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Short-term effect of thinning on the carbon budget of young and middle-aged Scots pine (Pinus sylvestris L.) stands
Abstract
Thinning is the main silvicultural method for improving stand growth and wood quality, however, despite the relevance and extensive use of thinning in forest management, its effect on stand carbon (C) balance is still poorly studied at the ecosystem level. The present case study estimated the two-year post-thinning effect on the C balance of a pole stand and a middle-aged Scots pine stand growing on mesotrophic sandy soils. Moderate thinning from below reduced the stand C storage by 21–24%, however, the amount of C accumulated in woody biomass, which was removed by logging, is expected to recover in both stands in the following four years. The reduced biomass of the trees contributed to the decreased annual net primary production (NPP) of the stand by 9–11%. The absolute value of net ecosystem production decreased by 0.9 and 0.7 t C ha⁻¹ yr⁻¹ in the pole and the middle-aged stand, respectively; still, both thinned plots maintained their C sink status. The production of the herbaceous understorey as well as the production of needles increased in the younger stand after thinning, but this could not compensate for C loss at the stand level. The effect of thinning on the production of mosses and dwarf shrubs was not expressed in either stand, probably due to the too short post-thinning period. Thinning did not significantly affect either total soil respiration or the heterotrophic respiration (Rh). However, it increased the contribution of Rh to total soil respiration, which can be attributed to decreased fine root biomass and root respiration, while the aboveground litterfall was not significantly changed after thinning. Fine root production, which accounted for the main belowground litter input, was significantly lower in both thinned plots. Moderate thinning in the pole and the middle-aged Scots pine stand did not change the ecosystem into a C source and the induced C loss will be compensated during a short post-thinning period.
... Fine-root growth has shown great plasticity, with the response to edaphic, climatic, and environmental conditions being species-specific (Förster et al., 2021;Helmisaari et al., 2002;Ostonen et al., 2017). The fine-root biomass (FRB) and FRP are shaped by local conditions, such as stand age, aboveground primary productivity (Förster et al., 2021;Makkonen & Helmisaari, 2001;Yuan & Chen, 2012), and forest management (Aun, Kukumägi, Varik, Becker, Aosaar, Uri, Morozov, et al., 2021). ...
... For comparison, higher values of Scots pine FRP have been obtained from mineral soils in pole (2.28-3.93 t ha −1 year −1 ) and middle-aged (1.69-2.52 t ha −1 year −1 ) stands (Aun, Kukumägi, Varik, Becker, Aosaar, Uri, Morozov, et al., 2021), and 8.60 t ha −1 year −1 in a 100-year-old Scots pine stand on mineral soil (Makkonen & Helmisaari, 2001). In drained peatland sites in Southern Finland, the FRP of Scots pine has been found to be higher in sites with lower nutrient availability. ...
... The same magnitude of estimates for dwarf shrubs were obtained from the drained bog and fen forests in Finland, at 0.68 and 0.27 t ha −1 year −1 , respectively (Bhuiyan et al., 2017). By comparison, considerably lower values of dwarf shrub FRP have been obtained from middle-aged Scots pine stands on mineral soils (0.05-0.11 t ha −1 year −1 ) (Aun, Kukumägi, Varik, Becker, Aosaar, Uri, Morozov, et al., 2021). The undrained Jaunjelgava site had an exceptionally high mean Scots pine FRP, which was at least three times greater than that in the other undrained sites (Table 4). ...
Information on the capacity of organic soils to capture and store carbon in old‐growth forests in the hemiboreal forest zone is scarce and fragmented. However, fine‐root data can provide valuable insights into soil carbon fluxes. Thus, the aim of the current study was to provide estimates of the fine‐root biomass (FRB), fine‐root production (FRP), and fine‐root turnover (FRT) rate by tree species and other functional groups in old‐growth (stand age 131–179 years) forests on mesotrophic organic soils dominated by Scots pine ( Pinus sylvestris L.), with and without the effects of forest drainage. The sequential soil coring method was used to estimate the FRB and FRP. The total FRB was significantly higher in the undrained sites (6.8 ± 0.3 t ha ⁻¹ ) than in the drained sites (3.97 ± 0.1 t ha ⁻¹ ). The FRB of Scots pine in the undrained forest was significantly higher (1.7 ± 0.1 t ha ⁻¹ ) than in the drained forest (0.5 ± 0.1 t ha ⁻¹ ), supporting an extensive foraging strategy. The significantly higher mean FRB of Norway spruce ( Picea abies [L.] Karst.) (1.4 ± 0.1 t ha ⁻¹ ) in the drained sites than the undrained sites (0.7 ± 0.2 t ha ⁻¹ ) can be explained by there being a higher proportion of spruce in the stand compositions, thus a higher standing volume of this species and an increased FRB. The FRB of dwarf shrubs (2.43 ± 0.2 t ha ⁻¹ ) formed the largest part of the total FRB in the undrained sites and the second largest (1.16 ± 0.1 t ha ⁻¹ ), following Norway spruce, in the drained sites. The total FRP was similar between the undrained (2.05 ± 0.31 t ha ⁻¹ year ⁻¹ ) and drained (1.82 ± 0.26 t ha ⁻¹ year ⁻¹ ) stands. However, considerable variability in the FRP was observed between different sites of the same forest site type. The FRT rate of Scots pine was twice as high in the drained sites than the undrained sites, suggesting faster nutrient and carbon input into the drained soil compared with the undrained soil. Estimates of FRB, FRP, and FRT rates for different functional groups can be used in carbon‐cycle modeling and in further calculations to estimate the carbon budget (balance) in forests on organic soils.
... For the P5 stand, FRP was empirically estimated in an earlier study by using the root net method ; for the FRP of dwarf shrubs, an average turnover value of 0.20 yr −1 from the same study was used. The values of fine root production for P25 and P45 originate Aun et al. (2021b). ...
... NEP was obtained by subtracting Rh from NPP (4) (Clark et al., 2001;Lovett et al., 2006;Meyer et al., 2013). Since C leaching in mineral soils is by one order of magnitude smaller than Rh (Becker et al., 2016;Uri et al., 2019;Aun et al., 2021aAun et al., , 2021b, this flux is usually not included in similar studies. ...
... In our study, soil moisture was the second significant factor after Ts. This explained temporal variation in Rh in the P10 and P25 stands among which the soil was the driest in the latter (mean for May-December 7.7%) (Aun et al., 2021b). Nevertheless, soil moisture is usually not a limiting factor for soil respiration in boreal and hemiboreal forests (Pypker and Fredeen, 2003;Payeur-Poirier et al., 2012;Kukumägi et al., 2017;Uri et al., 2019;Kriiska et al., 2019). ...
To evaluate the impact of stand age on the ecosystem's C budget, as well as the post-harvest recovery of the C storages and fluxes, a chronosequence of Scots pine stands from the clear-cut stage up to the age of 110 years was studied. An age-related trend of net primary production (NPP) demonstrated effective C accumulation in the young and middle-aged stands and their levelling out thereafter.
The understorey vegetation contributed 8–46% to total NPP, being lower in the pole and middle-aged stands, but without a clear age related trend. Annual cumulative soil heterotrophic respiration (Rh) demonstrated stable values along the chronosequence, varying between 3.8 and 5.4 t C ha⁻¹ yr⁻¹. The Rh flux of 2.9 t C ha⁻¹ yr⁻¹ at the clear–cut site did not exceed the corresponding value for stands. The NEP along the chronosequence followed the dynamics of the annual biomass production of the trees, peaking at the middle-aged stage and decreasing in the older stands; the NPP of the trees was the main driver directing the dynamics of NEP.
There was no significant correlation between Rh and dynamics of aboveground litter or fine root production, which can partly explain why no relationship was established between annual Rh and stand age.
The total ecosystem C stocks followed the same trend as cumulative tree biomass, peaking in the older stands, however, the soil C stocks varied along the chronosequence irrespective of stand age.
The post-harvest C compensation point was reached at the age of 7-years and C payback occurred at a stand age of 11–12 years. Stands acted as C accumulating ecosystems and average annual C accumulation was around 2.5 t C ha⁻¹ yr⁻¹, except for the youngest stand and the clear-cut area which acted as C sources. In the oldest stand C budget was almost balanced, with a modest annual accumulation of 0.12 t C ha⁻¹ yr⁻¹.
... Moreover, the experiment was conducted with even-aged stands between 40 and 42 years of age. This age range was chosen deliberately because of high thinning intensity in forest stands between 30 and 45 years of age (Aun et al., 2021;Niemistö et al., 2018;Saarinen et al., 2020) when e.g., in the 45-year-old (middle-aged) stands, the thinning intensity could be up to 24% (Aun et al., 2021). Therefore, our findings have significant application potential, especially in forest management practice, because the thinning intensity may not reflect the range of bark stripping damage on Scots pine stands compared to Norway spruce, where the influence of bark stripping has a significant impact on wood production and stand stability (Cukor et al., 2019b;Krisans et al., 2020;Z. ...
... Moreover, the experiment was conducted with even-aged stands between 40 and 42 years of age. This age range was chosen deliberately because of high thinning intensity in forest stands between 30 and 45 years of age (Aun et al., 2021;Niemistö et al., 2018;Saarinen et al., 2020) when e.g., in the 45-year-old (middle-aged) stands, the thinning intensity could be up to 24% (Aun et al., 2021). Therefore, our findings have significant application potential, especially in forest management practice, because the thinning intensity may not reflect the range of bark stripping damage on Scots pine stands compared to Norway spruce, where the influence of bark stripping has a significant impact on wood production and stand stability (Cukor et al., 2019b;Krisans et al., 2020;Z. ...
Bark stripping damage reduces timber quality due to fungal infection and structural defects. Weakened stems may break and induce the death of trees, which strongly affects forest stability. Some tree species, such as Norway spruce (Picea abies [L.] Karst.), are highly susceptible to bark stripping, but Scots pine (Pinus sylvestris L.) has been studied to a lesser extent. The objective of this study was to predict the effect of the degree of bark stripping damage and rot on the production parameters of Scots pine and to determine the influence of climatic factors on various damaged trees. The research was conducted on 15 pine forest stands aged 40–42 years with a numerous sika deer (Cervus nippon nippon) population in the western part of the Czech Republic (425–492 m a.s.l.). The results showed significant differences in tree diameter and volume (but not height) between healthy and extensively damaged trees according to 417 pines measured. However, no differences were found between lightly damaged trees. Similarly, circumference damage did not significantly affect mean tree stem volume, in contrast to previously reported results for Norway spruce. The trees were first damaged by deer at the age of 18.5 years on average. According to the prediction model based on 40 felled and sampled trees, rot did not reach a distance > 50 cm from the site of the bark stripping on the stem, with a mean speed of vertical spreading of 0.9 cm yr⁻¹. Concerning the effect of climatic factors on radial growth (60 core samples taken), the difference between healthy and minor to extensively damaged trees was negligible. However, healthy trees responded more to the effects of temperature, and damaged trees were more sensitive to the precipitation amounts. Scots pine appears to be a suitable tree species for afforestation in areas with high game pressure during continuing climate change.
... In young stands and clear-cut areas, in addition to the dynamics already explored in this article, heterotrophic respiration rates are enhanced. The combination of these factors (stand age, type of management, and heterotrophic respiration rate) tends to result in a negative carbon balance in the forest ecosystems [32]. The indicators of enzymatic activity, soil organic carbon, and water-holding capacity in Mediterranean forests of Pinus halepensis are affected by soil characteristics and climate. ...
