In fragmented forest landscapes, edge environments can alter forest structure, turnover, and composition. Decreasing structural contrast between forests and adjacent land-uses may mitigate the effect of forest edges on fauna and micro-climates in certain ecosystems. If this “buffering effect” is a general phenomenon, it represents a conservation opportunity for landscape management; edge effects could be ameliorated by planting trees adjacent to existing forests. In the southeastern U.S., monoculture timber plantations make up a third of the total tree cover. In this study, we compared the effect of low-contrast (timber plantation) and high-contrast (pasture and agriculture) forest edges on neighboring forest edge structure. We used long aerial transects of LiDAR data (~3,000 km in all) to assess changes in canopy structure from the edge to interior of natural forest patches. High-resolution (1 m) LiDAR data from Goddard’s LiDAR, Hyperspectral, and Thermal Airborne Imager (G-LiHT) were combined with time series of Landsat imagery to identify edge age and adjacent land cover information. Forest structural metrics (height, gap fraction, and canopy roughness) were examined across forest edge types and configurations. We hypothesized that 1) structural edge effects would be strongest, in penetration and severity, in natural forest fragments with high edge exposure indices, and 2) timber plantations would mitigate structural edge effects in adjacent natural forests.
Results/Conclusions
We selected a random subset of large (>4 ha) forest fragments making up the 8562 distinct forest edges measured during G-LiHT data collections in 2011 across the southeastern U.S. We analyzed forest structural metrics (height, gap fraction, and canopy roughness) and quantified forest edge effects as declining trends in structural metrics with increasing distance from edge or edge exposure. In general, the relationship between forest structural metrics, edge exposure indices, and distance-from-edge was highly variable across the first 100 meters, regardless of edge type. The severity and penetration of edge effects on canopy height varied with fragment size, configuration, and the presence of adjacent pine plantations. We found limited support for a general buffering effect on forest structure in this region. High-resolution remote sensing is uniquely situated to advance our understanding of the drivers of forest canopy structure in fragmented landscapes. By quantifying local variability in forest edge effects at a regional scale, our results highlight the importance of non-edge processes for forest structure, biomass, and biodiversity in the southeastern U.S.