Журнал наук о Земле и изменения климата

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Landsat Image Analysis of Tree Mortality in the Southern Sierra Nevada Region of California during the 2013-2015 Drought

Christopher S Potter*

The United States Forest Service (USFS) observed marked increases in tree mortality in the southern Sierra Nevada foothills and mountains of California using aerial monitoring surveys in April 2015. Aircraft flew over 4 million acres of forested land and found that about 20 percent of forest stands had detectable mortality, totaling 10.45 million dead trees. In this study, Landsat satellite imagery was analyzed at over 90% of these high tree mortality sites in the southern Sierra to understand how the three consecutive years (2013-2015) of extreme drought conditions compared to changes in forest stand growth rates dating to the mid-1980s across this region. Results showed that changes in Landsat droughtsensitive indices from the years 2011 to 2015 closely matched patterns of tree mortality across USFS April 2015 aerial survey locations in the southern Sierra Nevada. The historically low snow year of 2015 could have essentially reset the average forest canopy density for many forests in the region to late 1980s levels, due to drought-related mortality, combined with numerous large stand-replacing wildfires. The corresponding patterns and trends in Landast droughtsensitive indices with observed tree mortality rates can better inform region-wide assessments of forest growth trends and enable long-term drought impact monitoring.