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A 6–9 month backward time shift of the carbon uptake gave the highest correlation between annual biomass increment and carbon uptake in this old even aged forest. Plants’ carbon uptake and allocation to different biomass compartments is an important process for both wood production and climate mitigation. Measurements of the net ecosystem carbon dioxide exchange between ecosystems and the atmosphere provide insights into the processes of photosynthesis, respiration and accumulation of carbon over time, and the increase in woody biomass can be assessed by allometric functions based on stem diameter measurements. The fraction of carbon allocated to radial stem growth varies over time, and a lag between carbon uptake and growth can be expected. The dynamics of non-structural carbohydrates and autotrophic and heterotrophic respiration are key mechanisms for understanding this lag effect. In this study, a 9-year record of carbon flux and tree-ring data from Norunda, Sweden was used to investigate the relationship between net and gross carbon uptake and carbon allocated to growth. The flux data were aggregated to monthly sums. When full 12-month periods of accumulated carbon exchange were successively shifted backwards in time, the highest correlation was found with a 6–9 month shift, showing that a large part of the previous growing season was important for explaining the biomass increment of the following year.

Global forests are the main component of the land carbon sink, which acts as a partial buffer to CO2 emissions into the atmosphere. Dynamic vegetation models offer an approach to making projections of the development of forest carbon sink capacity in a future climate. Forest management capabilities in dynamic vegetation models are important to include the effects of age and species structure and wood harvest on carbon stocks and carbon storage potential. This article describes the introduction of a forest management module in the dynamic vegetation model LPJ-GUESS. Different age- and species-structure setup strategies and harvest alternatives are introduced. The model is used to represent current European forests and an automated harvest strategy is applied. Modelled carbon stocks and fluxes are evaluated against observed data at the continent and country levels. Including wood harvest in simulations increases the total European carbon sink by 32 % in 1991–2015 and improves the fit to the reported European carbon sink, growing stock and net annual increment (NAI). Growing stock (156 m3 ha−1) and NAI (5.4 m3 ha−1 y−1) densities in 2010 are close to reported values, while the carbon sink density in 2000–2007 (0.085 kgC m−2 y−1) is 63 % of reported values. The fit of modelled values and observations for individual European countries vary, but NAI is generally closer to observations when including wood harvest in simulations.

We used eddy-covariance (EC) measurements of net ecosystem exchange (NEE) above canopy to assess the effects of thinning on CO2 fluxes at the ICOS Sweden site Norunda in central Sweden. This forest site consists of mixed pine and spruce stands approx. 100 years old. The thinning during late autumn 2008, performed in a semi-circle from the mast extending 200 m outwards harvested about 25% of the volume. Measurements were conducted from 2007 to 2016 and thus, above canopy fluxes were recorded two years before and eight years after the thinning. We also measured the net flux from the forest floor with automatic chambers in three locations and with below-canopy EC during shorter periods before and after thinning. The chamber measurements during the first part of the growing season after thinning showed strongly enhanced effluxes in the order of 150–250% of the pre-thinning values. These chamber measurements were made on drier places within the thinned area because waterlogging made it impossible to use chambers at all available locations. The below-canopy EC measurements, which had a larger footprint as compared to the chambers, showed less enhanced fluxes (in the order of 35%). This footprint included also wetter areas. The above canopy EC measurements showed a reduction of daytime net flux by approx. 30% during the first summer after thinning. The median growing season fluxes then slowly increased but were not restored to the pre-thinning levels eight years after thinning. There was also a small decrease in growing season ecosystem respiration during the first summer after thinning and with a continued decreasing trend over time. It was concluded that this decrease in respiration was caused by successively decreasing decomposition of coarse organic substrates resulting from the thinning. This respiration decrease over time persisted even under gradual biomass increase, which otherwise would indicate increasing autotrophic respiration. The light-response and respiration models fitted to all data did not show any trends in daytime or nighttime fluxes so the conclusion was that the trends were caused by the thinning and not because of trends in meteorological drivers. The annual values contrasted with the summertime results since only a minor effect was observed on the annual NEE. Both ecosystem respiration and gross primary productivity were reduced as an effect of thinning. We explained the different summertime versus annual effects to be caused by the decrease in ecosystem respiration since respiration is dominating the NEE during non-growing season periods when photosynthesis is very low or even zero. Our results are a strong indication that the NEE of a forest could be maintained over time with harvesting practices that avoids clear-cutting and thereby enhance the total carbon uptake of forests.

Climate change can lead to an increased frequency of extreme weather events, which may induce a decline in tree vitality, rendering the forest more vulnerable to other stress factors. In this study we used the ecosystem model LPJ-GUESS to compare the NPP of boreal conifers on till soil and sandy soil, simulating the growth of Norway spruce during the 21st century using climate model projections corresponding to RCP 8.5. Model runs with and without nitrogen cycling enabled, in combination with two different approaches to implement the dynamics of non-structural carbohydrates (NSC) were compared. The simulations showed that the forest productivity in Sweden is influenced by an interplay between site-specific temperature conditions and precipitation. Local differences in soil conditions can have an impact on the productivity, mediated by soil water and nutrient content. A warmer climate will lead to a longer growing season, but the productivity increase will partly be offset by a higher frequency of drought stress in summer and higher autotrophic respiration in winter. The ecosystem model runs indicated that periods with drought stress can cause low NSC levels, leading to time periods with decreased defence capacity against attacks by secondary agents such as bark beetles. The risks may however not become apparent until the forest stands are middle-aged. The model results are discussed in relation to current forestry practice, with Norway spruce (Picea abies) commonly being planted on dry soils better suited for Scots pine (Pinus sylvestris) in order to reduce moose browsing damage of seedlings, which in the longer term may create a forest landscape more sensitive to spruce bark beetle attacks.

