The IGBP Terrestrial Transects

The transect approach, in which research is organised along a fundamental environmental gradient, has been a common tool in ecological studies for many decades. The basic rationale behind this approach is that organising experiments and observations along a well-defined and continuous variation in an environmental factor allows insights into how that factor influences important system processes. Recently IGBP has adapted this approach for global change research. In this context, transect studies:

• facilitate the scale transition from local process studies through landscape effects to regional and global understanding;
• facilitate application of global change research to more immediate environmental and resource management problems;
• provide ideal "ground-truth" test beds for both remotely sensed data and global models;
• promote interdisciplinary research through sharing of sites and resources;
• promote efficient use of scare research resources.

Each IGBP Transect has been designed around the variation of a major environmental factor (e.g., temperature or precipitation) as it affects terrestrial ecosystem structure and functioning (e.g., carbon and nutrient cycling, biosphere-atmosphere trace gas exchange, and hydrologic cycling). Important ecosystem properties, such as biome type, tree:grass ratios, leaf-area index, net primary production (NPP), and above-ground biomass, are often directly related to the major underlying gradient.

In addition to these relatively straightforward biophysical gradients, a set of IGBP Transects is based on "conceptual gradients" of intensity of land use within a region. These are more complex spatially in that ecosystems that experience varying intensities of land use are rarely distributed continuously in geographical space.

The IGBP Terrestrial Transects are largely established in a "bottom-up" fashion, with regional priorities and human and financial resources a major factor in their development. They are thus continuously evolving as the various regions reach the critical level of coordination and support. Figure 2 shows the approximate geographical location of the operational IGBP Transects or those in the advanced planning stages. Table 1 shows the priority regions, the land cover, the primary and secondary gradients, the contributing transects, and their current status.

For further information:

Koch, G.W., Scholes, R.J., Steffen, W.L., Vitousek, P.M., and Walker, B.H. (eds.) (1995). The IGBP Terrestrial Transects: Science Plan. IGBP Report No. 36, The International Geosphere-Biosphere Programme, Stockholm, 61 pp.

Steffen, W.L., Valentin, C., Scholes, R.J., Zhang, X-S, and Menaut, J-C. (1998). The IGBP Terrestrial Transects. In: Walker, B.H., Steffen, W.L., Canadell, J., and Ingram, J.S.I. (eds.) The Terrestrial Biosphere and Global Change: Implications for Natural and Managed Ecosystems. A Synthesis of GCTE and Related Research. IGBP Book Series No. 4, Cambridge University Press, Cambridge, in press.
 
 

Table 1. The Initial Set of IGBP Terrestrial Transects

 
 

Region	Land cover	Primary global change gradient	Secondary gradient	Contributing transects in initial set	Status
Humid tropics	Tropical forest (humid and dry) & its agricultural derivatives	Land-use intensity	Precipitation	Amazon Basin (LBA)  Central Africa (Miombo Network)  Southeast Asia	Operational  Advanced planning  Advanced planning
Semi-arid tropics	Forest- woodland- shrubland- grassland (savannas)	Precipitation	Land-use intensity  Nutrient status	Savannas in the Long Term (SALT) - West Africa  Kalahari - Southern Africa  Northern Australia Tropical Transect (NATT)	Operational    Operational  Operational
Mid-latitude	Forest- shrubland- grassland	Precipitation	Land-use intensity	Great Plains (USA)  Argentina  North East China Transect (NECT)	Operational  Operational  Operational
High latitude	Boreal forest- tundra	Temperature	Precipitation  Nutrient status	Alaska  Boreal Forest Transect Case Study (BFTCS) - Canada  Central Siberia  Far East Siberia  Scandinavia-Northern Europe (SCANTRAN)	Operational  Operational    Advanced planning  Advanced planning  Advanced planning