Perspectives on global change theory

Background/Question/Methods Global changes in ecological drivers, such as CO₂ concentrations, climate, and nitrogen deposition, are increasingly recognized as key to understanding contemporary ecosystem dynamics, but a coherent theory of global change has not yet been developed. There are four attributes that characterize phenomena considered under global change that present unique challenges to existing theories: (1) global change drivers have an anthropogenic origin, (2) these drivers result in trajectories of change that differ from those studied in the past, and are often characterized by threshold behavior and regime shifts, (3) global change drivers and their interactions with natural processes operate at different spatial and temporal scales, and (4) drivers and processes interact across scales such that spatial context and connectivity among spatial units must be considered. Thus, there is a critical need for existing theory in ecology to be adapted and modified such that global change drivers and responses to them can be integrated across scales, permitting a more complete understanding of ecosystem dynamics.

Results/Conclusions We outline the characteristics of a theory of global change that draws upon other theories from a range of sub-disciplines, including population biology, landscape ecology, and Earth system sciences. The theory is based on the following propositions: (1) global scale patterns can be understood via the hierarchy of interacting processes at finer scales, from plants to landscapes and regions, and fine-scale patterns often cannot be understood without knowledge of global processes; (2) dynamics at any location on the globe are affected to varying degrees by transfer processes that connect adjacent as well as distant locations, (3) transfer processes (wind, water, animals, humans) connect locations via the movement of organisms, materials, disturbance, and information, (4) spatial heterogeneity (i.e., pattern) determines how drivers and transfer processes interact across scales, and (5) the relative importance of fine- or broad-scale pattern-process relationships can vary through time, and alternate as the dominant factors controlling system dynamics. We develop the basis for this theory and provide supporting evidence for it. This multiple, interacting scale theory has the potential to integrate much of our information about global change drivers and responses.