Background The aim of this study was to provide an update of the recent incidence trends of cardia and non-cardia gastric adenocarcinoma in Sweden. Methods Temporal trends in the age-standardised incidence were assessed separately for cardia and non-cardia gastric adenocarcinoma in 1970-2014 among all people in Sweden aged ≥50 years. Data were retrieved from the Swedish Cancer Registry. The log-linear joinpoint regression method was used to identify change points in the incidence trends. The annual percent changes with 95% confidence intervals (CI) were calculated for each segment before and after change points. Results The overall incidence of cardia adenocarcinoma increased during the earlier period of 1970-1988, but was stable during the later period of 1989-2014 (annual percent change: -0.3%, 95% CI: -0.7 to 0.2%). In contrast, in women aged 50-69 years the incidence of cardia adenocarcinoma increased by 6.6% annually (95% CI: 1.9 to 11.5%) during the period 2005 to 2014. The incidence of non-cardia gastric adenocarcinoma decreased by 4.4% per year (95% CI: -4.6 to -4.2%) in 1984-2014 and the decrease was stronger in men aged 70 years or older compared to other groups. Conclusion The incidence of cardia adenocarcinoma is seemingly rapidly increasing in younger women, while it has been stable in other groups during recent years in Sweden. The incidence of non-cardia gastric adenocarcinoma continues to decrease, particularly in older men.

Weather and climate conditions can have large impacts on the outcome of forest management operations: Suboptimal conditions can increase the amount of driving damage to forest ground caused by the heavy machines used for harvesting, forwarding and soil scarification. Planting of tree seedlings is commonly practised after clear cutting, and drought in summer or soil frost uplifting in autumn reduces the likelihood of successful plant establishment. Weather and climate also influence the risk of forest fires and the occurrence and development of pest and pathogens, and thereby the timing suitable for surveillance and countermeasures. In this study, the potential use of seasonal forecasts to support the operational planning of forest management in northern Europe was assessed. The analysis was based on temperature and precipitation data from WFDEI System 4 with 15 ensemble members representing seasonal hindcasts (retrospective predictions) for the period of 1981–2010. The data was used directly and as input to a soil model from which monthly indices of frozen soil and plant water stress were calculated. Relatively low skills were found for most months, and in particular for longer lead times. Highest skill was found for bias corrected temperature of January to March, with one month lead time. The skill was higher for the soil model indices, in particular those related to soil frost, as they are influenced by cumulative processes and the initial model conditions contribute to the skill. Probabilistic forecasts on frozen soil can thus be valuable for planning of which areas to harvest, taking the risk of driving damage to forest soils and forest roads into account.

The challenge of multi-use forestry is to fulfil a range of economic, ecologic and social goals in a sustainable way, accounting for synergies and trade-offs among the ecosystem services provided. Climate changes add to the complexity via effects on forest ecosystem processes, such as primary production and respiration, and also by adding a new goal on the agenda: the role of forests in climate mitigation. In recent years, the generation of climate model projections, representing a range of future scenarios, has enabled the development of strategic decisions in relation to risk management, and created a demand for cross-sectorial adaptation and mitigation processes. In this ecosystem model study we address these issues from the perspective of Swedish forest owners, by focusing on climate impacts and forest management effects on the potential harvest level, net income, predisposition to storm damage, biodiversity and carbon storage. The objective was to evaluate alternative management strategies, applicable to northern boreal, southern boreal and nemoral conditions. A general finding is that targeted combinations of forest stand management strategies can lead to a higher degree of goal fulfilment at the landscape level than current forest management practice.

A great deal of biodiversity can be found in private forests, and protecting it requires taking into consideration the preferences of key stakeholders. In this study, we examine divergence in stakeholders' preferences for forest attributes across the general public, private non-industrial forest owners and public and private forest officials in Sweden by conducting a discrete choice experiment. Our results indicate that citizens have a positive valuation of biodiversity protection. Moreover, their valuation is statistically significantly higher than those of forest owners. Interestingly, our results suggest that both forest owners and forest officials have a strong orientation towards production, with higher valuation than the general public of the common management practice of even aged stands and clear felling. Even though the Swedish Forestry Act regards production and environmental goals as equally important, we find that forest officials prefer management practices that promote production rather than biodiversity protection.

The uncertain effects of climatic change and changing demands for ecosystem services on the distribution of forests and their levels of service provision require assessments of future land-use change, ecosystem service provision, and how ecosystem service demands may be met. We present CRAFTY-Sweden, an agent-based, land-use model that incorporates land owner behaviour and decision-making in modelling future ecosystem service provision in the Swedish forestry sector. Future changes were simulated under scenarios of socio-economic and climatic change between 2010 and 2100. The simulations indicate that the influence of climatic change (on land productivities) may be less important thanthat of socio-economic change or behavioural differences. Simulations further demonstrate that the variability in land owner and societal behaviour has a substantial role in determining the direction and impact of land-use change. The results indicate a sizeable increase in timber harvesting in coming decades, which together with a substantial decoupling between supply and demand for forest ecosystem services highlights the challenge of continuously meeting demands for ecosystem services over long periods of time. There is a clear need for modelapplications of this kind to better understand the variation in ecosystem service provision in the forestry sector, and other associated land-use changes.

