Abstract
(Englisch)
|
Since the late 1980's, researchers in Europe have reported that trees seem to be growing faster. The causes for this increase have now been investigated in the RECOGNITION project ('Relationships Between Recent Changes of Growth and Nutrition of Norway Spruce, Scots Pine and European Beech Forests in Europe)..
The main objective of RECOGNITION was the quantitative assessment of interrelationships between recent changes in forest growth, stand nutrition, and soil properties on the European level. The specific objectives of the project are: to identify the potential causes of recent growth trends in European forests and to investigate their interactions with focus on the relative importance of nutrients (primarily nitrogen and CO2), climate (primarily temperature and precipitation) and land-use changes; to focus on growth analyses on selected sites where conditions and availability of historical data allow testing of specific hypotheses about causes of changes in site productivity; and to analyse the long-term consequences and risks of observed changes for sustainability and to assess the implications for future management strategies.
During the reporting period the Swiss partner prepared and analysed site-specific environmental variables from the NITREX and the ICP-Level-II site in Alptal for subsequent data analysis. At the ICP-Level II site in Othmarsingen, a total of 10 old-growth beech trees were selected and felled. The stem disks taken at 2m intervals are currently being analysed at the laboratory of our project partner in Freiburg, Germany.
When testing the hypotheses about the causes for increased growth, the project analysed data from long-term research plots as well as from current and recent growth investigations. Computer models were used to analyse the interrelations between site productivity and potential causes of increased growth, and also to make projections of the potential consequences.
The project was quite unique in combining the experts from several disciplines (forest researchers, climatologists, modellers) and using different methods in order to obtain reliable results. The best available data, including data from the UN/ECE forest intensive monitoring programme (the so-called LEVEL II data) were used as a basis of the analyses.
The results of the RECOGNITION project indicate that increased nitrogen deposition from the atmosphere is the main cause for the observed increases in forest growth in Europe:
These results indicate that the nitrogen nutritional status and tree height growth of Scots pine stands consistently increased between 1960 and 1990. Height growth of Norway Spruce (Picea abies) and Scots Pine (Pinus sylvestris) has increased compared to the former growth on average by about 20%. This trend is especially clear in Central Europe, but less so for Northern Europe. The increase in the nitrogen level in trees is caused by increased human induced nitrogen deposition, maybe speeding recovery from past land uses such as litter raking.
Changes in climate and increased atmospheric CO2 concentration seem to be of secondary importance in causing the observed growth acceleration compared to increased nitrogen nutrition. The model results suggest, however, that in the future the nitrogen effects will diminish and CO2 and climate change will be the major causes of increases in the forest growth rate expected in coming decades, especially in Northern Europe.
Increased growth and accumulating wood volume in the forests indicate that if the structure of the forests should be maintained, changes in the intensity of management practices, e.g. more frequent or intensive thinnings, are needed. Sustainable forest management in the future may require more attention on the nutritional budget of forest ecosystems.
|
