The previous editions of this book earned the authors the prestigious ‘Exceptional Life-time Achievement Award’ of the British Ecological Society – the aim for the fifth edition is not only to maintain standards but indeed to enhance its coverage of Ecology. in the firs edition, 34 years ago, it seemed acceptable for ecologists to hold a comfortable, objetive, not to say aloof position, from which the ecological communities around us were simply material for wich wewhich we sought a scientific understanding. Now, we must accept the immediacy of the many environmental problems that threaten us