Drivers of secondary succession rates across temperate latitudes of the Eastern USA: climate, soils, and species pools.

Climate change is widely expected to induce large shifts in the geographic distribution of plant communities, but early successional ecosystems may be less sensitive to broad-scale climatic trends because they are driven by interactions between species that are only indirectly related to temperature and rainfall. Building on a biogeographic analysis of secondary succession rates across the Eastern Deciduous Forest (EDF) of North America, we describe an experimental study designed to quantify the relative extent to which climate, soil properties, and geographic species pools drive variation in woody colonization rates of old fields across the EDF. Using a network of five sites of varying soil fertility spanning a latitudinal gradient from central New York to northern Florida, we added seeds of nine woody pioneer species to recently tilled old fields and monitored first-year growth and survivorship. Results suggest seedlings of southern woody pioneer species are better able to quickly establish in fields after abandonment, regardless of climate regime. Sites of lower soil fertility also exhibited faster rates of seedling growth, likely due to the slower development of the successional herbaceous community. We suggest that climate plays a relatively minor role in community dynamics at the onset of secondary succession, and that site edaphic conditions are a stronger determinant of the rate at which ecosystems develop to a woody-dominated state. More experimental research is necessary to determine the nature of the herbaceous-woody competitive interface and its sensitivity to environmental conditions.