Changing Precipitation and Terrestrial Ecosystems.

Changing Precipitation and Terrestrial Ecosystems

Weltzin, J.F. and G.R. McPherson (eds.) 2003. Tucson, AZ: University of Arizona Press. 237 pages, ISBN 0-8165-2247-2 (hardcover), CDN $77.95

I like to tell students that global warming is a hot topic. Any ecologist is aware that the ramifications of global warming are far greater than the direct effects of temperature on plants and animals. Weltzin and McPherson in Changing Precipitation and Terrestrial Ecosystems address one of the most important corollaries of warming: changes in the amount and timing of precipitation.

This book emanates from a symposium organized by the Ecological Society of America in 1998. By the time you read this, at least nine years will have elapsed since the original meeting. This time lag reinforces the importance of current research papers, which fortunately are readily found via sources like Google Scholar. The book is a collection of chapters contributed by different authors. The first five chapters provide overviews that can be generalized to almost any system. Weltzin and McPherson state in the introduction that much research on climate change concerns temperature and C02, and less addresses precipitation and evaporation. A central theme is that global climate models tend to produce conflicting predictions about precipitation. For many regions, the direction of change predicted depends on the model used. This is not unrea- sonable given the vagaries of climate modelling, but it does leave experimental ecologists uncertain about the direction of precipitation change they should be exploring: drier or wetter? This is addressed by going in both directions, both experimentally and conceptually.

People are usually concerned with the aboveground parts of ecosystems, but McAuliffe (Ch. 2) describes how precipitation effects are mediated by soil structure and root morphology. A theme that arises several times in the book is the difference between grasses with extensive, shallow roots and woody plants with deeper roots. Grasses are consequently more likely to respond to short-term changes in precipitation (Williams and Snyder, Ch. 3)--so are the seedlings of woody plants, a point critical to the establishment of new populations, with subsequent effects on succession, invasion and productivity.

Another important axis of precipitation change, the variability or seasonality of precipitation, is highlighted in Ch. 4. Here, Neilson discusses how vegetation models use the seasonality of rainfall to account for the presence of grasslands in the US Corn Belt. In this case, the total amount of precipitation should support forest vegetation, but the seasonal distribution (wet summers and dry winters) allows for the emergence of grasslands. A central theme of the book is that precipitation can be manipulated in large, well-replicated experiments. Owens (Ch. 5) reviews many and diverse techniques for changing the amount and timing of rainfall, including the use of fixed and automated moving shelters. The review is based on both published accounts and personal communications from experienced workers.

The remainder of the book comprises case histories, all of which involve experimental rainfall manipulation. Most of these are from the semiarid US, where rainfall is especially variable and has long attracted attention. Svejcar et al. (Ch. 6) discuss how a change in the seasonality of precipitation decreases the productivity but not the species composition of a sagebrush ecosystem in Oregon. Heitschmidt and Haferkamp (Ch. 7) examine the interaction of grazing and drought in Montana prairie, noting that reducing precipitation by 90% had only small effects, partly because drought is a normal variation for this community. Decreasing the frequency but increasing the intensity of rainfall in Kansas tallgrass prairie (Fay et al., Ch 9) was found to decrease both plant growth and soil nutrient mineralization rates. Oaks were examined in Arizona savanna (Weltzin and McPherson, Ch. 8), and in Tennessee forest (Hanson et al., Ch. 10). In both cases, tree recruitment was found to be affected by water availability, suggesting that climate change will alter the species composition and productivity of these communities. In their summary, Weltzin and McPherson (Ch. 11) note that many systems are under-studied. Mesic, boreal and arctic-alpine systems may be even more responsive to drought than semiarid areas because of the limited evolutionary experience. We know little about this.

Overall the book is well-written. It does an excellent job of reviewing the state of the art at the time of its publication, and identifies future steps forward. This book provides a useful window into this field for workers in related disciplines and in other ecosystems. It shows that climate change may be a hot topic, but it isn't dry.

Reviewed by Scott Wilson, Department of Biology, University of Regina, Regina, Saskatchewan, Canada