Is successional research nearing its climax? New approaches for understanding dynamic communities

Succession has been a focus of extensive ecological study for well over a century. Despite this sustained interest, succession remains a central theme in ecological research and is positioned to continue that prominence in this era of expanding human impacts. Community ecology is currently experiencing a profound conceptual expansion, providing many new insights into succession. Here we present an existing conceptual framework of successional drivers that includes variation in site conditions, species availability and species performance, and expand it to include both evolutionary and geographic sources of variation. This framework is useful because it specifies relationships among individual drivers and is causally complete. While we generally think about succession as a within-site process, the inclusion of phylogenetic and geographic processes allows integration across broader scales. We use the conceptual framework to highlight several opportunities for successional research that have developed within community ecology, but have not been fully integrated into succession work. These ideas represent not only individual drivers of succession, but also potential synergistic processes operating through interaction with other drivers. The complexity of drivers in succession strongly argues for the need to move away from single factor studies towards combinatorial studies that incorporate multiple drivers. Utilizing a trait-based approach should allow researchers to address successional drivers at multiple ecological scales and lead to new insights that integrate ecological systems. Our ability to do this will depend on the availability of equivalent data across multiple systems, suggesting the need for more standardization in successional studies. Addressing the research opportunities highlighted here will not only produce insights into successional systems, but also expand our understanding of fundamental questions in community ecology as a whole. Of particular importance is the ability to address broader scale questions that go beyond the idiosyncrasies of individual sites and systems. Understanding the dynamics of successional systems will remain critical to understanding, managing and predicting anthropogenic impacts on natural systems.