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Carbon budgets in fertile grey alder ( Alnus incana (L.) Moench.) stands of different ages
Abstract
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.
... The strength of the study lays in empirically estimated C fluxes, which give new knowledge on C cycling in forest ecosystems. Further, similar approaches have been used previously in several earlier studies (Uri et al. 2014(Uri et al. , 2017aAun et al. 2021aAun et al. , b, 2022. ...
... An allometric Eq. (1) was used to estimate the aboveground woody biomass of the trees in the stand (Uri et al. , 2017a where y is the aboveground biomass or stemwood biomass of a model tree; x is D 1.3 (cm); and a and b are parameters of the model (Table 3). ...
... A negative value of NEP was considered to be carbon loss and a positive value to be the net transfer of C from the atmosphere into the forest ecosystem. NPP was estimated by summing up the annual production of the aboveground and belowground biomass fractions of trees and understorey vegetation (Varik et al. 2015;Uri et al. 2017aUri et al. , b, 2019Lõhmus et al. 2019;Aun et al. 2021a, b;Uri et al. 2022a). ...
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.
... For estimation of soil nutrient and C content as well as pH, samples from twelve random points over the study site were taken from different depths (0-10 and 10-20 cm) with a soil corer. Samples were pooled to form a composite sample for chemical analyses (Table 2) (Uri et al. 2017a(Uri et al. , 2017b, thus the concentration of C and nutrients in the different soil layers was analysed in three replicates. At all sites, the decomposition of organic matter was favourable owing to high soil fertility and readily degradable leaf litter ) and thus the soil organic layer (forest floor) was not formed. ...
... Aboveground biomass and production of the trees The aboveground biomass and production of silver birch was estimated using the model tree method (Bormann and Gordon 1984;Uri et al. 2012Uri et al. , 2017aUri et al. , 2017b beginning from 4-year-old stands, as the biomass of the trees in the first 2-3 post-harvest years was practically negligible and was therefore not considered. Five model trees were cut from each stand according to the height distribution of the trees. ...
... Depending on the height of the model trees, 2-5 stem discs were taken for measuring the proportions of the stemwood and stembark, as well as dry matter content and annual stemwood production. Allometric function (1) was used for the estimation of aboveground biomass and stemwood production (Uri et al. 2017a(Uri et al. , 2017b ...
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.
... where y is the aboveground biomass or stemwood production of model tree (g),X is breast height diameter (cm) or height (m).a and b are parameters (S3). For estimating the biomass of the different compartments at the stand level, the percentage distribution of the fractions of the model trees was applied (Uri et al., 2017a(Uri et al., , 2017b. ...
... The current annual production of the stemwood was estimated on the basis of the measured radial increments (Uri et al., 2012(Uri et al., , 2017a(Uri et al., , 2017b of the model tree. Cross-section disks were cut from the stump and the middle of each stem section and were dried and polished, and the total width of the last five annual rings was measured to 0.001 mm using the software WINDENDRO (Regent Instruments Inc.). ...
... The production of the coarse root fraction was calculated on the basis of the equal relative increments of aboveground woody biomass, while the relative increments of the above-and belowground wooden biomasses were assumed to be proportionate (Varik et al., 2015;Uri et al., 2017aUri et al., , 2017b. ...
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.
... Aboveground biomass was estimated using the model tree method (Bormann and Gordon, 1984;Uri et al., 2012Uri et al., , 2017a. In both stands 5-7 model trees were felled in both treatments (outside of the sample plots) in August 2017, according to the diameter distribution of the trees. ...
... A C budget for the studied stands was compiled by balancing the input and output C fluxes for the studied plots for 2017, i.e. for the second post-thinning year. For defining net ecosystem production (NEP) (3), a well-known approach was employed: we calculated the difference between net primary production (NPP) and C loss through heterotrophic respiration (Rh) and leaching (L) (Clark et al., 2001;Lovett et al., 2006;Meyer et al., 2013), which we have used also in our recent studies (Uri et al., 2017a(Uri et al., ,b, 2019: ...
... C leaching was very low (Table 11), which is consistent with earlier similar studies (Uri et al., 2017a;Becker et al., 2016). Because of its negligible share of the leached TOC flux in the whole budget, it is often ignored in C budgeting . ...
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.
