Model computations on the effect of rising temperature on soil moisture and water availability in forest ecosystems dominated by scots pine in the boreal zone in Finland (original) (raw)
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In semi-arid developing countries, most poor people depend on contaminated surface or groundwater resources since they do not have access to safe and centrally supplied water. These water resources are threatened by several factors that include high evapotranspiration rates. In the Okavango Delta region in the northwestern Botswana, communities facing insufficient centrally supplied water rely mainly on the surface water resources of the Delta. The Delta loses about 98% of its water through evapotranspiration. However, the 2% remaining water rescues the communities facing insufficient water from the main stream water supply. To understand the effects of climate change on evapotranspiration over the Okavango Delta water resources, this study analysed trends in the main climatic parameters needed as input variables in evapotranspiration models. The Mann Kendall test was in the analysis. Trend analysis is crucial since it reveals the direction of trends in the climatic parameters, which is helpful in determining the effects of climate change on evapotranspiration. The main climatic parameters required as input variables in evapotranspiration models that were of interest in this study were wind speeds, solar radiation and relative humidity. Very little research has been conducted on these climatic parameters in the Okavango Delta region. The conducted trend analysis was more on wind speeds, which had relatively longer data records than the other two climatic parameters of interest. Generally, statistically significant increasing trends have been found, which suggests that climate change is likely to further increase evapotranspiration over the Okavango Delta water resources.
Agricultural and Forest Meteorology, 2014
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.
Simulated water balance of Scots pine stands in Sweden for different climate change scenarios
Journal of Hydrology, 1995
The effects of climate change on the water balance of Scats pine were studied with a coupled water and heat flow model called 'SOIL'. Two forest soil types (a silty-sand and a sand) at five locations in Sweden were chosen to represent sites with different air temperature, growing season length and precipitation excess. The simulated water balance for the period 1961-1987 was compared with those simulated with two climate change scenario schemes: one is based on increased temperature and the other on both increased temperature and increased precipitation.
Response of water use efficiency to summer drought in boreal Scots pine forests in Finland
Biogeosciences Discussions, 2016
The influence of drought on plant functioning has received considerable attention in recent years, although our understanding of the response of carbon and water coupling in terrestrial ecosystems remains unclear. In this study, we investigated the response of water use efficiency to summer drought in boreal forests at daily time scales mainly using eddy covariance flux data. In addition, simulation results from the JSBACH land surface model were evaluated against the observed results. Two Scots pine (<i>Pinus sylvestris</i>) sites at Hyytiälä (southern Finland) and Sodankylä (northern Finland) were used in the study. Based on observed data, the ecosystem level water use efficiency (EWUE) showed a decrease only during a severe soil moisture drought at Hyytiälä, whereas the inherent water use efficiency (IWUE) increased when there was a severe soil moisture drought at Hyytiälä and a moderate soil moisture drought at Sodankylä. This indicates a decrease in surface conducta...
Silva Fennica, 2010
This study considered how climate change affects the accumulation of snow, the soil moisture and soil frost at sites without tree cover in boreal conditions in Finland (60°-70°N). An increase of 4.5 °C in annual mean temperature and 20 % in annual precipitation were assumed for Finland by the year 2100 according to A2 emission scenario. Along with climate, the soil type of the permanent inventory plots of the Finnish National Forest Inventory was used. Soil and climate data were combined by using a process-based ecosystem model. Calculations were done for four periods: current climate (1971-2000), near future (2001-2020), mid-term future (2021-2050) and long-term future (2071-2100). According to our simulations, the average monthly duration and depth of snow decreased over the simulation period. However, the increasing precipitation may locally increase the snow depths in the mid-term calculations. In the autumn and winter, the average volumetric soil moisture content slightly increased in southern Finland during the near future, but decreased towards the end of the century, but still remained on a higher level than presently. In northern Finland, the soil moisture in the autumn and winter increased by the end of this century. In the summertime soil moisture decreased slightly regardless of the region. Throughout Finland, the length and the depth of soil frost decreased by the end of the century. In the south, the reduction in the depth was largest in the autumn and spring, while in the midwinter it remained relatively deep in the middle of the century. In the north, the depth tended to increase during the first two calculation periods, in some areas, even during the third calculation period (2071-2100) due to reduced insulation effects of snow during cold spells. The wintertime increase in soil moisture and reduced soil frost may be reflected to reduced carrying capacity of soil for timber harvesting.