The maritime pine (Pinus pinaster) is the main conifer species in Portugal, occurring mainly in the central and northern regions of the country. In addition to its environmental significance, it plays an important socio-economic role, supported by a robust forest sector. In the face of climate change driven by the release of CO2 into the atmosphere, forests play an essential role in mitigating these changes by storing large amounts of carbon in their biomass. This study assesses the impact of forest management, focusing on thinning, on carbon accumulation in naturally regenerating maritime pine forests in the municipality of Boticas, Portugal and compares scenarios with and without forest intervention. To simulate forest growth scenarios, the Modispinaster software is used, and through mathematical models adjusted for the species and input of initial field data, it generates scenarios of forest evolution regarding biomass and carbon accumulation. Additionally, it allows for the visualization of the forest’s dendrometric characteristics throughout the cycle, enabling the creation of the carbon balance and its analysis across multiple scenarios. The results demonstrate that management based on thinning increases carbon retention, reducing early mortality and promoting the growth of larger diameter trees. Although natural forests initially accumulate more carbon, the reduction in competition in managed forests allows for greater carbon accumulation from the 24th year onwards, reaching 178 tons at the end of the cycle, in contrast to 143 tons in unmanaged areas. The carbon balance result in the unmanaged (natural) forest was negative (−18 tons), while in the managed forest, the result was positive (54 tons). This supports the thesis that thinning, although more intense and less frequent than mortality events, is more effective than the absence of interventions. Thinned forests optimize the carbon balance in Pinus pinaster, improving long-term retention by reducing competition and mortality. Managed forests show a positive carbon balance, highlighting the importance of sustainable management in mitigating climate change and strengthening ecological resilience.
... Thinning can lead to biomass redistribution within a stand (Aun et al. 2021). Thinning does not accelerate an accumulation of total standing biomass in all the three species (Fig. 1). ...
This study was conducted to analyze the effect of thinning intensity on biomass within coniferous plantations (Pinus densiflora, Pinus koraiensis, Larix kaempferi) located in Gangwon and North Gyeongsang provinces, South Korea. According to the analytic results, thinning intensity had a strong influence on the biomass storages of individual trees. As the thinning intensity increased, the biomass of individual trees was found to increase, while the total stand biomass decreased. In control plots, total biomass was the greatest, but the majority of stand biomass came from smaller trees in DBH when compared to the thinned plots. Thinning also influenced the increment of stand biomass. In control plots, stand biomass increased the most but the growth rate was the lowest. This study is expected to be useful with basic information for establishing forest management plans to achieve diverse goals including biomass, sawtimber production, and carbon management.
... Yet, higher litter amount due to thinning and more pronounced in fertilized (N+) than in control (CTR) plots ( Fig. 2a and Fig. 2b) may support increased Rh in N+. Although thinning effects on boreal Scots pine Rh are generally modest (Aun et al., 2021), larger inputs of higher-quality litter from harvest residues in N+ plots, including fine roots, needles, and branches, likely stimulated Rh (Liski et al., 2006;. ...
Nutrient availability effects microbial respiration kinetics and their sensitivities to environmental conditions, thus the soil organic C (SOC) stocks. We examined long-term nitrogen (N) addition effects on soil heterotrophic respiration (Rh), methane (CH4) oxidation, and nitrous oxide (N2O) emissions in an N-limited boreal Scots pine (Pinus sylvestris) forest. Measurements included long term 1960–2020 tree biomass monitoring, 2023 SOC, 2021–2023 monthly aboveground litterfall, 2021–2023 growing seasons biweekly CO₂, CH₄, and N₂O fluxes, and quarter-hourly soil temperature (T), and soil water content (SWC) in both control and N-fertilized plots. We assessed mean greenhouse gas (GHG) flux differences and Rh dependence on T and SWC using polynomial and parametric non-linear regression models. Tree biomass, litterfall and SOC increased with long-term N fertilization. However, N fertilization significantly increased mean Rh, reduced CH₄ oxidation slightly, and modestly raised N₂O emissions. SOC-normalized Rh (Rh/SOC) did not significantly differ between treatments, yet relationships between Rh/SOC and T and SWC diverged with fertilization. In control plots, Rh/SOC peaked at 15 °C but increased monotonically with T in N-fertilized plots. Under N fertilization, Rh/SOC was weakly SWC-dependent, contrasting with a distinct humped SWC response in control plots, enhancing annual Rh/SOC. Annually, N-fertilized plots respired 11.2 % of SOC, compared to 12.6 % in controls, suggesting N fertilization promoted SOC retention. Consequently, N fertilization reduced net CO₂ emissions by 262.5 g CO₂ m⁻² year⁻¹, while combined effects on CH₄ and N₂O fluxes and the production energy of N fertilizer contributed a minor CO₂-equivalent increase of 15.8 g CO₂-eq m⁻² year⁻¹. In conclusion, long-term N fertilization in boreal forests could mitigate climate warming by reducing soil GHG emissions, slowing Rh/SOC, and altering its responses to T and SWC, thereby enhancing SOC sequestration in addition to the increased tree biomass carbon sink.
... Some studies have reported that thinning reduces overstory trees, thus increasing sunlight availability and providing more water and mineral nutrients for the forest ecosystem [16,17]. These processes can promote the growth of tree height and DBH, alleviate interspecies competition, and stimulate the biomass increments of both the overstory and understory [18,19], although on occasions some authors have found that there was no such response [9,20]. For example, Liu et al. [21] reported that increased sunlight availability enhances aboveground biomass or productivity for the overstory in pine forests in southern China while simultaneously increasing underground biomass for the understory. ...
Masson pine (Pinus massoniana Lamb.) is a tree species that is widely distributed throughout southern China and holds significant economic and ecological value. The main objective of our study was to assess the effects of thinning on aboveground biomass increments and tree diversity in both the overstory and understory. Additionally, the underlying factors and mechanisms responsible for driving changes in biomass increment were analyzed. Four different thinning treatments (control, light thinning, moderate thinning, and heavy thinning) were implemented in 214 plots (~1800 tree ha−1) in three Masson pine forests in Hunan Province, China. A robustly designed experiment was used with over six years of repeated measurements. The differences in biomass increment and tree diversity among the different treatments were compared using repeated measures ANOVAs. The Mantel test was used to determine environmental metrics correlated with biomass increments across tree strata. Structural equation modeling was utilized to explore the multivariate relationships among site environment, tree diversity, and post-treatment biomass increment. The results indicated that thinning overall increased biomass increment, the Shannon index, and the Gini index, while decreasing the Dominance index over time. Moderate thinning (25%–35% of trees removed) was found to promote overstory biomass increment to 9.72 Mg·ha−1·a−1 and understory biomass increment to 1.43 Mg·ha−1·a−1 six years post-thinning, which is significantly higher than that of other treatments. Environmental metrics such as light intensity, soil organic matter, and other soil physiochemical properties were positively correlated with biomass increments, and their effects on the overstory and understory differed. Structural equation modeling revealed that thinning treatments, environmental metrics, tree diversity, and their interactions could be the main drivers for biomass increments across tree strata. Specifically, thinning treatments, light intensity, and tree size diversity (Gini index) had significant effects on overstory biomass increment, while understory species richness (Shannon index) and soil organic matter affected understory biomass increment. In conclusion, moderate thinning is an effective silvicultural treatment for stimulating biomass increments of both the overstory and understory in Masson pine forests in southern China if a middle period (e.g., six years) is considered. Some factors, such as species richness, tree size diversity, and environmental metrics (e.g., light and soil), are suggested for consideration to improve the efficiency of thinning.
... The biomass C of the tree layer can be determined by the biomass accumulation rate and C density of the tree species. Tree species, community composition, and stand age have marked effects on soil C stocks [31,32] and the persistence of C sequestration [33] . Second, management measures can increase the diameter at breast height, tree height, crown width and stand volume growth of individual trees, increase the number of species, and cover of understory vegetation (Fig. 5); and change the rates of litter decomposition and soil C accumulation, thus affecting the vegetation C stock in tree plantation ecosystems [34,35] . ...
... Aboveground biomass decreased the least after light thinning and late stage (Fig. 2) but was still lower than that of the unthinned stand (Shen et al., 2019). However, some studies have indicated that after a period of recovery, the biomass of thinned stands can recover to the same level as that of unthinned stands (Aun et al., 2021;Meng et al., 2022). We also found that changes in Aboveground biomass were significantly correlated with stand density, recovery age, and thinning intensity (Fig. 7c), which is consistent with previous findings (Zhou et al., 2013). ...
Thinning, a major measure of forest management, is known to alter carbon sequestration by affecting the forest microclimate and soil environmental conditions. However, how thinning effect on forest ecosystem carbon stocks have presented inconsistent results. Therefore, we conducted 1776 pairs of thinning experiment observations worldwide to explore how thinning affects forest vegetation and soil carbon stocks. The results showed that overall thinning significantly increased total tree aboveground biomass carbon stocks (AGC total , +23.9%, +1.3 Mg ha-1 yr-1), understory vegetation carbon stocks (UVC, +68.3%, 0.12 Mg ha-1 yr-1), and soil organic carbon stocks (SOC stocks , +4.8%, 1.0 Mg ha-1 yr-1) at the global, but exhibited significantly decreased carbon stocks of litterfall (LBC,-9.6%,-0.03 Mg ha-1 yr-1). Belowground biomass carbon stocks remained unchanged under thinning. The sensitivity of carbon sequestration to thinning gradually disappeared after 6 years, except for AGC total , as they were jointly subject to stand density and thinning intensity and not just recovery ages. The response to UVC was more positive in medium-density (1500-3000 trees ha-1) and moderately thinned (30-50%) stands, and the thinning effects on UVC and SOC stocks were more noticeable in the subtropical and temperate zones. In summary, thinning enhanced forest ecosystem carbon sinks (+2.4 Mg ha-1 yr-1) but reduced carbon stocks in low-density stands (≤ 1500 trees ha-1). Soil moisture content (SMC, +6.6%) and bulk density (BD,-1.5%) dynamics after thinning were important factors regulating vegetation growth and soil carbon cycling processes.
... According to recent Estonian studies, the FRB and FRP were lower after thinning in Scots pine stands (Aun et al. 2021b). However, in silver birch stands, the respective results were inconsistent (Aun et al. 2021a). ...
Pre-commercial thinning (PCT) is a common silvicultural practice for directing the development of the young stand in Nordic and Baltic countries. However, its impact on the stands carbon (C) cycling is still poorly studied. We carried out a comprehensive case study for estimating net ecosystem production (NEP) in unthinned control plot and in moderately and heavily thinned plots (2,500 and 1,500 trees ha⁻¹ remaining, respectively), in the next growing season after PCT in young Betula pendula stands on mineral soil (Site 1) and Betula pubescens stands on drained organic soil (Site 2). Thus, the study demonstrates post-thinning changes in C cycling in stands of two species of the same genus. The control plots of both sites served as C sinks: NEP 1.5 and 3.6 t C ha⁻¹ yr⁻¹ in Site 1 and Site 2, respectively. However, the thinned plots acted as C sinks on Site 1 (1.8 t C ha⁻¹ yr⁻¹) and as C sources on Site 2 (−1.4 and −3.1 t C ha⁻¹ yr⁻¹ in heavily and moderately thinned plot, respectively). The declined net primary production of trees after PCT was compensated for by the production of herbaceous vegetation and stump sprouts. Soil heterotrophic respiration (Rh) was the largest flux in the C budget of both sites and all treatments. Despite the increasing trend of Rh with increasing thinning intensity on Site 2, no statistically significant difference in the annual Rh flux occurred between the treatments in either site.
... We would like to highlight that branches are just one part of tree canopies and analyses of stem, bark, dead branches, needles, and leaves are needed for a full account of the water capacity of trees. Including the feedback of the overstory on the understory ground vegetation and litter layer (Kunhamu et al. 2009;Sohn et al. 2016;Wang et al. 2019;Aun et al. 2021) will complement our understanding of forest's interception potential for water and air pollutants. Figure A1. ...
... There are no similar comprehensive topsoil phosphorus content databases for other land-use categories available in Estonia. Comparable values of topsoil phosphorus content for other land-use types (forest, wetland, peat extraction areas, and quarries) on different soil types were searched through a literature review of scientific papers [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44], reports [45,46], and the Estonian Environmental Monitoring System and supplemented by original unpublished datasets of the authors. Therefore, the datasets for these landuse categories vary by sample size, sampling, and analysis methods. ...
Phosphorus (P) is a macronutrient that often limits the productivity and growth of terrestrial ecosystems, but it is also one of the main causes of eutrophication in aquatic systems at both local and global levels. P content in soils can vary largely, but usually, only a small fraction is plant-available or in an organic form for biological utilization because it is bound in incompletely weathered mineral particles or adsorbed on mineral surfaces. Furthermore, in agricultural ecosystems, plant-available P content in topsoil is mainly controlled by fertilization and land management. To understand, model, and predict P dynamics at the landscape level, the availability of detailed observation-based P data is extremely valuable. We used more than 388,000 topsoil plant-available P samples from the period 2005 to 2021 to study spatial and temporal variability and land-use effect on soil P. We developed a mapping approach based on existing databases of soil, land-use, and fragmentary soil P measurements by land-use classes to provide spatially explicit high-resolution estimates of topsoil P at the national level. The modeled spatially detailed (1:10,000 scale) GIS dataset of topsoil P is useful for precision farming to optimize nutrient application and to increase productivity; it can also be used as input for biogeochemical models and to assess P load in inland waters and sea.
... The data of the aboveground foliage litter flux, as well as of the total litter flux were gathered from different studies, among them original national projects, focusing solely on litter data collection and analysis during the period 2014-2017. Several earlier research projects aimed at forest C budgeting were an essential source of data (Uri et al., 2012;Uri et al., 2017;Uri et al., 2022;Aun et al., 2021a;Aun et al., 2021b;Becker et al., 2018). Some existing data of aboveground litter from earlier Estonian studies published in international and local scientific articles was included in the dataset (Kasesalu, 1965;Kollist, 1967;Kollist, 1968;Kõlli and Ingermaa, 1970;Sepp, 1959). ...
Canopy litterfall represents an essential aboveground flux in every forest ecosystem, affecting soil carbon and nutrient dynamics as well as soil fertility. However, despite the important role of the canopy litter flux in ecosysteḿs functioning and carbon sequestration, litterfall dynamics is still poorly studied in hemiboreal forests. The main aim of the current study was to estimate average annual litter fluxes in Scots pine, Norway spruce and birch (Betula pendula and Betula pubescens) stands, as well as to compile regional litter models for estimating the annual litter flux. The annual litter flux from a total of 33 pine, 15 spruce and 21 birch stands, with 85, 43 and 53 datapoints, respectively, was included in the study.
Although the annual litter flux depended on site quality index and stand age, no significant relationship was established between stand basal area and litter flux. Average annual canopy litterfall was similar for the studied tree species, being 3.24 ± 0.14 for pine, 3.62 ± 0.16 for spruce and 3.22 ± 0.07 t ha⁻¹ yr⁻¹ for birch across the stands of different ages. For all studied tree species, the relative proportion of needles or leaves in the total annual litter flux declined with stand age, due to the increased share of twigs and other fractions in the litter of older stands. The developed models of the litter flux allow to estimate the annual litter production of the canopy for the studied tree species on the basis of site quality index and stand age.
... However, it should be taken into account that thinning reduced the annual net primary production of trees considerably less compared to the decrease in the growing stock due to the method applied, i.e. in the course of thinning low productivity trees were primarily removed. In the indicated P25 stand the annual C accumulation of aboveground tree biomass in the thinned and control plots was 4.20 and 4.41 t C ha −1 yr −1 , respectively, i.e. the production of the trees in the control plot was only 5 % larger than in the thinned plot (Aun et al., 2021). In the P45 stand the respective values were 4.75 and 4.96 t C ha −1 yr −1 and the difference between the treatments was 4.2 %. ...
... • Since studies on the capacity of forests to store carbon either focused on carbon sequestration or storage in trees aboveground (Aun et al., 2021;DeSoto et al., 2020) or on the amount of organic carbon in the soil (Achat et al., 2015) (James and Harrison, 2016), we make a plea for studies that quantify and integrate above-and belowground processes for the same forests with experimental stand density treatments to better understand how and where forests store carbon in response to forest management and climate change. Linking above-and belowground carbon storage empirically is critical in order to identify when and where trade-offs and synergies occur between carbon storage in trees and soils (Terrer et al., 2021). ...
As a response to the increased pressure of global climate change on most ecosystems, national and international agreements aim at creating forests that are productive, resilient to climate change, and that store carbon to mitigate global warming. However, these aims are being challenged by increased tree mortality rates and decreased tree growth rates in response to increased incidence of extreme drought events. These phenomena make us aware of a lack of crucial insights into the effects of forest management on the growth and survival of trees, and on carbon storage in both trees and forest soils under increased incidence of drought. Here we compile current knowledge on how forest management and drought impact on tree growth and survival, and above- and belowground carbon storage in forest ecosystems. Based on this, we propose that climate-smart forestry may benefit from controlling stand density at intermediate levels (>60%, e.g.∼80%) by applying low levels of tree harvest intensity on a regular base. Furthermore, we propose that the actual optimal density will depend on the tree species, site conditions and management history. As a next step, studies are needed that take an above- and belowground approach and combine forest experiments with mechanistic models on water, carbon and nutrient flows in trees and soils within forests in order to transform current results, which focus on either soil or trees and are often highly-context dependent, to a more generic forest framework. Such a generic framework would be needed to enhance understanding across forest ecosystems on how forest management may promote forest resilience, productivity and carbon storage with increasing drought.
Globally, boreal forests act as important carbon sinks, however, drought and forest management could substantially alter the sink strength, though the controlling mechanisms of drought and management remain unclear. In this study, we combined the detailed process-based CoupModel with multiple measurements to study the impacts of recent drought and forest thinning on a boreal forest during 2018 - 2021. CoupModel after calibration showed high ability to represent the dynamics of long-term net ecosystem exchange and its responses to environmental changes. The model simulation showed that the canopy temperature exacerbated the dominant role in regulating the boreal forest growth during the 2018 extreme drought year with slight increase in the annual mean net carbon uptake by 76.65 g C/m2/yr compared to 2017. The posterior model simulations ensemble suggested that thinning of trees in 2019 - 2020 caused the boreal forest in 2020 to be a sink to slight source ([-229.95, 94.90] g C/m2/yr, 90% confidence interval), while the observations depicted a small source (69.35 g C/m2/yr). Moreover, rapid recovery of the boreal forest to a carbon sink was found in 2021, though remaining smaller than the carbon sink in 2017. Overall, the negative impacts from drought and harvest (2018 - 2021) were found to have offset the positive impacts from climate by 8% - 92%, on the net carbon uptake. This study highlights the resilience of boreal forests as carbon sink and provides new insights into the boreal forests' responses to both climate change and management.
Shelterwood cutting (SC) has been highlighted as an alternative method to clear-cut (CC)-based even-aged forest management. However, compared to CC, the effect of SC on stand carbon (C) balance is still poorly understood at the ecosystem level. We examined the prompt effect of SC versus CC on ecosystem net primary production (NEP) on a short-term scale, using the C budgeting method combined with eddy covariance (EC) measurements in hemiboreal mature Scots pine stands. The early effect of SC on annual C budget after removing 30–40 % of the growing stock revealed diverse patterns in the studied stands; NEP varied from 0.62 to -1.3 t C ha-1 yr-1 for the C sink and the C source, respectively. However, C loss decreased already in the second post-thinning year and levelled out attaining
-0.41 t C ha-1 yr-1, which is close to balance. Furthermore, C loss declined in the second post-harvesting year at the CC sites as a result of the increased
production of the ground vegetation and the decreased soil heterotrophic respiration (Rh) flux. However, C loss from dry mesotrophic clear-cuts was almost -1.8 t C ha-1 yr-1 for both study sites. Since estimation of the individual C fluxes for C budgeting is associated with variability-induced errors, the estimated values of NEP contain uncertainties of various levels. The estimated annual cumulative Rh flux was significantly higher in the SC versus CC areas and the mean annual Rh values across the study sites were 3.57 ± 0.25 and 2.59 ± 0.09 t C ha-1 yr-1, respectively. Annual estimated NEE after SC was 1.8 ± 0.52 t C ha-1 yr-1, gross primary ecosystem production was 9.28 ±0.97 and total ecosystem respiration was 7.47± 0.28 t C ha-1 yr-1. The discrepancy between the estimated values of NEE and NEP was 1.2 t C ha-1 yr-1. In the short term SC demonstrated some advantage over CC from the perspective of the C cycle, but the difference in NEP values between the SC and CC treatments was not convincingly overwhelming. Hence, SC allows to maintain the forest cover for a longer period and to avoid drastic changes in the landscape; still, after SC, C budget varied between the C sink and the C source.
Background: Chinese pine (Pinus tabuliformis Carr.) is one of the major afforestation species in northern China and plays a key role in restoring forest ecosystems and preserving soil and water. However, most Chinese pine plantations are experiencing ecological problems such as the low diversity of understory plants and difficulty in natural regeneration. Thinning has been widely used to maintain and improve a variety of forest ecosystem services from plantations. To date, however, few studies have been conducted to systematically determine the effects of thinning on understory plant diversity and the regeneration of Chinese pine in plantations. Methods: We conducted a literature search, and selected 22 publications covering a total of 83 treatments related to thinning effects on the species richness of understory plants and 15 publications covering a total of 43 treatments related to thinning effects on the regeneration of Chinese pine, in tree plantations of northern China. The data from the literature were synthesized and evaluated with meta-analysis approach to determine the treatment effects. Results: Compared with the control stands, thinning increased the species richness of shrubs and herbs by an average of 25.3% and 26.5%, respectively. While the varying thinning intensities all had significantly positive effects on the species richness of understory plants, only moderate thinning (30%–50%) had a positive effect on the density of regenerating seedlings and saplings of Chinese pine (60.2%). The species richness of understory plants was greatest after 14 years of thinning with an increase of 36.3%, whereas the density of regenerating Chinese pine seedlings and saplings reached a maximum after ≥11 years of thinning with an increase of 76.5%, compared to that of the unthinned stands. Thinning in the half-mature plantations had the greatest effects on the understory shrub richness (44.1%) and the density of regenerating Chinese pine seedlings and saplings (86.5%). Both single and multiple thinning were found to significantly promote the species richness of understory plants and the density of regenerating Chinese pine seedlings and saplings, and the positive effects of thinning were greater in areas with a humidity index (HI)
Clear-cutting is an extensively used silvicultural method in the Nordic and Baltic countries, which strongly influences the site’s carbon (C) budget. In the current study, C budgets for a young silver birch stand chronosequence (2–8-year-old) were compiled using the C budgeting method. High variability of annual NEP between stands of similar ages occurred, as the C accumulation ability of young stands was site specific. Heterotrophic respiration (Rh), the main C efflux from the ecosystem, varied between (3.7 and 6.3 t C ha⁻¹ yr⁻¹) across all stands. Modelling of the annual NEP dynamics across the chronosequence revealed the C compensation point at a stand age of 6 years. The estimated cumulative C loss for the period when NEP was negative was almost 5 t C ha⁻¹ and the amount of lost C could have been recaptured already in a 10-year-old stand. The C sink capacity of the studied sites depended mostly on the production of herbaceous plants until the production of the new tree generation became the main driver of ecosystem’s net primary production. Hence, site’s C accumulation capacity largely depends on the density and quality of the new forest regeneration.
Studies were carried for 200 trees coming from eight pure pine stands aged 25–95 years, growing in a fresh mixed coniferous forest habitat, in the Murowana Goślina Forest Experimental Station (52°34′ N, 17°00′ E) in western Poland. The aim of the study was to determine the size of the assimilatory apparatus of single pines (Pinus sylvestris L.): weight of leaved twigs (ugc), needle weight (ic), the volume of leaved twigs (ugo) and needle volume (io) and its relationship with selected dendrometric and increment traits of trees. The basic dendrometric traits were determined (height—h and diameter at breast height—d1.3) together with selected increments (heights—Ih5 and Ih10, diameter at breast height—Id5 and Id10, basal area at breast height—Ig5 and Ig10, volume—Iv5 and Iv10). A statistically significant linear correlation and a multiple linear correlation were shown between analysed traits, which confirms a strong relationship of the size of the assimilatory apparatus with tree increment. In this context, the strong correlation with the increment in basal area at breast height (correlation coefficient 0.8731 ÷ 0.9836) and with the increment in diameter at breast height (correlation coefficient 0.7835 ÷ 0.9581), after determining the increment in diameter at breast height requires only simple mathematical transformations to determine the increment in basal area at breast height. For the above-mentioned reasons, the increment in basal area at breast height is predisposed to be commonly used in the determination of the efficiency of the assimilatory apparatus of trees.
Keywords: pine; weight of leaved twigs; needle weight; volume of leaved twigs; needle volume; dendrometric traits; increment traits
Background
Soil and understory vegetation are vital components of forest ecosystems. Identifying the interaction of plantation management to vegetation and soil is crucial for developing sustainable plantation ecosystem management strategies. As one of the main measures of close-to-nature management of forest plantation, few studies have paid attention to the effect of crop tree management on the soil properties and understory vegetation.
Methods
A 36-year-old Pinus massoniana plantation in Huaying city, Sichuan Province was taken as the research object to analyse the changes in undergrowth plant diversity and soil physicochemical properties under three different crop tree densities (100, 150, and 200 N/ha).
Results
Our results showed that the contents of available phosphorus, organic matter and hydrolysable nitrogen in the topsoil increased significantly after crop tree management, while content of available potassium decreased. The composition of shrub and herb layer was richer, and the dominant species were obviously replaced after crop tree management. The Shannon–Wiener index and Richness index of shrub layer, and the diversity of herb layer increased significantly after crop tree management. Herb layer diversity indexes and Richness index of shrub layer were closely related to soil organic matter, available phosphorus, hydrolysable nitrogen, available potassium, soil moisture and bulk density. As the main limiting factors for plant growth, nitrogen, phosphorus and potassium were closely related to plant diversity and to the distribution of the dominant species. At the initial stage of crop tree management, each treatment significantly improved the soil physicochemical properties and plant diversity of Pinus massoniana plantation, and the comprehensive evaluation was 200 N/ha >100 N/ha >150 N/ha >CK. Compared with other treatments, 200 N/ha had the best effect on improving the undergrowth environment of the Pinus massoniana plantation in the initial stage of crop tree management.
Soil CO 2 efflux, the second largest flux in a forest carbon budget, plays an important role in global carbon cycling. Forest logging is expected to have large effects on soil CO 2 efflux and carbon sequestration in forest ecosystems. However, a comprehensive understanding of soil CO 2 efflux dynamics in response to forest logging remains elusive due to large variability in results obtained across individual studies. Here, we used a meta-analysis approach to synthesize the results of 77 individual field studies to determine the impacts of forest logging on soil CO 2 efflux. Our results reveal that forest logging significantly stimulated soil CO 2 efflux of the growing season by 5.02%. However, averaged across all studies, non-significant effect was detected following forest logging. The large variation among forest logging impacts was best explained by forest type, logging type, and time since logging. Soil CO 2 efflux in coniferous forests exhibited a significant increase (4.38%) due to forest logging, while mixed and hardwood forests showed no significant change. Logging type also had a significant effect on soil CO 2 efflux, with thinning increasing soil CO 2 efflux by 12.05%, while clear-cutting decreasing soil CO 2 efflux by 8.63%. The time since logging also had variable effects, with higher soil CO 2 efflux for 2 years after logging, and lower for 3-6 years after logging; when exceeded 6 years, soil CO 2 efflux increased. As significantly negative impacts of forest logging were detected on fine root biomass, the general positive effects on soil CO 2 efflux can be explained by the accelerated decomposition of organic matter as a result of elevated soil temperature and organic substrate quality. Our results demonstrate that forest logging had potentially negative effects on carbon sequestration in forest ecosystems.
Almost half of the total organic carbon (C) in terrestrial ecosystems is stored in forest soils. By altering rates of input or release of C from soils, forest management activities can influence soil C stocks in forests. In this review, we synthesize current evidence regarding the influences of 13 common forest management practices on forest soil C stocks. Afforestation of former croplands generally increases soil C stocks, whereas on former grasslands and peatlands, soil C stocks are unchanged or even reduced following afforestation. The conversion of primary forests to secondary forests generally reduces soil C stocks, particularly if the land is converted to an agricultural land-use prior to reforestation. Harvesting, particularly clear-cut harvesting, generally results in a reduction in soil C stocks, particularly in the forest floor and upper mineral soil. Removal of residues by harvesting whole-trees and stumps negatively affects soil C stocks. Soil disturbance from site preparation decreases soil C stocks, particularly in the organic top soil, however improved growth of tree seedlings may outweigh soil C losses over a rotation. Nitrogen (N) addition has an overall positive effect on soil C stocks across a wide range of forest ecosystems. Likewise, higher stocks and faster accumulation of soil C occur under tree species with N-fixing associates. Stocks and accumulation rates of soil C also differ under different tree species, with coniferous species accumulating more C in the forest floor and broadleaved species tending to store more C in the mineral soil. There is some evidence that increased tree species diversity could positively affect soil C stocks in temperate and subtropical forests, but tree species identity, particularly N-fixing species, seems to have a stronger impact on soil C stocks than tree species diversity. Management of stand density and thinning have small effects on forest soil C stocks. In forests with high populations of ungulate herbivores, reduction in herbivory levels can increase soil C stocks. Removal of plant biomass for fodder and fuel is related to a reduction in the soil C stocks. Fire management practices such as prescribed burning reduce soil C stocks, but less so than wildfires which are more intense. For each practice, we identify existing gaps in knowledge and suggest research to address the gaps.
Mixed-species forests have potentially more benefits than monocultures particularly in terms of greater carbon sequestration. A 16-year-old Chinese fir (Cunninghamia lanceolata) monoculture in Zhejiang, China, was converted to a Chinese fir—broadleaved plantation by thinning from below (TFB) and crop tree release (CTR) methods coupled with planting of Chinese sweet gum (Liquidambar formosana) seedlings. Carbon pools in trees, snags, shrubs and herbs, seedlings, litterfall, forest floor, and mineral soil were measured for 5 years. The total tree biomass carbon increase in un-thinned control and CTR stands was approximately 15% higher than that in TFB. The average individual tree biomass C stock increased by 20.5% and 9.2% in CTR and TFB, respectively. Carbon flux through litterfall decreased after thinning but recovered, thereafter, to a level similar in the un-thinned control. Compared to the control, lower tree mortality and higher growth of seedlings in both converted stands resulted in no change in ecosystem C stocks. Carbon stocks in trees and seedlings increased more in CTR than in TFB stands, implying that CTR should be favored when converting pure plantations into mixed-species stands.
Litterfall is one of the most important fractions of forest net primary production (NPP) and important carbon flux into soil, a large carbon pool in forests worldwide, and believed to account for about one-third of forest NPP. The aim of the study was to determine litterfall amount and carbon input into the soil via litterfall as well as to understand the effects of thinning (removing 20–25% of the initial basal area) and seed cutting (i.e. regeneration cutting with removing 60% of the initial basal area) on litterfall in Scots pine (Pinus sylvestris L.) stands. Litterfall samples were collected three times in a year from 32 sample plots for 5 years in Turkey. Carbon concentrations of the litterfall components were determined by dry combustion. Data were evaluated by one-way ANOVA and multiple regression analysis. As a result, litterfall varied from 1389 kg ha⁻¹ year⁻¹ in young stands to 4488 kg ha⁻¹ year⁻¹ in mature stands. Carbon inputs into the soil changed between 714 kg C ha⁻¹ year⁻¹ and 2289 kg C ha⁻¹ year⁻¹ depending on the development stage and silvicultural treatment applied to the stands. Thinnings reduced litterfall amount at a ratio of 22% in mature stands while had no significant effect in overmature stands with a decrease ratio of 8%. Seed cutting reduced considerably the litterfall amount both in mature and overmature stands. A combination of basal area, site index, and stand age accounted for 75% of the variation in needle litterfall. In conclusion, seed cutting was recommended to do preferably in mature stands instead of overmature ones and thinning to be applied lightly in mature stands in order not to reduce carbon input into the soil via litterfall dramatically.
1. Fine root turnover plays a critical role in carbon and nutrient cycling in forest ecosystems. In this study, we focused on the most abundant deciduous species in Nordic countries, silver birch (Betula pendula Roth) and its fine root dynamics, including the amount of litter produced by fine roots as well as by aboveground vegetation.2. The minirhizotron method was used to quantify fine root longevity of silver birch and understory fine roots and rhizomes in northern Finland. Fine root biomass per basal area and ectomycorrhizal short root numbers per mg were also quantified. The fine root litter production was estimated by fine root biomass and longevity, and then compared with the aboveground litter collected with litter traps.3. Birch fine root biomass was 1.4-fold higher than that of understory fine roots and rhizomes (234 ± 22, 171 ± 19 g m⁻² respectively). Fine root longevity of birch (372 days) was significantly (P < 0.05) shorter than that of understory vegetation (643 days). The birch fine root longevity was positively related to root diameter and soil depth. Hazard analysis showed that thicker roots, long roots, roots produced late in the growing season, and roots growing deeper in the soil had relatively lower mortality hazard compared to the reference data. The total annual soil C input, including both birch and understory, was 283 g C m⁻² yr⁻¹. The proportion of understory annual C input was 35% of the total. Total annual belowground C input was 1.4-fold greater than that of aboveground.4. Our study indicated that the total annual belowground litter production was greater than that of the aboveground litter in a boreal deciduous forest stand. Therefore, more emphasis should be put to quantify the C cycling of both above- and belowground parts of different tree species as well as understory in boreal forests.
Aim of the study: Thinning experiments in Scots pine (Pinus sylvestris L.) stands have been carried out for many years in different regions of its distribution. The aim of this paper is to gather knowledge regarding the effects of thinning on Scots pine stands, from the effects on growth and yield to the provision of ecosystem services in the context of climate change.Area of study: The review covers studies from different regions of the distribution area of Scots pineMaterial and methods: We reviewed the effect of thinning on four aspects: growth and yield, stability against snow and wind, response to drought, and ecosystem services.Main results: Heavy thinning involves a loss in volume yield, although the magnitude depends on the region, site and stand age. Thinning generally does not affect dominant height while the positive effect on tree diameter depends on the thinning regime. The stability of the stand against snow and wind is lower after the first thinning and increases in the long term. The impact of extreme droughts on tree growth is lower in thinned stands, which is linked to a better capacity to recover after the drought. Thinning generally reduces the wood quality, litter mass, and stand structural diversity, while having neutral or positive effects on other ecosystem services, although these effects can vary depending on the thinning regime. However, scarce information is available for most of the ecosystem services.Research highlight: Existing thinning experiments in Scots pine stands provided valuable information about thinning effects, but new experiments which cover a broad range of ecosystem services under different site conditions are still needed.
