Alpine Vegetation- patterns of biodiversity and response to

environmental changeBill Bowman- Ecology and Evolutionary Biology

Mountain Research Station, INSTAAR(william.bowman@colorado.edu)

reference: Körner, Ch. 1999. Alpine Plant Life. Springer Verlag, Berlin

Nival

Alpine

treelineSubalpine

Montane

What is the alpine?Is it tundra?

elevation of treeline corresponds with:

1) minimum growing seasontemperature around 6 °C

2) wind

3) geomorphic disturbance- avalanches

krummholz- "twisted wood"

Global distribution of treeline

large variation in altitude at mid-latitudes

associated with continentality- treelines lower in moist, maritime locations

from Körner, 1999

Alpine is a globally distributed biome-plants have similar "growth forms:"

graminoids (grasses, sedges)

forbs (broad leaved herbaceous plants)

prostrate shrubs

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(CO2) - dependent on elevation

Alpine environmental conditions:

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)

0

1

2

3

4

5

6

7

8

a

b

ns ns

a

b

a

b

ns

Low N (0.3mmol:suboptimal for growth)High N (1 mmol)

tota

l bio

mas

s (g

)

Dominant sedges Common grasses

Greenhouse experiment- artificial imposition of N limitation

amount of growth is biologically constrained in some species

Alpine is an extensive biome- globally distributed

How has Pleistocene glaciation influenced alpine diversity and plant distribution?

Continuous and isolated alpine habitat: Colorado

Glacial (ca. 20K BP)

interglacial (present)

35 40 45 500

2

4

6

r2=0.46, P< 0.01

Latitude (degrees)

% o

f fl

ora

endem

ic

35 40 45 500

100

200

300n.s.

num

ber

of s

pec

ies

35 40 45 5020

30

40

50

r2=0.49P< 0.01

% o

f fl

ora

circ

um

pol

arsp

ecie

s

Biogeographic trends in Rocky Mountain alpine plant diversity

~ same number speciesmore Arctic species to north

more endemic species to south

Wind RiverWind River

Big HornBig Horn

Medicine BowMedicine Bow

Indian PeaksIndian Peaks

NeedlesNeedlesSangre de CristosSangre de Cristos

BeartoothBeartooth

AbsorokaAbsorokaGros VentreGros Ventre

UintahUintah

TetonTeton

San Fransisco PeaksSan Fransisco Peaks

Biogeographic similarities (after Hadley

1987)Sørenson’s index

3434

4444

4848

5858 5151

5454

5151

(50-83)(50-83)

5959

5050

Global Plant Diversity

Boulder County: 1550 species(50% of flora of Colorado)

Weld County: ~600 species

Regional scale plant diversity in S. Rockies; the influence of mountains:

Alpine Mesotopographic Gradient(After Billings)

Fellfield

Snowbed

Moist Meadow Wet

Meadow

DryMeadow

Prevailing wind

Fellfield

Snowbed

Similarity of flora among communities (Sørenson’s index): 25-77%

snow

What controls variation in diversity across the landscape?soil resources?

0.0 0.2 0.4 0.6 0.8 1.00.0

0.5

1.0

Increasing stressand belowgroundcompetition

Decreasing belowgroundcompetition; more spp. coexist

Increasing abovegroundcompetition; competitiveexclusion

Soil Resource Availability

Div

ersi

ty

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

1

2

3

N and P supply (proportion ofmaximum)

Div

ersi

ty (H

')

Alpine plant diversity relationship to soil N+P availability on Niwot Ridge

other factors: disturbance (climate & animal) water availability

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 TravisCU Geography

Moist meadows- elevated Ninputs due to topographic location

Snow is an effective reservoir of atmospheric N

inputs

Where in the alpine landscape is change most probable?

Moist meadow plant N uptake from snow(% growth demand)

Desch

amps

ia (g

rass

)

Acom

asty

lis

Arte

misia

Bist

orta

Calth

a0

250

500

750

a

bb

b

c (13)

(5)

(1)

(6)

(10)

15 N

upta

ke ( g

N g

-1 ti

ssue)

+ responder to N non responders

}

15N labeling experiment:

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

Implications of differential N uptake by alpine vegetation: