Increasing forest growth in europe — possible causes and implications for sustainable forest management

ABSTRACT

Recent studies have shown that growth rates of Pinus sylvestris, Picea abies and Fagus sylvatica in Europe has increased. Average volume growth rate has increased by around +50% and height growth rate by around +10%. This paper attempts to match this size of growth change to those that have been reported after experimental manipulation of certain environmental forcing agents, that are known to have changed recently (CO₂; anthropogenic N; changes in temperature or rainfall and recovery from past forest utilisation). It concludes that it is unlikely that any one agent alone is capable of consistently and solely increasing growth rates to the levels observed. Thus the cumulative growth gains probably arise as a result of a combination of factors. Given the difficulty of experimenting on large trees, the paper advances a series of hypotheses, which might be used to separate the relative impacts of each agent through field-based studies. The consequences for sustainable forest management are two-fold. In the first place what constitutes sustainability is obviously dynamic and affected by management. Sustainable levels of production set in the immediate post-war years would have been lower than is the case today. Indeed, in Europe that is largely what has happened. Partly as a result, the harvest in Europe is today 70% or less of what is really sustainable. In the second place, we need to be aware of the likely human factor in the recently accelerated growth rate. It seems likely that at least a component of the recovery in growth rates is due to the cessation of deleterious practices — grazing, litter-raking, charcoal-burning.

KEY WORDS:

• European forests
• growth rates
• land use
• N-deposition
• carbon dioxide
• temperature