标题：Spatial and temporal patterns of greenness on the Yamal Peninsula, Russia: interactions of
ecological and social factors affecting the Arctic normalized difference vegetation index
摘要：The causes of a greening trend detected in the Arctic using the normalized difference
vegetation index (NDVI) are still poorly understood. Changes in NDVI are a
result of multiple ecological and social factors that affect tundra net primary
productivity. Here we use a 25 year time series of AVHRR-derived NDVI data
(AVHRR: advanced very high resolution radiometer), climate analysis, a global
geographic information database and ground-based studies to examine the spatial and
temporal patterns of vegetation greenness on the Yamal Peninsula, Russia. We
assess the effects of climate change, gas-field development, reindeer grazing and
permafrost degradation. In contrast to the case for Arctic North America, there has
not been a significant trend in summer temperature or NDVI, and much of the
pattern of NDVI in this region is due to disturbances. There has been a 37%
change in early-summer coastal sea-ice concentration, a 4% increase in summer
land temperatures and a 7% change in the average time-integrated NDVI over
the length of the satellite observations. Gas-field infrastructure is not currently
extensive enough to affect regional NDVI patterns. The effect of reindeer is difficult
to quantitatively assess because of the lack of control areas where reindeer are
excluded. Many of the greenest landscapes on the Yamal are associated with
landslides and drainage networks that have resulted from ongoing rapid permafrost
degradation. A warming climate and enhanced winter snow are likely to exacerbate
positive feedbacks between climate and permafrost thawing. We present a diagram
that summarizes the social and ecological factors that influence Arctic NDVI.
The NDVI should be viewed as a powerful monitoring tool that integrates the
cumulative effect of a multitude of factors affecting Arctic land-cover change.
