Life in a tree house

For many years much of forestry practice around the world has been predatory and has paid little attention to sustainability or to other organisms that inhabit the forests from where timber is extracted.

This book seeks to reverse that trend and to encourage a more holistic approach to the management of forest ecosystems in order to maintain the biodiversity they contain. Thirty-four writers have contributed 19 wellintegrated chapters and, unlike many multi-authored volumes, this one flows well and develops the case for the retention of bio-

diversity in managed forests.

As 25 of the authors are from the United States, there is a definite North American bias and many of the case studies are taken from that sub-

continent. However, many chapters contain information and examples from all major forested regions of the world, and so the American emphasis in no way detracts from the usefulness of this book to sustainable forest-management practice throughout the world.

This book is divided into four parts. The introductory section consists of two chapters, one by the editor and the other co-authored by him. The chapters define and describe biodiversity and the principles of ecological forestry. A challenge is given to forestry and to the authors of the subsequent chapters to produce an acceptable balance between the conflicting demands of the extraction of timber and the maintenance of the integrity of the ecosystem and the species that forests contain.

Part two consists of seven chapters on the macro-approach to managing forest landscapes and opens with species composition. A wide range of plant and animal species is mentioned and much natural history about the links between different organisms is presented. Of particular importance to forest management is the chapter on dynamic forest mosaics. The understanding of temporal and spatial variability in forests is crucial for maintaining biological diversity because diversity in natural forests is maintained more by disturbance and biotic processes than by stability.

The emphasis on abiotic factors takes the fires in Yellowstone National Park as its main example and shows how different abiotic factors such as topography, climate and soil interact with the biology of forest ecosystems. Species richness may vary across landscapes due to the influence of abiotic factors, and so management to conserve areas of species richness depends on knowledge of these factors. The break-up of continuous forest into patches has produced a large increase in forest edges and research has shown the considerable influence of the "edge effect".

The discussion of forest edges demonstrates how important it is to understand the difference between forest edges and interiors and how animals use the edge of forests.

Islands and fragments are then examined. Much of the world's fragmented forest is now more similar to islands and so some of the principles of island bio-geography pertain to them.

Ecologically harmful mechanisms are triggered by forest fragmentation. This topic concludes with a useful list of questions to be asked when a forester is faced with the task of managing a fragmented area.

There are also discussions of two more specialised but vitally important ecosystems: riparian forests and forested wetlands.

Part three concerns the micro-approach for managing forest stands. Dead, dying and fallen trees are appropriately given a chapter because they are often crucial for the management of biodiversity. Birds use cavities in dead trees for their nests; invertebrates and fungi live in dead wood; and rotting wood is often crucial to the maintenance of nutrient cycling.

A fascinating chapter on vertical structure shows how different animals and plants occupy the different strata. To maintain bio-

diversity, due attention must be given to preserving vertical structure. Plantation forestry, which can also be managed to maximise biodiversity, is covered, as are special species that merit individual consideration for either their ecological importance, sensitivity to habitat change, economic significance or role as indicators of forest health.

Synthesis and implementations are covered and the text brings together information in a practical way and deals with restoration ecology, forest reserves, forest management and policy, economic issues and social perspectives.

I have read much about the destructive nature of forestry, and that is not denied here, but it is encouraging to read a book about the work of so many foresters and ecologists who are trying to work positively for the environment. I hope that this most informative volume about the natural history, biodiversity and scientific studies of the world's forests will be heeded. It is a clear demonstration that much biodiversity can be maintained in economically productive managed forests if the correct procedures are followed.

Sir Ghillean Prance is visiting professor, department of plant sciences, University of Reading, and former director, Royal Botanic Gardens, Kew.