Synergistic use of spaceborne lidar and optical imagery for assessing forest disturbance: An Alaska case study

Fire disturbance at high latitudes modifies a broad range of ecosystem properties and processes, thus it is important to monitor the response of vegetation to fire disturbance. This monitoring effort can be aided by lidar remote sensing, which captures information on vegetation structure, particularly canopy height metrics. We used lidar data acquired from the Geoscience Laser Altimetry System (GLAS) on ICESAT to derive canopy information for a wide range of burned areas across Alaska. The GLAS data aided our analysis of postfire disturbance and vegetation recovery by allowing us to derive returned energy height metrics within burned area perimeters. The analysis was augmented with MODIS reflectance data sets, which were used to stratify vegetation cover into cover type and density. We also made use of Landsat burn severity maps to further stratify the lidar metrics. Results indicate that canopy height decreases following fire, as expected, but height was not a good overall indicator of fire isturbance because many locations within the burned area perimeters either did not actually burn or experienced different levels of burn severity, typically leaving many standing trees or snags even after intensive burning. Because vegetation recovery following fire is differentially affected by burn severity, significantly greater height growth was documented in more severely burned areas due to a greater proportion of deciduous vegetation regrowth. When these factors were considered, GLAS height metrics were useful for documenting properties of regrowth in burned areas, thereby facilitating monitoring and mapping efforts following fire disturbance. A new satellite lidar sensor designed for vegetation studies would thus prove valuable information for improving ecosystem models that incorporate disturbance and recovery.