Accurate predictions of net ecosystem productivity (NEPc) of forest ecosystems are essential for climate change decisions and requirements in the context of national forest growth and greenhouse gas inventories. However, drivers and underlying mechanisms determining NEPc (e.g., climate and nutrients) are not entirely understood yet, particularly when considering the influence of past periods. Here we explored the explanatory power of the compensation day (cDOY)-defined as the day of year when winter net carbon losses are compensated by spring assimilation-for NEPc in 26 forests in Europe, North America, and Australia, using different NEPc integration methods. We found cDOY to be a particularly powerful predictor for NEPc of temperate evergreen needleleaf forests (R2=0.58) and deciduous broadleaf forests (R2=0.68). In general, the latest cDOY correlated with the lowest NEPc. The explanatory power of cDOY depended on the integration method for NEPc, forest type, and whether the site had a distinct winter net respiratory carbon loss or not. The integration methods starting in autumn led to better predictions of NEPc from cDOY then the classical calendar method starting 1 January. Limited explanatory power of cDOY for NEPc was found for warmer sites with no distinct winter respiratory loss period. Our findings highlight the importance of the influence of winter processes and the delayed responses of previous seasons' climatic conditions on current year's NEPc. Such carry-over effects may contain information from climatic conditions, carbon storage levels, and hydraulic traits of several years back in time. (Less)

Temperature measurements in trunks and branches in a mature ca. 100 years-old mixed pine and spruce forest in central Sweden were used to estimate the heat storage in the tree biomass. The estimated heat flux in the sample trees and data on biomass distributions were used to scale up to stand level biomass heat fluxes. The rate of change of sensible and latent heat storage in the air layer below the level of the flux measurements was estimated from air temperature and humidity profile measurements and soil heat flux was estimated from heat flux plates and soil temperature measurements. The fluxes of sensible and latent heat from the forest were measured with an eddy covariance system in a tower. The analysis was made for a two-month period in summer of 1995. The tree biomass heat flux was the largest of the estimated storage components and varied between 40 and −35 W m−2 on summer days with nice weather. Averaged over two months the diurnal maximum of total heat storage was 45 W m−2 and the minimum was −35 W m−2. The soil heat flux and the sensible heat storage in air were out of phase with the biomass flux and they reached maximum values that were about 75% of the maximum of the tree biomass heat storage. The energy balance closure improved significantly when the total heat storage was added to the turbulent fluxes. The slope of a regression line with sum of fluxes and storage as independent and net radiation as dependent variable, increased from 0.86 to 0.95 for half-hourly data and the scatter was also reduced. The most significant finding was, however, that during nights with strongly stable conditions when the sensible heat flux dropped to nearly zero, the total storage matched the net radiation very well. Another interesting result was that the mean energy imbalance started to increase when the Richardson number became more negative than ca. −0.1. In fact, the largest energy deficit occurred at maximum instability. Our conclusion is that eddy covariance measurements can function well during stable conditions but that the functioning under strong instabilities might be a so far unforeseen problem.

Monthly averages of ecosystem respiration (ER), gross primary production (GPP) and net ecosystem exchange (NEE) over Scandinavian forest sites were estimated using regression models driven by air temperature (AT), absorbed photosynthetically active radiation (APAR) and vegetation indices. The models were constructed and evaluated using satellite data from Terra/MODIS and measured data collected at seven flux tower sites in northern Europe. Data used for model construction was excluded from the evaluation. Relationships between ground measured variables and the independent variables were investigated. It was found that the enhanced vegetation index (EVI) at 250 m resolution was highly noisy for the coniferous sites, and hence, 1 km EVI was used for the analysis. Linear relationships between EVI and the biophysical variables were found: correlation coefficients between EVI and GPP, NEE, and AT ranged from 0.90 to 0.79 for the deciduous data, and from 0.85 to 0.67 for the coniferous data. Due to saturation, there were no linear relationships between normalized difference vegetation index (NDVI) and the ground measured parameters found at any site. APAR correlated better with the parameters in question than the vegetation indices. Modeled GPP and ER were in good agreement with measured values, with more than 90% of the variation in measured GPP and ER being explained by the coniferous models. The site-specific respiration rate at 10°C (R10) was needed for describing the ER variation between sites. Even though monthly NEE was modeled with less accuracy than GPP, 61% and 75% (dec. and con., respectively) of the variation in the measured time series was explained by the model. These results are important for moving towards operational remote sensing of forest carbon balance across Northern Europe.

Plant canopies affect the canopy micrometeorology, and thereby alter canopy exchange processes. For the simulation of these exchange processes on a regional or global scale, large-scale vegetation models often assume homogeneous environmental conditions within the canopy. In this study, we address the importance of vertical variations in light, temperature, CO2 concentration and humidity within the canopy for fluxes of photosynthesis and transpiration of a boreal coniferous forest in central Sweden. A leaf-level photosynthesis-stomatal conductance model was used for aggregating these processes to canopy level while applying the within-canopy distributions of these driving variables. The simulation model showed good agreement with eddy covariance-derived gross primary production (GPP) estimates on daily and annual timescales, and showed a reasonable agreement between transpiration and observed H2O fluxes, where discrepancies are largely attributable to a lack of forest floor evaporation in the model. Simulations in which vertical heterogeneity was artificially suppressed revealed that the vertical distribution of light is the driver of vertical heterogeneity. Despite large differences between above-canopy and within-canopy humidity, and despite large gradients in CO2 concentration during early morning hours after nights with stable conditions, neither humidity nor CO2 played an important role for vertical heterogeneity of photosynthesis and transpiration.

