Abstract
We used twelve Landsat scenes from the 1980s–2009 and regional 2000–2009 MODIS data to examine the long-term trend in the normalized difference vegetation index (NDVI) within unburned areas of the Alaskan boreal forest. Our analysis shows that there has been a declining trend in NDVI in this region, with the strongest “browning trend” occurring in eastern Alaska where the climate during the growing season is relatively dry and warm. Possible reasons for the "browning trend" are decreased vegetation due to temperature-induced drought stress and increased infestations of insect pests.
Highlights
The greatest climate warming over the past 50 years in North America has occurred in Alaska and northwest Canada [1]
In 2001 and 2007 the GIMMS Normalized Difference Vegetation Index (NDVI) decreased, while the MODIS NDVI increased from the western boreal region
Because of the potential of cloud-contamination artificially causing a ―browning trend‖ based on GIMMS NDVI data, we restricted the remaining analysis to MODIS and Landsat Thematic Mapper (TM)/ETM+ NDVI values
Summary
The greatest climate warming over the past 50 years in North America has occurred in Alaska and northwest Canada [1]. In contrast to the increasing NDVI in arctic tundra, there has been a declining trend in NDVI in boreal Alaska documented at several spatial scales [9,10,11]. These boreal results were all based on the NDVI data produced as part of the National. This observed ―browning‖ trend may be due to a bias towards negative trends in the Remote Sens. 2010, 2
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