Forest site degradation—temporary deviation from the natural site potential¹

Abstract

Intensively cultivated areas, such as Central European forests, have been heavily changed by human activities. It is quite possible that at least some of the forest decline symptoms of today are late consequences of inappropriate land use practices in the past. Centuries of forest pasture, litter raking, fire cultivation, charcoal production, deforestation of whole landscapes and reafforestation with monocultures of inadequate species led to an export of nutrient elements to a degree sometimes exceeding the remaining stock in the soil. Amelioration experiments, as well as spontaneous developments of soils and plant communities on the other hand, suggest the reversibility of even heavy degradations. Improving nitrogen status and increasing growth rates indicate a gradual regeneration since the historical impacts ceased. A concept is discussed that distinguishes between the natural site potential, based on permanent site factors and the current site condition based on variable site attributes. Every ecosystem is characterized by a particular resilience, and a range of possible, reversible deviations from the site potential. Within this range it is ecologically legitimate, to improve the site quality by means of amelioration measures. Such measures should, however, not create artificial sites of higher productivity, nor destroy biotopes that are worth being protected.

Introduction

In discussions on the sustainability of forest ecosystems, European forestry is often mentioned as an example that even over long periods, an extensive and yet sustainable forest management is possible. It is the question, however, whether forest productivity in Europe is indeed ecologically sustainable.

Large areas of Europe are covered with forests far away from an ecological equilibrium and from the natural, potential forest communities. For millenia, such forests have been heavily affected by human activities and even some of the forest decline symptoms discussed in the past decade, or at least the high susceptibility of forests to environmental stresses, might be a late result of historical land use practices. The extent of these historical impacts and their consequences often seem to be underestimated. In this paper, the attempt is made to estimate the magnitude of possible nutrient losses during past centuries. Degradations like that are at a certain extent to be seen as a temporal deviation from a natural, medium term natural equilibrium. Some ideas on their reversibility and the possibilities of natural or artificial regeneration will be discussed.