Effects of Species on Nutrient Cycles and Soil Change [and Discussion]

The choice of species to be favoured in forest management is subject to several considerations, among them the possibility of adverse effects on site productivity. Information on this possibility is reviewed from three viewpoints: nutrient cycling, soil genesis and classification, and relatively short-term (i.e. within one generation) changes in soil properties and growth rate. Nutrient cycle models describe flows between soil and plant components of ecosystems but generally can reveal little about variation in nutrient supply over the life of a stand. Profound changes in profile characteristics and mineral weathering occur on a time scale of millennia and can scarcely be expected within a single generation of one or another species. Many reported comparisons of species effects on soil profile development, physical structure, or nutrient status are invalid for a variety of reasons, including inadequate perception of inherent soil heterogeneity. Claims of decreased yields resulting from successive generations of conifers are not borne out by recent studies. Finally, maximum changes in soil due to choice of species appear minor in comparison with the mechanical and chemical impacts associated with present day intensive forest management.