ENVIRONMENTAL-CHANGE IN GRASSLANDS - ASSESSMENT USING MODELS

Modeling studies and observed data suggest that plant production, spec ies distribution, disturbance regimes, grassland biome boundaries and secondary production (i.e., animal productivity) could be affected by potential changes in climate and by changes in land use practices. The re are many studies in which computer models have been used to assess the impact of climate changes on grassland ecosystems. A global assess ment of climate change impacts suggest that some grassland ecosystems will have higher plant production (humid temperate grasslands) while t he production of extreme continental steppes (e.g., more arid regions of the temperate grasslands of North America and Eurasia) could be red uced substantially. All of the grassland systems studied are projected to lose soil carbon, with the greatest losses in the extreme continen tal grassland systems. There are large differences in the projected ch anges in plant production for some regions, while alterations in soil C are relatively similar over a range of climate change projections dr awn from various General Circulation Models (GCM's). The potential imp act of climatic change on cattle weight gains is unclear. The results of modeling studies also suggest that the direct impact of increased a tmospheric CO2 on photosynthesis and water use in grasslands must be c onsidered since these direct impacts could be as large as those due to climatic changes. In addition to its direct effects on photosynthesis and water use, elevated CO2 concentrations lower N content and reduce digestibility of the forage.