Terrestrial transects for global change research

The International Geosphere-Biosphere Program has proposed a set of large-scale terrestrial transects to study the effects of changes in climate, land use, and atmospheric composition (''global change'') on biogeochemistry, 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 affected by forcing from components of global change or where the impacts of global change are likely to feed back to affect atmospheric, climatic, or hydrologic systems. Experimental studies on the transects will examine short-term changes in ecosystem function and biosphere-atmosphere interaction in response to variation in primary controlling variables. A hierarchy of modeling approaches will develop predictions of long-term changes in biome boundaries and vegetation distribution. The proposed initial set of IGBP terrestrial transects are located in four key regions: (1) humid tropical forests undergoing land use change, (2) high latitudes including the transition from boreal forest to tundra, (3) semi-arid tropical regions including transitions from dry forest to shrublands and savannas, and (4) mid latitude semi-arid regions encompassing transitions from shrubland or grassland to forests. We discuss here the rationale and general research design of transect studies proposed for each of these priority regions.