We used a gap-type forest ecosystem model to study how even- and uneven-aged management affected the carbon dynamics and timber production in boreal Norway spruce stands. In business-as-usual management, the intensity of thinnings (from below) and single-tree selective cuttings followed those recommended for even-aged (BT) and uneven-aged management (BSC) in practical forestry in Finland. Moreover, higher or lower basal area thresholds, and shorter or longer production cycles, were used in simulations. We found that, the mean annual carbon uptake, volume growth, and carbon stock in trees and harvested timber, were nearly the same under even-aged (BT) and uneven-aged (BSC) management, when assuming full seed crop in latter one. However, the carbon stock in the soil and ecosystem and the mean annual net ecosystem exchange were slightly smaller under BT. The carbon retention time was longer under BSC. The net present value (NPV with interest rate of 3 per cent) of timber production was clearly lower under BT, when the calculation was initiated at planting on clear-cutting area, in opposite to when initiating calculation a few years before the second thinning. Higher basal area thresholds and longer production cycles increased carbon stocks, carbon retention and timber yield, regardless of management system. On the other hand, the results of uneven-aged management (BSC) were very sensitive to the success of natural regeneration and ingrowth of seedlings, as a reduction of the seed crop by 25–75 per cent from the full seed crop decreases the volume growth by 44–74 per cent and timber yield up to 46 per cent.

We investigated how the initial age structure of a managed, middle boreal (62°N), Norway spruce-dominated ( Picea abies L. Karst.) forest area affects the net climate impact of using forest biomass for energy. The model-based analysis used a gap-type forest ecosystem model linked to a life cycle assessment (LCA) tool. The net climate impact of energy biomass refers to the difference in annual net CO 2 exchange between the biosystem using forest biomass (logging residues from final felling) and the fossil (reference) system using coal. In the simulations over the 80-year period, the alternative initial age structures of the forest areas were (i) skewed to the right (dominated by young stands), (ii) normally distributed (dominated by middle-aged stands), (iii) skewed to the left (dominated by mature stands), and (iv) evenly distributed (same share of different age classes). The effects of management on net climate impacts were studied using current recommendations as a baseline with a fixed rotation period of 80 years. In alternative management scenarios, the volume of the growing stock was maintained 20% higher over the rotation compared to the baseline, and/or nitrogen fertilization was used to enhance carbon sequestration. According to the results, the initial age structure of the forest area affected largely the net climate impact of using energy biomass over time. An initially right-skewed age structure produced the highest climate benefits over the 80-year simulation period, in contrast to the left-skewed age structure. Furthermore, management that enhanced carbon sequestration increased the potential of energy biomass to replace coal, reducing CO 2 emissions and enhancing climate change mitigation.

In boreal conditions, climate change is expected to increase mean annual temperature and precipitation, increasing forest growth and productivity in managed forests. In this study, we aimed at finding out how climate change affects the optimal management of Scots pine-, Norway spruce- and silver birch-dominated stands on sites of varying fertility (high-herb, mesic and sub-xeric sites) in the boreal forests of central Finland. The objective function was to maximise net present value (NPV), considering the future incomes from timber sales and costs of forest operations. The results showed that under the gradually changing climate, the optimised management schedules differed from those observed under the current climate. In Norway spruce- and birch-dominated stands, cuttings were done earlier under the changing climate than under the current climate, while in Scots pine-dominated stands they were delayed under the changing climate. The optimised management schedules also varied, depending on tree species and site fertility types. Under the changing climate, both timber production and NPV increased compared to the current climate, regardless of species and site fertility type.

