CRITICAL ISSUES FOR UNDERSTANDING GLOBAL CHANGE EFFECTS ON TERRESTRIAL ECOSYSTEMS

Marked alterations in the Earth's environment have already been observed, and these presage even greater changes as the impact of human (i.e., land use and industrial) activities increases. Direct and indirect feedbacks link terrestrial ecosystems with global change, and include interactions affecting fluxes of water, energy, nutrients, and "greenhouse" gases and affecting ecosystem structure and composition. Community development can affect ecosystem dynamics by altering resource partitioning among biotic components and through changes in structural characteristics, thereby affecting feedbacks to global change. The response of terrestrial ecosystems to the climate-weather system is dependent on the spatial scale of the interactions between these systems and the temporal scale that links the various components. The International Geosphere-Biosphere Programme (IGBP), which was initiated by the International Council of Scientific Unions (ICSU) in 1986, has undertaken to develop a research plan to address a predictive understanding of how terrestrial ecosystems will be impacted by global changes in the environment and the potential feedbacks. The IGBP science plan, which incorporates established Core Projects and activities related to research on terrestrial ecosystem linkages to global change, includes the International Global Atmospheric Chemistry Project (IGAC); the Biospheric Aspects of the Hydrological Cycle (BAHC); the Global Change and Terrestrial Ecosystems (GCTE); Global Analysis, Integration, and Modelling (GAIM); IGBP Data and Information System (DIS); and IGBP Regional Research Centers (RRC). The coupling of research and policy communities for the purpose of developing mechanisms to adapt to these impending changes urgently needs to be established.