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| Management of Boreal Forests under Changing climate |
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Seppo Kellomäki
University of Joensuu, Faculty of Forestry, P.O.Box 111, FIN-80101 Joensuu, Finland
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There are no studies, which would conclude how the climate change may impact on the timber yield over Europe. However, it is expected that even under the current climate the forests resources in Europe may increase substantially by the year 2040. The increase of the forest resources in northern Europe would double. In other parts of Europe forests the forest resources would increase substantially. The climate change along with the elevating CO2 may further enhance the growth of forest resources as exemplified some model studies.
Based on a process-based model, the regeneration of Scots pine (Pinus sylvestris L.) was studied at the northern timber line in Finland (70o N) in relation to elevating temperature and atmospheric CO2 (Kellomäki et al. 1997b). If a transient increase of 4oC was assumed during the next 100 years, the length of growing season increased from the current 110-120 days to 150-160 days. The temperature elevation alone, or combined with elevating CO2, increased flowering and the subsequent seed crop of Scots pine with a decrease in the frequency of zero crops. In both cases, temperature elevation substantially increased the success of regeneration in terms of the number of seedlings produced after each seed crop. The increasing number of mature seeds was mainly responsible for the enhanced regeneration, but increasing soil temperature also increased the success of regeneration. Even under the changing climatic conditions, however, the growth of the seedling stands was slow, which indicated that the northward advance of the timber line would probably be very slow, even though regeneration was no longer a limiting factor.
Kellomäki et al. (1997a) applied a process-based model for Pinus sylvestris stands on moraine soils in southern Finland (61st latitude). A temperature increase of 0.4°C per decade, and the combination of temperature and precipitation increases would increase timber yields by 10%, which is well in line with the earlier findings by Kellomäki and Kolström (1993). An elevation in CO2 by 33 mmol mol-1 per decade alone would increase removals of timber by 20%, and a combination of increases in temperature, precipitation and CO2 would increase removals by 30%. A rise in precipitation had no effect on the length of the rotation, but the other combinations shortened the rotation (currently 100 years); by 9% for the elevating temperature, by 17% for the CO2, and by 23% for the combined elevation of temperature, precipitation, and CO2. These changes can be expected to affect the supply of timber and also the profitability of forestry.
A gap-type model (Kellomäki and Kolström 1992, 1993) was applied over the Finland based on the input representing the permanent sample plots of the national forest inventory. The calculations indicated that the total annual stem wood growth may increase by 40% in the time period of 1990 - 2100 (from the 60 million m3 up to 80 million m3), with the main increase in the northern Finland (above 63rd latitude). In these calculations, the current management and a gradual increase of annual mean temperature by 4o C with 10% increase in precipitation over 100 years were assumed. The same calculations showed that the sustainable cuttings allowed 22% more timber to be harvested. It was obvious that the share of hardwood timber (Betula sp.) would increase from the current 10% up to 30% of the total timber yield, which currently represents mainly soft wood (Pinus sylvestris, Picea abies). At the same time, the stem wood stock would increase by 30%. It is estimated that the value of increasing growth would be one billion Euros by 2040.
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References
Kellomäki, S. & Kolström, M. 1992. Simulation of tree species composition and organic matter accumulation in Finnish boreal forests under changing climatic conditions. Vegetatio 102:47-68.
Kellomäki, S. & Kolström, M. 1993. Computations on the yield of timber by Scots pine when subjected to varying levels of thinning under a changing climate in southern Finland. Forest Ecology and Management 59:237-255.
Kellomäki, S., Väisänen, H. & Kolström, T. 1997a. Model computations on the effect of elevating temperature and atmospheric CO2 on the regeneration of Scots pine at the timber line in Finland. Climate Change 37: 683-708.
Kellomäki, S., Karjalanen, T. & Väisänen, H. 1997b. More timber from boreal forests under changing climate? Forest Ecology and Management 94:195-208.
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