The carbon (C) cycling in semiarid and arid areas remains largely unexplored, despite the wide distribution of drylands globally. Rehabilitation practices have been carried out in many desertified areas, but information on the C sequestration capacity of recovering vegetation is still largely lacking. Using the eddy-covariance technique, we measured the net ecosystem CO2 exchange (NEE) over a recovering shrub ecosystem in northwest China throughout 2012 in order to (1) quantify NEE and its components and to (2) examine the dependence of C fluxes on biophysical factors at multiple timescales. The annual budget showed a gross ecosystem productivity (GEP) of 456 g C m−2 yr−1 (with a 90% prediction interval of 449–463 g C m−2 yr−1) and an ecosystem respiration (Re) of 379 g C m−2 yr−1 (with a 90% prediction interval of 370–389 g C m−2 yr−1), resulting in a net C sink of 77 g C m−2 yr−1 (with a 90% prediction interval of 68–87 g C m−2 yr−1). The maximum daily NEE, GEP and Re were −4.7, 6.8 and 3.3 g C m−2 day−1, respectively. Both the maximum C assimilation rate (i.e., at the optimum light intensity) and the quantum yield varied over the growing season, being higher in summer and lower in spring and autumn. At the half-hourly scale, water deficit exerted a major control over daytime NEE, and interacted with other stresses (e.g., heat and photoinhibition) in constraining C fixation by the vegetation. Low soil moisture also reduced the temperature sensitivity of Re (Q10). At the synoptic scale, rain events triggered immediate pulses of C release from the ecosystem, followed by peaks of CO2 uptake 1–2 days later. Over the entire growing season, leaf area index accounted for 45 and 65% of the seasonal variation in NEE and GEP, respectively. There was a linear dependence of daily Re on GEP, with a slope of 0.34. These results highlight the role of abiotic stresses and their alleviation in regulating C cycling in the face of an increasing frequency and intensity of extreme climatic events.

This paper describes the technical information and performance of a new multi-objective chamber system enabling the control of environmental variables (e.g., temperature, CO2, air humidity, wind speed, and UV-B radiation) for understanding plant responses to climate change. Over a whole growing season, four different climate scenarios were evenly programmed into the system’s 16 chambers as ambient environment (AMB), elevated temperature (ET), elevated CO2 concentration (EC) and elevated temperature and CO2 concentration (ETC). Simultaneously, the chamber effects were assessed regarding the physiological responses and growth of a boreal perennial grass (reed canary grass, Phalaris arundinacea L.). During the growing season, the chamber system provided a wide variety of climatic conditions for air temperature (T a), relative humidity (RH) and CO2 concentration (C a) in the AMB chambers following outside conditions. The target temperature (+3.5°C) was achieved to a good degree in the ET and ETC chambers, being on average 3.3°C and 3.7°C higher than ambient conditions, respectively. The target concentration of CO2 (700 ppm) was also well achieved in the EC and ETC chambers, being on average 704 ppm and 703 ppm, respectively. The stable airflow condition inside all of the chambers provided a homogeneous distribution of gases and temperature. The decreases in RH and increases in vapour pressure deficit (VPD) in the elevated temperature chambers were also maintained at a low level. Chamber effects were observed, with some physiological and growth parameters of plants being significantly lower in the AMB chambers, compared to outside conditions. The plant growth was negatively affected by the reduced radiation inside the chambers.

Under elevated atmospheric CO(2) concentrations, soil carbon (C) inputs are typically enhanced, suggesting larger soil C sequestration potential. However, soil C losses also increase and progressive nitrogen (N) limitation to plant growth may reduce the CO(2) effect on soil C inputs with time. We compiled a data set from 131 manipulation experiments, and used meta-analysis to test the hypotheses that: (1) elevated atmospheric CO(2) stimulates soil C inputs more than C losses, resulting in increasing soil C stocks; and (2) that these responses are modulated by N. Our results confirm that elevated CO(2) induces a C allocation shift towards below-ground biomass compartments. However, the increased soil C inputs were offset by increased heterotrophic respiration (Rh), such that soil C content was not affected by elevated CO(2). Soil N concentration strongly interacted with CO(2) fumigation: the effect of elevated CO(2) on fine root biomass and -production and on microbial activity increased with increasing soil N concentration, while the effect on soil C content decreased with increasing soil N concentration. These results suggest that both plant growth and microbial activity responses to elevated CO(2) are modulated by N availability, and that it is essential to account for soil N concentration in C cycling analyses.

