Forest Hydrology and Catchment Management: An Australian Perspective, 2015.
2015. Springer. ISBN 978-94-017-9337-7 eBook $149.00
According to Leon Bren, 'Forest hydrology tends to be ... concerned with the detailed behaviour of small streams and the impact of land management on this.' It is about the role of vegetation in the hydrology of headwater catchments. As the consolidation of several decades of high-class work in Australia, Bren's Forest Hydrology and Catchment Management: An Australian Perspective is a welcome addition to the science, as well as an excellent source of teaching material. Bren has aimed the book at undergraduate students, practising land managers, and interested citizens; and it will serve as a useful reference for practising scientists too. He states its purpose as providing a concise account of forest hydrology in Australia, 'with some consideration of overseas work as well'. But though its material is chiefly Australian, the book certainly has global relevance. It gives us a sound and useful expansion of the range of literature on this topic, for Australia as well as the USA, South Africa, and elsewhere.
The approach Bren adopted is to address general principles while using case studies to illustrate these principles, relying on research findings mainly but not only from Australia, and to focus on the techniques required to research phenomena that make up the field of forest hydrology. And he concludes several chapters with a brief summary, often an appraisal of the significance of the findings to management.
The book has 11 chapters. The first five treat the basics of catchment hydrology, modern measurement techniques, the physiography of headwater catchments, the processes that influence the fate of water after precipation onto the catchment, and the special problems of the experimental determination of the hydrological effects of forests. Included is a sound examination of subsurface flow processes and the variable source area model of streamflow generation in the headwater catchment--vital concepts for students in this field, as well as the managers of the resource, that are often overlooked. Hortonian overland flow, i.e. flow over the soil surface that occurs during rainstorms because the surface soil lacks sufficient infiltration capacity, is absent from the range of catchments from all over Australia reported on here: infiltration capacities greatly exceed rainfall intensity. This is except where wildfires have occurred, when soil porosity is lost.
The last of the these five chapters includes a thorough treatment of the paired-catchment experiment and the problems of calibration, followed by an exhaustive examination of modern statistical analysis techniques for these experiments. There is also a critical examination of plot studies as a complement to the catchment experiment, and of mathematical modelling approaches to extrapolating beyond the scale of the catchment.
In Chapters 6-8, Bren turns to what has been learnt in Australian forest hydrology. He summarises the information from experiments that tells of the impacts of native forest management, and continues by dealing with the hydrology of manmade, plantation, forests. This part includes a useful comparative analysis of hydrological processes in euclaypt and pine forests, as well as an exhaustive account of the hydrology of eucalypt forests in Australia in general. There is a penetrating analysis of evidence for the peculiar "age-yield" relationship or "bushfire response function" in mountain ash (Eucalyptus regnans) forests, first reported in 1974. Mountain ash, occurring in higher rainfall areas of Victoria and Tasmania, reaches 80m in height, regenerates only from seed and then (in nature) only after fire, recovering as an even-aged stand. This cycle induces an initial increase in streamflow, followed by a slow decline to about 40 years age, and then streamflow begins to increase and recover to prefire levels at about 100 years, as the stand of trees undergoes self-thinning and a progressive reduction in leaf area and thus transpiration. This phenomenon appears to be confined to this type of forest, but there is evidence of the same tendency in pine and eucalypt plantations in South Africa (Scott and Prinsloo 2008).
Then comes the major question, in Australia especially but now more and more in the rest of the world, of the impacts of wildfire on catchment hydrology and management. Of special concern are the hydrological consequences of moderate to high-intensity wildfires in the eucalypt forests. The pronounced responses in streamflow and sediment yield to such fires, clearly summarised in this work, is attributed to the development of water repellency and "brick" formation in the excessively heated soils under bushfire conditions, and the switch from subsurface flow to the stream, to Hortonian overland flow carrying huge amounts of sediment with it. The evidence for the force of this brief post-fire hydrolgical regime as a land-forming process in eucalypts forests is startling.
Chapter 9 deals with water quality and nutrient issues, particularly the research on the question of the impacts of land management on water quality. It focuses on the technical difficulties of stream chemistry in the clean waters of forested catchments, and includes brief sections on the effects of the use of fertilizers and herbicides in forestry--these effects being negligible in the studies Bren reports on. Chapter 10 deals with flooding forests--swamp forests, in other parts of the world--and the effects of river management on these important habitats. Chapter 11, headed as catchment management issues world-wide, focuses largely on the management of catchments for city water supplies. Here Bren raises several issues, including water supply as an ecosystem service, difficulties in the economic valuation of catchment water supply, options for catchment management, and the management of catchment risk, incduing the promotion of catchment resilience. He makes the important claim, that 'Good catchment management is a fundamental protector of public health' (p. 260), and perhaps it is in this direction that the economic value of catchment management should be sought.
If there are areas where improvement would be desirable in a next edition, or another book, ideas might begin with the fact that Bren's account is largely confined to the headwaters of rivers. This means that the downstream effects of forest and land management tend to be underplayed, e.g. the effects on flooding (treated in this volume only in regard to certain bushfire instances). Second, the book's short sections, interspersed with (useful) case studies makes for a staccato style, at the price of overall coherence, while greater fluency would be preferable.
Bren has done a fine service by collating a large body of relevant work from several decades of research in Australia. His book should be in the libraries of all forest and natural resources schools and research organisations, as well as in the libraries of management agencies in this field. At US$189.00 for the print copy and $149.00 for the eBook, it will be beyond the reach of most students in the West, never mind the global South; students and others would do well to carry a copy in print or pdf of John Hewlett's classic, The Principles of Forest Hydrology (Hewlett 1982), as a basic text, and read Bren's Forest Hydrology and Catchment Management: An Australian Perspective, as needed, in the library.
HEWLETT, J.D. 1982. The Principles of Forest Hydrology. Athens: The University of Georgia Press.
SCOTT, D.F. and PRINSLOO, F.W. 2008. "Longer-Term Effects of Pine and Eucalypt Plantations on Streamflow." Water Resources Research 44. doi: 10.1029/2007WR006781.
Centre for Environmental Management, University of the Free State, Bloemfontein, South Africa.
c/o OTS, P.O. Box 33, Skukuza 1350, South Africa
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|Publication:||International Forestry Review|
|Article Type:||Book review|
|Date:||Dec 1, 2015|
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