AimsUnderstanding the linkage of soil respiration (Rs) with forest development is essential for long-term C cycle models. We estimated the variation and temperature sensitivity (Q10 value) of Rs and its hetero-, (Rh) and autotrophic (Ra) components in relation to abiotic and biotic factors in Norway spruce stands of different ages, and the effect of trenching on microbial and soil characteristics. Methods
Trenching method was used to partition Rs into Rh and Ra. Ingrowth core method was used to estimate fine root production. Soil microbial biomass was measured using manometric respirometers. ResultsRs varied in differently aged stands demonstrating non-linear response to development stage. The variation of Rs was explained by changes in biotic factors rather than by changes in soil microclimate. Rh was more sensitive to Ts than Rs or Ra. After 4 years of trenching soil pH, N, SOM and dehydrogenase activity were significantly changed in trenched plots compared to control plots. Conclusions
Different Q10 values of Rh and Ra in stands of different ages indicate the importance of Rs partitioning. Trenching should be used during a limited number of years because of the possible changes in chemical characteristics of soil and in the activity of soil microbial community.
An important aspect of sustainable forest management is to assess the impact of forest operations on ecosystem services. This work analyzed the long-term effect of two standard thinning regimes on carbon stocks both in tree biomass and soil compartments as well as its effect on soil condition. The target population was a 90-year-old Scots pine (Pinus sylvestris L.) stand in southwestern Europe. Soil condition was
measured as dry mass of the forest floor and concentration of carbon, nutrients in the forest floor as well as exchangeable cations, effective cation exchange capacity, pH and bulk density in the mineral soil. Repeated thinnings from below in a southern European population of Scots pine led to a reduction in current on-site carbon stock in tree biomass of 28% in moderately thinned stands (D grade: average residual basal area of 65–79% relative to the control plots) which was consistent with an observed loss of volume production. However, the inclusion of the amount of carbon exported off-site with harvested biomass reduced the decrease in stock to 4.8%. Nutrient concentrations in the forest floor increased in moderate thinned stands (P, K, Mg and Mn) or were unchanged (C, N and Fe). The selected thinning regime did not alter mineral soil condition. A decreasing pattern of Ca and Mn stocks with depth was consistent with a high reduction of nutrient concentration of elements and higher bulk density with depth. However K, Mg and Na showed stable stocks across depths because of a much smaller reduction of nutrient concentrations in deeper layers relative to the surface layer. We hypothesized that this stable pattern with soil depth was due to leaching. The sustainability of forest thinning is a trade-off between loss of standing biomass and increasing stand stability as long as other indicators, like soil condition, do not significantly change.
The major part of carbon (C) flow into forest soil consists of continually renewed fine roots and aboveground litterfall. We studied the belowground C input from the fine root litter of trees and understorey vegetation in relation to their aboveground litterfall in two Norway spruce (Picea abies L.) stands located in northern and southern Finland. The production of fine roots was estimated by using turnover and biomass data from minirhizotrons and soil cores. The foliage litter production of trees was estimated from litter traps, and that of the understorey vegetation from its annual growth and coverage. Finally, we augmented the data with four spruce plots in Sweden in order to study the above- and belowground litter ratios along latitudinal and soil fertility gradients.
Afforestation has been proposed as a strategy to mitigate the often high greenhouse gas (GHG) emis-sions from agricultural soils with high organic matter con-tent. However, the carbon dioxide (CO 2) and nitrous ox-ide (N 2 O) fluxes after afforestation can be considerable, de-pending predominantly on site drainage and nutrient avail-ability. Studies on the full GHG budget of afforested or-ganic soils are scarce and hampered by the uncertainties associated with methodology. In this study we determined the GHG budget of a spruce-dominated forest on a drained organic soil with an agricultural history. Two different ap-proaches for determining the net ecosystem CO 2 exchange (NEE) were applied, for the year 2008, one direct (eddy co-variance) and the other indirect (analyzing the different com-ponents of the GHG budget), so that uncertainties in each method could be evaluated. The annual tree production in 2008 was 8.3 ± 3.9 t C ha −1 yr −1 due to the high levels of soil nutrients, the favorable climatic conditions and the fact that the forest was probably in its phase of maximum C assimilation or shortly past it. The N 2 O fluxes were deter-mined by the closed-chamber technique and amounted to 0.9 ± 0.8 t C eq ha −1 yr −1 . According to the direct measure-ments from the eddy covariance technique, the site acts as a minor GHG sink of −1.2 ± 0.8 t C eq ha −1 yr −1 . This con-trasts with the NEE estimate derived from the indirect ap-proach which suggests that the site is a net GHG emitter of 0.6 ± 4.5 t C eq ha −1 yr −1 . Irrespective of the approach ap-plied, the soil CO 2 effluxes counter large amounts of the C sequestration by trees. Due to accumulated uncertainties in-volved in the indirect approach, the direct approach is consid-ered the more reliable tool. As the rate of C sequestration will likely decrease with forest age, the site will probably become a GHG source once again as the trees do not compensate for the soil C and N losses. Also forests in younger age stages have been shown to have lower C assimilation rates; thus, the overall GHG sink potential of this afforested nutrient-rich or-ganic soil is probably limited to the short period of maximum C assimilation.
A new equipment for the collection of water percolating through the soil and bulk material constructed in 2008 was an essentially improved variant [1]. Constructed equipment/sampler is cheap to construct on the spot, their installation does not damage the soil layer and no vacuum was necessary for taking of water samples. From the beginning of 1994 our so called, “old equipment” [2, 3] is still in operation in the international integrated monitoring stations of the Estonian national programme of environmental monitoring. The new one can be used for the collection of samples of water percolating through the soil as well as heaps of bulk materials (such as grain, fuels, construction materials) of all kinds of corner. They are necessary for monitoring the condition of natural soil, as well as for the research of the changes in the physical state of soil during construction activities and redesign of relief related to the establishment of ditches, ponds, artificial hills and other objects.
OriginalRussian Text (O.Roots,M. Voll. 2011,published in Ekologicheskaja Khimija, 2011,vol. 20,No.3,pp.150-154.
• Context
The amount and chemistry of litterfall have been known to strongly vary among the years with important implications for ecosystem nutrient cycles, but there are few quantitative data describing such variations.
• Aims
We studied the climatic implications on the variation in litterfall and its C and N input to soil in two distinct European coniferous forests.
• Methods
Year-to-year variations in canopy litterfall were measured in a Scots pine stand (Hyytiälä, Finland) over 13 years, and a Douglas fir stand (Speulderbos, The Netherlands) over 3 years.
• Results
Important inter-annual variations in litterfall were observed in Scots pine. Litterfall was mainly driven by leaf senescence; however, premature needle fall was observed in high wind speed and early frost events. The seasonal variation in litterfall was characterized by a maximum in September in Scots pine, and by a biphasic variation pattern in Douglas fir, in May and November. Lower seasonal variations and lower annual average in litterfall N content were observed in Scots pine.
• Conclusion
Significant inter- and intra-annual variations in litterfall and chemistry and between the sites were demonstrated; and it depended on year-to-year differences in climate and extreme weather events.
The below- and above-ground biomass and the annual biomass production of sapling (15-year-old), pole stage (35-year-old) and mature (100-year-old) Scots pine (Pinus sylvestris L.) stands were studied in eastern Finland. The fine-root (diameter<2 mm) biomass (including mycorrhizal root tips), necromass and biomass production were determined for the organic layer and the upper 30 cm mineral soil layer by soil core samplings. The biomass and the annual production of needles, cones, stemwood and stembark, branches (wood and bark), and coarse-roots were calculated for the whole stand using biomass measurements of different components of felled sample trees, and measurements of the tree stand.
a b s t r a c t During recent decades, studies of the carbon (C) balance of forest ecosystems have became more actual, mainly in connection with the global increase of CO 2 in the atmosphere. In the present study the stand chronosequence approach was applied to analyse C sequestration dynamics. Study was made of C accu-mulation both in biomass and in the soil in 6–60-year-old silver birch (Betula pendula) stands growing at fertile (Oxalis) sites. As the growth of the studied stands was vigorous, their yield was higher than that presented in several yield tables for earlier periods. The C concentration (C%) in different compartments of the trees varied between 47% and 55%. However, the weighted average of C concentration in the silver birch trees was approximately 50% regardless of stand age. The average C concentration of the herbaceous understorey plants was 43.3 ± 0.5%. The soil C org pool was independent of stand age, and so far there occurred no C accumulation during stand succession, expressed as C org values or stage of forest floor formation. This might indicate fast C org turnover in the soils of the Oxalis site. The total C pool in a mature silver birch stand was 185 t ha À1 of which 50% was accumulated in the aboveground part of the trees. In young birch stands the C pool in aboveground biomass and in the soil accounted for 21–39% and 53–71%, respectively, of the total C pool of a stand. In pre-mature and mature stands the corresponding share accounted for 50–59% of the above-ground C of the trees and 29–38% of the soil C pool. Due to closed canopies, the role of herbaceous under-storey plants as a C sink was modest, constituting 1% or even less of the total C pool of the older stands. The annual C flux 1.6 t ha À1 yr À1 into the soil via litter fall was the largest in the middle-age stand. Our results show that the main C sink in fertile silver birch stands is located in the wooden parts of trees. The C pool in tree biomass increased with stand age, whereas the soil C org pool remained stable. For a more profound understanding of C cycling in silver birch forest, soil respiration fluxes should be measured.
a b s t r a c t Mycorrhizal fungi constitute a considerable sink for carbon in most ecosystems. This carbon is used for building extensive mycelial networks in the soil as well as for metabolic activity related to nutrient uptake. A number of methods have been developed recently to quantify production, standing biomass and turnover of extramatrical mycorrhizal mycelia (EMM) in the field. These methods include mini-rhizotrons, in-growth mesh bags and cores, and indirect measurements of EMM based on classification of ectomycorrhizal fungi into exploration types. Here we review the state of the art of this methodology and discuss how it can be developed and applied most effectively in the field. Furthermore, we also discuss different ways to quantify fungal biomass based on biomarkers such as chitin, ergosterol and PLFAs, as well as molecular methods, such as qPCR. The evidence thus far indicates that mycorrhizal fungi are key components of microbial biomass in many ecosystems. We highlight the need to extend the application of current methods to focus on a greater range of habitats and mycorrhizal types enabling incorporation of mycorrhizal fungal biomass and turnover into biogeochemical cycling models.
Although thinning is a widely used silvicultural method, its effect on stand carbon (C) cycling is still poorly studied at the ecosystem level. The present case study estimated the two-year post-thinning effect on the C balance of a pole and a middle-aged silver birch stand. The results demonstrate the multifaceted impact of thinning on the different C fluxes of deciduous forest ecosystems.
The effect of thinning on the C budget of the studied stands was modest: net ecosystem production (NEP) decreased by 1.2 and 1.6 t C ha⁻¹ yr⁻¹ in the pole and the middle- aged stand, respectively; still, both stands remained C sinks. Lower annual production in the thinned stands as a result of the decreased standing biomass of the trees was the main factor for reduced C sequestration capacity. Thinning increased the C accumulation of the herbaceous plants in both stands, however, it did not compensate for the lower C accumulation by the trees. In general, thinning did not affect significantly the soil respiration fluxes; the small post-thinning increase of the annual soil heterotrophic flux, 0.33–0.68 t C ha ⁻¹, was most probably related to elevated soil temperature during the active growing season. The annual aboveground litter flux, i.e. the labile C source of Rh, was not significantly changed by thinning. Fine root production and the belowground C input to the soil remained at the same level in the pole stand and decreased slightly in the middle-aged stand. We conclude that the high production ability and fast C accumulation recovery of silver birch stands growing on fertile soils leads to a balanced C budget already during the short post-thinning period.
