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Changes in forest growth
- Pretzsch, Hans
- Forstwissenschaftliches Centralblatt 1999 v.118 no.1-6 pp. 228-250
- age structure, biotic stress, forest growth, forest inventory, forest management, forest stands, forests, growth curves, growth models, temperature, yield tables, Germany
- The forest growth curves over a long period of time are suitable indicators for changes in forest ecosystems. Hence, the investigation of growth trends is based on the analysis of long-term yield figures on experimental plots, increment cores and consecutive inventories. Growth changes may be diagnosed from these data, together with yield table comparisons, constant age method, comparison of generations and the evaluation of consecutive inventories. It has been found that increments in forest stands, considered on a supra-regional scale, are showing a considerable upward trend over the past few decades. For the past two decades repeated forest inventories in Bavaria have diagnosed an increase of 10–20 % in standing volume and show that species-specific annual volume increment exceeds yield tables by 12 to 43 %. In the Northern hemisphere the uncontested rise in temperature and prolongation of the vegetation period offer a probable explanation for supra-regional increment increase. This increase is overlaid by various factors with local and regional impacts such as local site conditions, nutrient inputs and biotic stress factors. This superimposition brings about a great variety of increment reaction patterns and positive as well as negative deviations from the expected increment curve for typical age classes. It also provides an approach towards explaining the paradox that downright hypertrophic growth, increment decreases and stand dissolutions may occur side by side and at the same time. Forest research and forest management need to react to these changes in growth conditions by developing and applying site-dependent growth models, for it is through these means that future silvicultural decisions may be put on a reliable basis of actual figures.