2002 ARCSS All-Hands Workshop

Detecting changes in arctic tundra plant communities is response to warming over decadal time scales

Howard E. Epstein¹, Monika P. Calef², Marilyn D. Walker³, F. S. Chapin III⁴, Anthony M. Starfield^5
1Environmental Sciences, University of Virginia, P.O. Box 400123, Charlottesville, VA, 22904-4123, USA, Phone 434-924-4308, Fax 434-982-2137, hee2b@virginia.edu
²Environmental Sciences, University of Virginia, P.O. Box 400123, Charlottesville, VA, 22904-4123, USA, mp6t@cms.mail.virginia.edu
³Institute of Northern Forestry Cooperative Research Unit, University of Alaska, P.O. Box 756780, Fairbanks, AK, 99775-6780, USA, Phone 907-474-2424, Fax 907-474-6251, ffmdw@uaf.edu
⁴Institute of Arctic Biology, University of Alaska, Fairbanks, AK, 99775-7000, USA, terry.chapin@uaf.edu
⁵Ecology, Evolution and Behaviour, University of Minnesota, St. Paul, MN, 55108, USA, starf001@maroon.tc.umn.edu

Detecting the response of vegetation to climate forcing as distinct from spatial and temporal variability may be difficult, if not impossible, over the typical duration of most field studies. We analyzed the spatial and interannual variability of plant functional type biomass from field studies in low arctic tussock tundra and compared these to climate change simulations of plant community composition using a dynamic tundra vegetation model (ArcVeg). There was substantial spatial heterogeneity of peak season live aboveground biomass in low arctic tundra at Ivotuk, Alaska (68.5 N, 155.7 W) in 1999, when samples were collected from 0.1 m² plots. Coefficients of variation for live aboveground biomass ranged from 41% for deciduous shrubs, 80% for graminoids and 84% for mosses to over 200% for lichens and forbs. Spatial heterogeneity in the ArcVeg dynamic vegetation model, generated as a result of grazing, soil disturbances and demographic stochasticity, compared favorably to the field data. Field studies also indicate a high degree of interannual variability with possible trends associated with warmer climates, such as increasing shrub biomass and declining moss biomass. These field data coupled with ArcVeg simulations suggest that some changes in plant community composition might be detectable within one or two decades following the onset of warming, and shrubs and mosses might be key indicators of community change. Model simulations also project increasing landscape scale spatial heterogeneity (particularly of shrubs) with increasing temperatures.

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