Locating and estimating the extent of Delmarva fox squirrel habitat using an airborne LiDAR profiler

Abstract

Two thousand five hundred thirty-nine kilometers of airborne laser profiling and videography data were acquired over the state of Delaware during the summer of 2000. The laser ranging measurements and video from approximately one-half of that data set (1304 km) were analyzed to identify and locate forested sites that might potentially support populations of Delmarva fox squirrel (DFS, Sciurus niger cinereus). The DFS is an endangered species previously endemic to tall, dense, mature forests with open understories on the Eastern Shore of the Chesapeake Bay. The airborne LiDAR employed in this study can measure forest canopy height and canopy closure, but cannot measure or infer understory canopy conditions. This airborne LiDAR profiler, then, must be viewed as a tool that identifies and locates potential, not actual, habitat. Fifty-three potentially suitable DFS sites were identified in the 1304 km of flight transect data. Each of the 53 sites met the following criteria according to the LiDAR and video record: (1) at least 120 m of contiguous forest; (2) an average canopy height >20 m; (3) an average canopy closure of > 80%; and (4) no roofs, impervious surface (e.g., asphalt, concrete), and/or open water anywhere along the 120 m length of the laser segment. Thirty-two of the 53 sites were visited on the ground and measurements taken for a DFS habitat suitability model. Seventy-eight percent of the sites (25 of 32) were judged by the model to be suited to supporting a DFS population. All of the LiDAR flight data, 2539 km, were analyzed to estimate county and statewide forest area in different height/canopy closure classes. Approximately 3.3% of Delaware (17,137 ha) supports forest over 20 m tall with crown closures exceeding 80%; the corresponding county percentages are Newcastle County—6.1% (6823 ha), Kent County—2.2% (3431 ha), and Sussex County—2.7% (6883 ha). Estimates of average within-patch crossing distance and average between-patch distances are reported, by county, and for the state. Study results indicate that: 1) systematic airborne LiDAR data can be used to screen extensive areas to locate potential DFS habitat; 2) 78% of sites meeting certain minimum length, height, and canopy closure criteria will support DFS populations, according to a habitat suitability model; 3) airborne LiDAR can be used to calculate county and state acreage estimates of potential habitat, and 4) the linear transect data can be used to calculate patch statistics. The authors suggest that the systematic county and state flight lines can be revisited at intervals to monitor changes to the areal extent of potential habitat over time.