Funded Grants

Coupled human-environment system dynamics and alternative stable states in complex mosaic ecosystems

Globally, our terrestrial ecosystems are in trouble. Since 1990 forest cover has been reduced by an area larger than France—roughly 0.5% of global land area—and the Millenium Ecosystem Assessment reports predictions of future declines, mainly in the developing world. Other terrestrial ecosystems, such as natural grasslands, face similar, if not greater, levels of endangerment because, while pressures from human activity also persist, they have generally received less attention in the past from conservation movements. To exacerbate this condition, grasslands, as opposed to forests, may be less favoured by future climatic change, as in the past forests have expanded over grasslands when climate conditions became favourable.

Much, if not all, of the human-dominated landscapes of our world, and indeed, several naturally occurring landscapes, are mosaic ecosystems. These are landscapes that exhibit complex spatial patterns of heterogeneity, in which, for terrestrial systems, patches can represent forest stands, grasslands, farms or even urban areas. Complex systems science suggests that certain mosaic ecosystems can exhibit alternative stables states, whereby for the same environmental parameters the ecosystem could equally well reside either in one state or another state depending on the initial conditions of the system. These are stable states over ecologically relevant timescales that are resilient to small perturbations. However, the shift from one state to another can occur due to a threshold response and thus the dynamics of such systems is not continuous but can lead to surprises for the observer, unless the underlying dynamics is fully understood.

Naturally occurring forest-grassland mosaics exemplify this phenomenon of alternate stable states. Because mosaic ecosystems with alternative stable states can be readily ‘flipped’ from one state to another, an understanding of the basic biophysical mechanisms involved is important. However, perhaps of greater significance is the fact that the potential human impact on these ecosystems is large. Despite this, the impact of changes in mosaic ecosystem states on human perceptions of conservation priorities, and the resulting feedback of changing human activities back onto mosaic ecosystem dynamics (coupled human-environment dynamics), has rarely been investigated.

Our objective is thus to generate models of complex forest-grassland mosaic ecosystems based on southern Brazilian and Indian examples where models of human behaviour (including strategic interactions) are coupled with ecological dynamics. We will attempt to parameterize the human models with data from surveys that we will administer in our regions of study. These models will help understand and ultimately enhance terrestrial ecosystem sustainability. Though our models will focus on two case studies, the general framework of our approach should motivate work in other kinds of human-influenced mosaic ecosystems, not just those involving forests and grasslands, but perhaps those involving forests and increasingly important mosaic components such as agricultural land. Related work in coupled human-mosaic marine and other aquatic ecosystems could also find cross-fertilization with our research. This kind of generalization is a hallmark of complex systems science and the broader scope of our research program.