... Several publications have reported the high biomass production of grey alder both on mineral and organic soils (e.g. Granhall et al. 1994;Rytter 1996;Uri et al. 2003aUri et al. , 2009Uri et al. , 2017Aosaar et al. 2013;Hytönen and Saarsalmi 2015;Rytter and Rytter 2016, etc.). Recently, the role of grey alder stands in carbon (C) accumulation in the Nordic countries was analyzed (Rytter and Rytter 2016) and a new yield-table for Estonian grey alder stands was published . ...
... Leaf litter was gathered every fortnight and weekly during intensive litter fall. The leaf litter data of MAT for 2012-2014 is partly published in Uri et al. (2017) where the annual C input into the soil via leaf litter is estimated. In the current paper, the corresponding N flux is presented. ...
... The fine root production of MAT was estimated using the root mesh method (Hirano et al. 2009;Lukac and Godbold 2010;Uri et al. 2017). Nylon meshes (20 × 7 cm) were installed in autumn 2012 and the first sampling was done one year later when 25 root meshes with the surrounding soil block were dug out in order to avoid loss of fine roots. ...
Grey alder (Alnus incana) is a highly productive indigenous tree species, potential for short-rotation forestry in the Baltic and Nordic countries. The aim of the study was to investigate the development of a new forest generation, as well as the nitrogen (N) and carbon (C) storages and fluxes in a grey alder regenerating coppice (COP) after clear-cut and in an adjacent unharvested 21-year-old stand (MAT), which had reached its bulk maturity. The regeneration of COP was rapid and 5 years after clear-cut, stem mass was 6.4 t ha⁻¹. The nitrogen demand of the aboveground part of the 5-year-old COP trees was estimated to be roughly half of the corresponding value for MAT, depending mostly on leaf production. The annual N leaching flux in MAT was in the range of 16-29 kg ha⁻¹, the corresponding values for COP were roughly half of that. Net nitrogen mineralization did not differ significantly between MAT (117 kg ha⁻¹) and COP (129 kg ha⁻¹). For the soil respiration study, a 32-year-old grey alder stand growing at a similar site was included; soil respiration was significantly higher in MAT compared to COP in all study years in both studied stands.
... Alder is a widely distributed tree species across hemiboreal and temperate zones, commonly found in riparian buffers, yet data on its forest C exchange remain surprisingly scarce. In a chronosequence of alder forest stands, studied by Uri et al. (2017), the oldest forest ("Kalliste") was of similar age as the current site at the time of the research (40 years old). The total annual 315 net ecosystem production (NEP) of Kalliste stand was -77 g C m -2 y -1 denoting the site as a weak net C source ecosystem (NEP = -NEE, Chapin et al., 2011), while the average of -586 g C m -2 y -1 makes our site a strong sink of C. The differences in C balance between the sites likely stem from differences in soil fertility, as the Kalliste stand was established on former grassland, whereas the present site is located on nutrient-rich former agricultural land. ...
... In waterlogged or anoxic layers, organic matter breaks down more slowly, potentially contributing to lower ER. Additionally, alder forests are known for their rapid growth and high nitrogen cycling (Aosaar et al., 2012;Rytter and Rytter, 2016;Uri et al., 2017), which may enhance GPP without necessarily accelerating decomposition if soil moisture remains high. On the other hand, reduced soil water availability during the drought year appeared to suppress heterotrophic respiration while GPP remained mostly unaffected. ...
Alder forests are widely spread across Northern Hemisphere, frequently occupying riparian buffer zones and playing a key role in enhancing soil fertility through symbiosis with nitrogen-fixing bacteria. Despite their ecological significance, studies on carbon (C) and water (H2O) exchange in alder forests remain scarce, particularly in the context of hydroclimatic variability and extreme weather events. In this study, we used eddy-covariance flux measurements from three contrasting years to assess the C balance and H2O exchange of a mature riparian grey alder forest in the hemiboreal zone in Estonia. The site was a strong and consistent carbon sink with annual net ecosystem exchange (NEE) ranging from -496 to -663 g C m⁻² y⁻¹, gross primary production (GPP) from -1258 to -1420 g C m⁻² y⁻¹ and ecosystem respiration (ER) from 595 to 923 g C m⁻² y⁻¹. Evapotranspiration (ET) varied from 194 to 342 kg H2O m⁻² y⁻¹ and ecosystem water use efficiency (EWUE) was 4.2 – 6.5 g C kg H2O-1. The drought and heatwave year (2018) featured the highest net carbon uptake, driven by an increase in GPP during spring and a reduction in ER during late summer and autumn. A minor impact of drought on GPP combined with a 35 % reduction in ET in 2018 lead to peak values of EWUE in response to H2O limitation. In 2019, we found no evidence of a short-term drought legacy effect, as carbon exchange components recovered to the 2017 levels and ET was the highest out of years. Given that this forest is beyond the typical harvestable age, its strong and consistent carbon sequestration, combined with high short-term resilience, provides valuable insights for sustainable forest management. These findings highlight the potential of riparian grey alder forests to maintain productivity under hydroclimatic variability, reinforcing their role in regional carbon cycling as a part of natural climate mitigation solutions.
