Biogeographic synthesis of secondary succession rates in eastern North America

Aim: Mechanistic models of old-field plant succession have generally lacked a broader biogeographic context in which climate, soils and species pools could play a significant role in mediating succession rates. We examine broad-scale patterns in old-field succession and introduce a hierarchical conceptual model to incorporate potential mechanisms operating at multiple spatial scales. Location: We reviewed secondary succession studies across the Eastern Deciduous Forest (EDF) of North America. Methods: We collected data from all published studies that reported the time necessary for woody species to reach either 10% or 50% cover in old-field systems throughout the EDF. We used regression approaches to determine whether rates of succession are controlled by climatic and edaphic factors that vary at broad spatial scales. Results: We found that the rate at which woody species colonize and dominate old fields decreases significantly with latitude. Rates of woody succession were highly correlated with both annual temperature (growing degree-days for years to 10% and 50% cover) and measures of soil fertility (cation exchange capacity and reported pre-agroindustrial (1930) maize yields for years to 10% cover), all of which show a significant latitudinal trend across the EDF. Main conclusions: We suggest that the driver of this pattern is geographic variation in the intensity of competition between herbaceous and woody species, which we relate to the effects of (1) temperature regime, (2) edaphic factors related to soil fertility, and (3) plant traits, which may vary latitudinally in response to climate and edaphic factors. Although insufficient data exist to evaluate the relative importance of these factors, we argue that research in this area is necessary to gain an understanding of how future landscapes will be affected by global climate and land use change.