Under The Microscope

ENVIRONMENTAL EFFECTS OF PLANTED FORESTS IN NEW ZEALAND by J.P. Maclaren; FRI Bulletin No. 198, New Zealand Forest Research Institute, 1996; 180 pages; $55.00

Reviewed by Craig Marshall

We all know that forests are "good". Forests attract rain, they prevent flooding and reduce erosion, they provide shelter for animals and plants and they are nice places to be. But what evidence do we have to bear out these notions? Do forests really do all these things? What problems do forests cause?

In this book, Piers Maclaren has attempted to collate all the available information about the effects of planted forests on the environment to provide answers to these questions. The book focusses on planted forests and only peripherally comments on forests indigenous to New Zealand. The environment is interpreted fairly widely, covering issues from the aesthetic appeal of forests to serious erosion and flooding.

Anyone contemplating a planted forest, whether they be a farmer, the owner of a lifestyle block, or the neighbour of someone else's plantation, would benefit from this book. You won't find out about what trees to plant, but you will discover what effect trees are likely to have on runoff, soil erosion, what creatures (pests or otherwise) that might be expected to move in, and you might well have read some interesting things about the aesthetics of planted forests.

Each chapter covers one aspect of planted forests, ranging from water yield to socioeconomic effects by way of the greenhouse effect, soil erosion and deterioration, and biodiversity. Each topic is briefly introduced and specific issues identified. The available evidence relating to each issue is summarized and any possible solutions are presented. Most importantly, a comprehensive list of references is included at the conclusion of each chapter allowing further investigation by the interested.

So, do forests attract rain? How effective are they at reducing run-off and controlling flooding? What might move in as the trees grow, and are good old Pinus really as boring as we tend to think.

I was certainly surprised by some of the answers to these questions. Forests probably do not attract rain and they may well reduce the yield of water from a catchment. On the other hand, there does seem to be good evidence that forests do reduce erosion and reduce peak flows. My favourite factoid, for better or for worse, was that earthworm numbers decline dramatically in pine forests.

I enjoyed reading this book a great deal. Each chapter contains a comprehensive account of some aspect of forests and forestry in an approachable and readable style. The selection of readings is wide and comprehensive and the index is reasonably complete. Photographs are mostly used effectively, and graphs, tables and diagrams help convey information.

Most readers will not find this a book to read all at once, but will find dipping into a chapter at a time very rewarding and I recommend it to anyone with an interest in forestry.

Craig Marshall is in Otago University's Biochemistry Department.