The use of ground vegetation and humus type as indicators of soil nutrientregime for an ecological site classification of British forests

In many countries ground vegetation and humus type are used as indicators o f forest soil quality, especially nutrient regime. This paper reports the d evelopment of such methods for use in British forests, within a new Ecologi cal Site Classification combining climate, soil moisture regime and soil nu trient regime. To develop a field assessment method for soil nutrient regime, a study was made of soil chemistry, humus type and ground vegetation in British forests . Sites were selected in both mature plantations and semi-natural woodlands . Soil and humus profiles were described and the soil was sampled volumetri cally for later chemical analysis. Vascular ground vegetation was recorded in quadrats by species cover fraction, and classified according to the exis ting British National Vegetation Classification. Soils were analyzed for a number of chemical variables. Vegetation data were treated by application o f the species indicator values for soil reaction (R) and soil nitrogen (N), as proposed by Ellenberg [Vegetation Ecology of Central Europe, 4th Editio n. Cambridge University Press, Cambridge]. Site mean indicator values mR an d mN (weighted by species cover fraction) were then calculated. Multivariat e statistical analysis techniques were applied to both the soil chemical an d the vegetation sample data. Soil nutrient regime was shown to be a composite gradient of several soil c hemical variables, of which the pH value and the availability of mineral (e specially nitrate) nitrogen, and of calcium, were of particular importance. The species composition of the ground vegetation was related to position o n this soil nutrient gradient. The vegetation: soil nutrient correlation us ing the site mean Ellenberg values was satisfactory (r=0.89), but was impro ved by using indicator values generated from within the present data. The o ccurrence of the major humus types (mor, moder and mull) is broadly related to soil nutrient regime defined in this way. Both ground vegetation and hu mus type can therefore be used as soil nutrient indicators in British fores ts. A division of the soil nutrient gradient into five classes (Very Poor, Poor , Medium, Rich and Very Rich) is proposed. Future sampling work may lead to the definition of an additional class of soils with carbonate nutrient reg imes. The Ecological Site Classification will provide forest managers in Gr eat Britain with an improved basis for the selection of tree species for pl anting, and the adoption of silvicultural methods best suited to the site. (C) 2001 Elsevier Science B.V. All rights reserved.