One popular application of lidar is characterizing live trees, but a wealth of information lies in the artifacts of these data. Canopy gaps are defined by the absence of vegetative structure and serve important roles for wildlife, such as facilitating animal movement. Gaps also occur around snags, keystone structures that provide important substrates to wildlife species for breeding, roosting, and foraging. We hypothesized that lidar and canopy gap analysis could improve snag modeling, with certain gap characteristics differentiating snags from their surroundings. We evaluated gaps around snags and live trees to determine whether correlations between canopy structure and snag occurrence exist in dense conifer stands of the Idaho Panhandle National Forest. We paired airborne lidar with ground reference data collected at fixed-radius plots to evaluate local gap structure. Plot data included characteristics of individual snags (location, DBH, height, decay status) and avian point counts. We extracted horizontal circular “slices” of lidar data with a 3m radius, centered on each live tree or snag. Slices occurred at 4 heights above ground (2m, 5m, 10m, and 25m). The R package ForestGapR was used to locate canopy gaps across each slice and generate metrics on gap extent across all heights for each sample.
Results/Conclusions
Preliminary results aligned with expectations for conifer forests, with more and larger gaps at higher canopy positions across all samples (n=232 slices total across 22 snags and 36 live trees). Results further suggest there were more gaps around snags, regardless of height (gaps present in 76% of snag slices vs. 28% of live trees). The relationship between canopy gaps and snags was more pronounced across all metrics: 95% of snags had gaps at both 10m and 25m (while only 22% of live trees did), and gap size was 1.5x larger on average for snags. Additionally, there was a positive correlation between gap size and snag diameter, becoming stronger as canopy height increased. We calculated gaps at the plot level (circular slices with 25m radius) and compared avian point counts with total gap area across 3 heights shown to differentiate individual snags from live trees. Primary cavity excavator occurrence was significantly correlated with greater gap extent (n=22 plots). These results show potential to improve understanding of gap dynamics, which will not only will inform snag modeling, but may elucidate how open space is structured within canopies in ways beneficial to wildlife, with direct management implications for woodpeckers and other cavity users.