Evidence for multiple pathways in old field succession?

A rich body of theoretical and experimental literature suggests that differences in species assembly order, and manipulation of environmental factors such as nutrient availability, can fundamentally alter the trajectory of community change in ecosystems. However, it is unclear how important these forces are in structuring natural communities, particularly in terrestrial settings. Partly, this is because it is difficult to define “community change” in terms of any widely applicable metric, as even manipulations of dubious ecological significance are likely to have some minor impact on any measureable ecological property. Moreover, because two initially identical and unperturbed communities will naturally diverge to some extent though time as a result of stochastic variations in birth and death rates, it is important to identify whether differences among communities exceed those expected from ecological drift.

Using a unique thirty-year study of old field succession in the LTER site at Cedar Creek, MN, we explore the direction and magnitude of prairie plant community changes following agricultural abandonment over the past century. By comparing relative abundance of species in old fields through time, we ask

1. Whether the fields approach one, many, or no “endpoint” in ecological succession
2. Whether the fields follow the same successional pathway to reach any endpoints.

Additionally, we assess the magnitude and duration of changes in soil carbon sequestration, nutrient enhancement, and primary productivity in fields corresponding to differences in community structure. Based on this study, we suggest that it may be prudent to focus not solely on the statistical significance of changes, but also to ask whether assembly order and environmental manipulation can have large and lasting effects on the structure and function of ecological communities across large spatial scales.