... Our results revealed that the ecosystem C pools in the aboveground and belowground components of the tree, shrubs, herbs, litter, and soil have changed significantly during A. nepalensis forest stands development. Developing forests exert a significant impact on biotic and abiotic factors, such as plant species, soil physicochemical properties, microbial communities, quality and quantity of outputs and inputs of plant debris (Kumar, Verma, & Garkoti, 2020;Myrold & Huss-Dannel, 1994;Susaeta, Carter, & Adams, 2014;Taeroe, Mustapha, Stupak, & Raulund-Rasmussen, 2017;Uri et al., 2014;Uri et al., 2017). ...
... icantly across the forest chronosequence and was mainly affected by tree species composition. Among tree species, the A. nepalensis alone contributed 25.91% to 79.88% to the total vegetation carbon stock, indicating that bulk of the vegetation carbon stock is determined by the A. nepalensis mainly due to its ability to fix atmospheric nitrogen, which could significantly increase the rate of accumulation of biomass(Brookshire et al., 2019;Chaer, Resende, Campello, de Faria, & Boddey, 2011;Hoogmoed, Cunningham, Baker, Beringer, & Cavagnaro, 2014;Knoth, Kim, Ettl, & Doty, 2014;Temperton et al., 2003;Uri et al., 2017). A previous study revealed that nitrogenfixing tree species have a major influence on forest soil and increase the carbon content of the soil. ...
... Our results revealed that the ecosystem C pools in the aboveground and belowground components of the tree, shrubs, herbs, litter, and soil have changed significantly during A. nepalensis forest stands development. Developing forests exert a significant impact on biotic and abiotic factors, such as plant species, soil physicochemical properties, microbial communities, quality and quantity of outputs and inputs of plant debris (Kumar, Verma, & Garkoti, 2020;Myrold & Huss-Dannel, 1994;Susaeta, Carter, & Adams, 2014;Taeroe, Mustapha, Stupak, & Raulund-Rasmussen, 2017;Uri et al., 2014;Uri et al., 2017). ...
... icantly across the forest chronosequence and was mainly affected by tree species composition. Among tree species, the A. nepalensis alone contributed 25.91% to 79.88% to the total vegetation carbon stock, indicating that bulk of the vegetation carbon stock is determined by the A. nepalensis mainly due to its ability to fix atmospheric nitrogen, which could significantly increase the rate of accumulation of biomass(Brookshire et al., 2019;Chaer, Resende, Campello, de Faria, & Boddey, 2011;Hoogmoed, Cunningham, Baker, Beringer, & Cavagnaro, 2014;Knoth, Kim, Ettl, & Doty, 2014;Temperton et al., 2003;Uri et al., 2017). A previous study revealed that nitrogenfixing tree species have a major influence on forest soil and increase the carbon content of the soil. ...
