Forest Decline and Growth Trends in Central Europe - a Review

Abstract

Reports of forest decline in the 1980s and recent reports of increasing increments seem to contradict one another. An investigation of the literature referring to Central Europe suggests that regional differences result from differences in views and survey methods rather than from site or climatic conditions.

Forest decline was first recognized in terms of needle loss, and this was defined as an indicator for decreasing vitality. Most of the research undertaken to find relationships between increment and crown transparency classes was methodically unable to detect anything other than increment decreases as the employed reference was usually a “best-growing” or healthy tree. Thus, trees with less needles than these could only show less or at most the same increment. The discussion focused only on the question at what degree of needle loss increment was affected.

Only few investigations at that time dealt with stand or plot increments, some of them observing positive deviations from the expectations taken from yield tables. Later observations especially of permanent plots where a second generation of stands was already being observed presented a tremendous increase in growth. These could well be regarded as singular events under singular site conditions. However, in Austria and Bavaria, regional and national forest inventories of sophisticated design have proved that increments increased by at least 25% between 1980 and 1990.

From this point of view, the observation that at the beginning of the 1980s needle losses suddenly seemed to exceed those expected might have to be interpreted as a sign of increasing differentiation between trees of different vigour together with competition effects due to increased per hectare increment

Nevertheless, not enough is yet known about how or if site potential has changed to be able to make long-term forecasts of forest growth