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The Effects of Competition and Nutrition on the Inter-Relations of Some Wet-Heath Plants

1969; Wiley; Volume: 57; Issue: 1 Linguagem: Inglês

10.2307/2258209

1365-2745

Khalid Hamid Sheikh,

Botany, Ecology, and Taxonomy Studies

The wet-heath vegetation which forms the subject matter of this paper is found in an Ecological Reserve set aside by the Forestry Commission in Bramshill Forest, northeast Hampshire. It is a variable association of three species-Molinia caerulea (L.) Moench, Calluna vulgaris (L.) Hull and Erica tetralix L.-the distribution and relative proportions of which vary according to local conditions of soil and drainage (Rutter 1955). Webster (1962) showed that the proportion of Molinia in the vegetation was negatively correlated with the concentrations of carbon dioxide and hydrogen sulphide in the ground-water. Loach (1964, 1966) analysed soil profiles and measured the growth of all three species, in the absence of interspecific competition, on sites representative of the various facies of wet-heath vegetation. He found that all three species made most growth in the soil of a Molinietum and least in the soil of a small area of Valley-bog. Analyses of soils and plants, and an experiment in which the responses of Molinia to nutrients were tested, all suggested that the Valley-bog soil was the most deficient in nutrients, especially phosphorus and to a less extent nitrogen and potassium. He tentatively concluded that either inadequate nutrition or poor aeration, or both, on the Valley-bog site so limited the growth of Molinia as to allow Erica tetralix to become more abundant in the vegetation. However, he did not directly investigate the significance of the aeration factor and his experiment on the responses of Molinia to nutrients was made with blocks of soil removed from the natural sites and subjected to uniform drainage conditions. In the present paper, field studies relevant to competition between the species and their responses to nutrition will be described, and in later papers aeration conditions and their ecological effects will be analysed in detail. Studies have been made on four sites within the reserve, characterized by different proportions of the three species under investigation. Three of the sites, designated Valley-bog, Central associes and drier Molinietum are the same as those investigated by Loach (1966) and point quadrat analysis of cover repetition are reproduced from his paper in Table 1. In the Valley-bog Erica was more abundant than elsewhere; in the Central associes Calluna was more abundant than on the other sites. There was very