To adapt to climate change, forest managers request information on management options for obtaining environmental, societal and economic goals. In this study, we assess the potential of adaptive forest management to influence the productivity and storm sensitivity of nemoral and boreal forest. The forest growth across Sweden over the 21st century was simulated by the ecosystem model LPJ-GUESS, comparing four management options: 1) default forest management, 2) shorter rotation period 3) increased fraction of broadleaved trees and 4) continuous cover forestry. The simulations indicated that a management strategy implemented by a majority of forest owners can have a large-scale effect on the standing volume and risk taking. The modelled risk of storm damage, expressed as the combined effect of tree properties, ground frost and wind load, was higher in the southern than in the northern part of the country due to latitudinal variations in all three components. We conclude that whereas the probability of a significant volume loss increase with the age of a forest, the calculated economic loss can be as high in young and mid-age forest stands. To reduce the risk of storm damage and fulfil a variety of management goals, a portfolio of adaptation strategies is needed. It should include active measures such as tree-species mixtures to spread the risks and shorter rotation periods of highly exposed stands, as well as reactive measures such as salvage and sanitary cutting to reduce the risk of subsequent spruce bark beetle outbreaks.

To the Editor,The Swedish patient registry has been a valuable resource for research since 1964, but it is important to validate the completeness and accuracy of the recorded data. The recording of...

Satellite sensor-derived data are suitable for regional estimations of several important biophysical variables. Data with a finer spatial resolution should improve regional estimations of GPP (gross primary productivity), since they better capture the variation in a heterogeneous landscape. The main objective of this study was to investigate if MODIS 500 m reflectance data can be used to drive empirical models for regional estimations of GPP in Nordic forests. The performance of the proposed models was compared with the MODIS 1 km GPP product. Linear regression analyses were made on 8-day averages of eddy covariance GPP from three deciduous and ten coniferous sites in relation to MODIS 8-day composite data and 8-day averages of modeled incoming PPFD (photosynthetic photon flux density). Time series of EVI2 (two-band enhanced vegetation index) were calculated from MODIS 500 m reflectance data and smoothed by a curve fitting procedure. For most sites, GPP was fairly strongly to strongly related to the product of EVI2 and PPFD (Deciduous: R2 = 0.45–0.86, Coniferous: R2 = 0.49–0.90). Similar strengths were found between GPP and the product of EVI2 and MODIS 1 km daytime LST (land surface temperature) (R2 = 0.55–0.81, 0.57–0.77) and between GPP and EVI2, PPFD and daytime LST in multiple linear regressions (R2 = 0.73–0.89, 0.65–0.93). One year of data was collected from all coniferous sites to derive a general empirical model for GPP versus (1) the product of EVI2 and PPFD (R2 = 0.70), (2) the product of EVI2 and daytime LST (R2 = 0.62) and (3) EVI2, PPFD and daytime LST (R2 = 0.72). These three models were then validated at six sites for the remaining years by linearly relating eddy covariance GPP to modeled GPP, which resulted in fairly strong to strong relationships for most sites (R2 = 0.49–0.91, RMSE = 0.63–1.22 g C m− 2 day− 1, R2 = 0.53–0.73, RMSE = 0.90–1.43 g C m− 2 day− 1, R2 = 0.56–0.87, RMSE = 0.79–1.11 g C m− 2 day− 1). In comparison, similar validation strengths were found for the latest collection 5.1 of the MODIS 1 km GPP product (R2 = 0.59–0.88, RMSE = 0.80–1.16 g C m− 2 day− 1). The main conclusion is that the suggested empirical models driven by MODIS 500 m reflectance data can be used for regional estimations of Nordic forest GPP, while preserving a finer resolution than the MODIS 1 km GPP product.

The DO3SE (Deposition of O3 for Stomatal Exchange) model is an established tool for estimating ozone (O3) deposition, stomatal flux and impacts to a variety of vegetation types across Europe. It has been embedded within the EMEP (European Monitoring and Evaluation Programme) photochemical model to provide a policy tool capable of relating the flux-based risk of vegetation damage to O3 precursor emission scenarios for use in policy formulation. A key limitation of regional flux-based risk assessments has been the assumption that soil water deficits are not limiting O3 flux due to the unavailability of evaluated methods for modelling soil water deficits and their influence on stomatal conductance (gsto), and subsequent O3 flux. This paper describes the development and evaluation of a method to estimate soil moisture status and its influence on gsto for a variety of forest tree species. This DO3SE soil moisture module uses the Penman-Monteith energy balance method to drive water cycling through the soil-plant-atmosphere system and empirical data describing gsto relationships with pre-dawn leaf water status to estimate the biological control of transpiration. We trial four different methods to estimate this biological control of the transpiration stream, which vary from simple methods that relate soil water content or potential directly to gsto, to more complex methods that incorporate hydraulic resistance and plant capacitance that control water flow through the plant system. These methods are evaluated against field data describing a variety of soil water variables, gsto and transpiration data for Norway spruce (Picea abies), Scots pine (Pinus sylvestris), birch (Betula pendula), aspen (Populus tremuloides), beech (Fagus sylvatica) and holm oak (Quercus ilex) collected from ten sites across Europe and North America. Modelled estimates of these variables show consistency with observed data when applying the simple empirical methods, with the timing and magnitude of soil drying events being captured well across all sites and reductions in transpiration with the onset of drought being predicted with reasonable accuracy. The more complex methods, which incorporate hydraulic resistance and plant capacitance, perform less well, with predicted drying cycles consistently underestimating the rate and magnitude of water loss from the soil. A sensitivity analysis showed that model performance was strongly dependent upon the local parameterisation of key model drivers such as the maximum gsto, soil texture, root depth and leaf area index. The results suggest that the simple modelling methods that relate gsto directly to soil water content and potential provide adequate estimates of soil moisture and influence on gsto such that they are suitable to be used to assess the potential risk posed by O3 to forest trees across Europe.