The growth of boreal forests in northern Europe is currently limited by a short growing season, low summer temperatures and short supply of nitrogen (Kellomäki et al, 1997; Nohrstedt, 2001; Olsson, 2006). Forest development is expected to be affected by the expected change in climate in response to the rapid increase of greenhouse gases in the atmosphere, particularly carbon dioxide (CO2) (IPCC, 2001). In Finland, the future climate is anticipated to be an increase of 2–7°C in annual mean temperature (T) and an increase of 6–37% in precipitation with a concurrent doubling of CO2 by 2100 (Carter et al. 2002). The increase in T may prolong the growing season and also enhance the decomposition of soil organic matter (SOM), thereby increasing the supply of nitrogen (Melillo et al. 1993; Lloyd & Taylor, 1994). These changes may substantially enhance forest growth, timber yield and the accumulation of carbon (C) in the boreal forests (Giardina & Ryan, 2000; Jarvis & Linder, 2000; Luo et al, 2001; Strömgren, 2001).

The global climate may change considerably in the future due to the rapid and significant increase in greenhouse gases in the atmosphere, especially carbon dioxide (CO2) (PARRY, 2000; IPCC, 2001; CARTER et al., 2002). For example, in boreal conditions, taking as a reference the average conditions for the period 1961–1990, an increase of 2–7°C in annual mean temperature (T) and an increase of 6–37% in precipitation with a concurrent increase in CO2 is forecasted by 2100 (CARTER et al., 2002). These environmental changes will impact on forest ecosystems and their management. In the long run, the increase in T may prolong the growing season and enhance the decomposition of soil organic matter, and thus increase the supply of nitrogen (RAICH and SCHLESINGER, 1992; KIRSCHBAUM, 1994). The expected changes in growing conditions may substantially enhance forest growth, timber yield and accumulation of carbon (C) in the soil and in tree biomass in boreal forests located in northern Europe, where a lack of soil moisture is not typically a limiting factor (KELLOMÄKI et al., 1997b).

Global climate change includes concomitant changes in many components of the abiotic flux necessary for plant life. In this paper, we investigate the combined effects of elevated CO 2 (720 ppm) and temperature (+2 K) on the phytochemistry of three deciduous tree species. The analysis revealed that elevated CO 2 generally stimulated increased carbon partitioning to various classes of phenolic compounds, whereas an increase in temperature had the opposite effect. The combined effects of both elevated CO 2 and temperature were additive, i.e., canceling one another’s individual effects. Obviously, the effects of global climate change on leaf chemistry must simultaneously consider both temperature and CO 2 . If these results are generally applicable, then the counteracting effect of the temperature is likely to play a major role in alpine, boreal, and arctic zones in determining the balance between populations of plants and herbivores.

Volume growth has typically been used as a selection trait of prime importance in forest tree breeding. Less attention has been given to the genetic or phenotypic relationships between the growth or yield and wood density traits. In the above context, we aimed to investigate the phenotypic relationships among different growth, yield, and wood density traits of 20 Norway spruce ( Picea abies (L.) Karst.) clones grown in southeastern Finland, in order to identify whether a high growth rate was associated with low wood density in any of the clones. Compared with growth or yield traits, the wood density traits showed lower phenotypic variations. The phenotypic correlations between growth, yield, and wood density traits were, on average, from moderate to high, suggesting that selection for one trait would simultaneously affect the other traits. Compared with volume production, selection based on stem mass could be more profitable if a clonal stand is managed for pulpwood rather than mechanical wood processing and vice versa; whereas selection for overall wood density alone would reduce both the stem volume and stem mass. However, by compromising the gain or loss in wood density and stem volume, clones with high stem volume and a relatively high wood density could be found.

The objective of this study was to investigate with aid of a hillslope hydrological model (1) how landscape forms and land-use types control runoff generation and nitrogen leaching and (2) how the inevitable simplifications made when representing the entire catchment by a single hillslope (characteristic profile) affect modelled water and nitrogen fluxes. Analysis of the effect of hillslope shape parameters (e.g. length and slope) indicated that in forested hillslopes the modelled nitrogen export had a strong linear relationship with the share of subsurface runoff from the total runoff. The fraction of subsurface runoff, however, showed a non-linear relationship to changes in the profile length and slope. Decrease in length, and increase in slope, lead to a greater fraction of subsurface runoff. The non-linearity in the relationship implies that estimation of both the subsurface fraction and the nitrogen load is distorted when sub-areas producing large fractions of subsurface flow are aggregated with areas generating only little subsurface runoff into a single characteristic profile. In constructing the characteristic profile, aggregation of areas having different forest stand/soil properties causes the upslope drainage areas and the flow pathways to the stream to become distorted. The effects of such distortion were found to be particularly high for ammonium as its behaviour – due to efficient retention in soil – is highly non-linear with respect to the distance from the source area into the stream (i.e. size of buffer zone). In case of nitrate, which was considered not to be retained in soil, the role of groundwater table at the source area (clear-cut) was identified to be a more important control than the buffer zone size. As the upslope parts of a catchment have a significant role in determining the groundwater table at the treatment site, a question arises whether in addition to buffer zones one should also turn the attention upslope of the nitrogen source areas. Clearly patterns of landscape, such as distribution of nitrogen source areas in this study, pose challenges in selecting the spatial description for environmental simulation models. In nutrient leaching models, which easily become complex when based on process descriptions, compromises are needed to trade off between model complexity and the way how realistically landscape is described.

The purpose of this study was to optimize forest management for a forest region (the total area of forest and scrub land 1.54 mill. ha) under changing climate by using the large-scale forestry scenario model MELA and sample plot data from the geo-referenced National Forest Inventory (NFI). The MELA model is based on integrated simulation and optimisation; in the simulation it utilises empirical tree-level models into which the impacts of climate change were introduced by transfer variables derived by using the physiological model FinnFor. Six scenarios with differences in climate and forest management were defined. In simulations, the accelerating tree growth caused by climate change resulted in an increase in maximum sustainable removal of trees at regional level. Changes in regionally optimized forest management were also detected during the analysis period of 30 years; the proportion of thinnings increased because the stands fulfilled the thinning requirements earlier than in the current climate. This study was the first attempt to solve endogenously maximum sustainable timber production and corresponding forest management at the regional level under different climate scenarios. When implemented in the MELA system, which is widely used in Finnish forestry, the transfer variables offer means of disseminating the results from physiological studies to planning of adjustment and mitigation measures under changing climate.

Macronutrients (N, P, K, Ca, Mg, and S) in litter of three primarily spruce (Picea purpurea Masters) (SF), fir (Abies faxoniana Rehder & E. H. Wilson) (FF), and birch (Betula platyphylla Sukaczev) (BF) subalpine forests in western China were measured to understand the monthly variations in litter nutrient concentrations and annual and monthly nutrient returns via litterfall. Nutrient concentration in litter showed the rank order of Ca > N > Mg > K > S > P. Monthly variations in nutrient concentrations were greater in leaf litter (LL) than other litter components. The highest and lowest concentrations of N, P, K, and S in LL were found in the growing season and the nongrowing season, respectively, but Ca and Mg were the opposite. Nutrient returns via litterfall showed a marked monthly pattern with a major peak in October and one or two small peaks in February and/or May, varying with the element and stand type, but no marked monthly variations in nutrient returns via woody litter, reproductive litter, except in May for the BF, and moss litter. Not only litter production but also nutrient concentration controlled the annual nutrient return and the monthly nutrient return pattern. The monthly patterns of the nutrient concentration and return were of ecological importance for nutrient cycling and plant growth in the subalpine forest ecosystems.

Litter production, components and dynamics were investigated and forest floor litter was quantified throughout a whole year in three subalpine forests, dominated by tree species of spruce (SF), fir (FF) and birch (BF), in Western Sichuan, China, in order to understand the key factors that influenced litter production and dynamics. Litterfall in the three forests consisted mainly of leaves, woody litter, reproductive organs and moss. Contribution of leaf litter to the total litterfall was significantly (P < 0.05) greater than that of woody litter, reproductive organs or moss. Regardless of the stands, litterfall exhibited a marked monthly variation with the maximum litterfall peaks occurring in October, with smaller peaks occurring in February for SF and FF, and May for BF. The analysis indicated that tree species, stand density, leaf area index (LAI), stand basal area and stand age were the key factors determining litter production. Meanwhile tree species and phenology controlled the litter dynamics, with wind and snow modifying the litter components and dynamics.

We used a combination of eddy flux, canopy, soil and environmental measurements with an integrated biophysical model to analyze the seasonality of component carbon (C) fluxes and their contribution to ecosystem C exchange in a 50-year-old Scots pine forest (Pinus sylvestris L.) in eastern Finland (62 degrees 47' N, 30 degrees 58' E) over three climatically contrasting years (2000-2002). Eddy flux measurements showed that the growing Scots pine forest was a sink for CO2, with annual net C uptakes of 131, 210 and 258 g C m-2> year-1 in 2000, 2001 and 2002, respectively. The integrated process model reproduced the annual course of daily C flux above the forest canopy as measured by the eddy covariance method once the site-specific component parameters were estimated. The model explained 72, 66 and 68% of the variation in daily net C flux in 2000, 2001 and 2002, respectively. Modeled annual C loss by respiration was 565, 629 and 640 g C m-2 year-1, accounting for 77, 77 and 65% of annual gross C uptake, respectively. Carbon fluxes from the forest floor were the dominant contributors to forest ecosystem respiration, with the fractions of annual respiration from the forest floor, foliage and wood being 46-62, 27-44 and 9-10%, respectively. The wide range in daily net C uptake during the growing season was largely attributable to day-to-day fluctuations in incident quantum irradiance. During just a few days in early spring and late autumn, ecosystem net C exchange varied between source and sink as a result of large daily changes in temperature. The forest showed a greater reduction in gross C uptake by photosynthesis than in C loss by respiration during the dry summer of 2000, indicating that interannual variability in ecosystem net C uptake at this site was modified mostly by summer rainfall and vapor pressure deficit.

The objective was to predict the risk of wind damage at forest edges in Scots pine (Pinus sylvestris), Norway spruce (Picea abies), and birch (Betula spp.) dominated stands in Central Finland. The method used here was to integrate a mechanistic wind damage model and an airflow model with forest database containing information at the tree, stand, and regional levels. Analyses were made for the current forest edges (Case I) and for situations in which new forest edges might be created through clear-cutting: (i) whenever a stand were to reach the minimum acceptable mean diameter and/or stand age (Case II); or (ii) whenever the stand age were to exceed 100 years (Case III). These case studies were used to analyse the number of stands and total area at risk, and length of vulnerable edges for different critical wind speeds and risk probabilities.It was evident that new clear-cuttings did increase the high wind speeds at forest edges, especially in Case II, as compared with the wind speeds at current forest edges (Case I). This local effect was however compensated at regional level by the more intensive cuttings in Case II, since the old stands, which were more vulnerable, were cut and the average tree size at the regional level decreased relative to Case I or III. The overall risk of wind damage at the regional level therefore decreased in Case II in terms of the number of stands and the total area at risk, and also in terms of the length of vulnerable edges. On the other hand, the risk increased at the regional level in Case III relative to Case I or II, because there were still a lot of vulnerable old stands left at the newly created edges. The sensitivity analyses of wind conditions also showed that Norway spruce was more vulnerable in overall than Scots pine under current conditions and birch the least vulnerable (i.e. Norway spruce has risks even in slow wind speeds, while Scots pine and birch have risks at higher wind speeds). Furthermore, Norway spruce was more sensitive than Scots pine under more windy conditions. (C) 2004 Elsevier B.V. All rights reserved.

The effects of elevated CO2 and temperature on the resource allocation pattern and resistance against mammalian herbivores of silver birch (Betula pendula Roth) were studied. Birch seedlings were grown through two growing seasons in closed-top chambers exposed to four different treatments: ambient CO2 and temperature, elevated atmospheric CO2 (700 ppm) and ambient temperature, elevated temperature (+3degreesC above ambient) and ambient CO2, and a combination of elevated CO2 and temperature. After winter hardening of the seedlings, the growth of the seedlings was measured and the concentration of secondary compounds such as phenolics and papyriferic acid determined. The top parts of the stem were fed to hares, and the basal parts of the same stems were offered to voles.Elevated CO2 increased the height and basal diameter of the shoots, shoot biomass and total biomass of the seedlings but did not have any effect on secondary chemistry. Elevated temperature increased the height and shoot biomass, but did not have a significant effect on the total biomass of the seedlings. Elevated temperature decreased the concentration of condensed tannins and their precursor, (+)-catechin, in the top part of the stems, but only the concentration of (+)-catechin in the basal part of the stems. There were no significant interactive effects between CO2 and temperature on phenolics in the stems, while the concentration of papyriferic acid showed significant interaction in the top part of the stems. This indicates high accumulation of papyriferic acid in ambient CO2 under increased temperature. Consequently, elevated temperature increased the resistance of birch against hares, but did not affect the resistance of the basal parts of the same birches to voles. Our results indicate that the predicted climatic change will not necessarily lead to increased browsing damage by the mountain hare and the field vole to silver birch.

Changes in pigment composition and chlorophyll (Chl) fluorescence parameters were studied in 20 year-old Scots pine (Pinus sylvestris L.) trees grown in environment-controlled chambers and subjected to ambient conditions (CON), doubled ambient CO2 concentration (EC), elevated temperature (ambient +2−6 °C, ET), or a combination of EC and ET (ECT) for four years. EC did not significantly alter the optimal photochemical efficiency of photosystem 2 (PS2; Fv/Fm), or Chl a+b content during the main growth season (days 150–240) but it reduced Fv/Fm and the Chl a+b content and increased the ratio of total carotenoids to Chl a+b during the ‘off season’. By contrast, ET significantly enhanced the efficiency of PS2 in terms of increases in Fv/Fm and Chl a+b content throughout the year, but with more pronounced enhancement in the ‘off season’. The reduction in Fv/Fm during autumn could be associated with the CO2-induced earlier yellowing of the leaves, whereas the temperature-stimulated increase in the photochemical efficiency of PS2 during the ‘off season’ could be attributed to the maintenance of a high sink capacity. The pigment and fluorescence responses in the case of ECT showed a similar pattern to that for ET, implying the importance of the temperature factor in future climate changes in the boreal zone.

Sixteen 20-year-old Scots pine (Pinus sylvestris L.) trees growing in the field were enclosed for 4 years in environment-controlled chambers that maintained: (1) ambient conditions (CON); (2) elevated atmospheric CO2 concentration (ambient + 350 mumol mol(-1); EC); (3) elevated temperature (ambient +2-6 degreesC; ET); or (4) elevated CO2 and elevated temperature (ECT). The dark respiration rates of 1-year-old shoots, from which needles had been partly removed, were measured over the growing season in the fourth year. In all treatments, the temperature coefficient of respiration, Q(10), changed with season, being smaller during the growing season than at other times. Respiration rate varied diurnally and seasonally with temperature, being highest around mid-summer and declining gradually thereafter. When measurements were made at the temperature of the chamber, respiration rates were reduced by the EC treatment relative to CON, but were increased by ET and ECT treatments. However, respiration rates at a reference temperature of 15 degreesC were reduced by ET and ECT treatments, reflecting a decreased capacity for respiration at warmer temperatures (negative acclimation). The interaction between season and treatment was not significant. Growth respiration did not differ between treatments, but maintenance respiration did, and the differences in mean daily respiration rate between the treatments were attributable to the maintenance component. We conclude that maintenance respiration should be considered when modelling respiratory responses to elevated CO2 and elevated temperature, and that increased atmospheric temperature is more important than increasing CO2 when assessing the carbon budget of pine forests under conditions of climate change. (C) 2003 Annals of Botany Company.