PS 11-142 - Change in future tree composition and structure due to oak wilt in a Northwestern Ohio Oak Openings forest

Abstract: In the dry sand forests of the Oak Openings Region of Northwest Ohio, the dominant tree species, black oak (Quercus velutina), is vulnerable to fungal pathogen attack. We examined variability in forest communities within contained treatment sites for oak wilt (Bretziella fagacearum), a fungal pathogen lethal to susceptible oak species, like the black oak. Containment treatments included quarantine lines in soil for limiting belowground fungal spread and sanitation, and cutting of 1–3 mature trees within oak wilt infection patches. At 28 sites, we compared tree structure and understory plant communities across a gradient of 1- to 6-year-old treatments and reference forest (untreated and without evidence of oak wilt). While oak seedlings were abundant at the sites, oak saplings (1–10 cm in diameter) were absent. Red maple (Acer rubrum) was the most common tree species in the sapling layer in all sites. This creates the long-term possibility of an oak to maple shift in forest canopy trees. Many measures of native understory plant community were highest in oak wilt treatments. Plant species richness doubled in the treatment sites, regardless of age, compared to the reference forest. Plant cover increased with treatment age, with 6-year-old treatments exhibiting 5 times more cover than reference forest. Non-native plants averaged only a small proportion of cover across treatments and reference forest. Variability in understory communities was predictable using treatment age, tree canopy cover, and geographic location. While oak wilt treatments did not facilitate oak regeneration nor many conservation-priority species of open savanna woodland habitats, the treatments did diversify and increase cover of native understory communities with minimal invasion of non-native plants.