A unifying framework for understanding how edge effects reshape the structure, composition and function of forests

Due to widespread deforestation and habitat fragmentation, today most of the world’s forests lie within 1 km of an edge. Forests near edges are warmer, drier, receive more light, and are more exposed to wind and other disturbances than intact forests, profoundly altering the demographic processes that drive their dynamics. For reasons that remain poorly understood, the magnitude and direction of edge effects on forest structure, composition and function varies considerably across forest ecosystems. Here, we develop a unifying framework that aims to reconcile these apparently contrasting outcomes to forest edge creation by explicitly accounting for the effects of edge age, climatic context and forest structure. We begin by identifying four stages of forest edge evolution, arguing that demographic trajectories after edge creation are actually broadly similar across different forest types. We then consider how regional differences in climate and forest structure help explain why in tropical rainforests aboveground biomass typically declines sharply at forest edges, while in cooler climates the opposite is often true. Finally, we outline a series of concrete predictions made by our framework and discuss how these could be tested using ever-growing archives of remote sensing products that capture ecosystem change across broad spatio-temporal scales. In doing so we aim to offer a fresh perspective on a research field that has captivated ecologists for half a century.