Nitrogen‐fixing Nepalese alder (Alnus nepalensis D. Don.) is a rapidly‐growing pioneer tree species that often forms pure stands in areas affected by landslides, but also occurs mixed with other late‐successional species in the central Himalaya. In this study, we assessed the distribution of carbon in vegetation and soil in a chronosequence of A. nepalensis (3‐270 years old) forest stands and evaluated its correlation with the stand and alder total basal area (TBA). The study was conducted in six different naturally occurring forest stands in a chronosequence viz., alder‐early regenerating (AER), alder‐late regenerating (ALR), alder young‐mixed (AYM), alder mature‐oak (Quercus leucotrichophora) mixed (AMOM), alder mature‐rhododendron (Rhododendron arboreum) mixed (AMR), and alder old‐oak (Q. leucotrichophora) mixed (AOOM) forests. The chronosequence consisted of three young unreserved, AER, ALR, and AYM (age 3‐25) and three older reserved, AMOM, AMR, and AOOM (age 80‐270) stands. We used structural equation modeling (SEM) to quantify the contribution of various carbon pools on ecosystem carbon stock. Forest carbon stock significantly increased (P<0.05) with forest age and TBA, indicating that succession is the driving factor of the forest ecosystem processes, carbon accumulation, and therefore, change in vegetation biomass carbon and soil carbon in the chronosequence of A. nepalensis forests. Total vegetation biomass carbon (tree, shrubs, herbs, and litter) contained ~ 12.54 ‐289.85 Mg ha‐1 (79.11‐ 57.77 % total carbon stock), and soil carbon (depths of 0‐10 cm in AER, 0‐30 cm in AYM, 0‐100 cm in remaining forest stands) contained ~3.31‐210.13 Mg ha‐1 (20.8‐42 % total carbon stock) and positively increased with stand and A. nepalensis total basal area. The tree layer biomass carbon stock was considerably higher than the understory (shrubs, herbs, and forest floor). The soil carbon stock was reported to be influenced by the successional stages. Therefore, these findings reflect that the A. nepalensis forest development in the central Himalaya lead to storage of large amount of carbon stock in both plant biomass and soil.
... The branch biomass was assumed to be 5-10% of the aboveground biomass depending on the tree species (Helmisaari et al., 2002;Uri et al., 2007; unpublished National Forest Inventory database). The coarse root biomass was estimated to be 20% of the aboveground biomass (Külla, 1997;Uri et al., 2017). The production of branches and coarse roots were calculated on the basis of the equal relative increments of the aboveground woody biomass, and the relative increments of the aboveground and belowground woody biomass fractions were assumed to be equal . ...
... The impact of leaching on the SOC pool was not considered in this study, because it has been shown in the literature (Stielstra et al., 2015;Uri et al., 2017) that the soil carbon loss is dominated by the CO 2 flux rather than leached DOC. In addition, the ICP Integrated Monitoring reports (available at the Estonian monitoring programmes website: http://seire.keskkonnainfo.ee/) ...
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.
... The aboveground biomass and the annual production of the trees were estimated in October 2015, 2016 and 2017 when the process of biomass formation was completed; the method of model trees (Uri et al., 2012(Uri et al., , 2017b was used. For this, four randomly situated round sample plots (25 m 2 ) were established in the study area and tree height as well as annual height increment of all trees were measured. ...
... Water from the canisters was sampled monthly from June 2016 to December 2017, through a plastic pipe, using a peristaltic vacuum pump. The annual leaching of C was calculated by summing the leached fluxes of the different months, taking account of the corresponding C concentrations from percolated water (Becker et al., 2016;Uri et al., 2017b). ...
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.
... Alnus species, particularly A. incana, are characterized by relatively short lifespans, rendering them susceptible to stem decay, particularly in mature stands [42,44,45]. Research in the Baltic region has highlighted that middle-aged gray alder stands tend to function as carbon sinks, while mature stands transition into carbon sources, underscoring the complex role of these species in the carbon cycle within forest ecosystems [46]. ...
Efforts to enhance carbon storage in forest ecosystems through policy and management decisions rely on accurate forest biomass assessments. However, most forest inventories consider tree mortality the only form of aboveground biomass loss, overlooking other important factors, such as wood decay in living trees. In this study, using linear mixed-effects models, we delve into the sustainability of mature and over-mature deciduous forests in Latvia by conducting a comprehensive analysis of stem rot severity, identifying species for which the impact of stem rot on their carbon stock reduction was most significant. The analysis focused on determining the proportion of discolored wood, decomposed wood, and hollow spaces within the stems of 190 living deciduous trees commonly found in hemiboreal forests. The study reveals a greater extent of stem rot and more extensive decay in Populus tremula trees than in Betula spp., Alnus glutinosa, and Alnus incana. It emphasizes the influence of tree species, age, and diameter at breast height on stem rot proportions. The stump rot area significantly predicts the amount of decomposed and discolored wood within the stem. The study provides valuable insights for sustainable forestry practices and highlights challenges in estimating stem rot severity, emphasizing the need for comprehensive diagnostic methods.
... Alnus species, particularly A. incana, are characterized by relatively short lifespans, rendering them susceptible to stem decay, particularly in mature stands [39,41,42]. Research in the Baltic region has highlighted that middle-aged gray alder stands tend to function as carbon sinks, while mature stands transition into carbon sources, underscoring the complex role of these species in the carbon cycle within forest ecosystems [43] According to a study by Hynynen et al. [44], silver birch (B. pendula) has a lower decay incidence than other boreal tree species, such as P. tremula, A. glutinosa, A. incana, and P. abies. ...
