Soil changes and tree growth in intensively managed Pinus radiata in northern Spain

Changes in soil properties and forest growth over 9 yr following the application of different site-preparation techniques were examined in an intensively managed Pinus radiata plantation in northern Spain. The site-preparation techniques included stem-only harvesting, scalping, and scalping plus down-slope ripping, which were carried out in the winter of 1992 93, and tree diameter and height were measured in the autumns of 1997, 1999, and 2001. Scalping and plowing were found to expose the denser subsoil, which increased bulk densities and decreased soil organic matter by exposure of the less-fertile subsoil. These alterations, however, were not related significantly to tree growth. Low microbial biomass carbon per unit soil organic C was found in the highly disturbed soils. The observed decrease in tree productivity over 9 yr on the most disturbed soils was attributed to the effects of intensive site preparation on nutrient concentrations in soils and foliage and on soil compaction and biological properties.