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World Watch

William Schlesinger

Global Change and Terrestrial Ecosystems. Brian Walker and Will Steffen (eds.). 691 pp., Cambridge University Press, 1996. $120 cloth, $39.95 paper.

A central goal of the International Geosphere-Biosphere Program (IGBP) is to understand the response of the earth's terrestrial ecosystems to global change—including changes in climate, chemistry and direct human impact. This volume contains the plenary papers from the first science conference of the IGBP program, "Global Change and Terrestrial Ecosystems," held in Woods Hole, Massachusetts in May 1994. The book focuses on what we need to know in order to understand our planet better. Like most symposium proceedings, there is much variation in the value of its 28 chapters, which are arranged in five sections (Ecosystem physiology; Ecosystem structure; Agriculture, forestry and soils; Ecological complexity; and Earth system science). Models abound, but the modelers themselves seem wary of the output.

There is consensus in this volume, perhaps best seen in Christian Korner's chapter on the response of complex systems to elevated carbon dioxide suggesting that the response of individual plants in simple experiments cannot be used to predict the response of entire ecosystems to elevated carbon dioxide. Add to that simultaneous exposures to increased nitrogen deposition and rising global temperature, as outlined by F. A. Bazzaz and his colleagues, and we find ourselves with only a scanty ability to predict how our planet will function in the next century.

There is less consensus regarding biodiversity, with some authors suggesting that a substantial amount of nature's diversity is redundant (C. S. Holling et al.), whereas others suggest that diversity is significant in determining ecosystem response to stress (F. S. Chapin et al.). Large variation in species behavior allows some compensatory responses that hold ecosystem-level function at relatively constant levels. Because the variation in species behavior is so great, ecosystem modelers must categorize species into a few "functional groups" that can be assumed to behave similarly. Another volume in this series, Plant Functional Types, begins this process quite effectively.

The real driver of change in terrestrial ecosystems is, of course, human population growth. The IGBP has a separate program, The Human Dimensions of Global Change, to address this difficult issue. I am struck, however, with the futile nature of predicting the future condition of our planet—for instance, global net primary production—when population-driven changes in land use are not yet incorporated into most global models. A chapter by R. Leemans, describing the model IMAGE 2, is a refreshing attempt to incorporate these factors in an integrated assessment of the effect of humans on the emission of greenhouse gases. Pointing to human population and economic growth, Jan Goudriaan concludes that at an "average rate of change of 2 percent per year, those processes will probably have a much larger impact on food security and crop production than the dynamics of climate change."—William H. Schlesinger, Botany, Duke University

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