Efforts to enhance carbon storage in forest ecosystems through policy and management decisions
rely on accurate forest biomass assessments. However, most forest inventories consider tree mortality the only
form of aboveground biomass loss, overlooking other important factors, such as wood decay in living trees. In
this study, using linear mixed-effects models, we delve into the sustainability of mature and over-mature
deciduous forests in Latvia by conducting a comprehensive analysis of stem rot severity, identifying species
for which the impact of stem rot on their carbon stock reduction was most significant. The analysis focused on
determining the proportion of discolored wood, decomposed wood, and hollow spaces within the stems of 190
living deciduous trees commonly found in hemiboreal forests. The study reveals a greater extent of stem rot
and more extensive decay in Populus tremula trees than in Betula spp., Alnus glutinosa, and Alnus incana. It
emphasizes the influence of tree species, age, and diameter at breast height on stem rot proportions. The stump
rot area significantly predicts the amount of decomposed and discolored wood within the stem. The study
provides valuable insights for sustainable forestry practices and highlights challenges in estimating stem rot
severity, emphasizing the need for comprehensive diagnostic methods.
Keywords: internal decay; stem quality; discoloration; old forests; tree cavities; decay assessment;
resource management; political ecology
... 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.
... These species have relatively short life spans, with those in matured stands being prone to stem decay [30,34]. Studies in the Baltic region have demonstrated that gray alder stands in the middle-age stage typically act as carbon sinks while mature stands become a carbon source [35]. These findings indicate the need to investigate the carbon balance of alder stands under different management regimes to increase the forests' climate change mitigation potential. ...
Species-specific basic density (BD) data are necessary to improve the indirect methods of biomass determination. The density of tree components (e.g., bark, branches, roots) is studied much less than that of stem wood. Nevertheless, ignoring the specific BD values of these components in biomass calculations can lead to errors. The study aims to investigate BD variation of aboveground and belowground tree components by studying a total of 162 gray alder (Alnus incana (L.) Moench) and common alder (Alnus glutinosa (L.) Gaertn.) trees. From them, 55 stumps were excavated to determine the BD of the belowground components. Our findings reveal that the volume-weighted BD of the stem (wood and bark) and the branch density of common alder are higher compared to gray alder. Both species have similar bark density, while the BD of belowground components is higher for gray alder. The stem wood density of both species increases upward from the stump to the top. Compared to gray alders, the stems of common alders have more distinct radial within-stem density variation. According to our results, the application of default Alnus spp. wood density values recommended in the IPCC guidelines for the calculation of total biomass and carbon stock is likely causing overestimation. The BD values obtained in our study on alders’ biomass components will allow for more accurate appraisals of total biomass and carbon stock for gray and common alder forests.
... (Official Journal of the EU, 2021). Studies approves that grey alder stands at middle-age stages act as carbon sink, while mature stands become carbon source (Uri et al., 2017). It can be hypothesized that also common alder matured stands at some stage can become a carbon source because of declined net primary production and stem decay. ...
The occurrence of wood decay in common alder stems (Alnus glutinosa (L.) Gaertn.) was studied based on data obtained in seven matured stands in Latvia age ranging from 65 to 122 years. The study was intended as a pilot study to test the possible use of nondestructive micro-drill (Rinntech Resistograph® R650) for detection of the different stages of wood decay within common alder stems. The drilling profiles were visually compared with the wood samples obtained from increment borer or cross-cut sections at actual drilling height. The study confirmed initially proposed hypothesis that drilling profiles obtained using the Resistograph enabled the diagnosis of the common alder stem health condition. Wood decay stages-spongy rot and cavity can be detected successfully by the Resistograph; however, this non-destructive method does not detect discoloration in the wood, which is the earlier stage of wood decay. We found significant (p<0.05) positive correlation between decay occurrence and some of examined forest stand characteristics such as mean stand diameter, stand age and mean tree volume. The tree inspection showed that the preservation of old common alder stands can lead to a significant loss of wood quality. Based on this pilot study, we conclude that if the economic interests are prioritized in management of studied stands, the reduction of actual harvesting age of the common alder stands have to be considered.
