Importance of soil and role of ecosystem disturbance for sustained productivity of cool temperate and boreal forests

Human population growth places increasing demands on the world's forests. Sustaining these forests will depend to a considerable extent on sustaining soil structure and function. Traditional scientific concerns about sustaining timber production focused largely on soil fertility, but recent interest has focused attention on the plant and animal community and on ''biodiversify''. Neither of these approaches is satisfactory on its own. They should be replaced with an ecosystem analysis approach that includes the biotic and abiotic components. The most fundamental issue in sustainable forest management is the long-term productive capacity of individual sites, which is determined to a considerable extent by the availability of soil resources. Understanding the sustainability of site productivity requires knowledge of the determinants of leaf area and its photosynthetic efficiency, and of the allocation of net production. Keys that determine production ecology in boreal and cool temperate forests include low soil temperature, slow rate of litter decomposition and the resultant character of the forest floor, and, in some areas, impeded soil drainage; these lead to limitations on nutrient availability. Natural disturbance influences these factors and thereby plays a vital role in maintaining productivity and several measures of biological diversity. Without stand-replacing disturbances, closed forest may not be the climax vegetation in many western and northern Canadian landscapes. While forests and soils should be protected from ''damage'', sufficient disturbance should be sustained to respect the disturbance-related ecology of these forests. Ecological site classification and use of ecosystem-level management simulation models are important for the design of appropriate disturbance regimes.