Tree mortality in forest communities can be the result of a number of factors including herbivory, disease, abiotic factors, and age. Ecotones are transitional areas between two ecosystems that are expected to have high rates of mortality because there is an increased potential for individuals to establish in unfavorable conditions. We set out to see how tree mortality and growth rates differ within ecosystems compared to within ecotones, and which factors we can use to predict tree mortality. Jennings Woods in Northeast Ohio is a temperate hardwood forest containing three ecosystems (upland forest, bottomland forest, riparian forest) with significantly differing tree communities and soil types. In 2008, an adult tree survey of ~2000 individuals was conducted, which also showed that individuals near ecotones experienced soil habitat outside of the optimal range for their species. In 2016, this survey was repeated to evaluate how the community has changed over that time. The two surveys were compared using a generalized linear mixed model (GLMM) to determine how ecosystem and species type affect mortality. In addition to mortality, we compared the rank abundances of tree species between the two years, as well as recruitment of new adult trees into the system.
Results/Conclusions
Preliminary results from the GLMM suggest that mortality depended more heavily on species than ecosystem. We saw less mortality overall at ecosystem edges and in ecotones than in the ecosystem cores. This was surprising as we hypothesized that there would be high mortality along ecosystem edges and with ecotones. For the most dominant species (Acer saccharum and Fagus grandifolia) in the forest, we found very little mortality (less than 10% each). However, both ash species in Jennings Woods (Fraxinus americana and Fraxinus nigra) experienced high rates of mortality (41.8% and 70.5%), likely due to herbivory by the invasive emerald ash borer. The lack of mortality for the majority of tree species resulted in little change in species rank abundance between the two time periods. Despite the dynamic nature of the forest, high rates of turnover (13% tree mortality overall), and significant heterogeneity in mortality among different species, 85% of the adult tree species showed no change in rank abundance, leading to our conclusion that the forest community has remained relatively unchanged over the past 8 years. Since we did not observe increased mortality near ecotones, further analysis and studies are necessary to understand factors maintaining different communities delineated by ecotones.