Eco‐hydrology: Plants and Water in Terrestrial and Aquatic Environments

Abstract

Eco-hydrology: Plants and Water in Terrestrial and Aquatic Environments. Pp. xviii + 402. With 90 Figures and 26 Tables, Routledge, London. ISBN 0-415-16272-6 Price £60 (hardcover), ISBN 0-415-16273-4, £18.99 (paperback). The relationship between water availability and plant ecology has probably exercised the human mind longer than any other environmental relationship. The very early use of irrigation in neolithic agriculture implies some ability to predict fluctuations in water levels, which is still the fundamental question of modern hydrology. The facility with which factors such as rainfall interception, run-off, soil and groundwater storage can be quantified attracts to hydrology minds that delight in the ability to pursue physical models and make predictions that draw largely on definable non-biological phenomena. Biological factors with their intrinsic tendency for uncertainty and variation have been limited hitherto in hydrological calculations to the more dependable properties of biomes such as albedo, interception and evapotranspiration. It is therefore very refreshing to have this collection of essays that deal specifically with contrasting ecological situations and highlight the very powerful modifying and variable influences that vegetation cover exerts on hydrological prediction. An opening chapter by Melvin Tyree on general principles of plant water relations provides a concise and informative introduction to the technicalities, concepts and terminology, which is fortunate as hydrology is a subject that delights in its own terminology. In the preface we are even asked not to confuse eco-hydrology with hydro-ecology. This is probably an important distinction for practitioners of this subject, but a little too much to ask of those who merely wish to contemplate the uses of eco-hydrology from a distance. The main body of the book is devoted to examining the special cases of plants and water in drylands, freshwater wetlands, forests, rivers and land adjacent to lakes. Here the subtleties of plant interactions with water become apparent. Dye staining experiments reveal that plants in dry areas can channel water to deep storage by extending the above ground phenomenon of stem-flow by directing water along the surface of roots. The consequences of this are that some desert plants, such as the creosote and tar bushes when they have a canopy size above 1 m2, can obtain sufficient water to decouple themselves from short-term climatic fluctuations (see chapter by John Wainwright et al.). In wetland areas, there is still dispute about the nature of the division of peat layers into the acrotelm and catotelm. The zonation of plant communities also appears to show much variation in relation to water table levels. The amphibious nature of some plants is evident in that many of the species that inhabit the transition zone between aquatic and terrestrial habitats are capable of enduring submergence as well as emerging above the land–water interface. The discussion of the physiology that makes this possible is not as penetrating as might be wished. For example, the phenomenon of post-anoxic survival, which is crucial to withstanding re-exposure to air after long periods of oxygen deprivation, is never mentioned. It could, however, be argued that plant physiology is not the main subject matter of this book. Nevertheless, mere statements that many plants possess distinct biochemical, anatomical or morphological adaptations without presenting information or discussion of the nature and relevance of these adaptations to changing hydrological conditions leaves an irritating intellectual gap. Similarly, with regard to pollution, riparian zones, which have been termed the ‘kidneys of the water landscape’, are merely described as ‘nutrient sinks’, with no physiological discussion of how this is achieved despite their importance to water purification and the whole subject of eco-hydrology. Notwithstanding these criticisms, the book is a valuable addition to eco-hydrological thought as it repeatedly emphasizes the importance of phenology in vegetation development and the role of plants in influencing hydrological predictions. The numerous illustrations could have been more imaginative and would have had greater impact if some colour had been used. Poorly reproduced monochrome LANDSAT images do nothing to enhance an otherwise thought-provoking chapter on scale and interaction by Wilby and Schimel. An excellent index is provided combining both subjects and authors. As a source of information, this work is a welcome addition to any ecological library for the synthesis it provides between the traditional physical aspects of hydrology and the dynamic and variable world of ecology.