CHARACTERIZING ASPEN DIEBACK SEVERITY USING MULTIDATE LANDSAT DATA IN WESTERN CANADIAN FORESTS

Dieback and mortality of Trembling aspen (Populus tremloides Michx.) stands, often referred to as aspen decline, appears to be increasing in Western Canada and in many other areas within the range of this species. This study was done within the aspen parkland and the boreal transition ecoregions where aspen dieback has been attributed to severe drought events in combination with repeat insect defoliation. A particular challenge has been the creation of a ground-based index to represent vegetation damage that could be linked to satellite-based observations. Health assessments from field surveys were used to relate the severity of aspen dieback to the relative difference in the infrared simple ratio (ISR) from multidate Landsat imagery. Aspen dieback damage ranged from 23% for light to 58% for moderate and 80% for severe. The variability in aspen dieback increased with severity class. Research results to date demonstrate a linear relationship between aspen dieback and the relative change in infrared simple ratio (R 2 = 0.7). Work is continuing to further develop these relationships and to apply these methods for mapping the severity of aspen dieback over larger geographic regions in Western Canada.