Thinning changes the functioning of the whole forest ecosystem, including carbon and nitrogen (N) cycling. The input of organic matter and N into soil, as well as soil temperature and moisture regimes change, which may have an impact on the intensity of the net nitrogen mineralization (NNM) process. The main aims of this study were to estimate the effect of thinning on annual NNM as well as N leaching intensity in young silver birch and Scots pine stands. Thinning increased annual NNM flux in the silver birch stand, as well as annual net nitrification, while there was no change in the annual net ammonification flux. The effect of thinning on nitrification was more pronounced in the first post-thinning year. The 13-year dynamics of annual NNM in the birch stand revealed a significant decrease, which may be attributed to the effect of previous land use. The annual NNM flux in the Scots pine stand was practically equal in both plots; thinning did not affect N net mineralization intensity. The effect of thinning on the annual NNM flux was site and tree species specific. Thinning did not induce more intensive N leaching. Moreover, in the birch stand thinning even reduced N leaching.
Estimation of soil-related carbon (C) fluxes is needed to understand the dynamics of the soil organic carbon pool, to determine changes in the carbon balance and functioning of forest ecosystems, and to support climate change policies.
The objective of the study was to analyse the variation in the most dynamic soil C input (tree and understory above- and belowground litter production) and output (soil respiration) fluxes, in addition to the forest floor, understory and fine root biomass stocks, in eight different Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst) sites growing on mineral soils in Estonia. Further, the impact of soil C input and output fluxes on the soil organic carbon (SOC) pool was examined, and the net ecosystem production (NEP) of the stands was estimated.
Fine root production (FRP) of the trees constituted 53% and 28% and needle litter constituted 25% and 28% of the total annual C input to the soil in the Norway spruce and Scots pine stands, respectively. The total FRP of the trees and the understory roots and rhizomes ranged from 211 to 1040 g m−2 yr−1, of which the understory comprised up to 28%. The mean annual soil respiration (Rs) rate was 5.7 ± 0.3 and 6.5 ± 0.3 Mg C ha−1 yr−1 in the pine and spruce stands, respectively, and did not differ significantly between the two groups of stands. The SOC pool of the studied stands depended significantly on both the above- and belowground C input fluxes. Tree-derived litter had the strongest effect on the SOC pool, while the Rh as the main soil C output flux showed no significant impact. The NEP ranged from 4.2 to −1.8 Mg C ha−1 yr−1 and demonstrated a strong negative correlation with stand age. The results affirm the importance of belowground as well as aboveground litter production on carbon accumulation in forest soils.
Clear-cutting is a conventional method of forest management which significantly changes carbon (C) cycling at the ecosystem level for a long time. Estimation of the interim period during which the ecosystem turns from a C source to a C sink is crucial for clarifying the environmental effects of management on forest C cycling. The current study provided new knowledge of C cycling in young pine stand and demonstrated the recovery of C sequestration of the forest ecosystem during the post harvesting period.
We estimated the C balance in a 6-year-old Scots pine stand by using two different methods: carbon budgeting, for estimating annual net ecosystem production (NEP), and eddy covariance (EC), for estimating net ecosystem exchange (NEE). For C budgeting, the above- and belowground biomass production of the ecosystem, as well as the soil heterotrophic respiration efflux at the studied site was estimated.
Annual NEE at the studied young forest ecosystem was 1.19 ± 0.36 t C ha−1, gross primary ecosystem production was 9.87 and total ecosystem respiration was 11.06 t C ha−1. Estimated NEE was in good accordance with the results of NEP (1.37 t C ha−1), which confirms the relevance of the C budgeting method.
Increased annual woody biomass production is the main factor which induced the young Scots pine ecosystem to act as a C sink: annual C accumulation in tree biomass in a 6-year-old stand was 1.0 t C ha−1 but reached already 2.4 t C ha−1 in the following year. Assuming that the annual Rh flux is of the same magnitude in the subsequent years, the ecosystem will become a C sink already during a short period after clear-cut. Annual soil respiration (Rs) and heterotrophic soil respiration (Rh) were 6.0 and 4.2 t C ha−1, respectively and the Rh/Rs ratio was 0.70. However, at this stage also the understorey vegetation contributed essentially to NEP, making up 56% of the annual C uptake accumulated in the plants. The methane flux and the leached C flux were negligible, 0.004 and 0.015 t C ha−1 yr−1, respectively. Our results demonstrate that well regenerated young Scots pine stand on a former clear-cut area will be able to turn into a C sequestering ecosystem already before ten years after cutting.
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.
Litterfall is a major, yet poorly studied, process within forest ecosystems globally. It is important for carbon dynamics, edaphic communities, and maintaining site fertility. Reliable information on the carbon and nutrient input from litterfall, provided by litter traps, is relevant to a wide audience including policy makers and soil scientists. We used litterfall observations of 320 plots from the pan-European forest monitoring network of the "International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests" to quantify litterfall fluxes. Eight litterfall models were evaluated (four using climate information and four using biomass abundance). We scaled up our results to the total European forest area and quantified the contribution of litterfall to the forest carbon cycle using net primary production aggregated by bioregions (north, central, and south) and by forest types (conifers and broadleaves). The 1,604 analyzed annual litterfall observations indicated an average carbon input of 224 g C · m⁻² · year⁻¹ (annual nutrient inputs 4.49 g N, 0.32 g P, and 1.05 g K · m⁻²), representing a substantial percentage of net primary production from 36% in north Europe to 32% in central Europe. The annual turnover of carbon and nutrient in broadleaf canopies was larger than for conifers. The evaluated models provide large-scale litterfall predictions with a bias less than 10%. Each year litterfall in European forests transfers 351 Tg C, 8.2 Tg N, 0.6 Tg P, and 1.9 Tg K to the forest floor. The performance of litterfall models may be improved by including foliage biomass and proxies for forest management.
Quantifying soil respiration (Rs ) and its components [autotrophic respiration (Ra ) and heterotrophic respiration (Rh )] in relation to forest management is vital to accurately evaluate forest carbon balance. Thus, Rs, Ra, and Rh were continuously monitored from November 2013 to November 2016 in Pinus massoniana forests subjected to four different management practices in China. We hypothesized that understory removal and thinning decrease Ra and Rh and thus Rs, and these decreases will change with time following UR and thinning. Mean values of Rs, Ra, and Rh in light thinned plots (LT=15% of tree basal area thinned) and heavily thinned plots (HT=70% of tree basal area thinned) were significantly higher than in control (CK) and understory removal plots (UR). The annual Rh /Rs ratio ranged from 58% to 70% across all treatments, and this ratio was significantly higher in HT and LT than in UR and CK. Only HT significantly increased soil temperature. Soil temperature could better explain Rh (R² =0.69-0.96) than Ra (R² =0.51-0.86). HT and LT increased Q10 for both Ra and Rh, except for Rh in UR. Soil moisture content (W; %) was significantly higher in HT than in other treatments, but W had limited effects on soil respiration in that rain-rich subtropical China. This result suggests that global warming alone, or in combination with clear-cutting or canopy tree thinning will markedly increase soil heterotrophic respiration and thus the total soil CO2 emission. To get firewood for local people and to reduce soil CO2 emissions under global warming, canopy trees are needed to be protected and understory shrubs may be allowed to be used in the subtropical China.
Estimation of the carbon (C) storages and fluxes in different forest ecosystems is essential for understanding their C sequestration ability. The net ecosystem production (NEP) and the net primary production (NPP) in five downy birch (Betula pubescens) stands, aged between 12 and 78 years, growing on fertile well-drained Histosols, were studied. Drainage of swamp forests is a large-scale manipulation, which causes significant shifts at the ecosystems level, altering C and nutrient cycling a great deal. Young and middle-aged downy birch stands (12–30-year-old) acted as C sink ecosystems, accumulating 1.4–3.0 t C ha⁻¹ yr⁻¹. In the 38-year-old stand NEP was roughly zero; annual C budget was almost in balance. The over-matured downy birch stand (78-year-old) acted as a C source emitting 0.95 t C ha⁻¹ yr⁻¹. Annual woody biomass increment of the stand was the main factor which affected the forest to act as a C accumulating system. Although the highest heterotrophic respiration (Rh) values were measured in the middle-aged stands, mean soil C emission did not differ significantly between the studied stands. Annual total soil respiration (Rs) and Rh ranged from 7.4 to 8.8 t C ha⁻¹ and 4.7 to 6.2 t C ha⁻¹, respectively. Soil temperature appeared to be the dominant driver of the soil CO2 effluxes. Temperature sensitivity (Q10 value) of respiration rates (3.0–5.5), as well as the Rh/Rs (0.6–0.7) varied irrespective of stand age. Both the annual aboveground litter (1.5–1.9 t C ha⁻¹ yr⁻¹) and fine root litter (0.9–1.5 t C ha⁻¹ yr⁻¹) input fluxes were quite similar for the studied stands. However, the annual organic C input into the soil via above- and belowground litter was smaller than the annual Rh efflux, indicating that continuous mineralization of the peat layer reduces the soil organic C pool. The main share of the C stock in the drained swamp downy birch stands was soil C; the storage of C accumulated in the woody biomass of the trees accounted for only 5–20% of the total C storage of the ecosystem.
Estimation of the carbon (C) storages and fluxes in different forest ecosystems is essential for understanding their C sequestration ability. Grey alder (Alnus incana (L.) Moench) is a fast growing tree species with a great potential for short-rotation forestry in the Nordic and Baltic countries and its stands are considered C accumulating ecosystems. We hypothesized that grey alder stands growing at fertile sites act as C sinks in the young and middle-age stages, while mature stands become C sources as a consequence of declined net primary production (NPP). Net ecosystem production (NEP) was studied in five grey alder stands aged between 9 and 40 years. It was found that the NEP of the studied grey alder stands of different ages varied from −1.98 to +4.14 t C ha⁻¹ yr⁻¹. The oldest grey alder stand proved to be a weak C source (−0.77 t C ha⁻¹ yr⁻¹). However, also young alder stands regenerated in a clear-cut area may emit C in the earlier stage, owing to previous cutting and decomposition of organic residues matter. In this aspect, the land use history is of great significance.
Key messageSelf-thinning lines are species- and climate-specific, and they should be used when assessing the capacity of different forest stands to increase biomass/carbon storage. ContextThe capacity of forests to store carbon can help to mitigate the effects of atmospheric CO2 rise and climate change. The self-thinning relationship (average size measure ∼ stand density) has been used to identify the potential capacity of biomass storage at a given density and to evaluate the effect of stand management on stored carbon. Here, a study that shows how the self-thinning line varies with species and climate is presented. AimsOur main objective is thus testing whether species identity and climate affect the self-thinning line and therefore the potential amount of carbon stored in living biomass. Methods
The Ecological and Forest Inventory of Catalonia was used to calculate the self-thinning lines of four common coniferous species in Catalonia, NE Iberian Peninsula (Pinus halepensis, Pinus nigra, Pinus sylvestris and Pinus uncinata). Quadratic mean diameter at breast height was chosen as the average size measure. The self-thinning lines were used to predict the potential diameter at a given density and study the effect of environmental variability. ResultsSpecies-specific self-thinning lines were obtained. The self-thinning exponent was consistent with the predicted values of −3/2 and −4/3 for mass-based scaling for all species except P. sylvestris. Species identity and climatic variability within species affected self-thinning line parameters. Conclusion
Self-thinning lines are species-specific and are affected by climatic conditions. These relationships can be used to refine predictions of the capacity of different forest stands to increase biomass/carbon storage.
