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.
Spatial heterogenity of tundra vegetation response to warming in northern Alaska.
Jia, Gensuo1, Epstein, Howard*,1, Walker, Donald2, 1 University of Virginia, Charlottesville, VA2 University of Alaska Fairbanks, Fairbanks, AK
ABSTRACT- We examined the inter-annual changes in NDVI along latitudinal gradients, and across vegetation types and bioclimate subzones, on the North Slope of Alaska from 1991-1999. Using color infrared (CIR) and Multi-Spectral Scanner (MSS) images, we defined a set of sample sites representing homogeneous tundra vegetation over at least 3 x 3 1-km pixels. These sites were chosen to represent 1) two north-south transects in western and eastern portions of the North Slope, 2) four vegetation types - sandy tundra, moist non-acidic tundra (MNT), moist acidic tundra (MAT) and low shrub tundra, and 3) three bioclimate subzones. After comprehensive data correction and registration, we calculated the Peak-NDVI and temporally integrated (TI) NDVI for each of the study sites over the nine-year period. Along latitudinal gradients, Peak-NDVI and TI-NDVI were relatively low and showed essentially no change between 71.2-70.4 °N. Both indices increased strongly from 70.4 to 69.4 °N, indicating a spatial transition area, and then remained high from 69.4 to 69.1 °N. The greatest interannual variance in Peak-NDVI was found near the coast to the north and along the spatial transition area, while higher variances in TI-NDVI were mainly located in the southern part of the transects. Corresponding to these spatial changes, vegetation types and bioclimate zones found further north (e.g. sandy tundra, MNT and subzone 3 - prostrate shrubs) responded to decadal changes in temperature with increases in Peak-NDVI. However, vegetation types and bioclimate zones found further south (e.g. MAT, low shrub tundra and subzone 5 - low shrubs) responded with increases in TI-NDVI, suggesting a lengthening of the growing season in addition to other vegetation changes. Our results indicate that while most of the North Slope of Alaska has become greener over the past decade, the changes are not spatially homogeneous and may represent differential responses of different tundra communities and ecosystems.
KEY WORDS: arctic tundra, vegetation dynamics, NDVI, climate change