Risk Appraisal for Forest Management with Respect to Site Quality and Environmental Changes

Abstract

Environmental changes and human interference have substantially modified forest site conditions in Europe for millenia. We illustrate how site conditions and ecosystem structure in forests were affected and frequently deteriorated to the point of severe degradation by human settlement and exploitation. Environmental changes, human interferences and the subsequent ecosystem transformations are varied and operating on different spatial and temporal scales, depending on the processes and responses under consideration. A particular characteristic of recent anthropogenic environmental changes is that they presumably occur much more rapidly than natural variations, and that they may lead to constellations of ecological effects that are unprecedented in history and evolution. Unusual combinations of growth and vitality factors arise from recent environmental changes, some factors under change bearing the potential to foster vitality and growth, e.g., CO2 enrichment and enhanced nitrogen deposition, while others may have strong detrimental effects, like soil acidification, compaction or loss by erosion. We quote a nationwide investigation of forest soil status in Germany, revealing that the majority of forest soils are indeed affected by acidification, at least in the upper soil layers which are most important for rooting. Appropriate silvicultural strategies are capable of significantly reducing risk with respect to many of the contributing factors. More diverse forest ecosystems mimicking structures and functions in natural forests are expected to bring about more stability. The classical risk formula calculates risk as the numerical product of probability and amount of damage. For such a quantification in forestry, however, probability of damage is altogether uncertain, at least at the individual stand or site level. Nevertheless, qualitative assessments can be performed with sonic confidence, and they should be performed before making management decisions, which will influence forest structure and functions for decades to centuries.