ISSUES IN CONSERVATION VEGETATIONAL SUCCESSION AND CLIMAX COMMUNITIES David Gregson INTRODUCTION A very important concept in ecology as applied to the study of communities of plants and animals is that of a vegetational succession. It basically means that, over a period of time, a habitat can be expected to change in a predictable manner and through a number of stages which can be recognised by a trained observer. The implications of this are very far reaching in the management of nature reserves, and influence greatly the decisions that are made regarding the work to be done. In this article I hope to explain the basis of successional change and to discuss its effects on the work of Naturalists' Trusts. PRIMARY AND SECONDARY SUCCESSION A primary succession is one which takes place on completely bare ground, while secondary succession occurs on areas which already have some vegetation cover, e.g. abandoned farmland. A good example of primary succession is that of a glacial moraine. Here we have completely bare ground left by the retreat of a glacier, a situation which we find today in parts of Alaska. This primary land surface is ripe for colonisation, and it occurs in the following way: 1. Initially pioneer vegetation enters, comprising mosses, fireweed and Dwarf Willow. 2. An inorganic soil forms which allows better growth of the willows (these Dwarf Willows are prostrate shrubs only a few inches high, not to be confused with the shrubs and trees which we know), and allows other tall shrubs to grow. 3. Leaves fall from these shrubs, allowing organic matter to enter the soil. A dense Alder thicket develops (50 years) which makes the environment more acid by its leaves. It also introduces more nitrogen into the soil. 4. The altered condition of the soil allows Spruce to grow (120 years). 5. Western Hemlock, a large conifer, enters the environment (200 years). The Spruce and Hemlock tend to reduce the available nitrogen and the Alder is replaced. It can be seen from this succession that as plants change so the environment changes. Each plant community alters the habitat, making it more favourable to the plants which will eventually follow. The term used for this series of changes is a sere. The above example is a long sere, but seres are not confined to vegetation and they are sometimes very rapid, e.g. in a cowpat. Insects enter a fresh cowpat and derive