Elephant fells 1,500 trees a year and saves savanna

There is a large body of scientific knowledge published in technical papers that is never interpreted in an understandable way to the layperson. This volume attempts to explain the research that was produced by a project of the Scientific Committee on Problems of the Environment that sought to link ecosystem processes with biological diversity. The result is a most readable volume.

The study sought to examine the consequences of the accelerating losses of biodiversity. If you do not consider species loss a serious issue, after reading this book you will be convinced, especially because this work is based on the conclusions of top ecosystem scientists. The strength of this book is that it brings together information from those scientists who study species and those who study populations. From an ecosystem point of view not all species are equal. The loss of some will have a greater impact than the loss of others, and so the second chapter focuses on keystone species, the loss of which will cause an ecosystem to change radically. When sea otters are removed sea urchins abound and devastate the kelp beds. Questions are asked about how many species are needed for an ecosystem to function and, although many appear to have the same function and to be redundant, nature often has many back-ups in case one species suffers from disease or adverse weather conditions. Communities with relatively few species are more likely to be strongly affected by the loss of key species or the invasion of alien ones. The following chapter shows how biological communities are tied together by a web of interactions through competition, mutualisms, pathogens, parasitism and consumption by predators or grazing animals. The elimination of certain species that tie the community together can have devastating effects on the ecosystem.

The valid roles and interactions between the biosphere and water, soil and climate are all addressed. Since two-thirds of all rainfall is recycled back to the atmosphere by plants through both evaporation and transpiration, water is a crucial part of the ecosystem. Soil is a community of organisms and is maintained by a partnership between above-ground and below-ground organisms. A chapter on plants and productivity shows that, beyond a rather low number of species, short-term productivity does not increase with the addition of more plant species. However, this does not mean that diversity is unimportant. Growth chamber experiments have shown higher productivity in more diverse systems. Experiments in the grasslands of Minnesota clearly demonstrate how diversity provides back-up. One species will take advantage of another's bad year to maintain high productivity. Diversity provides a more robust and steady productivity over the long term.

We know that humans, with their powerful machines, are shaping the land today. However, a fascinating chapter shows how plants and animals are also a powerful force in determining the layout of forests, grasslands, deserts and other habitats. The megafauna, which went extinct at the end of the last ice age, were among the land movers, but many other smaller animals went extinct at the same time because of their dependence on the land-moving role of the megafauna. The elephants of Africa maintain the savanna landscape because one animal can uproot 1,500 trees a year. The effect of moose on bears, the burrowing activities of gophers and the vast banks of coral all define the character of land and seascapes.

The conclusion from reading this fascinating book is that both species and community richness are vital to the survival of our own species. Clean air, pure water, fertile soils and many other essentials are dependent on diversity. There are still far too many gaps in our knowledge to consider any species redundant. To maintain the quality of life on our planet, scientific evidence indicates a greater effort should be made to protect the species with which we share the earth. Ecosystems and the services they provide require further study so as to keep them resilient in face of the human-caused global changes taking place.

Sir Ghillean Prance is director, Royal Botanic Gardens, Kew.