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In the Nordic countries, temperature and precipitation regimes are predicted to change as a result of climate change, which may reduce water availability and thus tree growth. This study presents a spatial approach for analysing variations in the annual radial increments of trees across a latitudinal transect. The aim was to evaluate the importance of daily temperature, precipitation and soil water content as regulators of tree growth across a north-south gradient. Increment cores were collected from living Scots pine ( Pinus sylvestris L.) trees growing on dry and sandy soils in five regions in Finland and two regions in Estonia. A total of 1 024 trees were measured across 551 sample plots. No clear latitudinal trend was evident in the magnitude of the correlation between the variations in annual increment and the current summer's temperature, but the time period most strongly related to the increment variation shifted towards earlier dates with a decrease in latitude southwards. Thus, the results challenge the traditional findings that the growth of trees located at lower latitudes is less affected by temperature. Moreover, the results demonstrate the importance of using high-resolution weather data when analysing variations in the radial increments of trees. In all of the regions, including the high northern latitudes, high precipitation in the current summer promotes tree growth, and the correlation between summer precipitation and the increment variation increases with a decrease in latitude. The correlations between increment variation and soil water content estimated using two different models were lower than those involving precipitation. The results suggest that accurate soil information is needed to describe the connection between water content and tree growth. [ABSTRACT FROM AUTHOR]

ABSTRACT Norway spruce ( Picea abies) is sensitive to decreases in soil water availability. In this study, we simulated how the climate change may influence the hydrological processes with impacts on the growth of Norway spruce in three sites located in southern Finland (61oN). The sites differed from each other in regard to the climate and soil water conditions; however, the initial structure of the tree stands was similar. Under the current climate, the canopy surface evaporation ( Ec) increased, whereas the transpiration ( Et) remained at a constant rate over the simulation period, as the seedlings in the initial stand grew to full maturity. Under the changing climate, on average, the cumulative of Ec and Eg (evaporation from soil surface) were 16% and 14% higher than those under the current climate, respectively, whereas the cumulative Et was 12% lower. The leaf area index ( L) increased constantly on the sites with high (SH) and medium (SM) soil moisture, unlike on the site with low (SL) soil moisture. The canopy conductance ( gcs) declined rapidly and earlier on the site SL, which implied the acclimation of stomatal behaviour to drought. The increasing water loss through evaporation decreased the water infiltration into the soil profile, resulting in an increasing soil water deficit ( Wd), especially on the site SL. It also occurred earlier in all three sites under the changing climate. It was predicted that climate change will create a suboptimal environment for Norway spruce in southern Finland, particularly on the upland sites with lower groundwater table. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Climate change may cause a decrease in snow cover in northern latitudes. This, on the other hand, may result in more severe soil frost even in areas where it is not common at present, and may lead to increased stress on the tree canopy. We studied the effects of snow removal and consequent changes in soil frost and water content on the physiology of Norway spruce (Picea abies [L.] Karst.) needles and implications on root biomass. The study was conducted at a 47-year-old Norway spruce stand in eastern Finland during the two winters of 2005/06 and 2006/07. The treatments in three replicates were: (i) natural snow accumulation and melting (CTRL), (ii) artificial snow removal during the winter (OPEN), and (iii) the same as OPEN, but the ground was insulated in early spring to delay soil thawing (FROST). In spite of the deeper soil frost in the OPEN than in the CTRL treatment, soil warming in spring occurred at the same time, whereas soil warming in the FROST was delayed by 2 and 1.5 months in 2006 and 2007, respectively. The soil water content was affected by snow manipulations, being at a lower level in the OPEN and FROST than CTRL in spring and early summer. The physiological measurements of the needles (e.g. starch, carbon and nitrogen content and apoplastic electrical resistance) showed differences between soil frost treatments. The differences were mostly seen between the CTRL and FROST, but also in the case of the starch content in early spring 2007 between the CTRL and OPEN. The needle responses in the FROST were more evident after the colder winter of 2006. The physiological changes seemed to be related to the soil temperature and water content in the early growing season rather than to the wintertime soil temperature. No difference was found in the fine root (diameter<2mm) biomass between the treatments assessed in 2007. In the future, conditions similar to the OPEN treatment may be more common than at present in areas experiencing a thick snow cover. The present experiment took place over the course of two years. It is possible that whenever thin snow cover occurs yearly, the reduced starch content during the early spring may be reflected in the tree growth itself as a result of reduced energy reserves. [Copyright &y& Elsevier]

A process-based ecosystem model was used to assess the impacts of changing climate on net photosynthesis and total stem wood growth in relation to water availability in two unmanaged Norway spruce (Picea abies) dominant stands with a mixture of Scots pine (Pinus sylvestris) and birch (Betula sp.). The mixed stands were grown over a 100-year rotation (2000–99) in southern and northern Finland with initial species shares of 50, 25 and 25% for Norway spruce, Scots pine and birch, respectively. In addition, pure Norway spruce, Scots pine and birch stands were used as a comparison to identify whether species' response is different in mixed and pure stands. Soil type and moisture conditions (moderate drought) were expected to be the same at the beginning of the simulations irrespective of site location. Regardless of tree species, both annual net canopy photosynthesis (Pnc) and total stem wood growth (Vs) were, on average, lower on the southern site under the changing climate compared with the current climate (difference increasing toward the end of the rotation); the opposite was the case for the northern site. Regarding the stand water budget, evapotranspiration (ET) was higher under the changing climate regardless of site location. Transpiration and evaporation from the canopy affected water depletion the most. Norway spruce and birch accounted for most of the water depletion in mixed stands on both sites regardless of climatic condition. The annual soil water deficit (Wd) was higher on the southern site under the changing climate. On the northern site, the situation was the opposite. According to our results, the growth of pure Norway spruce stands in southern Finland could be even lower than the growth of Norway spruce in mixed stands under the changing climate. The opposite was found for pure Scots pine and birch stands due to lower water depletion. This indicates that in the future the management should be properly adapted to climate change in order to sustain the productivity of mixed stands dominated by Norway spruce. [ABSTRACT FROM PUBLISHER]