HR: 1340h
AN: B33E-1091    [Abstracts]
TI: Uneven Response of Arctic Tundra to Recent Environmental Changes
AU: * Jia, G J
EM:
AF: University of Virginia, Environmental Sciences, 291 McCormick Rd., Charlottesville, VA 22904-4123 United States
AU: * Jia, G J
EM:
AF: RCE-TEA, Institute of Atmospheric Physics, CAS. PO Box 9804, Beijing, 100029 China
AU: Epstein, H E
EM:
AF: University of Virginia, Environmental Sciences, 291 McCormick Rd., Charlottesville, VA 22904-4123 United States
AU: Walker, D A
EM:
AF: University of Alaska Fairbanks, Institute of Arctic Biology, Fairbanks, AK 99775 United States
AB: Tundra vegetations are expected to be highly sensitive to fluctuation and directional changes of surface temperature and therefore have relatively rapid response to recent environmental changes. Recent studies have shown that tundra ecosystems have changed substantially in terms of primary production, shrub abundance, and carbon exchange as warming of the Alaskan Arctic has accelerated over the past three decades. However, both continental-scale satellite studies and site-scale field measurements suggest heterogeneous changes in vegetation in response to warming and to large scale disturbances. Here, we investigated the heterogeneity of recent decadal dynamics in vegetation photosynthetic activities in response to changes in summer temperatures along spatial gradients in northern Alaska. We used image spatial analysis to examine the spatial pattern of greenness dynamics over past decade as indicated by variations of the maximum normalized difference vegetation index (NDVI) and time-integrated NDVI crossing three bioclimate subzones along the latitudinal gradients. NDVI indices are generally highly variable over the decade, with great heterogeneity across the gradients. The largest variance in maximum NDVI occurred in the central part of bioclimate subzone dominated by erect dwarf shrub and was associated with maximum fractional cover of wet tundra and moist non-acidic tundra, while the greatest variance in time-integrated NDVI was observed in the southern bioclimatic subzone associated with maximum shrub tundra/moist acidic tundra fractional cover. Relatively high temporal NDVI variances were also found around several transitions along the gradients. Existence of azonal vegetation and water bodies lowered the temporal NDVI variances in corresponding areas due to their insensitivity to environmental dynamics. The decadal temporal variances of NDVI were likely driven by the 1.1-2.3°C warming and by the effect of the Mt. Pinatubo eruption, and reflected an increasing vegetation growth along the latitudinal gradients with heterogeneous enhancement of shrub abundance, which is likely due to the distribution of the minimum temperature limit for shrub occurrence. Several factors may have contributed to the spatial heterogeneity of NDVI temporal variances. Among them are the fractional cover of tundra vegetation types dominated by various plant functional groups, the abundance of frost boils on the arctic coastal plain, and the distribution of azonal sandy tundra.
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0429 Climate dynamics (1620)
DE: 0456 Life in extreme environments
DE: 0476 Plant ecology (1851)
DE: 0480 Remote sensing
SC: Biogeosciences [B]
MN: Fall Meeting 2005