The Impact of Land-Uses on the Recruitment Dynamics of Tree Species

Abstract

Patterns of human land use vary as distance from an urban center increases. These changes in land use alter nutrient loads, invasive species pressure and have been associated with altered patterns in plant communities. Additionally, habitat fragmentation increases in the proximity of urban centers ushering in further environmental changes (increasing edge effects, dispersal distance, isolation, etc.) that also affect plant communities. The combined impacts of habitat fragmentation and human land use patterns surrounding remnant forest patches may further alter plant communities. Few studies however, have empirically tested the impacts of these combined effects on plant species. Here, I study the impacts of the surrounding landscape on the growth and survival of eight native and two invasive tree species in remnant forest patches. For that I planted seedlings of these species at 4 forests along a 40 km urban-rural gradient in southeast Michigan. Seedlings were planted at three different forest habitats, forest edge, middle distance to the edge, and forest interior. Over the course of the summer I measured seedling growth and mortality, in addition to environmental characteristics of the sites, i.e., soil moisture and light availability. To analyze the data, I constructed hierarchical models using a Bayesian framework that reflected the spatial scale of my data. My results shows differential growth and survival along this land use gradient for each of the studied species. In general, the invasive species had greater survival closer to urban areas, while several large seeded native species had lower survival rates closer to urban centers. Later successional and more shade tolerant species had higher survival in more rural forests. Other species had higher growth and survival at specific landscape-habitat combinations. For example, Acer saccharum tended to have higher growth and survival in the more shaded interior plots than edge plots across the land use gradient. On the other hand, Prunus serotina had higher survival in the edge plots, but only at the two more rural sites. These results suggest that human land use patterns have the potential to affect species composition in remnant forest patches.