Functional Approaches to Predicting the Ecological Effects of Global Change

Plant ecology offers two main lines of investigation for predicting the ecological consequences of the changes in climate and atmospheric chemistry associated with the man-made greenhouse effect. The first approach is based on mechanistic studies of individual plants, often in response to a range of carefully controlled environments. These responses of individual plants must be aggregated and scaled up in order to predict community, ecosystem or vegetation responses (Harper, 1977; Jarvis & McNaughton, 1986; Woodward, 1987, 1991; Paw U & Gao, 1988). This aggregation can lead to quite inaccurate predictions of community and ecosystem processes (Polanyi, 1968; Martin, 1989; Roberts, Skeffington & Blank, 1989). At the other extreme of scale and difficulty of experimental manipulation are community or ecosystem studies. In some instances present day correlations between ecosystems and climate have been used to predict distributions in a future, warmed climate (Emanuel, Shugart & Stevenson, 1985). This technique, based on the climatic classification of vegetation developed by Holdridge (Holdridge 1947, 1964), has no explicit mechanistic base. Such models are liable to be inaccurate when important features of the environment change and influence ecosystem behaviour but which are excluded from the correlations. Examples include changes in CO2 concentration and climatic extremes and the influx of potentially dominant alien species (Vitousek,