Nutrient exports under different harvesting regimes in fast-growing forest plantations in southern Europe

In the humid and temperate areas of southern Europe, forest plantations are dominated by fast-growing species (Eucalyptus globulus, Pinus radiata and Pinus pinaster), which are grown on acidic soils with low reserves of available nutrients. In this study the amounts of nutrients exported from the plantations under different regimes and intensities of harvesting were evaluated and, on the basis of the results obtained, silvicultural management methods aimed at improving the nutritional status of the plantations were proposed. We found high ratios between nutrients exported by harvesting and those available in soil stores, indicating limitation for P, Ca and Mg over the long term, which is consistent with frequently found deficiencies of these nutrients. Current harvesting practices (removal of stem wood and bark) result in high rates of export of P, K, Ca and Mg, especially in eucalypt plantations, because of the high productivity and low nutrient efficiency of this species. Comparison of the amounts of nutrients exported by harvesting, with natural inputs (rainfall and weathering) and outputs (stream water), suggests that intensive exploitation of these plantations may result in negative budgets, especially if whole tree harvesting is carried out. The application of fertilizers containing P, Ca and Mg should be encouraged in all cases to favour the return of nutrients, especially where logging residues are extracted. The cost of harvesting in terms of nutrients can also be reduced by careful selection of the tree species planted and of the tree fractions harvested and by reducing the intensity of harvesting.