The role of long-term site productivity in maintaining healthy ecosystems: A prerequisite of ecosystem management

Abstract

Forest health is a central issue across North America. Most definitions imply that forest health is a condition of the forest ecosystem which sustains complexity or diversity while still providing for human needs. Imbedded in this definition is the need to maintain the productive capacity of managed sites. Although site productivity is largely a function of climate, soil properties, and the biotic potential of the vegetation occupying the site, forest management can also play an influential role in altering site productivity.In terms of site productivity, different concerns exist when managing different ecosites. Based on a recently-conducted expert opinion survey, the major concerns when harvesting black spruce from shallow-soil, upland sites were: 1) harvest-related nutrient removals, and 2) loss of organic matter. In contrast to these ecosites, the major concerns for organic sites (including wet, mineral soils) were: 1) altered hydrology, and 2) rutting. The water table on these sites is typically near the surface for a significant portion of the frost-free season, minimizing organic matter decomposition and associated nutrient release. Any forest management practice which exacerbates this situation would have a negative impact on site productivity. Tree nutrient cycling studies conducted on shallow-soil sites in northwestern Ontario were presented to show that calculated nutrient replacement times, with the exception of K, did not exceed current rotation periods. However, the forest floor nutrient pool represented a major component of the soil reserves. Based on the importance of this nutrient pool, best practices designed to protect and allow for the rebuilding of this active soil pool are essential if long-term site productivity is to be maintained.This paper outlines a series of steps to evaluate and correct management-induced changes in long-term site productivity. These steps included: 1) the development of "best practice" guidelines, 2) the development of a set of "criteria and indicators", and 3) the establishment of long-term experimental field trials. The results of this third step should, in turn, be used to refine the "best practice" guidelines and suggest alternative "criteria and indicators" that should be incorporated into a monitoring program of forest sustainability. Key words: forest health, ecosystem management, site productivity, nutrient cycling