The maximum light use efficiency (LUE = gross primary production (GPP)/absorbed photosynthetic photon flux density (aPPFD)) of plant canopies has been reported to vary spatially and some of this variation has previously been attributed to plant species differences. The canopy nitrogen concentration [N] can potentially explain some of this spatial variation. However, the current paradigm of the N-effect on photosynthesis is largely based on the relationship between photosynthetic capacity (A(max)) and [N], i.e., the effects of [N] on photosynthesis rates appear under high PPFD. A maximum LUE-[N] relationship, if it existed, would influence photosynthesis in the whole range of PPFD. We estimated maximum LUE for 14 eddy-covariance forest sites, examined its [N] dependency and investigated how the [N]-maximum LUE dependency could be incorporated into a GPP model. In the model, maximum LUE corresponds to LUE under optimal environmental conditions before light saturation takes place (the slope of GPP vs. PPFD under low PPFD). Maximum LUE was higher in deciduous/mixed than in coniferous sites, and correlated significantly with canopy mean [N]. Correlations between maximum LUE and canopy [N] existed regardless of daily PPFD, although we expected the correlation to disappear under low PPFD when LUE was also highest. Despite these correlations, including [N] in the model of GPP only marginally decreased the root mean squared error. Our results suggest that maximum LUE correlates linearly with canopy [N], but that a larger body of data is required before we can include this relationship into a GPP model. Gross primary production will therefore positively correlate with [N] already at low PPFD, and not only at high PPFD as is suggested by the prevailing paradigm of leaf-level A(max)-[N] relationships. This finding has consequences for modelling GPP driven by temporal changes or spatial variation in canopy [N].

Disturbance of ecosystems is a major factor in regional carbon budgets, and it is believed to be partly responsible for the large inter-annual variability of the terrestrial part of the carbon balance. Forest fires have so far been considered as the most important disturbance but also other forms of disturbance such as insect outbreaks or wind-throw might contribute significantly to the largely unexplained inter-annual variability, at least in specific regions. The effect of wind-throw has not yet been estimated because of lack of data on how carbon fluxes are affected. The Gudrun storm, which hit Sweden in January 2005, resulted in ca. 66 million m(3) of wind-thrown stem wood on an area of ca. 272 000 ha. Using a model (BIOME-BGC) calibrated to CO2 flux measurements at two sites, the annual net ecosystem productivity during the first year after the storm was estimated to be in the range -897 to -1259 g C m(-2) yr(-1). This is a much higher loss compared with harvested (clear-cut) forests in Europe, which ranged between ca. -420 and -100 g m(-2) yr(-1). The reduction in the carbon sink scaled to the whole wind-thrown area was estimated at ca. 3 million tons C during the first year. By historical data on wind-throw in Europe combined with modelling, we estimated that the large Lothar storm in 1999 reduced the European carbon balance by ca. 16 million tons C, this is ca. 30% of the net biome production in Europe. We conclude that the impact of increased forest damage by more frequent storms in future climate change scenarios must be considered and that intermittent large wind-throw events may explain a part of the large inter-annual variability in the terrestrial carbon sink. (Less)

This study analyses the effects of thinning on stand transpiration in a typical mixed spruce and pine forest in the southern boreal zone. Studies of transpiration are important for models of water, energy and carbon exchange, and forest management, like thinning, would change those processes. Tree transpiration was measured by the tissue heat-balance sapflow technique, on a reference plot and a thinning plot situated in a 50-year-old stand in central Sweden. Sapflow was measured during one season (1998) on both plots before thinning, to establish reference values. In winter 1998/1999 24% of the basal area was removed from the thinning plot. Thinning was done so as to preserve the initial species composition and the size distribution. The measurements continued after thinning during the growing seasons of 1999 and 2000. The climate showed remarkable differences between the 3 years; 1998 was wet and cool, with frequent rain, and the soil-water content was high throughout the year. In contrast, 1999 was dry and warm, and the soil-water content decreased to very low values, ca. 5-6% by volume. In 2000, the weather was more normal, with variable conditions. Stand transpiration was similar on both plots during the year before thinning; the plot to be thinned transpired 6% more than the reference plot. After thinning, transpiration was initially ca. 40% lower on the thinned plot, but the difference diminished successively. When the following drought was at its worst, the thinned plot transpired up to seven times more than the reference plot. During the second season after thinning, the thinned plot transpired ca. 20% more than the reference plot. The increased transpiration of the thinned plot could not be attributed to environmental variables, but was most probably caused by changes in biological factors, such as a fertilization effect. (Less)

This paper develops a statistical model for daily gross primary production (GPP) in boreal and temperate coniferous forests. The model applies the light use efficiency (LUE) approach, which estimates the conversion efficiency of daily absorbed photosynthetically active radiation (APAR) into daily GPP as a product of potential LUE and modifying factors. The latter were derived from daily total APAR and daily mean temperature, vapour pressure deficit (VPD) and soil water content (SWC). Modelling data came from five European eddy covariance measurement towers over 2-8 years. The model was tested against independent data from two AmeriFlux stations. The model with the APAR, temperature and VPD modifiers worked well in almost all the site-year combinations, but the SWC modifier only improved the fit in few cases. Geographical variation was found in the modifiers and potential LUE in site-specific models. When a model was fitted to pooled data, differences between sites could be explained by potential LUE, leaf area and environmental conditions. The test against the AmeriFlux data corroborated this finding. The potential LUE varied from 1.9 to 3.1 g C MJ(-1), and a weak correlation was found between foliar nitrogen concentration and potential LUE. Some year-to-year variation remained which could be captured by neither the pooled nor the site-specific models. (Less)

