Alpine Vegetation- patterns of biodiversity and response to ...

Alpine Vegetation- patterns of biodiversity
and response to environmental change
Bill Bowman- Ecology and Evolutionary Biology
Mountain Research Station, INSTAAR
(william.bowman@colorado.edu)
reference: Körner, Ch. 1999. Alpine Plant Life. Springer Verlag, Berlin

What is the alpine
Is it tundra
Nival
Alpine
treeline
Subalpine
Montane

elevation of treeline corresponds
with:
1) minimum growing season
temperature around 6 °C
2) wind
3) geomorphic disturbance- avalanches
krummholz- "twisted wood"

Global distribution of treeline
from Körner, 1999
large variation in
altitude at midlatitudes
associated with continentalitytreelines
lower in moist, maritime
locations

Alpine is a globally distributed biomeplants
have similar
"growth forms:"
graminoids
(grasses, sedges)
forbs
(broad leaved
herbaceous plants)
prostrate shrubs

Alpine environmental conditions:
cold
temperatures may change rapidly
windy (mainly temperate zone)
soils often poorly weathered
low water and nutrient availability
high UV irradiance (although offset
by cloud cover)
low p(CO 2 ) - dependent on elevation

Adaptations to the alpine environment include:
being short
high investment into
belowground biomass (high
root:shoot ratio)
low growth rates
tolerance to low temperatures
(= intolerance of high
temperatures)

Alpine is an extensive biome- globally distributed

How has
Pleistocene
glaciation
influenced alpine
diversity and
plant
distribution

Continuous and isolated alpine habitat: Colorado
interglacial (present)
Glacial (ca. 20K BP)

i
c
e
p
s
f
o
r
e
b
m
u
n
300
200
100
c
i
m
e
d
n
e
0
35 40 45 50
a
6
r
o
l
f
f
o
4
2
n.s.
u
c
r
i
c
Biogeographic trends in Rocky Mountain alpine plant diversity
~ same number species
a
r
o
l
f
f
o
%
s
e
i
c
e
p
s
50
40
30
20
35 40 45 50
r 2 =0.46, P< 0.01
r 2 =0.49
P< 0.01
more Arctic species to north
more endemic species to south
%
0
35 40 45 50
Latitude (degrees)

Biogeographic similarities (after Hadley 1987)
Sørenson’s index
Beartooth
(50-83)
Absoroka
Gros Ventre
Teton
51
Big Horn
Wind River
58 51
Uintah
44
48
Needles
54
Medicine Bow
59
Indian Peaks
50
Sangre de Cristos
San Fransisco Peaks
34

Global Plant Diversity

Regional scale plant diversity in S. Rockies; the influence of
mountains:
Weld County: ~600 species
Boulder County: 1550 species
(50% of flora of Colorado)

MOUNTAINS
• Have the highest plant species diversity
• High mountain environments have a high
percentage of endemic plants
• Alpine areas have a much higher plant
diversity than forested areas

Fellfield Fellfield
Alpine Mesotopographic Gradient
(After Billings)
Prevailing wind
Snowbed
snow
Snowbed
Moist
Meadow Wet
Meadow
Dry
Meadow
Similarity of flora among communities
(Sørenson’s index): 25-77%

What controls variation in diversity across the landscape
soil resources
y
t
i
s
r
e
v
i
D
1.0
0.5
Decreasing belowground
competition; more spp. coexist
Increasing stress
and belowground
competition
Increasing aboveground
competition; competitive
exclusion
0.0
0.0 0.2 0.4 0.6 0.8 1.0
Soil Resource Availability

)
'
H
(
Alpine plant diversity relationship to soil N+P availability on
Niwot Ridge
y
t
i
s
r
e
v
i
D
3
2
1
other factors:
disturbance (climate &
animal)
water availability
0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
N and P supply (proportion of
maximum)

Environmental change in alpine - primarily “indirect:”
climate, N deposition, stratospheric ozone degredation (↑UV)
locally most immediate threat is N deposition

Colorado ranks 3rd in U.S. population growth, with most of the increase in the
Front Range urban corridor:
source: William Travis
CU Geography

Where in the alpine landscape is change most probable
Snow is an effective reservoir of
atmospheric N inputs
Moist meadows- elevated N
inputs due to topographic location

)
e
u
s
s
( i
g
t
1
e
-N
k
a
tµg
p
u
750
500
250
15
N labeling experiment:
Moist meadow plant N uptake from snow
(% growth demand)
c (13)
b
(5)
b
(6)
b
(10)
5 N
1
a
(1)
(grass)
D eschampsia 0
A comastylis A rtemisia B istorta C altha
}
+ responder to N non responders

Implications of differential N uptake by alpine vegetation:
change in plant species composition ("weedy" native
species)- may already be occurring
change in ecosystem properties:
> enhancement of N cycling (net N mineralization
and nitrification) rates- loss of N from terrestrial to
aquatic ecosystems
> greater climatic control (lower biological control)
over variation in primary production