Aerial insect surveys provide valuable information about the extent and severity of tree mortality and damage caused by forest insects across the United States. Annual trends in tree mortality and damage revealed by surveys are especially valuable to forest managers and researchers; trends can help managers anticipate future tree mortality, and studying long-term trends in relation to other factors can reveal causes and patterns of mortality that are not immediately apparent. Similar to surveys, remote sensing data can be used to measure and map tree mortality and damage across large areas and multiple years. Thus, remote sensing is a logical means for complementing aerial surveys as the Forest Service anticipates relying less on aerial detection surveys and more on satellite images in the future.
Fir engraver, spruce, Douglas-fir, and mountain pine beetles have been causing significant tree mortality in recent years in the Nez Perce National Forest near Elk City, Idaho. We gathered field observations of current and historic tree mortality in the area around Elk City, which we then related to fine-scale satellite imagery to map dead trees. Different techniques for converting legacy aerial survey measures of severity were assessed with our tree mortality maps. Additionally, we created a model predicting tree mortality from Landsat imagery. We applied our model to an annual time series of Landsat imagery to map tree mortality for a large area near Elk City, Idaho for the years 1984-2018.
We are still in the analysis stage of this project and have not yet published results. However, initial results show that: