Climatic changes including a lengthening growing season (Menzel & Fabian 1999), increasing CO2 and nitrogen deposition (Makinen et al. 2003, Spiecker 1999, Spiecker 2000, Spiecker 2002) are assumed to cause increased forest growth. Climate change has been defined at global and local scales (Da Motta 2004, Knowlton et al. 2004, Mauro 2004, Meyneeke 2004, Miller 2003). Predictions of the future development of forest resources cannot be made without studying the response of trees to climate change.
Previous results indicate that northern forest ecosystems are among the regions at greatest risk from the impacts of climate change (IPCC 2001). According to IPCC (2001), warming trends have already started and in the future will increase. Most studies attribute the warming trends to accumulation of greenhouse gas (IPCC 2001).
In Europe, most forests are managed, except for those in north-western Russia, where there is a dominance of old-growth natural forests. It is important to understand the response of unmanaged natural forest to changing climate because it is possible to adapt forest management practices to a changing environment (Lopatin et al. 2006). Dendroclimatic analysis can be used to identify the major climatic factors that influence radial growth of tree species.
The largest administrative region of North-western Russia (forest area of Komi Republic is 33% of total North-western Russia’s forest area) was selected for the assessment of long-term forest growth trends. Komi is situated at the eastern boundary of the European part of Russia, in the boreal region where large areas of natural forest still exist. Borehole temperature measurements in Komi Republic indicate strong subsurface warming, reflecting changes in the trends of both surface air temperature and solid precipitation (Oberman & Mazhitova 2004).
The main objective of this research is to investigate the effect of climate change on radial growth of Siberian spruce (Picea obovata Ledeb.) and Scots pine (Pinus sylvestris L.) in north-western Russia (Komi Republic).
Climatically, Komi (Fig. 1) lies within the Arctic, Atlantic-Arctic and Atlantic-Continental provinces (Stolpovski 1997). Annual mean temperature varies between +1° C in the southern part of the republic and -6° C in the northern part, with the lengths of the growing season (days with mean temperature above +10° C) being 10 - 45 days. Annual rainfall decreases from 700 mm in the south to 450 mm in the north. Characteristic for the winter period, which lasts 130 - 200 days is accumulation of a thick snow cover (70-80 cm - Galenko 1983). The territory of Komi is characterized by surplus moisture. Mean annual evapotranspiration is significantly lower than annual rainfall (Tab. 1).
The vegetation cover of Komi is dominated by Middle and Northern taiga forests, with the exception of mountainous parts of the republic where forest-tundra and tundra ecosystems have developed (Larin 1997). Boreal vegetation is dominated by Scots pine (Pinus sylvestris L.), Siberian spruce (Picea obovata Ledeb.) and Siberian fir (Abies sibirica Ledeb.). Downy birch (Betula pubescens Ehrh.) forests are the first stages of post-fire succession, frequently with abundant aspen (Populus tremula L.).
Forests with Siberian spruce in Komi reach 16 mln. ha, i.e. 60% of the whole forest area. Siberian spruce in optimal conditions could reach a height of 35-40 meters and 90-110 cm diameter at breast height. Scots pine is distributed on 24% of the forest area and represents 23% of the total growing stock. The forest stands with high productivity are concentrated in the middle boreal zone of Komi. The mean heights are about 22-24 m, and the mean diameter is 28-30 cm with a growing stock of 160-190 m3 ha-1 (Kozubov & Taskaev 1999).
Komi is the most forest-rich region in north-western Russia. The forested area includes about 300 000 km2, making up 4.1% of Russian forested areas. The total stock of wood in the forests of Komi reaches 2855.8 mln. m3. The mean volume of wood is about 80-100 m3 ha-1. In southern regions the mean standing volume is 300 m3 ha-1.