Stumps of conifer trees are a prospective source of bioenergy and stump harvesting is a novel practice in forestry management in the Baltic and Nordic countries. However, as stump harvesting may cause possible environmental risks there has emerged a clear need for research focusing on sustainable forest management. Three Norway spruce (Picea abies) clear-cut areas on different soils in Estonia were selected for the present study. We analysed the effect of stump harvesting on net nitrogen mineralization (NNM) and on nutrient leaching. On dry and sandy Endogleyic Arenosol (Oxalis site type), stump harvesting reduced the annul NNM flux significantly; 134 and 202 kg N ha yr À1 at the harvested and at the control site, respectively. In clear-cut area where Endogleyic Cambisol was dominating (Hepatica site type), stump harvesting had no effect on NNM (92 vs 88 kg N ha yr À1). However, in a clear-cut area where the soil type was Endogleyic Albic Podzol (Myrtillus site type), stump harvesting increased the total annual NNM flux: 102 vs 70 kg N ha yr À1 at the harvested and at the control site, respectively. Stump harvesting affected also the proportion of nitrification and ammonification processes in NNM. At the Myrtillys site type stump harvesting increased the annual nitrogen (N) leaching flux. One year after stump harvesting, leaching at the harvested site was 11.7 vs 4.5 kg N ha À1 yr À1 at the control site. In the second year N leaching decreased and the difference levelled off. Increased N leaching was induced by a larger amount of water; average N concentration of the harvested and control sites did not differ. Although at the Oxalis site N leaching was larger at the harvested than at the control site, the total annual leached N flux was small ($2 kg N ha À1). At the fertile Hepatica site type treatment had no impact on N leaching, which was only ca 1 kg N ha À1 yr À1. Phosphorus (P) leaching was very small in all study areas, being below 0.1 kg P ha À1 yr À1. The effect of stump harvesting on annual NNM as well as on N leaching was soil specific and highly variable. Stump harvesting affected also the proportion of the nitrification and ammonification processes in total NNM. Considering the first short-term results obtained from different site types, we can conclude that harvesting of spruce stumps does not induce serious environmental hazards in relation of N cycling.
Transects were established on two hillslopes and two study nitrogen budgets in two complex riparian buffer zones receiving different nitrogen loading. In the heavily loaded site the average total-N content decreased from 23 mg l-1 to 3.1 mg l-1 in a 40-years-old riparian grey alder forest (80 % removal). At the site with low loading the average removal of total-N was 48 %. In both transects the budget of N fluxes was established. In the older forest it was estimated as high as 321.1 kg ha-1 yr-1, being 285.3 kg ha-1 yr-1 in the younger one. Considering all inputs and outputs, the N removal efficiency in grey alder stands slows down with increase of age. In the same time, immobilization in soil is increasing. This suggests that grey alder buffer communities should be managed by regeneration cutting and tending to keep their nitrogen removal rate high.
Fire suppression and limited forest management have caused overstocking in many forests across the western United States. Overstocked stands have higher competition for limiting resources and causes tree stress. The amount of stress a tree experiences is related to the current availability of resources (site productivity), and the competition for those resources (stand density). Stressed trees are more susceptible to insects, disease, and mortality, which cause fuel buildup and increase wildfire risk. Pre-commercial thinning (PCT) can alleviate stress by decreasing the amount of competition in younger stands. The objective of this study was to determine how reducing competition through PCT might improve resource availability to trees at a range of initial stand conditions.
Environmental conditions and nutrient supply do not only affect the above-ground growth of forest trees, but also the below-ground growth. In model experiments, N additions to soil can result in both increases and decreases in root dry weight or root length. More consistently, in most cases a decrease in the root/shoot biomass ratio is observed as a result of increased N supply in soil (George and Seith 1998; see also Chapin III et al. 1987). Some nitrogen fertilisation experiments suggest that much of the increased above-ground production may be due to a carbon translocation from below-ground to above-ground parts (Linder and Axelsson 1982). Although this change in carbon allocation is not necessarily harmful to the tree, on low-nutrient soils a nutrient imbalance may occur in the tree as a consequence of the decreased root/shoot ratio, and this may be one of the factors causing forest decline symptoms. Such effects can also be studied in the field in N-fertilisation experiments (Ahlstrom et al. 1988; Persson et al. 1995a) or N-addition and removal experiments (Clemensson-Lindell and Persson 1995; Persson et al. 1998). In the present experiment, we compared root growth of Norway spruce (Picea abies) and European beech (Fagus sylvatica) at different sites with contrasting climate and N deposition.
Background: Trends in forest cover and land use intensity
Increasing global population and expanding land use mean that an ever greater percentage of human needs for wood products are being met by managed forests (Foley et al., 2005). Currently, about 7% of world’s forests are plantations and 57% are secondary forests recovering from anthropogenic disturbance (FAO, 2010). From 2000 to 2005 the rate of increase in the area of planted forests was 2% yr-1 and is accelerating (FAO, 2009), whereas total forest decreased at a rate of about 6% per decade. A recent analysis of Landsat TM data series concluded that forest use is intensifying in time, with 30% of the forestland in the southeastern US having been harvested and re-grown between 2000 and 2012 (Hansen et al., 2013). This is consistent with the typical rotation lengths in the region (discussed below), and an estimate that over 50% of the world’s industrial plantations are in the SE-US (Allen et al., 2005). While the exact interplay between factors effecting forest cover change vary by region, and can respond to both local development and global economic forces (Drummond and Loveland, 2010), the trends described above are likely to continue unless the valuation of forest products and services changes dramatically.
As the primary metric of a forest’s value has been its merchantable productivity, plantation forestry has long selected species and genotypes to maximize this one trait. For the most intensively studied species, like loblolly pine (Pinus taeda), it has been estimated that a typical plantation is about 3-5 times more productive than a natural stand, and that growth gains of up to 20-fold can be achieved in intensive culture and outside the species’ natural range (Cubbage et al., 2007; Ryan et al., 2010). Fox and coworkers (Fox et al., 2007a) estimated that, on average, the productivity of commercial P. taeda plantations is more than 4-fold higher than of natural P. taeda stands, with planting, site preparation, competition control, fertilization and genetic improvement contribute 13%, 10%, 13%, 17% and 23% of the total productivity, respectively. The productivity eucalypts in Brazil has nearly doubled over the past 20 years, owing to intensive management techniques (Goncalves et al., 2013). However, in global databases the management effects are confounded with temperature (Litton et al., 2007), and it remains unclear, whether or how the contribution of forests to global C cycling may change with their transition from natural to managed state (Piao et al., 2009; Stinson et al., 2011).
Of the explicit management-related effects, the increased frequency of disturbance makes for a very dynamic and rapidly changing biogeochemical exchange, to the point where age-related variability may be the predominant source of spatial variation (Desai et al., 2008), which on the global scale explains more than 90% of the variability in net ecosystem productivity (NEP; Pregitzer and Euskirchen, 2004). There are significant changes in forest structural and functional traits as related to age (Law et al., 2001a; Law et al., 2001b; 2006; Noormets et al., 2007), which have been recognized as having far greater influence on forest productivity and CO2 exchange than climate (King et al., 1999; Pregitzer and Euskirchen, 2004; Magnani et al., 2007). However, it is not only productivity that is altered during the harvesting and management cycle. Long-term accumulation/sequestration of carbon in the ecosystem is determined by the magnitude and types of input (which is part of the management strategy), and the magnitude and pathway of losses, which in turn depend on various C stabilization mechanisms. The allocation of carbon to the production of different organs changes dramatically during stand development, with greater allocation belowground early in the development (Genet et al., 2010). Second, the stimulation of respiratory losses following a harvest is well documented, and results from a number of causes, including (i) disturbance of soil (Diochon and Kellman, 2008; Diochon et al., 2009; Diochon and Kellman, 2009), (ii) production of large amount of dead biomass (Harmon et al., 1986), (iii) change in the stoichiometry of carbon pools (Harmon et al., 2011), and (iv) change in microclimate (Chen et al., 1993; Noormets et al., 2007). These changes have both short- and long-term consequences, as they affect both the pool sizes, and fluxes of carbon between these pools. However, the decomposition of harvest residues sustains both tree growth and soil properties (Laclau et al., 2010; Versini et al., 2013) and thus contributes to maintaining ecosystem C stocks (Huang et al., 2013). As none of these effects are included in the global land surface models, their estimates of allometric proportions between different C pools are often inconsistent with observations (Wolf et al., 2011a and references therein), particularly in the young stands, and the allocation patterns may be outside the spread of data (Malhi et al., 2011). Although the process-level understanding of carbon partitioning has made strides in the past decade (section: Soil carbon dynamics), a cohesive modeling framework that would tie them all together is yet to emerge (Franklin et al., 2012). Chen et al. (2014) analyzed a number of global ecosystem models, and traced the allocation submodels back to that used by Friedlingstein et al. (1999), who had acknowledged that the modeled biomass estimates were very sensitive to the allocation algorithms used – with nearly 6-fold range in the root:shoot ratio at low-NPP sites. Thus, it is critical that the dynamic responses in allocation, and disturbance-related changes in different C fluxes be realistically depicted in land surface models.
The goal of the current study is to (i) evaluate available information on the controls of photosynthetic carbon gain, allocation, and respiration in forest ecosystems, the responses of these processes to disturbance and management-related drivers, (ii) develop testable hypothesis about carbon cycling in managed/plantation forests, based on the results of (i), and (iii) explore the usability of existing global databases for answering these questions. The main focus is on on-site carbon sequestration potential, as estimated by expected changes in belowground allocation, rate of decomposition, and mechanisms of stabilization. All trends are viewed in the context of expected global increases in nitrogen deposition (Ndep), [CO2] and temperature.
We evaluated the effects of stand density on nitrogen (N"2) fixation, net primary production (NPP) photosynthate partitioning, and canopy characteristics in 5-yr-old red alder (Alnus rubra Bong.) plantations. Our study used acetylene reduction and dimension analysis techniques. Trees in low-density stands (initially spaced 2.74 x 2.74 m) had the highest mass, and surface-area components as well as N"2 fixation. Mid-density stands (initially spaced 1.22 x 1.82 m) had the highest per-unit-area values for leaf mass, canopy volume, branch mass and surface area, root and stump mass, net branch production, aboveground net production, and N"2 fixation. The highest density stands (initially spaced 0.61 x 1.22 m) had the highest values per unit area of the variables: wood volume, bole and total aboveground dry mass, and net bole production. Nodule dry mass per unit area was approximately equal in the mid- and high-density stands, averaging 146 kg/ha. A high correlation between N"2 fixation and leaf mass per tree (r = 0.892) supports an earlier hypothesis (Gordon and Wheeler 1978) about field-grown alder. The lack correlation between leaf mass and N"2 fixation per unit area (averaging 2.15 Mg/ha and 70 kg@?ha^-^1@?yr^-^1, respectively) suggests that high-density stands allocated less photosynthate to nodules of N"2 fixation.
