The Nation's forest and rangelands and water have the physical capacity to produce 

 much larger quantities of renewable resource products and support higher levels of 

 use. A primary objective of this update to the 1989 RPA Assessment is to further 

 identify conditions and opportunities for management of the renewable resource base 

 for use in the 1995 RPA Program. 



If it occurs, global change could affect the productivity, health, and diversity of forest 

 and range ecosystems, with associated impacts on other renewable resources 

 (fig. 14). Forest ecosystems are a central concern in the global change issue because 

 of the strong natural linkage between climate and forests, and because of the envi- 

 ronmental, economic, and social importance of forests. Forests are likely to be 

 affected directly by elevated carbon dioxide levels since carbon dioxide is a funda- 

 mental component of photosynthesis, as well as by changes in temperature and 

 precipitation. While science is not currently capable of modeling and predicting the full 

 range and complexity of global change impacts, progress is being made in assessing 

 significant aspects and sub-components of the issue. 



Figure 14 — If it occurs, global change might alter the distribution of existing ecosystems. 



Issue Highlight- 

 Global Change 



A number of ecological models have been proposed to examine the biophysical 

 effects of climate change (Joyce, 1994). The robustness of these projections has not 

 been compared across models. Understanding the causes for differences and/or 

 similarities in ecological projections is an important and necessary step toward 

 improving our modeling capability as well as our understanding of climate change. 

 We initiated a study with the objectives of comparing projected net primary productiv- 

 ity responses of the Terrestrial Ecosystem Model and the Osnabruck Model. We 



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