Edaphic and Vegetational Zoning on the Carboniferous Limestone of the Derbyshire Dales

Abstract

Many interesting descriptions of the soils and vegetation types of the chalk downlands have been published, but there is little available information on the carboniferous limestones of north-western Britain. In these uplands, the hard nature of the parent rock and the damp, cool climate produce an environment markedly different from that of the wellknown chalk grasslands in the south and east. This is reflected in the nature of the vegetation, typical calcareous grassland being limited to the steep slopes and flushed valleys, while on the gentler slopes and high plateaux there is an acidic type of grassland or heath. The distribution of the various communities is closely correlated with an edaphic zonation. The development of the soil is determined, first by climate, and secondly by topography through its influence on soil accumulation and stability and on drainage conditions. Hence the sequence of soil and vegetation types can be described as a catena, using the term as defined by Morison, Hoyle and Hope-Simpson (1948), 'a grouping of soil vegetation types linked in their occurrence by conditions of topography and repeated in the same relationship to each other wherever the same conditions occur'. This concept has been applied in the following description of the plant communities and soils of the Derbyshire limestone where all stages in the transition from calcareous grassland to moorland and from rendzina to podsol can be found. The carboniferous limestone exposed in the southern Pennines, known as the Derbyshire Dome, is an undulating plateau dissected by steep-sided dales. The limestone is in the form of a massive bed, the upper layers of which are impregnated with nodules and bands of chert. This is a flint-like substance which is not readily weathered but is broken down by mechanical action and remains as scattered fragments in the soil. Between this chertified limestone and the pure white limestone under it, there are occasional beds of a doleritic intrusion, toadstone, which outcrops at the surface in several areas producing locally an acid type of soil bearing heath vegetation, not to be confused with heath of leached limestone areas. The climate can be described as submontane with high humidity and rather low temperature throughout the year. The annual rainfall is from 40 to 50 in., falling mainly in October, November and December, but the soil remains very wet throughout the winter and spring owing to the low rate of evaporation. In general, with increase in altitude the rainfall rises and temperature decreases, leading to an increase in the precipitation: evaporation ratio. There are also frequent snowfalls on high ground and strong * Now at the Nature Conservancy, 91 Victoria St., London.