The Influence of Soil Conditions on the Course of Succession on the Chalk of Southern England

Abstract

During both the First and Second World Wars as in other periods of agricultural prosperity many areas of chalk-down in south-east England were ploughed and used for growing cereal crops, only to be abandoned when peace was restored and demand less. The process of re-colonization by native plants of the abandoned arable land does not appear to have been described in detail, but now some 25 years after the Second World War and 50 years after the First, the vegetation still retains a distinctive character. Indeed there is evidence from sites in Kent and Surrey (Cornish 1954) that chalk-downs ploughed in the last century may still be recognized by the composition of the vegetation they now support. The outstanding feature of the vegetation which has developed on shallow chalk soils which were ploughed during the Second World War is the great scarcity of grasses and their failure to form a true turf. Patches of bare chalky soil persist even after the lapse of 25 years, and the vegetation is composed largely of dicotyledons including a wide variety of herbs and several species of shrub, among which Thelycrania sanguinea and Crataegus monogyna are particularly characteristic. On older sites scrub develops, frequently dominated by Thelycrania, and at no time is there a stage in the succession corresponding to typical chalk grassland, unless grazing is severe (Hope-Simpson 1940). From some preliminary experiments made in 1961 it seemed that an inadequate supply of nitrogen and phosphorus might account for the poor growth of grasses on these younger sites, and that it was possibly this scarcity of grasses which favoured the early invasion of shrubs. The experiments now described were designed to test this hypothesis. The site selected for the investigation appears to be typical of many in the Chilterns and on the North Downs and is described in the following section.