The role of landscape configuration on tree seedling recruitment in remnant forests in Southeast Michigan
Anthropogenic land use change alters the environment plants experience in remnant habitat patches. Here vegetation dynamics will depend on both regional climate drivers and configuration of adjacent land uses. The composition of these forests will be a function of how each species fares in light of the landscape-specific environment. Few studies have empirically tested the impacts of landscape surrounding forest fragments on tree species population dynamics, and regeneration in particular. We conducted a transplant experiment to determine the role of landscape configuration on the survival of seven native and three invasive species establishing in remnant forests. Seedlings were transplanted into edge (high light) and interior (low light) plots within eight forest patches along a 40 km urban-rural gradient in southeast Michigan. We measured important environmental variables for seedling establishment (soil moisture, light, nutrients) and protected some seedlings from deer herbivory.Over the course of the summer we measured seedling growth and mortality. To analyze the data, we constructed hierarchical models using a Bayesian framework that reflected the spatial scale of our data.
Once differences in resource availability were accounted for our results still show differential survival along this gradient for each of the studied species. Most species had the highest survival in rural forests in interior plots. An exception was Robinia pseudoacacia, an invasive tree, which had the highest survival in edge plots in urban forests. Several native species showed the lowest survival in urban forests: Acer rubrum, Carya glabra and Quercus velutina. C. glabra had the highest survival in exurban forests. Invasive species as a whole exhibited much higher growth and survival in the urban forests than the native species. These results suggest that the landscape surrounding remnant forests has the potential to affect tree species recruitment beyond the effects caused by a change in resources and thus may play a role in the future structure and functioning of these forests.