Assessing the Impact of Disturbance on Carbon Stocks in Western Forests using Remote Sensing and Forest Inventory Data

Abstract:

Forest disturbances have important impacts on regional and global carbon-climate feedbacks. Tree mortality resulting from disturbance can cause large areas to transition from carbon (C) sinks to C sources. Although severe acute disturbance, such as fire, has been quantified extensively in the literature, the impacts of disturbance that cause more spatially heterogeneous, gradual, mortality, such as beetle kill, are more difficult to quantify and have not been studied as extensively. Combining a 13 year time series of 250 meter, 16-day, MODIS Enhanced Vegetation Index (EVI) data with field data on insect mortality collected by the U.S. Forest Service Forest Inventory and Analysis (FIA) program, we have produced large-scale maps of dead woody biomass resulting from insect epidemics.

Using a change detection algorithm, we were able to determine the timing and severity of changes in EVI due to insect epidemics across the western United States. A model was created to predict biomass based on EVI and a variety of environmental variables. Using the difference between post- and pre-outbreak EVI values, we were able to estimate the loss of biomass during insect outbreaks. These biomass data were then converted to carbon as a percentage of dry biomass using the Jenkins equations. This spatially explicit map of C currently stored in beetle kill wood will allow us to assess the vulnerability of this C to re-entering the atmosphere as CO2 via combustion or decomposition.