SOIL FACTORS AFFECTING TREE GROWTH ON FORMER OPENCAST COAL LAND

The growth of three tree species (Alnus glutinosa, Betula spp. and Que rcus spp.) was related to soil factors on two restored opencast coal s ites in South Wales, UK. The main factors favouring tree growth were g reater soil depth and organic content. Factors limiting growth include d poor site drainage and high magnesium levels. Whilst all species wer e related to most of the above factors, soil depth was of particular i mportance for Alnus glutinosa and Betula spp., whilst site drainage ha d the greatest influence for Betula spp. Soil-tree associations tended to be closer on the older of the two sites. Combinations of soil dept h, percentage clay and percentage organic content in a multiple regres sion predicted around 40 per cent of the growth variation in Alnus glu tinosa, between 6.9 and 32 per cent of that for Betula spp. and betwee n 14.5 and 32.6 per cent of that for Quercus spp. Growth prediction fo r Betula spp. improved to 40.9 and 34.8 per cent when a site drainage factor was included in the regression. The development of such predict ive relationships might contribute to the planning of site reinstateme nt for tree planting after opencast mining, and to a better 'matching' of tree species to site characteristics.