TERRESTRIAL TRANSECTS FOR GLOBAL CHANGE RESEARCH

The International Geosphere-Biosphere Program has proposed a set of la rge-scale terrestrial transects to study the effects of changes in cli mate, land use, and atmospheric composition (''global change'') on bio geochemistry, surface-atmosphere exchange, and vegetation dynamics of terrestrial ecosystems. The transects (approximate to 1000 km) will be located along existing environmental and land use intensity gradients that span transitions between biomes in regions likely to be widely a ffected by forcing from components of global change or where the impac ts of global change are likely to feed back to affect atmospheric, cli matic, or hydrologic systems. Experimental studies on the transects wi ll examine short-term changes in ecosystem function and biosphere-atmo sphere interaction in response to variation in primary controlling var iables. A hierarchy of modeling approaches will develop predictions of long-term changes in biome boundaries and vegetation distribution. Th e proposed initial set of IGBP terrestrial transects are located in fo ur key regions: (1) humid tropical forests undergoing land use change, (2) high latitudes including the transition from boreal forest to tun dra, (3) semi-arid tropical regions including transitions from dry for est to shrublands and savannas, and (4) mid latitude semi-arid regions encompassing transitions from shrubland or grassland to forests. We d iscuss here the rationale and general research design of transect stud ies proposed for each of these priority regions.