Potential influences of forest mesophication on corticolous arthropods as a food base for insectivores in eastern deciduous forests

Abstract

Decreased disturbance has allowed plant communities in some landscapes to transition from early- and mid-successional communities to later successional communities. In eastern deciduous forests, this process has been termed mesophication because of the transition from a xeric to a more mesic environment. Mesophytic trees tend to produce foliage that is less palatable than xerophytic trees, supporting fewer arthropods that provide an important food source for higher trophic organisms such as insectivorous birds and mammals. An additional characteristic that differs between xerophytic and mesophytic trees is bark texture. Xerophytic tree species tend to produce more deeply furrowed bark that protects trees from overheating. To better understand the potential impact of continued mesophication of eastern deciduous forest on forest dwelling insectivores, we tested the hypothesis xerophytic trees support a greater abundance, biomass, diversity, and richness of arthropods in the Shawnee National Forest of southern Illinois. More specifically, we tested the prediction we would catch a greater number and more diverse community of arthropods on the trunks of white oak (Quercus alba) and pignut hickory (Carya glabra) trees than on the trunks of sugar maple (Acer saccharum) and American beech (Fagus grandifolia) trees, with tulip poplar (Liriodendron tulipifera), a species with an intermediate level of bark roughness and found in both mesic and xeric conditions having an intermediate number of arthropods. Consistent with our prediction, we found the model that included tree species to be most parsimonious when describing variation in arthropod diversity, total arthropod length (as a surrogate for biomass), and arthropod abundance, but not arthropod richness. Differences in arthropod abundance and total length among tree species were driven by the greater total length and abundance of arthropods found on pignut hickory, while the difference in arthropod diversity among tree species was driven by lower Shannon diversity observed on pignut hickory. These results suggest that continued mesophication of eastern deciduous forests may be detrimental to branch and trunk gleaning insectivores, primarily due to the loss of pignut hickory in the forest community. Because both oak and hickory trees support more abundant and diverse foliage dwelling arthropod communities than more mesophytic species, because at least some species of hickory trees support greater total length and abundance of arthropods on their trunk bark, and because species of both genera are most frequently found in more xeric conditions, we recommend forest managers implement management activities that reset succession and maintain a more xerophytic tree community.