Our understanding of abrupt transitions in ecological systems has grown dramatically in recent years as a result of the discovery of new mathematical tools and characteristics of ecosystems that yield early warning signals. While new statistical tools may help predict tipping points, identifying best actions to avoid or to take in the face of them requires more detailed understanding of the systems themselves. Water limited ecosystems include a variety of grasslands, shrublands, and open and closed-canopy forests with a range of woody vegetation. Many grasslands and savannas worldwide are undergoing rapid shifts in dominance from herbaceous to woody plants driven by social and economic, as well as environmental and ecological factors. The objective of this workshop, cofunded by NSF's Biological Sciences Directorate and Office of International Science and Engineering, is to synthesize current understanding of the transition from grasslands to woodlands, its coupled social and ecological determinants, and the consequences for the provisioning of ecosystem services.
The meeting is sponsored by the South American Institute for Resilience and Sustainability Studies, an international research institute in Uruguay. Though mainly foucsed on the state of the science, the last day of the workshop will be open to the general public, focusing ing on policy makers, conservation organizations and industry representatives from the private and public sectors in Uruguay, Argentina and Brazil. Products will include a synthesis paper co-authored by all participants, multiple scientific papers, and the public session. All of the presentations and results from the workshop will all be archived and made freely available on the Institute's web page.
Grasslands, shrublands and savannas cover about half of the land on Earth and while characterized by low precipitation, represent about a third of the productivity on land and contain a third of the human population. Dry land systems produce a range of ecosystem services that are expected to change as the systems shift. The one day conference with decision makers has already attracted substantial local and regional interest. And this project will also support a graduate student from Arizona State University as an active participant and workshop organizer.
This project organized an international workshop in Uruguay in December 2012 to synthesize our current understanding of grass-woodland transitions, its socio-ecological determinants and the consequences for the provisioning of ecosystem services. A large fraction of the world’s grasslands and savannas are undergoing a rapid shift from herbaceous to woody-plant dominance. Just in North America, the increase of woody-cover ranges from 0.5 to 2% per year. This fundamental alteration of habitat is among the most striking land-cover changes that have occurred over the past 150 years. Mechanisms accounting for woody-plant encroachment are numerous and include intensification of grazing by livestock, changes in climate and fire regime, declines of browsing animals as well as directional changes in nitrogen deposition and carbon dioxide concentration in the atmosphere. As a result of an effort to sustain livestock carrying capacity, which is threatened by woody-plant encroachment, land managers have implemented many control measures. In other parts of the world, land managers are converting natural grasslands to tree plantations driven by market incentives to reduce atmospheric carbon dioxide concentrations through the clean development mechanism or simply seeking high economic returns through wood production instead of beef. Ecologists, biogeochemists, economists and hydrologists working together identified the major drivers of the grass-woodland transitions in different parts of the world including the Tallgrass prairie in Kansas, the Pampas of Argentina, the cold deserts of Wyoming and Utah and plantations in Uruguay. These drivers were of different nature ranging from local and national policies to global markets and climate change. Transitions from grassland to woodlands have major consequences for the provision of ecosystem services ranging from livestock production to carbon sequestration, biodiversity conservation and water yield. Sustainability of grasslands and woodlands and their ability to provide ecosystem services depend on the matching of the scale of the major driver of grass-woodland-grass transitions and the scale at which consequences of the transitions occur.
