Alpine Vegetation- patterns of biodiversity and response to environmental change

1. 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

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

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

4. large variation in altitude at mid-latitudes Global distribution of treeline from Körner, 1999 associated with continentality- treelines lower in moist, maritime locations

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

6. 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(CO2) - dependent on elevation

7. 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)

8. Greenhouse experiment- artificial imposition of N limitation Dominant sedges Common grasses amount of growth is biologically constrained in some species

9. Alpine is an extensive biome- globally distributed

10. How has Pleistocene glaciation influenced alpine diversity and plant distribution?

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

12. Biogeographic trends in Rocky Mountain alpine plant diversity ~ same number species more Arctic species to north more endemic species to south

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

14. Global Plant Diversity

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

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

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

18. Alpine plant diversity relationship to soil N+P availability on Niwot Ridge • other factors: • disturbance (climate & animal) • water availability

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

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

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

22. } + responder to N non responders 15N labeling experiment:

23. 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