Tree performance on minespoils in the South Wales coalfield.
Variable growth of Larix leptolepis [L. kaempferi] (Japanese larch) has been observed on restored opencast coal workings in South Wales, UK. A study of the relationship of tree growth with minespoil chemical, nutritional, physical and hydrological factors was carried out at 10 sites with trees 6-19 years old in 1988. Tree height and yield growth were positively related to nitrogen and phosphorus foliar concentrations, but negatively to those of magnesium; 73% of the variation in tree growth was explained by variation in foliar chemistry. Soil pH and extractable magnesium were negatively correlated with tree growth, with cation exchange capacity positively related to it. Minespoils had bulk densities that commonly exceeded 1.7 g/cm3 below 0.2 m depth. Stone contents were high and typically 25% by volume. Root systems of excavated trees were characterized by a high root density within 0.3 m of the minespoil surface. Restricted rooting was attributed to high bulk density and the incidence of shallow water tables. Waterlogging during the spring and early summer, and the consequent presence of anaerobic soil conditions during periods of active growth, was found to be detrimental to tree growth. It is suggested that landform design, selection of suitable soil or soil-forming materials, spoil placement technique and appropriate species choice are central to the future success of forestry schemes on restored ground in South Wales.