COVER PHOTO CREDITS:
Freshwater and pink coral, Eric Mielbrecht Portage glacier icebergs and Steller sea lions, Lynn Rosentrater Grassland and alpine meadow, Jonathan Gelbard
BUYING TIME: A USER'S MANUAL
Grasslands at a Crossroads: Protecting and Enhancing Resilience to Climate Change Jonathan L. Gelbard, Ph.D. Department of Environmental Science and Policy, University of California, Davis THE STRUCTURE AND FUNCTION OF the world’s grasslands makes them one of the most vulnerable to global climate change of any terrestrial ecosystem (Sala et al., 2000; IPCC, 2001a). The low-stature of vegetation confers high light availability, leaving many grasslands naturally vulnerable to invasive species (Wagner, 1989), especially following disturbance (Hobbs and Huenneke, 1992). A critical role for fire in maintaining plant community structure in many grassland types leaves them vulnerable to vegetation change should changes to temperatures and precipitation occur that are sufficient to alter biomass and fire frequency. Grasslands are also vulnerable due to human environmental impacts, including conversion to agriculture (both cropland and grazing land) (Dale et al., 2000; Ricketts and Dinerstein, 2001), the introductions and spread of invasive species (Mack et al., 2000; Mooney and Hobbs, 2000), the proliferation of roads (Forman and Alexander, 1998; Forman, 2000), alterations to fire regimes (D’Antonio, 2000; Dale et al. 2000), and pollution that alters soil fertility and rates of plant growth (Schlesinger, 1997; Lejeune and Seastedt, 2001). Combine the above natural and anthropogenic vulnerabilities, and it is apparent that when faced with human-induced global climate change (Schlesinger, 1997; IPCC, 2001b), what remains of the world’s grassland ecosystems as we know them are in trouble (Forseth, 1997).
Fortunately, however, the fate of grassland ecosystems faced with climate change, which has the potential to favor different groups of species and alter ecosystem processes, is not yet sealed. Although in some regions, habitats are far more degraded and in need of restoration and recovery than others (see Ricketts and Dinerstein, 2001 and the World Wildlife Fund’s Ecoregions website, http://www.worldwildlife.org/ecoregions/index.htm, for an overview of the world’s grassland types and assessment of their conservation status), scientists, land managers, and policymakers, with the help of private landowners, still have time to devise and implement adaptations that will be needed to protect and conserve grasslands from threats posed by global climate change. This chapter summarizes current scientific knowledge concerning potential steps that will be required to achieve this goal.
It first outlines the components of grassland ecosystems that will prove crucial to their resilience to climate change and describes human environmental impacts to them. Resilience is defined as the ability to withstand not only possible episodic climate changes, but also possible long-term directional changes (Malcolm and Markham, 1996); it may vary depending on the ecosystem component in question (Lavorel, 1999). The chapter then outlines potential impacts of predicted climate changes on grasslands given their current human-altered environmental condition. Finally, it proposes adaptations that may prove useful for preventing or minimizing these effects, and discusses complex challenges that could arise during translation of proposed strategies into the management plans and policies that will be required to maintain and restore grassland resilience.
Crucial Components of Grassland Ecosystems
The condition of vegetation and soils will prove critical to grassland resilience to climate change. Healthy, vigorous stands of native vegetation are likely to be more resilient to warming temperatures and increasing frequency and duration of droughts than degraded grasslands because...