Ecological Modelling, 2010
An integrated process-based model was used to study how the changing climate affects the availability of water and nitrogen, and consequently the dynamics of productivity of Norway spruce (Picea abies) on sites with different initial soil water conditions in southern Finland over a 100-year period. The sensitivity of the total stem volume growth in relation to short-term availability of water and nitrogen was also analyzed. We found that a high proportion (about 88-92%) of the total precipitation was lost in total evapotranspiration (incl. canopy evaporation (E c ), transpiration (E t ) and ground surface evaporation (E g )), under both current and changing climate. Furthermore, under the changing climate the cumulative amount of E c and E g were significantly higher, while E t was largely lower than under the current climate. Additionally, the elevated temperature and increased expansion of needle area index (L) enhanced E c . Under the changing climate, the increasing soil water deficit (W d ) reduced the canopy stomatal conductance (g cs ), the E t , humus yield (H, available nitrogen source) and nitrogen uptake (N up ) of the trees. During the latter phases of the simulation period, the canopy net photosynthesis (P nc ) was lower due to the reduced N up and soil water availability. This also reduced the total stem volume production (V s ) on the site with the lower initial soil moisture content. The growth was slightly more sensitive to the change in precipitation than to the change in nitrogen content of the needles, when the elevated temperature was assumed. According to our findings, drought stress episodes may become more frequent under the changing climate. Thus, adaptive management strategies should be developed to sustain the productivity of Norway spruce in these conditions, and thus, to mitigate the adverse impacts of climate change.
Agricultural and Forest Meteorology, 2017
Planted even-aged forests dominated by Norway spruce (Picea abies) progressively replaced mixed natural forests in large parts of Central Europe during past centuries due to the productivity-motivated preferences of forest owners. These managed forests have become vulnerable to climate change, specifically to increasingly severe drought. To evaluate the response of trees to warming, we collected samples from a randomized landscape inventory grid of 7 × 7 km to account for spatial gradients in climate/growth interactions in the entire forested part of the Czech Republic. The purely climate-driven forward growth model − Vaganov-Shashkin "Lite" − was calibrated by real (observed) radial growth series to identify a course of climatic limiting factors on an intraannual scale. Relative proportions of moisture and temperature limited parts of total tree-ring width were determined as well as trends in limiting conditions over the period 1940-2012 and along the elevation gradient. Significant match between modelled and observed growth was shown in 47% of the grid cells. The coherence between modelled and observed site series was significantly improved when individual grid cells were aggregated into elevation belts. In grid cells below 600 m, from 51 to 58% of tree-ring width was formed under moisture-limited conditions, with the proportion of growth under optimal conditions being minimal. The effect of drought stress was outweighed by earlier spring onset of growth, resulting in positive trends in total tree-ring width above 500 m. About 26% of tree-ring growth has occurred under optimal climatic conditions at elevations above 800 m, where, moreover, 45% of total annual growth was temperature limited. Except for one mediumelevation belt, the proportion of growth under moisture-limited conditions significantly increased during the period analysed. Recent warming and increasing frequency of drought events deepened the divergence in growth trends between low-elevation areas and stands at medium and high elevations.
Water use by Swedish boreal forests in a changing climate
Functional Ecology, 2015
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The impact of soil moisture on stem growth of spruce forest during a 22-year period
Forest Ecology and Management, 2002
The relationship between tree growth and water availability for a Norway spruce stand has been studied during a 22-year period at a forest in southern Sweden. The results suggested that shortage of soil water has a strong effect on tree growth in an area of southern Sweden with generally high precipitation. Trees growing on sites with deeper groundwater levels showed a larger between-year variation in simulated water stress and stem growth. Furthermore, the larger leaf area caused larger interception and transpiration losses, leading to severer water stress. Simulated yearly stand transpiration increased from 120 to 370 mm, interception losses from tree canopies increased from 160 to 550 mm and soil evaporation decreased from 130 to 20 mm as leaf area index (LAI) increased from 1.5 to 8.5 during a 15-year period. A plot with a large soil moisture content may suffer from continuous but relatively small water stress because of large soil resistance against tree water uptake. On the other hand, this type of soil was shown to resist water de®cit during extreme dry periods and to be less sensitive to a lowering of the groundwater level. Simulation of water stress for a common mature spruce forest in southern Sweden for the period from 1975 to 1997 showed that the reports of forest damage emerged following summers with large water stress and that the water stress during the mid-1970s and early 1980s was more severe than that which occurred during the late 1980s and 1990s.