标题：Satellite observations of high northern latitude vegetation productivity changes between
1982 and 2008: ecological variability and regional differences
摘要：To assess ongoing changes in high latitude vegetation productivity we compared
spatiotemporal patterns in remotely sensed vegetation productivity in the tundra and
boreal zones of North America and Eurasia. We compared the long-term GIMMS (Global
Inventory Modeling and Mapping Studies) NDVI (Normalized Difference Vegetation
Index) to the more recent and advanced MODIS (Moderate Resolution Imaging
Spectroradiometer) NDVI data set, and mapped circumpolar trends in a gross productivity
metric derived from the former. We then analyzed how temporal changes in productivity
differed along an evergreen–deciduous gradient in boreal Alaska, along a shrub cover
gradient in Arctic Alaska, and during succession after fire in boreal North America and
northern Eurasia. We find that the earlier reported contrast between trends of increasing
tundra and decreasing boreal forest productivity has amplified in recent years, particularly
in North America. Decreases in boreal forest productivity are most prominent in areas of
denser tree cover and, particularly in Alaska, evergreen forest stands. On the
North Slope of Alaska, however, increases in tundra productivity do not appear
restricted to areas of higher shrub cover, which suggests enhanced productivity
across functional vegetation types. Differences in the recovery of post-disturbance
vegetation productivity between North America and Eurasia are described using burn
chronosequences, and the potential factors driving regional differences are discussed.
