Growth Trends in European Forests

Annual ring data collected from strict nature reserves and long-term permanent plots of the Finnish Forest Research Institute (ME1LA) did not reveal any longterm trend in the radial increment of Scots pine (Pinus sylvestris) in the southern part of Finland during the last 100 years. This result was supported by the analysis of stand wise increment data from permanent thinning experiments. The height development of dominant sample trees had been faster than that of previous site index curves. This was supposed to be mainly due to differences in the data of this study and of the index curves. According to our investigations, there were some indications of increasing productivity on some sample plots in the southernmost part of the country during the last 40 years. Possible reasons for non-existing growth trends are as follows: 1. The wide climatic variation of tree growth in northern latitudes could conceal the possible trend. The years 1961-1990 were slightly cooler than the years 1931-1960 in Finland. 2. The S0 2 and N-depositions in Finland during the past few decades have been too low to be able to cause growth trends of such magnitude that could be separated from natural growth variation. 3. The study material consists of untreated stands or stands with known management history. Thus, trends caused by changing silviculture are outside the scope of this study. On the basis of the non-existing trends in this study and results from eight successive national forest inventories beginning as early as in the 1920s, it can be concluded that the main factors leading to a 44% increase in the total growth of Finnish forests during the last four decades are changes in stand structures (age, density) and silvicultural practices (regeneration, thinnings, drainage, fertilization). European Forest Institute Research Report No. 5 Growth Trends in European Forests Edited by H. Spiecl<er, K. Mielikiiinen, M. Kohl and J. P. Skovsgaard ©Springer-Verlag Berlin Heidelberg 1996 42 Growth Trends of Scots Pine in Unmanaged and Regularly Managed Stands

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