Initial plant diversity, soil resource supply, and enemy access drive different ecological tradeoffs during old-field succession

Community succession is the process of species turning over through time following a disturbance. The time since disturbance influences which assembly processes are strongest in determining the current composition of communities. Examining the functional identity of species across environments which are heterogeneous in space or time during succession can reveal the multiple processes driving community dynamics. Specifically, extant plant communities following disturbance may alter colonization dynamics indicated by newly arrived species’ seed mass; soil resource supply may alter competition outcomes by selecting for species with higher height potential as light becomes an important limiting resource; and pressure from herbivores and pathogens may alter competition outcomes by selecting for species with better defended tissue.

I examine these co-occurring processes in an experimental old field across a four-year sequence where I expect dominant processes to differ. I manipulated initial plant diversity following artificial disturbance, soil resource supply via nutrient addition, and enemy access via pesticide spraying. The natural colonization of these experimental plots was monitored and community weighted mean trait scores were calculated for seed mass, vegetative height, and specific leaf area (SLA). Results suggest that early in succession community membership is filtered through colonization limitations related to seed mass. As time proceeds, soil resource supply and enemy access became stronger filters of community membership, with seed mass, height, and SLA influencing community membership. Community trait values shifted in response to soil resource supply and enemy access due to both among-species and within-species trait variation, suggesting that some species are able to respond to environmental heterogeneity by altering their physiology. Ultimately, the system showed a rapid change in dominant assembly processes following disturbance, where community membership shifted from being colonization dominated to competition dominated.

• Announcement as PDF