As research on forest ecology has a long tradition in Germany and other European countries, the influence of tree species identity or forest management systems on ecological processes is well known. However, knowledge on the relationship between species diversity and ecosystem functioning is still weak and derives mainly from comparative observations of forest stands differing in biodiversity. However, environmental differences among these systems may obscure potential within-habitat effects of biological richness on ecosystem processes in such comparative studies (Schmid 2002).
Especially in Europe, where almost all forests have been managed for long time periods, land-use history certainly will have long-term influences on both biodiversity and ecological processes. Thus, comparative studies can be used to document the relationship between diversity and ecosystem processes (e.g. Caspersen & Pacala 2001), but they cannot be used to establish causality or underlying mechanisms of this relationship.
Therefore, within-site manipulative biodiversity experiments manipulating species diversity while keeping other ecological factors as constant as possible are needed to complement observational diversity-function studies.
Schmid, B., The species richness-productivity controversy. Trends in Ecology & Evolution, 2002. 17(3): p. 113-114.
Caspersen, J.P. and S.W. Pacala, Successional diversity and forest ecosystem function. Ecological Research, 2001. 16: p. 895-903.
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