TWEL Donald C. Radcliffe Thesis

Topographic, edaphic, and stand structural factors associated with oak and hickory mortality and maple and beech regeneration in mature forests of Appalachian Ohio

Donald C. Radcliffe, MS

Advisor: Stephen N. Matthews

Thesis

Oak (Quercus spp.) and hickory (Carya spp.) trees are failing to replace themselves in forests of the eastern U.S., likely due to fire suppression and a moister climate during the past century. Our study explored the implications of this mesophication process for future forest composition in southeastern Ohio. In 2016-2018 we resampled permanent plots first established in 1993-1995, in mature forests of the Athens and Marietta Units of the Wayne National Forest. We used mixed logistic regression models to characterize mortality patterns of five oak and one hickory species, and generalized linear mixed models to characterize sapling density patterns of three common shade-tolerant tree species that are likely to dominate future forest composition. For both the mortality and sapling models, we chose a set of a priori topographic, edaphic, and stand structural variables, and used the full set of a priori covariates for analysis of each species. Our mortality data revealed relatively high mortality rates for all species of the red oak subgenus (Erythrobalanus). Models indicated that chestnut oak (Quercus montana) and pignut hickory (Carya glabra) mortality were positively associated with competition, while white oak (Quercus alba) mortality was negatively associated with competition. Northern red oak (Quercus rubra) mortality was associated with mesic topographic positions and older stand age. Our sapling data showed that American beech (Fagus grandifolia) nearly doubled in density between the two sampling periods (217 trees per hectare[tph] 1990s, 429 tph 2010s), while both red maple (Acer rubrum) and sugar maple (Acer saccharum) nearly halved in density (red maple 441 tph 1990s, 216 tph 2010s; sugar maple 608 tph 1990s, 298 tph 2010s). Models indicated that soil acidity was positively related with red maple sapling density, and negatively associated with sugar maple sapling density. Higher slope positions were positively related with red maple sapling density and negativel associated with American beech sapling density. Overall, these results indicated that stand structural variables are more important than soil characteristics and topographic position in explaining mature tree mortality of most common oak and hickory species, and that topographic and acidity gradients will likely partially explain future relative dominance patterns of red maple, sugar maple, and American beech.