Trends in Montane Grasslands in Snowdonia, expressed in Terms of “Relative Entropy”

Abstract

BETWEEN 1957 and 1960 a series of experiments was set up at four sites in Snowdonia, North Wales, to study the influence of sheep grazing on two widely distributed plant communities characterized by the dominance within them of Nardus stricta (on soils of peaty podsol/peaty gley character), and Agrostis tennis and Festuca ovina (on soils of brown earth character), respectively. Some of the experiments were established by M. J. Chadwick¹. The experimental sites cover an altitude range of 1,300–3,000 feet O.D. (396–914 m) and, at each site, three treatments are set out in a randomized design incorporating four replicates per treatment. The experimental treatments were: (i) Normal grazing: open to the sheep from the surrounding mountain pastures (most of the breeding ewes and yearling sheep are removed from the mountain in winter); (ii) winter protection from grazing: the plots were protected by fencing from October to April each year; normal grazing took place during the summer; (iii) no grazing; the plots were ungrazed throughout the period of the experiment. (The approximate densities of the sheep populations grazing the experimental plots, expressed in ewe units/acre (hectares), are set out in Tables 1 and 2.)