SOIL FERTILITY AND NATURE CONSERVATION IN EUROPE - THEORETICAL CONSIDERATIONS AND PRACTICAL MANAGEMENT SOLUTIONS

I. Summary It is well known that an increase in fertility in many semi-natural communities leads to the dominance of productive species, which brings about a loss of diversity and hence also of conservation interest. Attempts to re-establish floristically rich communities on fertile sites often flounder as a result of invasion by such dominant species. This chapter reviews the relationship between nutrient supply and conservation value in both theoretical and practical terms in an attempt to provide a synthesis that would be of practical value for conservation management. From a theoretical viewpoint it is often assumed that the relationship between diversity and fertility follows a hump-back curve. This model appears to provide a reasonable broad-brush fit to empirical data in a range of situations, but exceptions occur. One area of weakness is that it takes no account of changing fertility, and two hypothetical catastrophe models are presented which illustrate the difficulties. From a practical conservation viewpoint, the three main sources of additional nutrients (successional accumulation, pollution and fertilizer) are illustrated along with a range of potential methods for measuring soil fertility and for the production of target values for different communities, above which management action is needed. The main aim of this chapter is to consider the effects of elevated soil nutrients in a systematic way. A formal model is produced which illustrates the many ways in which (1) the nutrient supply can increase and (2) the manager can manipulate the system to reduce the supply. This process stratifies management techniques into two groups: those that involve an increase in nutrient offtake, and those that involve manipulation of eco-system stores and fluxes. The complexities of conservation management aimed at reducing fertility are highlighted, and the need for studies inte-grating applied management and nutrient cycling processes is emphasized. © 1993, Academic Press Limited.