 2007)
Alpine zone about 250 cm yr-1 precipitation on Mt
Kenya
Despite high precipitation, fire is an important
ecological factor
Sixteen glaciers on Mt Kenya. Six have disappeared
since 1978, rest are all in major retreat.
Ice crystals grow in the wet soil during clear freezing
nights. Cushions of Grimmia ovata are pushed off the
soil surface, roll around, and form detached ‘moss
balls’
After 2 very cold nights at MacKinder’s Hut, snow and
hail on the second afternoon, and much snow on the
third morning, we were forced to retreat and descend
the ‘vertical bog’
Never again!
Photo: Harry Jans
Flora
Harsh Afro-alpine environment supports a limited
number of vascular plants “region of extreme floristic
impoverishment” (White 1978)
Element
No. taxa
%
Endemic (Afro-alpine, Afro-montane)
82
32
S African and Cape
25
10
S Hemisphere temperate
6
2
N Hemisphere temperate
34
13
Mediterranean
18
7
Himalayan
8
3
Pan-temperate
87
33
Total
260
100
Hedberg 1997
Altitudinal distributions of Afro-alpine species. Very few
are entirely restricted to alpine zone above 4000 m.
Many descend to 2000 m.
Hedberg 1997
Five main life-forms
A. Giant rosette
B. Tussock grass
C. Stemless
rosette
D. Cushion plant
E. Sclerophyllous
scrub
Hedberg 1997
How do alpine plants survive such
extreme conditions?
1. High radiation
- Thick, pale pubescent cover on upper and
lower surface of leaves. Common in many
alpines.
- Leaves often deeply pigmented, thick
cuticle, small leaves (? protection from high
UV radiation). Similar in New Zealand and
Tasmania.
2. Frost-heave
- Powerful rhizomes and root systems.
- Many minute ‘aquatics’ (e.g. Limosella
africana, Callitriche stagnalis, Subularia
monticola) (wave tolerant plants!).
- Many annuals (e.g. Cardamine, Arabis).
- May be the missing ‘habitat’ in Grime’s
model of primary plant strategies, namely
high stress and high disturbance. Thought to
be ‘uninhabitable’.
3. Temperature insulation
- almost all grasses form big tussocks. Can be
-5°C by tussock, +2.5°C in centre of
tussock, and +3.0°C in upper roots
- giant leaf rosettes. Thick unbranched stems
with huge leaf rosette. Continuous growth,
shoot apices have no dormant stage
- Dendrosenecio keniodendron: in day leaves
are flat, at night bend towards centre of
rosette. Young leaves appressed to centre of
rosette. Inside +1.8°C, outside -4.0°C
Stem insulated by old leaves.
Outside -5.0°C, inside pith +3.0°C.
Allows effective transpiration as
soon as high radiation starts. Cells
have thin walls, few cell contents,
and full of water, even 6 days after
dissection.
Hedberg 1995
Dendrosenecio
keniodendron
- Dendrosenecio keniensis
(= Senecio brassica):
leaves fold in at night.
Outside -4.0°C, inside
+1.5°C
Day
Night
Hedberg 1995
Dendrosenecio
keniensis – air
temperature, leaf
temperature, and
leaf-bud
temperature
Beck 1994
- Lobelia telekii: leaves
flat in day, bend inwards
at night. Outside -3.5°C,
inside +1.0°C
Malachite sunbird
Flowers hidden between long hairy bracts.
Up to 1.5 m tall.
Hedberg 1995
- Lobelia keniensis:
protects bud from frost
by producing ‘antifreeze’ liquid in its
rosettes. Forms a thin
layer of ice. Liquid below
+4.0°C, outside -3.5°C
Day
Night
Hedberg 1995
Lobelia keniensis leaf section.
Large inter-cellular spaces –
insulation like ‘styrofoam’
Air and leaf
temperature and of
the cisterna fluid
Beck 1994
Frost hardiness of Mt Kenya Afro-alpine plants
Dendrosenecio keniodendron
Limits (°C)
-5 to -14
Dendrosenecio keniensis
Lobelia telekii
Lobelia keniensis
-5 to -10
-10 to -14
-10
Haplocarpha rueppellii
Ranunculus oreophytus
Carduus chamaecephalus
-13
-14
-15
Data from Beck 1994
4. Other growth habits
- Xeromorphy, scleromorphy, and reduced
internodes
- Cushion growth forms
Occur in alpines in other areas (e.g. Andes,
Patagonia, Pamirs)
AMBOSELI NATIONAL PARK
What do 15 keen alpine
botanists do after being forced
off Mt Kenya?
Give up alpine botany and be
zoologists or tourists for a few
days and visit Amboseli
National Park, just below
Kilimanjaro, to see ‘big animals’
in an area where hardly a plant
is to be seen!
POTENTIAL THREATS TO EAST
AFRICAN ALPINE BIODIVERSITY
Introduced species
– no, too extreme an environment
Atmospheric nitrogen deposition
– probably not
Land-use changes
– no control over such changes, great political
unrest, much potential damage, tribal ‘wars’
Tourism
– ever increasing, especially on Mt Kenya with
much damage to its very wet areas and
accidental fires
Global warming
– projected warming by 2055 in alpine and arctic
areas according to IPCC Fourth Assessment Report.
Average increase in Equatorial African mountains
between 1.8 and 2.4°C (2055) and 2.6-2.6°C
(2085)
Nogués-Bravo et al. 2008
Some evidence (old photographs in Hedberg
1995) of changes in of Dendrosenecio in Teleki
Valley since 1948. Greater frequency of fires due
to tourism, more frequent severe storms, or use
by tourists as fuel? Can be 250 years old.
Teleki
Valley,
July
1948.
Photo:
Å. Holm
Hedberg
1995
October 2007
CONCLUSIONS
1. Afro-alpine flora is very remarkable. Not very rich
but certainly very different. Unbelievable
morphology and adaptations. Interesting parallels in
morphology and growth with Espeletia paramo in
Ecuador-Colombian Andes
Burga et al. 2004
2. One of the better known alpine floras thanks to
the dedicated work of the late Olov Hedberg since
1948 and of his wife Inga Hedberg.
Inspiring lecturer. When
we were students, very
fortunate in 1965-1967
to hear lectures at Max
Walter’s ‘taxonomy teaclub’ by Olov Hedberg,
Eilif Dahl, David Moore,
and William Weber.
Inspired our interests in
Afro-alpine, Scandinavian
(and Isle of Skye!), Patagonian, and N American
alpines and ecology.
ACKNOWLEDGEMENTS
John Grimshaw
William and Simon
Harry Jans
Joruge the cook
Meseret Mekuria
John and the other 17
porters on Mt Kenya
Cathy Jenks