Abandoned agricultural land in the Eastern United States returns to forest in a well-established pattern in which "old fields" of herbs and grasses gradually give way to trees. This field-to-forest transition is a key event in ecosystem development because it drives wildlife abundance, influences how ecosystems store carbon and cycle nutrients, and often changes the balance between landscapes dominated by alien or native plant species. One puzzling aspect of this process is that old fields can persist for decades in the Northeast, but tend to transition to forests in less than 10 years in the Southeast, despite having many of the "field invading" tree species in common. Is this due to the warmer climate of the Southeast, where trees can grow more quickly in competition with herbs and grasses? If so, will "old fields" become forests more quickly as the climate warms? Alternatively, the regions may be different in other ways (e.g. soil quality). In this project the PIs have designed an experiment to definitively answer this question, using a network of six field experiments from New York to Florida. At each site, researchers will control the composition of the old field plants and invading trees (using species common to both the North- and Southeast), as well as varying the soil conditions to approximate northern and southern soils. Researchers will monitor the rate at which trees invade each experimental community, and use the results to formulate a model that can make predictions about how climate, soil fertility, and characteristics of particular species influence the rate of forest development in the Eastern United States.
These results will be key for understanding how agricultural landscapes of the Eastern United States will continue to change over the next century, and will inform stakeholders on land management issues with respect to carbon sequestration, biological diversity, and other ecosystem services. Two graduate students and several undergraduates will be trained, through the support of two junior faculty. The project also includes use of several core ecological research facilities in the Eastern United States.