HR: 0800h
AN: B41A-0087    [Abstracts]
TI: Land Surface Phenology and Climatic Variation in the IGBP High-Latitude Transects.
AU: * de Beurs, K M
EM: kdebeurs@calmit.unl.edu
AF: University of Nebraska-Lincoln, School of Natural Resources 102 E. Nebraska Hall, Lincoln, NE 68588-0517 United States
AU: Henebry, G M
EM: ghenebry@calmit.unl.edu
AF: University of Nebraska-Lincoln, School of Natural Resources 102 E. Nebraska Hall, Lincoln, NE 68588-0517 United States
AB: The International Geosphere-Biosphere Program (IGBP) has delineated five study areas that form a northern high-latitude network for the analyses of vegetation dynamics, carbon dynamics, and water and energy exchanges. The five transects are located in Far East Siberia (FEST), East Siberia (EST), Scandinavia and northern Europe (ScanTran), boreal forest in Canada (BFTCS), and Alaska (AT). We examined the magnitude and significance of changes in land surface phenology in these transects using the Pathfinder AVHRR Land (PAL) dataset, which consists of maximum NDVI 10-day composites at 8 km spatial resolution. Daily minimum and maximum temperatures were extracted from the NCEP/NCAR Reanalysis Project to generate daily growing degree-days (base 0 oC) as 10-day composites (GDD10) and as seasonal accumulations (AGDD). Each transect spans a range of climatic and land surface conditions; thus, we partitioned the area within each transect according to the World Wildlife Fund's global ecoregions. For each of 24 ecoregions distributed over the five transects, we tested for significant differences in average GDD10 and average NDVI from April and September between the years corresponding to the observational periods of NOAA-9 (1985-1988) and NOAA-14 (1995-1999). We used the seasonal Mann-Kendall trend test to detect significant trends within these time periods for GDD10 and NDVI. Finally, we modeled the land surface phenology using a nonlinear spherical model to relate the PAL NDVI data from the first half of the growing season to AGDD. Models for each ecoregion within each transect were fit for each of the two satellite periods separately and then their parameter estimates were compared. We found significant increases and trends in average GDD10 in Canadian and Alaskan transects only. The other three transects exhibited neither significant step changes nor trends in GDD10 in any ecoregion. Furthermore, we found significantly higher NDVI in 3 of 5 ecoregions in ScanTran and in 2 of 6 ecoregions in AT. Spherical models fit well the first half of the growing season for 22 of 24 ecoregions with pseudo-R2's ranging from 0.65 to 0.95. The majority of ecoregions displayed equivalent NDVI for low AGDD in both study periods. The FEST is the only transect that displayed a nearly consistently higher sill in the spherical model from 1995 to 1999, indicating a higher NDVI plateau for larger AGDD. In 10 of 24 ecoregions distributed across the transects, the start of the growing season advanced slightly but significantly (between 2 and 18 days) between the first and second study periods; however, this progression seems to be more pronounced and larger in Alaska and Canada than in the other transects.
DE: 3322 Land/atmosphere interactions
DE: 1851 Plant ecology
DE: 1640 Remote sensing
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting