PARENT SESSION
Oral Session #48: Vegetation Change and Response.
Presiding: D. Zobel
Tuesday, August 6. 1:00 PM to 4:45 PM. Mesquite Room, Radisson.
Relationship of structural complexity to land surface exchange along a gradient from arctic tundra to forest.
Copass, Catharine*,1, Beringer, Jason2, Chapin, F1, McGuire, A. David1, Walker, Donald1, 1 Institute of Arctic Biology, Fairbanks, AK2 School of Geography and Environmental Science, Clayton, Victoria, Australia
ABSTRACT- Climate change has the potential to influence vegetation dynamics in high latitude ecosystems through changes in the land surface. Vegetation structure can affect climate by determining surface characteristics such as albedo, roughness length and canopy resistance. We investigated the relationship between vegetation structure and land surface energy exchange in Council, on the Seward Peninsula, in western Alaska. Our approach was to use a sequence of sites analogous to transitions that might be expected along a latitudinal gradient in arctic ecosystems in response to warming. The sites ranged from a lichen-sedge dominated tundra, through low and tall shrub tundra and woodland to a closed canopy evergreen forest. We evaluated both changes within a functional group, focusing on the consequences of increases in the deciduous shrub functional group, and also the affect of changing the dominant functional group from deciduous shrubs to evergreen trees. We measured biophysical characteristics including leaf area, biomass, production and cover that were thought to drive site differences in albedo and therefore energy partitioning to ground, latent and sensible heating fractions. In the sequence from tundra to forest, leaf area index increased from .43 to 2.7 while albedo decreased from .19 to .10. Increasing canopy complexity and albedo controlled site differences in energy partitioning, especially to sensible heating fractions, suggesting that vegetation transitions in high latitudes may result in further positive feedbacks to warming.
KEY WORDS: vegetation dynamics, high latitude ecosystems, land surface exchange