Vernal Pools: Natural History and Conservation. Elizabeth A. Colburn. McDonald and Woodward, Blacksburg, VA, 2004. 426 pp., illus. $29.95 (ISBN 0939923912 paper).
The goal of writing Vernal Pools: Natural History and Conservation was, in the words of author Elizabeth Colbum, to provide “an authoritative synthesis of the current understanding of the habitat characteristics of vernal pools, the plants and animals that live in them, and the factors that govern the interactions among pool organisms and their environment.” Temporary pools are ubiquitous in their distribution; sadly, however, most ecologists have ignored their role in the diversity of aquatic and terrestrial systems. This book is a good start, albeit focused exclusively on vernal pools of the glaciated southeastern Canada and northeastern United States. It is organized into 14 chapters that define vernal pools; describe them as aquatic habitats, with an emphasis on seasonal hydrologic patterns; address their natural history, dominant organisms, and ecology; and describe the endangered status of northeastern North American woodland vernal pools, threats to their existence, and governmental mechanisms to stem their disappearance. The last chapter on conservation is especially valuable in that it addresses key limiting factors of forest vernal pools, chief mechanisms of their change and decline, strengths and weaknesses of protective legislation, and efforts to incorporate vernal pools into the framework of natural resources management.
Vernal Pools is a text reminiscent of early natural history works. Reading it, I recalled how Stephen Forbes's 1887 paper “The Lake as a Microcosm” engendered my early interest in aquatic systems, the organisms that lived there, and what those organisms did. Colburn's volume offers valuable source material for a module on these unique water bodies, but not the detail required for a complete aquatic ecology course. It is a natural history book building on Ann Haven Morgan's 1930 classic, Field Book of Ponds and Streams, not a limnology text.
A key strength of Vernal Pools is its coverage of the diverse invertebrate and vertebrate fauna of these temporary water bodies, including discussions of life history and food chains. Colburn discusses adaptive strategies that are necessary for invertebrates to survive in these ephemeral environments. The detailed, referenced lists of faunal taxa will guide students as they assess these relatively unknown aquatic systems. These chapters not only capture the author's vast experience with vernal pools but also her enthusiasm for sharing their secrets with others.
The line drawings of aquatic invertebrates, largely from Morgan's work, are excellent. The black-and-white photographs of key taxa are of less than ideal quality, apparently because of light refraction and limited resolution. They detract from the book; more value would accrue from additional line drawings. The color plates, however, provide effective ecosystem overviews.
With her eastern focus, Colburn defines vernal pools as always associated with timberlands; but certainly roadside ditches and prairie ponds often fit hydrological criteria of vernal pools (here today, gone tomorrow) and are vital as refugia or genetic corridors between woodland-associated pools. Given the title, I expected that Vernal Pools would at least briefly describe vernal pools that exist in other North American regions (e.g., woodland pools in the southeastern Piedmont and the foothills of the Appalachians, vernal pools in prairie pothole ecosystems of the upper US Midwest and Canadian prairie provinces, vernal pools that form during wet cycles in the arid Southwest, vernal pools in lowland forests among the coastal mountains of the Pacific Northwest, and vernal pools in the interior Rocky Mountain foothills). Neither should we ignore the springtime roadside ditches across the continent that for three months explode with complex algal and zooplankton communities, supporting myriad amphibians before sending them off to complete their life cycles on the uplands. At a minimum, expansion of the color plates to include representative examples of these systems would be very helpful. Considering the book's broad targeted audience, I consider a wider perspective essential.
Vernal Pools provides little in-depth coverage of habitat mechanisms, physical–chemical cycles, and controlling mechanisms of aquatic populations. Even in an introductory text, it's difficult to address aquatic populations and communities without some quantitative, physical- and chemical-specific coverage of their controlling factors. The book offers weak coverage of habitat descriptions—the physical–chemical environment interacting with pool biota. It provides no trend analyses of key habitat descriptors (temperature, dissolved oxygen, plant nutrients, and total organic carbon, a key measure of heterotrophic activity in woodland vernal pools). There is very little quantification of organism density, frequency of occurrence, seasonal patterns of populations, or metrics of ecological integrity, all measures that contribute to a system overview.
The brief chapter “Energy Flow, Seasonal Cycles, and Variations in Community Composition” limits its coverage of energy flow to an effective but generic illustration of woodland vernal pool components. The role of detrital-based food webs is recognized, but nowhere in the chapter is there any measure of energy flow and production rates between system components.
A significant contribution is the 63-page appendix, “An Annotated List of the Fauna of Vernal Pools and Seasonal Ponds in and near the Glaciated Northeast.” With its taxonomic organization and its comments on the physical and hydrologic setting of listed taxa, it should serve as a starting point for other workers to add to this ecological database.
