Quantifying the effects of land use change on ecosystem services.

摘要

Ecosystems provide multiple benefits, or ecosystem services, to people. It is thought that provisioning services, like food and water, increase at the expense of ecosystems' abilities to regulate climate, water quality and other ecosystem services. In order to account for such tradeoffs in decision-making, simple but robust tools are needed. This study develops new approaches for estimating the biophysical and ecological processes underlying several ecosystem services (and the tradeoffs among them) at global and regional scales.;Chapter 1 presents an alternative approach for quantifying the physical regulation of climate by ecosystems. The approach estimates how land-cover change affects the loading of heat and moisture into the atmosphere, while also accounting for the relative contributions of wind-transported heat and moisture. Results are comparable to those generated by complex land surface and general circulation models, yet require several thousand fewer hours of computer processing time. Ecosystems have the strongest influence on surface climate in boreal and tropical regions, where temperature and moisture changes could substantially offset or magnify greenhouse-forced changes.;Chapter 2 calculates the tradeoffs between crop production and carbon storage. Average crop yields are quantified using distribution and yield data for 175 crop types. Carbon released from clearing natural vegetation is estimated using approaches developed for the International Panel on Climate Change. The tradeoff between crop production and carbon storage is strongest in the tropics, where newly cleared land releases nearly three tons of carbon for every ton of annual crop yield compared to a similar area cleared in the temperate zone.;Chapter 3 quantifies the tradeoffs of ecosystem services in scenarios where future food demand is met by intensification of cropping vs. extensification of area cropped with no change in management practices. If crop yields were increased to the 90th percentile of current yields, intensification could increase production by 43% while decreasing excess nitrogen by 85%. Extensification would require an additional 1.6 x 108 hectares to achieve the same production levels. In addition to the loss of land for other uses, this cleared area adds 1.2 x 107 tons of nitrogen and releases 1.1 x 1010 tons of carbon.