Science to Support Managing Terrestrial Ecosystems to Limit the Magnitude of Climate Change

Managing land ecosystems provides opportunities to both limit the magnitude of climate change and ameliorate its negative consequences for society. Tropical deforestation and degradation, for example, contributed approximately 17 percent of anthropogenic carbon emissions in 2004 (Barker et al., 2007a). The opportunity to reduce emissions from deforestation and degradation (REDD) has been recognized within the United Nations Framework Convention on Climate Change as a relatively low-cost option to limit climate change (Gullison et al., 2007; Stern, 2007). Research is needed to support and improve such policies. While it is now a feasible goal to monitor changes in forest area by satellite throughout the tropics (DeFries et al., 2007; GOFC-GOLD, 2009), substantial uncertainties remain about the amount and distribution of biomass (carbon contained organic plant material such as leaves, branches, and roots). Accurate biomass estimates are critical for improving estimates of GHG emissions generated by deforestation (Houghton, 2005). Both ground-based measurements and new satellite technologies (e.g., Asner, 2009) for estimating above- and below-ground carbon are needed to improve these estimates.

Understanding the socioeconomic and ecological drivers of deforestation and degradation is also critically important for developing effective policies to reduce deforestation. Global-scale drivers, from international trade in agricultural products to subsistence needs by small-scale farmers, are complex and vary in different locations

(Nepstad et al., 2006; Rudel, 2005). Research focused on ecosystems needs to include intertwined climatic, ecological, and socioeconomic factors. For example, more clearing and more fires occur during relatively dry years in the tropical forests of southeast Asia, creating a positive feedback between emissions and climate change (van der Werf et al., 2008). The synergies and trade-offs between REDD and biodiversity conservation, watershed protection, and livelihood needs for local people require more rigorous analysis. (Research needs are discussed at the end of this chapter.)

Ecosystems also provide the opportunity to limit climate change through the enhancement of carbon storage or surface reflectivity. In forest ecosystems, protection from fire, insect damage, and forest thinning through logging and other human use can enhance carbon storage as can secondary regrowth of forests in abandoned croplands, tree plantations, and agroforestry (Rhemtulla et al., 2009; Gough et al., 2008). The extent to which these strategies might be able to offset GHG emissions on a global scale is poorly known. As noted above, land use and land cover changes also alter the reflectivity of the land surface, and this fact could potentially be exploited to limit the magnitude of climate change. Research is needed to evaluate these many interacting factors and quantify the potential and of these strategies relative to costs of adapting to climate change (Bala et al., 2007; Bonan, 2008; Jackson et al., 2008; Ollinger et al., 2008).

Ecosystems management is also a potential strategy to ameliorate some of the societal impacts of climate change. Restoration of wetlands in the Gulf of Mexico, for example, can reduce damage from hurricanes by damping wave action and diminishing wind penetration (Day et al., 2007). Mangroves protected people from a 1999 Asian cyclone (Das and Vincent, 2009) and will potentially provide some protection against storm surges that will move further inland with sea level rise. Quantitative and rigorous analysis of these ecosystem management opportunities, including their effectiveness and costs, is needed to assess their potential in different locations.

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