MODIS/NDVI BASED DETECTION OF DROUGHT INDUCED VEGETATION DIEOFF IN WESTERN NORTH AMERICAN ECOSYSTEMS

Vegetation mortality can be attributed to many factors including drought-induced water stress and insect infestations which exploit these stressed trees. Reduction of canopy cover and reduced photosynthetic activity are easily identifiable in a time series of remotely-sensed multispectral satellite images. A suite of images from NASA's MODIS sensor was used to calculate the change in Normalized Difference Vegetation Index (NDVI) during the 2000-2006 western North American growing seasons. Fluctuations in NDVI over this period show a significant negative change in vegetative health in temperate coniferous forests. Historically, areas suffering from dieoff have recovered as climate conditions return to a normal regime. However, recent western North American droughts and associated vegetative change do not show signs that this change is reversible, an indication that the shifts being observed are long-term, or too severe for recovery to occur. Loss of vegetative cover in temperate latitudes due to drought is a growing global problem, and these occurrences will have serious negative effect on environmental health. Principal Component Analyses and ANOVA confirm the significance of these changes, and give clues as to the causes of these dieoff events and their common morphometric variables. Change similar to what has been found in the western United States is also occurring in other mid-latitude regions worldwide. Observations of the spatial pattern of temperate forest vegetation globally can be used to develop an accurate large scale picture of vegetative health in temperate regions containing marginal ecosystems and how they are reacting to global climate change.