A model for estimating net primary production (NPP) across Scandinavia has benn developed. The model is based on the light-use efficiency (LUE) concept, where NPP is calculated as a product of the amount of absorbed photosynthetically active radiation (APAR) and a LUE-factor ( e ) controlling the efficiency by which vegetation transforms photosynthetically active radiation (PAR) into biomass. The fractional APAR (FAPAR) is obtained by a linear transformation of 250 m normalized difference vegetation index (NDVI) data from the Moderate Resolution Imaging Spectroradiometer (MODIS). Prior to the transformation, the NDVI time series were seasonally adjusted by fitting local asymmetric Gaussian curves to the data thereby minimizing cloud contamination and other noise factors such as BRDF-related variation. The APAR is then calculated as a product of FAPAR and incident PAR, where the latter is obtained from the “Swedish Regional Climate Modelling Programme” (SWECLIM). The LUE-factor is modeled as a daily function of temperature, latitude, and day of the year (DOY). The FAPAR dataset was validated against measurements of fractional intercepted PAR (FIPAR) that were carried out at Norunda experimental site in central Sweden (60°5′N, 17°29′E) between August and October, 2001. The calculated FAPAR time series are in good agreement with the measurements. The modeled NPP is evaluated against flux measurements carried out in Norunda 1997–1999. The determination coefficients obtained when comparing modeled with measured data are R 2 = 0.82 for 2000 (RMSE = 2.71 g C m −2 d −1 ), and R 2 = 0.68 for 2001 (RMSE = 3.57 g C m −2 d −1 ) (time series averaged every 10th day).

Detailed information from the Swedish National Forest Inventory was used to simulate the carbon balance for Sweden by the process-based model Biome-BGC. A few shortcomings of the model were identified and solutions to those are proposed and also used in the simulations. The model was calibrated against CO2 flux data from 3 forests in central Sweden and then applied to the whole country divided into 30 districts and 4 age classes. Gross primary production (GPP) ranged over districts and age classes from 0.20 to 1.71 kg C m−2 y−1 and net ecosystem production (NEP) ranged from −0.01 to 0.44. The 10- to 30-year age class was the strongest carbon sink because of its relatively low respiration rates. When the simulation results were scaled up to the whole country, GPP and NEP were 175 and 29 Mton C y−1, respectively, for the 22.7 Mha of forests in Sweden. A climate change scenario was simulated by assuming a 4°C increase in temperature and a doubling of the CO2 concentration; GPP and NEP then increased to 253 and 48 Mton C y−1, respectively. A sensitivity analysis showed that at present CO2 concentrations NEP would peak at an increase of 5°C for the mean annual temperature. At higher CO2 levels NEP showed a logarithmic increase.

The aim of this study was to analyse the relationship between different biometric parameters and sapflow and growth, respectively, in order to assess their potential for use in scaling. The effect of thinning on these relationships was also investigated. The studied stand consisted of Scots pine (ca. 60%), Norway spruce (ca. 35%) and downy birch (ca. 5%). Sapflow was measured by the tissue heat-balance method, and growth in circumference was measured by dendrometer bands, during a 3-year period. The thinning was carried out after 1 year of measurements. Regressions were calculated between sapflow and growth and tree diameter, needle mass estimated by allometry, and a competition index (CI), which depended on the distance and diameter of neighbouring trees. Both sapflow and growth were affected by strip-roads from a thinning ca. 8 years earlier. Before thinning, the variation in sapflow for spruce was best explained by CI when trees close to a strip-road were excluded; for pine, needle mass was equally as good as CI. In 1999 and 2000, needle mass generally explained the variation in sapflow best. Before thinning, the variation in pine growth was explained almost as well by diameter alone, as by CI. For spruce, needle mass explained most of the variation if all trees were included. If trees beside strip-roads were excluded, r(2) for CI increased and CI explained the variation best. Almost all spruces close to strip-roads had lower growth than was expected from their CI relationships; for pine, 13 of 23 trees had higher growth than expected. For the years after thinning, diameter was mostly at least as good as the other variables for predicting BA growth. It was concluded that a competition index is potentially useful for scaling, and that strip-roads affected both sapflow and growth of nearby trees. This should be considered in sampling design as well as in scaling up to stand level. (C) 2003 Elsevier B.V. All rights reserved. (Less)

Variation in transpiration and conductance between individual trees of Scots pine and Norway spruce was investigated in a mixed 50-year-old stand in central Sweden. Daily transpiration rates were measured by the tissue heat balance method on five trees of each species during a dry, warm growing season. Daytime averages of sapflow, climatic variables and soil water content were used to fit an empirical model of tree conductance for each tree. Conductance per unit needle area was about twice as high in pine as in spruce, while equal-sized trees transpired similarly in both species. Conductance generally decreased more steeply with increasing vapour pressure deficit and increased faster with increasing light in pine than in spruce, although one individual spruce behaved more like the pines. Inclusion of a linear or exponential function for air temperature improved the model for pine, but of the spruces, only one tree showed a clear temperature dependency. The response to decreasing soil water content varied widely; the spruces tended to be more sensitive to drought than the pines. When the drought was at its worst, no sapflow could be detected in some of the trees. On average, the reduction in transpiration began when ca. 80% of the extractable water in the rooting zone had been depleted.