Carbon uptake by forests is a major sink in the global carbon cycle, helping buffer the rising concentration of CO2 in the atmosphere, yet the potential for future carbon uptake by forests is uncertain. Climate warming and drought can reduce forest carbon uptake by reducing photosynthesis, increasing respiration, and by increasing the frequency and intensity of wildfires, leading to large releases of stored carbon. Five years of eddy covariance measurements in a ponderosa pine (Pinus ponderosa)-dominated ecosystem in northern Arizona showed that an intense wildfire that converted forest into sparse grassland shifted site carbon balance from sink to source for at least 15 years after burning. In contrast, recovery of carbon sink strength after thinning, a management practice used to reduce the likelihood of intense wildfires, was rapid. Comparisons between an undisturbed-control site and an experimentally thinned site showed that thinning reduced carbon sink strength only for the first two posttreatment years. In the third and fourth posttreatment years, annual carbon sink strength of the thinned site was higher than the undisturbed site because thinning reduced aridity and drought limitation to carbon uptake. As a result, annual maximum gross primary production occurred when temperature was 3 °C higher at the thinned site compared with the undisturbed site. The severe fire consistently reduced annual evapotranspiration (range of 12–30%), whereas effects of thinning were smaller and transient, and could not be detected in the fourth year after thinning. Our results show large and persistent effects of intense fire and minor and short-lived effects of thinning on southwestern ponderosa pine ecosystem carbon and water exchanges.
Thinning, as a forest management strategy, may contribute towards mitigating climate change, depending on its net effect on forest carbon (C) stocks. Although thinning provides off-site C storage (in the form of wood products) it is still not clear whether it results in an increase, a reduction or no change in on-site C storage. In this study we analyze the effect of thinning on C stocks in a long-term experiment. Different thinning intensities (moderate, heavy and unthinned) have been applied over the last 30 years in a Scots pine (Pinus sylvestris L.) stand, with a thinning rotation period of 10 years. The main C compartments were analyzed: above and belowground tree biomass, deadwood, forest floor and upper 30-cm of the mineral soil and tree biomass removed in thinning treatments. The results revealed that unthinned stands had the highest C stocks with 315 Mg C ha-1, moderate thinning presented 304 Mg C ha-1 and heavy thinning 296 Mg C ha-1, with significant differences between unthinned and heavily thinned stands. These differences were mainly due to C stock in live biomass, which decreased with thinning intensity. However, soil C stocks, forest floor and mineral soil, were not influenced by thinning, all of the stands displaying very similar values 102-107 Mg C ha-1 for total soil; 15-19 Mg C ha-1 for forest floor; 87-88 Mg C ha-1 for mineral soil). These results highlight the sustainability of thinning treatments in terms of C stocks in this pinewood afforestation, and provide valuable information for forest management aimed at mitigating climate change.
The application of the eddy covariance flux method to measure fluxes of trace gas and energy between ecosystems and the atmosphere has exploded over the past 25 years. This opinion paper provides a perspective on the contributions and future opportunities of the eddy covariance method. First, the paper discusses the pros and cons of this method relative to other methods used to measure the exchange of trace gases between ecosystems and the atmosphere. Second, it discusses how the use of eddy covariance method has grown and evolved. Today, more than four hundred flux measurement sites are operating world-wide and the duration of the time series exceed a decade at dozens of sites. Networks of tower sites now enable scientists to ask scientific questions related to climatic and ecological gradients, disturbance, changes in land use, and management. The paper ends with discussions on where the field of flux measurement is heading. Topics discussed include role of open access data sharing and data mining, in this new era of big data, and opportunities new sensors that measure a variety of trace gases, like volatile organic carbon compounds, methane and nitrous oxide, and aerosols, may yield. This article is protected by copyright. All rights reserved.
A system of intensive analysis of weight, production and surface relationships was applied to seven species of trees and shrubs in the Brookhaven oak-pine forest. Distributions of biomass and net production among major plant parts are discussed in terms of regressions and of averages for the sets. Study of allometric relationships for individuals of all species combined show trends in the dimensional relations of plant parts which shift gradually and continuously with plant size from small shrubs to forest trees. Regressions within species may be effectively used to estimate weight, production and surface relations of shrub communities and forests. For this purpose, and in relation to studies of gaseous exchange, nutrient circulation and dominance-diversity structure, the system of analysis has substantial usefulness for the study of shrubland and forest eco-systems.
Short-rotation energy forestry is one of the potential ways for management of abandoned agricultural areas. It helps sequestrate carbon and mitigate human-induced climate changes. Owing to symbiotic dinitrogen (N2) fixation by actinomycetes and the soil fertilizing capacity and fast biomass growth of grey alders, the latter can be suitable species for short-rotation forestry. In our study of a young grey alder stand (Alnus incana (L.) Moench) on abandoned arable land in Estonia we tested the following hypotheses: (1) afforestation of abandoned agricultural land by grey alder significantly affects the soil nitrogen (N) status already during the first rotation period; (2) input of symbiotic fixation covers an essential part of the plant annual N demand of the stand; (3) despite a considerable N input into the ecosystem of a young alder stand, there will occur no significant environmental hazards (N leaching or N2O emissions). The first two hypotheses can be accepted: there was a significant increase in N and C content in the topsoil (from 0.11 to 0.14%, and from 1.4 to 1.7%, respectively), and N fixation (151.5kgNha−1yr−1) covered about 74% of the annual N demand of the stand. The third hypothesis met support as well: N2O emissions (0.5kgNha−1yr−1) were low, while most of the annual gaseous N losses were in the form of N2 (73.8kgNha−1yr−1). Annual average NO3–N leaching was 15kgNha−1yr−1 but the N that leached from topsoil accumulated in deeper soil layers. The soil acidifying effect of alders was clearly evident; during the 14-year period soil acidity increased 1.3 units in the upper 0–10cm topsoil layer.
Fine root bio- and necromass, net primary production (NPP) of fine roots and its proportion of the NPP of trees, as well as turnover rate were investigated in a fertile middle-aged Norway spruce (Picea abies (L.) Karst) stand by sequential core and ingrowth core methods. The stand's site type is Oxalis, the site quality class is Ia and the soil type is Umbric Luvisol (FAO classification). Twenty soil cores (volumetric samples, core diameter 38mm) were taken monthly during the period June-1996 to November 1996 and in June-1997. Ingrowth cores were collected, 15 at a time, during the growing seasons from 1997 to 1999, once after first year and three times in the second and third years. Spruce roots from samples collected by both methods were separated into living and dead roots (two diameter classes:
We present four years (2005–2008) of biometric (B) and eddy-covariance (EC) measurements of carbon (C) fluxes to constrain estimates of gross primary production (GPP), net primary production (NPP), ecosystem respiration (RE) and net ecosystem production (NEP) in an age-sequence (6-, 19-, 34-, and 69-years-old in 2008) of pine forests in southern Ontario, Canada. The contribution of individual NPP and respiration component fluxes varied considerably across the age-sequence, introducing different levels of uncertainty. Biometric and EC-based estimates both suggested that annual NPP, GPP, RE, and NEP were greatest at the 19-year-old site. Four-year mean values of NEP(B) and NEP(EC) were similar at the 6-year-old seedling (77 and 66gCm−2y−1) and the 69-year-old mature site (135 and 124gCm−2y−1), but differed considerably at the 19-year-old (439 and 736gCm−2y−1) and the 34-year-old sites (170 and 392gCm−2y−1). Both methods suggested similar patterns for inter-annual variability in GPP and NEP. Multi-year convergence of NEP(B) and NEP(EC) was not observed over the study period. Ecosystem C use efficiency was correlated to both forest NEP(EC) and NPP(B) suggesting that high productive forests (e.g. middle-age stands) were more efficient in sequestering C compared to low productive forests (e.g. seedling and mature stands). Similarly, negative and positive relationships of forest productivity with the total belowground C flux (TBCF) to GPP ratio and with the ratio of autotrophic to heterotrophic respiration (RA:RH), respectively, determined inter-annual and inter-site differences in C allocation. Integrating NEP across the age-sequence resulted in a total net C sequestration of 137 and 229tCha−1 over the initial 70 years as estimated by the biometric and EC method, respectively. Total ecosystem C sequestered in biomass at the 69-year-old site suggested an accumulation of 160tCha−1. These three estimates resulted in a mean C sequestration of 175±48tCha−1. This study demonstrates that comparing estimates from independent methods is imperative to constrain C budgets and C dynamics in forest ecosystems.
The resolution of the Kyoto Protocol to include effects of land use and land-use change in global carbon budgets has put focus on C sequestration following afforestation of former arable land. Carbon is sequestered in the aggrading biomass of the new forests, but the question remains, to what extent the former arable soils will contribute as sinks for CO2. The present study explored changes in soil C stores following afforestation of former arable land with oak (Quercus robur L.) and Norway spruce (Picea abies (L.) Karst.). Seven stands of each tree species on nutrient-rich soils made up a chronosequence ranging from 1 to 29 years. An adjacent ∼200-year-old mixed deciduous plantation was included to give information on the possible long term changes in soil C. Soil sampling included organic layers and three layers of the mineral soil to a depth of 25 cm.
We reviewed the experimental evidence for long-term carbon (C) sequestration in soils as consequence of specific forest management strategies. Utilization of terrestrial C sinks alleviates the burden of countries which are committed to reducing their greenhouse gas emissions. Land-use changes such as those which result from afforestation and management of fast-growing tree species, have an immediate effect on the regional rate of C sequestration by incorporating carbon dioxide (CO(2)) in plant biomass. The potential for such practices is limited in Europe by environmental and political constraints. The management of existing forests can also increase C sequestration, but earlier reviews found conflicting evidence regarding the effects of forest management on soil C pools. We analyzed the effects of harvesting, thinning, fertilization application, drainage, tree species selection, and control of natural disturbances on soil C dynamics. We focused on factors that affect the C input to the soil and the C release via decomposition of soil organic matter (SOM). The differentiation of SOM into labile and stable soil C fractions is important. There is ample evidence about the effects of management on the amount of C in the organic layers of the forest floor, but much less information about measurable effects of management on stable C pools in the mineral soil. The C storage capacity of the stable pool can be enhanced by increasing the productivity of the forest and thereby increasing the C input to the soil. Minimizing the disturbances in the stand structure and soil reduces the risk of unintended C losses. The establishment of mixed species forests increases the stability of the forest and can avoid high rates of SOM decomposition. The rate of C accumulation and its distribution within the soil profile differs between tree species. Differences in the stability of SOM as a direct species effect have not yet been reported.
Sustainable forestry is based on the principle that harvesting practices should avoid negative influence on soil fertility, wood production and long-term soil carbon (C) stocks. We examined C and nutrient concentrations and stocks of Scots pine (Pinus sylvestris L.) stands on Arenosols in south-western Lithuania. The stands were 10, 20, 40, 50 and 65 years of age. C concentrations were relatively constant, while the concentrations of N, P, K, Ca, Mg and S often varied between compartments and stand ages.
The total aboveground stocks of nitrogen (N) were estimated to be in the range of 185–260 kg ha−1, and 78–189 kg ha−1 for calcium (Ca), 75–104 kg ha−1 for potassium (K), 22–33 kg ha−1 for phosphorus (P), 21–41 kg ha−1 for magnesium (Mg) and 16–28 kg ha−1 for sulphur (S). Corresponding stocks of the crown alone were 139–207 kg ha−1 of N, 54–88 kg ha−1 of Ca, 44–79 kg ha−1 of K, 15–26 kg ha−1 of P, 15–23 kg ha−1 of Mg, and 11–15 kg ha−1 of S. Biomass, C and nutrient stocks in the crown did not change with age, whereas the stemwood stocks increased with stand age. The total removals of C and N over a whole 100-year rotation were simulated to be 129 Mg ha−1 and 449 kg ha−1, respectively. An example scenario was created to compare the magnitude of potential nutrient removals with the atmospheric influx, soil stocks, and the internal litterfall flux. We suggest that intensified utilisation of these stands for bioenergy may be sustainable.
Keywords
Scots pine;
Pinus sylvestris;
Aboveground biomass;
Forest bioenergy;
Carbon;
Nutrients