Global change includes changes in atmospheric composition, and changes in land cover and climate. The response of forests is caused specific combinations of these components and is thus highly regionally specific. The accumulative impact of changes in forests has strong significance for biogeochemical and physical properties of the Earth system.
The response of forests to global change has been assessed with many different models. Initially, the climatically determined large-scale vegetation patterns were described and redistributed for changed climatic conditions based on scenarios. These models indicate large shifts of forests and their results have been used to determine changes in global C pools and threats to biodiversity.
However, such models don't address a transient response and the impacts of a changing atmospheric composition. These limitations are covered by several dynamic models, that are based on species-specific ecophysiological responses and stand properties. For example, forest-succession models simulate the structure and development of forest stands under changing conditions.
Simulations indicate that the response is often not gradual, but can yield sudden events, such as large-scale die-back followed by a replacement of other species. Significant time-lags could also occur.
Little research is directed towards understanding the gradual changes in land use and the consequences for the extent and condition of forests. Regional differences in (de)forestation are driven by the demand for land to satisfy human activities. Such developments determine the capabilities of forests to respond, adapt, develop or disappear. Currently several approaches are developed to evaluate the importance of these changes.
I will review different approaches to assess the impacts of global change. This review will focus on applications, limitations and recent developments. Finally, I will emphasize the importance of integrated assessments to fully appraise the significance of forested ecosystems within the Earth system.
Key words: global change, land cover patterns, response models.
Correspondence: R. Leemans, Department of Terrestrial Ecology and Global Change, National Institute of Public Health and Environmental Protection, RIVM, P.O.Box 1, 3720 BA Bilthoven, The Netherlands
Telefax: +31-30-292897
E-mail: rik.leewans@rivm.nl