The electricity market reform in Sweden has had great, but little discussed, consequences for the district heating industry. Formerly regulated municipal district heating companies are now obliged to operate in a commercial manner and pricing, previously regulated by the Local Authority Act, is now free. The Swedish Competition Authority has on several occasions mentioned to the Government that a price regulation ought to be reinstated, since district heating is (?) a natural monopoly and in many cases in a dominant market position on local heating markets. The Competition Authority also believes that cross-subsidies occur in multi service utilities, i.e. between monopolistic district heating and competitive electricity production and sales. Municipal district heating is often organised together with electricity sales and production in a municipally owned limited company. Many municipalities have recently sold their energy utilities to private or state owned commercial actors, thus creating private monopolies exempt from price regulations. In 1999 the National Energy Administration (STEM) was given the task to monitor the district heating market and to suggest means to come to terms with these issues. STEM does not favour a price regulation as the first measure. STEM also has an operative goal of increasing the use of district heating as a means of reducing electricity dependence in the heating of premises. Here, an interesting conflict of interest exists between the two government authorities. We argue that the differences in opinion go beyond the actual tasks given to the authorities, but rather depend on perspectives: economics and consumer perspective versus an engineering, environmental and production perspective. We would also like to encourage a broad discussion about the state of district heating and its regulatory condition and that neither economical models nor energy models are taken for granted.

Wind is the dominant agent of damage in forests in Western Europe. Traditional winddamage models calculate a probability for damage or a critical wind speed at which damage occurs. However, in a dynamic vegetation model actual damage to stands and individual trees is needed to get a dynamical progression of the vegetation. We present a prototype for a new approach to modelling forest wind damage at the regional scale, which we incorporate within a dynamic vegetation model. The approach is based on knowledge from both empirical and mechanical models and calculates the damaged fraction of a cohort based on wind load and a sensitivity that depends on the current physical state and history of the cohort in relation to the ecosystem. The modelling concept has been developed, calibrated and evaluated for Swedish conditions but can be applicable to other similar areas with minor modification. Because of the stochastic nature of local wind load and the difficulty of describing the stand-level exposure, the ability to explain observed damage at stand level was low. Regional level variation in damage, which more depends on the wind load, was however explained reasonably well (R2 = 0.43). We suggest that this is a useful concept for evaluating alternatives of forest management under different climate scenarios in the process of adaptation to future storm-damage risks.

Six to nine years of net ecosystem carbon exchange (NEE) data from forests in Hyytiälä in Finland, Sorø in Denmark and Norunda in Sweden were used to evaluate the interannual variation in the carbon balance. For half-monthly periods, average NEE was calculated for the night-time data. For the daytime data parameters were extracted for the relationship to photosynthetic active radiation (PAR). The standard deviation of the parameters was highest for Norunda where it typically was around 25% of the mean, while it was ca. 15% for Hyytiälä and Sorø. Temperature was the main controller of respiration and photosynthetic capacity in autumn, winter and spring but explained very little of the interannual variation in summer. A strong correlation between respiration and photosynthesis was also revealed. The start, end and length of the growing season were estimated by four different criteria. The start date could explain some of the variation in yearly total NEE and gross primary productivity (GPP) in Hyytiälä and Sorø, but the average maximum photosynthetic capacity in summer explained more of the variation in annual GPP for all sites than start, end or length of the growing season.DOI: 10.1111/j.1600-0889.2006.00324.x

Data on net CO 2 exchange from eight forests in Denmark, Sweden, Finland and Iceland were used to analyse which factors were controlling photosynthesis and respiration. The forests consisted of different species ranging in climatic condition from temperate to subarctic. Only well mixed conditions were analysed ( u * > 0.3 m s -1 ). The parameters of a light response function showed strong seasonal variations with similar behaviour for all stands except for a beech forest where the development of a vigorous ground vegetation in spring affected the photosynthesis parameters differently as compared to the other forests. The beech forest also showed the highest respiration rates in the earlier part of the growing season in contrast to the other forests that showed maximum values in late part of July. The mean half-monthly nighttime respiration rates were well explained by an equation with one fitting parameter, the respiration rate at 10 °C, with an r 2 = 0.864 for all stands together. The difference between the stands concerning both photosynthesis and respiration parameters were largely explained by the differences in LAI. After normalizing for LAI, the only remaining correlation was between respiration and stand age. These results are promising for application of remote sensing for estimation of respiration as well as gross primary productivity from forests. DOI: 10.1111/j.1600-0889.2007.00330.x

Scenario planning is a commonly used method in order to analyse complex aspects of the energy system. Historically it has been an important tool to prepare for long-term action. Today however, due to the deregulated market, it could be assumed that scenario analysis is abandoned. Maybe more (the only) attention is on short-term action.This paper presents a review over the time period of 1970 to 2010 on scenario-planning articles. The overall purpose is to evaluate how historical scenario studies stand in a situation of today’s deregulated energy markets.Articles surveyed are published in well-respected and internationally well-spread peer-reviewed journals. Focus is put on 1, when, and by whom, articles have been published 2, for what reasons projects have been taken and with what method 3, what aspect that have been in focus. The articles are also analysed in terms of possible use in today’s deregulated situation.Three conclusions are drawn. Firstly, the main use of scenario planning still tends to be a support to political processes. Secondly, three major issues and drivers for change dominate when different aspects of the energy system are analysed in scenario projects: climate change, security in terms of demand/supply and economic development. Thirdly, it is concluded that scenario planning still tend to be of value when analysing the future of the deregulated energy sector in Europe.However, in order to be fully utilized for the future scenario methodology must take into account that energy industry actors are not being controlled by politics as they where during the regulated period. © 2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.QC 20120117

The deregulation of energy industries in combination with internationalization and a changing Europe requires strategic efforts to be undertaken in a different way than earlier. Policy activitites do not control this sector to the same extent as before - corporate strategies and activities have also become important to understand. During 2002 the Royal Swedish Academy of Engineering Sciences engaged more than one hundred experts from industry, government and academia to analyze energy within the project “Energy Foresight - Sweden in Europe”. One part of the project, the structure foresight panel, sketched out four different scenarios that each describes a possible European setting for the energy industries - meaning: corporate action was in the center. In this article the aim is to evaluate the result from that scenario project in hindsight and to compare it with other similar scenario projects in this field.

