Assessing the cumulative impact of disturbance on canopy structure and chemistry in Appalachian forests

Background/Question/Methods   Eastern forests experience a range of disturbance events over time from stand-replacing disturbances, such as clear cuts, to ephemeral disturbances, such as insect outbreaks. By understanding the cumulative impact of disturbances on canopy structure and chemistry, we can gain insight into management strategies, assess a variety of ecosystem services, and even contribute to a larger body of knowledge on global climate change. We used a series of Landsat images covering approximately 25 years to map cumulative disturbance in Green Ridge State Forest and Savage River State Forest in western Maryland. We used AVIRIS imagery flown during the summers of 2008 and 2009 to map canopy nitrogen across both forests. Field data collected during both summers served as calibration and validation for the remotely sensed maps of canopy nitrogen and disturbance and also contributed information on forest structure and composition. Through this project, we sought to test the utility of a Landsat-based cumulative disturbance index to map disturbance across a broad spatial scale and to assess the impact of cumulative disturbance on forest nitrogen availability using the canopy nitrogen maps.

Results/Conclusions   Our results indicated that cumulative disturbance can be accurately mapped using Landsat imagery. Additionally, we found that increased values of cumulative disturbance had a measurable impact on forest canopy structure as well as lead to a decrease in nitrogen availability, particularly at the watershed scale. Thus, our study suggests that Landsat time series data can be synthesized into cumulative metrics incorporating multiple disturbance types, which help explain important disturbance-mediated changes in ecosystem functions.