Compositional attributes of invaded forests drive the diversity of insect functional groups

Abstract

Forest canopies are important habitats for animal biodiversity globally. The structural and compositional components of canopies influence biodiversity, and recent advancements in remote sensing have given insight to these relationships. As invasive shrubs alter both the structure and composition of forests, we use handheld, mobile LiDAR to relate these elements and the overarching tree composition to insect biodiversity in Georgia, USA. Both LiDAR-derived structural metrics (vegetation density and Shannon vertical complexity index) were related to invasive shrub cover. We sampled four insect functional groups using two methods: woodboring beetles, mycophagous beetles, and bees were sampled using flight intercept traps 5 m aboveground, while litter-foraging ants were sifted from leaf-litter. From our generalized linear models, we found that tree composition strongly influenced all groups, though responses varied among functional groups. Woodboring beetles were negatively influenced more strongly by invasive shrub cover than vegetation density and also responded positively to tree and deadwood diversity. By contrast, bees and mycophagous beetles were unaffected by both the structure and composition of invasive shrubs, but were sensitive to tree composition. In the leaf-litter, ants were negatively influenced by invasive shrub cover and were sensitive to tree composition. Thus, the composition of forests is an important driver of insect diversity in our system, but with idiosyncratic responses among functional groups. Our results demonstrate the utility of LiDAR in clarifying the relationship between structure and composition on biodiversity in forest canopies, especially in regards to invasive plants.