International audience; Terrestrial ecosystems sequester 2.1 Pg of atmospheric carbon annually. A large amount of the terrestrial sink is realized by forests. However, considerable uncertainties remain regarding the fate of this carbon over both short and long timescales. Relevant data to address these uncertainties are being collected at many sites around the world, but syntheses of these data are still sparse. To facilitate future synthesis activities, we have assembled a comprehensive global database for forest ecosystems, which includes carbon budget variables (fluxes and stocks), ecosystem traits (e.g. leaf area index, age), as well as ancillary site information such as management regime, climate, and soil characteristics. This publicly available database can be used to quantify global, regional or biome-specific carbon budgets; to re-examine established relationships; to test emerging hypotheses about ecosystem functioning [e.g. a constant net ecosystem production (NEP) to gross primary production (GPP) ratio]; and as benchmarks for model evaluations. In this paper, we present the first analysis of this database. We discuss the climatic influences on GPP, net primary production (NPP) and NEP and present the CO2 balances for boreal, temperate, and tropical forest biomes based on micrometeorological, ecophysiological, and biometric flux and inventory estimates. Globally, GPP of forests benefited from higher temperatures and precipitation whereas NPP saturated above either a threshold of 1500 mm precipitation or a mean annual temperature of 10 degrees C. The global pattern in NEP was insensitive to climate and is hypothesized to be mainly determined by nonclimatic conditions such as successional stage, management, site history, and site disturbance. In all biomes, closing the CO2 balance required the introduction of substantial biome-specific closure terms. Nonclosure was taken as an indication that respiratory processes, advection, and non-CO2 carbon fluxes are not presently being adequately accounted for.

International audience; The drought of 2003 was exceptionally severe in many regions of Europe, both in duration and in intensity. In some areas, especially in Germany and France, it was the strongest drought for the last 50 years, lasting for more than 6 months. We used continuous carbon and water flux measurements at 12 European monitoring sites covering various forest ecosystem types and a large climatic range in order to characterise the consequences of this drought on ecosystems functioning. As soil water content in the root zone was only monitored in a few sites, a daily water balance model was implemented at each stand to estimate the water balance terms: trees and understorey transpiration, rainfall interception, throughfall, drainage in the different soil layers and soil water content. This model calculated the onset date, duration and intensity of the soil water shortage (called water stress) using measured climate and site properties: leaf area index and phenology that both determine tree transpiration and rainfall interception, soil characteristics and root distribution, both influencing water absorption and drainage. At sites where soil water content was measured, we observed a good agreement between measured and modelled soil water content. Our analysis showed a wide spatial distribution of drought stress over Europe, with a maximum intensity within a large band extending from Portugal to NE Germany. Vapour fluxes in all the investigated sites were reduced by drought, due to stomatal closure, when the relative extractable water in soil (REW) dropped below ca. 0.4. Rainfall events during the drought, however, typically induced rapid restoration of vapour fluxes. Similar to the water vapour fluxes, the net ecosystem production decreased with increasing water stress at all the sites. Both gross primary production (GPP) and total ecosystem respiration (TER) also decreased when REW dropped below 0.4 and 0.2, for GPP and TER, respectively. A higher sensitivity to drought was found in the beech, and surprisingly, in the broadleaved Mediterranean forests; the coniferous stands (spruce and pine) appeared to be less drought-sensitive. The effect of drought on tree growth was also large at the three sites where the annual tree growth was measured. Especially in beech, this growth reduction was more pronounced in the year following the drought (2004). Such lag effects on tree growth should be considered an important feature in forest ecosystems, which may enhance vulnerability to more frequent climate extremes. (c) 2007 Elsevier B.V. All rights reserved.

International audience; The tissue heat-balance method (Čermák) and the heat-dissipation method (Granier) were compared in three Scots pines and two Norway spruces in a forest in central Sweden. The Granier system measured up to 50% lower sapflow than the Čermák system at high flow rates. New coefficients for the Granier system were estimated, based on sapflow density from the Čermák measurements. Without compensation, natural temperature gradients may cause large errors in measurements made by the Granier system. By using a horizontal reference sensor, no compensation was necessary. It was also shown that radial flow patterns must be considered when calculating total tree sapflow. Transpiration of two adjacent stands, one measured by the Granier method and the other by the Čermák method, showed good agreement internally and with total evaporation measured by the eddy-correlation method.; Évaluation des méthodes des équilibres thermiques et de dissipation thermique concernant la mesure de flux de sève pour le pin et l'épicéa. La méthode des équilibres thermiques (Čermák), et la méthode de dissipation thermique (Granier) ont été comparées pour trois Pins sylvestres et deux épicéas dans une forêt du centre de la Suède. Le système Granier a donné des valeurs de flux de sève jusqu'à 50 % plus faible que le système Čermák pour les flux élevés. De nouveaux coefficients basés sur les mesures de densité de flux obtenues avec le système Čermák ont été estimés pour le système Granier. Le système Granier sans compensation pour les gradients naturels de température dans le tronc peut présenter de larges erreurs, mais si un capteur de référence horizontal est utilisé, les compensations ne sont pas nécessaires. Il a aussi été démontré que les variations radiales de flux doivent être prises en compte lors des calculs de flux de sève pour l'arbre entier. Les transpirations de deux couverts adjacents, l'un mesuré avec la méthode Granier, et l'autre avec la méthode Čermák, sont en accord entre elles et avec l'évaporation totale mesurée par la méthode des corrélations turbulentes.