Second, with the expectation that human populations and economies will continue to grow, the direct human impact on ecosystems is almost certain to increase. Increased management of the biosphere will be a crucial part of any response to global change to ensure the sustainability of key natural resources in the face of climate change and direct human impacts.131 In addition, management of ecosystems is an important aspect of mitigation for CO2 and other trace gases, the emissions of which to the atmosphere are dependent on land cover, fertilization, and other human impacts. 132 Quantitative knowledge of the roles of ocean and terrestrial ecosystems is indispensable for any future agreements to stabilize CO2, N 2O, and methane. It is essential to assess proposed mitigation measures for greenhouse gas emissions and experimental manipulations with ecosystem models prior to implementing such measures. These efforts may depend on the response of long-lived species such that experimental evaluation would require decades. The economic and nonmarket impacts of ecosystem change are just beginning to be recognized, and these impacts will likely become increasingly important drivers of policy. 133

As the needs and potential for ecosystem management in environmental mitigation increase, the scientific potential of mitigation must be continually assessed. Attempts at ecological mitigation and restoration have a mixed record of success, and scientific progress does not guarantee that the knowledge required for successful management has been developed. As the global change program advances, the feasibility and value of mitigation through ecosystem management must be assessed continually. Although many proposals for mitigation such as afforestation, as proposed by the IPCC,134 have great appeal, many of the realized projects are either more difficult to accomplish than originally envisioned135 or are affected by the “law of unintended consequences”—that is, the mitigation practice has some unexpected environmental consequences. While it is likely that ecologically based mitigation will play an increasing role in environmental management, better understanding at the system level is required for new management strategies to have a high probability of success.

In conclusion, as we look five or ten years into the future of global change research, integration of empirical knowledge and theory of specific systems must be used to produce more general and generally applicable theories, in some cases for phenomena for which we currently have no quantitative understanding. As the human impact on ecosystems becomes ever greater and the motivation to involve ecosystem management in mitigation strategies increases, there is evergreater need for an improved scientific capability to assess the likely success of proposed manipulations at the system level. Ecology must develop a robust predictive capability for environmental change and management consequences.

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