... There are several empirical studies about suitable tree species for afforesting agricultural land in various parts of northern Europe, such as willow [26,27], alder [28,29], birch [30,31], hybrid aspen [32,33], poplar [34][35][36], spruce [37,38] and larch [39]. These studies report very high production of biomass and shorter rotation cycles compared to the same species growing on forestland. ...
The new European Union Forest Strategy for 2030 aims to plant an additional 3 billion trees on non-forest land to mitigate climate change. However, the choice of tree species for afforestation to achieve the maximum climate benefit is unclear. We compared the climate benefit of six different species in terms of carbon (C) sequestration in biomass and the harvested wood substitution in products to avoid carbon dioxide (CO2) emissions from fossil-based materials over the 100-year period by afforesting about ¼ of the available area in northern Europe. The highest climate benefit was observed for larch, both at a stand scale (1626 Mg CO2 eqv. ha⁻¹) and at the landscape level for the studied scenario (579 million Mg CO2 eqv.). Larch was followed by Norway spruce, poplar, hybrid aspen and birch, showing a climate benefit about 40–50% lower than that for larch. The climate benefit of willow was about 70% lower than larch. Willow showed 6–14-fold lower C stocks at the landscape level after 100 years than other tree species. The major climate benefit over the 100-year period comes from wood substitution and avoided emissions, but C stock buildup at the landscape level also removes significant amounts of CO2 already present in the atmosphere. The choice of tree species is important to maximize climate change mitigation.
... Recent studies on methane (CH 4 ) and nitrous oxide (N 2 O) balance have highlighted the importance of trees, which may act either as sources or sinks for both gases [1][2][3]. Grey alder (Alnus incana (L.) Moench) is a fast-growing, common pioneer tree species in the Northern hemisphere, often found in riparian zones [4][5][6] and with excellent potential for short-rotation forestry [7][8][9]. Wetland plants such as alder adapt to wet conditions by possessing air-filled aerenchyma to supply tissues with oxygen [10] and constitute a pathway for general gas exchange through plants [11,12]. Further, the decomposed litter of nutrient-rich alder forests improves soil properties, alters microbial activities in the soil, and consequentially affects the CH 4 and N 2 O exchange [13,14]. ...
Tree stems play an important role in forest methane (CH4) and nitrous oxide (N2O) flux dynamics. Our paper aimed to determine the unknown diurnal variability of CH4 and N2O exchange in grey alder tree stems. The gas fluxes in tree stems and adjacent soil were measured using manual static and dynamic chamber systems with gas chromatographic and laser-spectroscopic analysis, respectively. The alder trees were predominant emitters of CH4 and N2O; however, N2O emission from stems was negligible. The soil mainly emitted N2O into the atmosphere and was both a source and sink of CH4, depending on environmental conditions. Neither the tree stems nor the riparian forest soil showed significant differences in their CH4 and N2O fluxes between the daytime and nighttime, independently of the exchange rates. In contrast to several previous studies revealing a diurnal variability of greenhouse gas fluxes from tree stems, our investigation did not show any clear daytime–nighttime differences. On the other hand, we found quite clear seasonal dynamics initiated by changing environmental conditions, such as temperature and soil water conditions and tree physiological activity. Our results imply a transport role of tree stems for soil-produced CH4 and N2O rather than the production of these gases in tree tissues, even though this cannot be excluded.
... The positive relationship between A. nepalensis basal area with SOC content, total N content, SOC stock, and total N stock ( Fig. 9) across the OMA stands, suggest that A. nepalensis contributes to increase in soil C and N storage. Similar relations explaining the role of alder in improvement of soil nutrient capital have also been described by earlier workers (Binkley et al., 1992;Mitchell and Ruess, 2009;Mitchell and Ruess, 2009;Preem et al., 2012;Uri et al., 2014;Uri et al., 2017;Pietrzykowski et al., 2018;Krishna et al., 2020). Fine root traits are typically influenced by soil physical and chemical properties and stand attributes (Ingestad and Agren, 1991). ...
The main objective of the study was to investigate influence of Nepalese alder (Alnus nepalensis D. Don) on fine root biomass (diameter ≤ 2 mm) dynamics and the physical and chemical properties of the soil in white oak (Quercus leucotrichophora A. Camus) forests. Five representative stands of each oak mixed alder (OMA) and oak without alder (OWA) were selected along the stand development gradient in the Indian central Himalaya. Fine root and soil samples from of 0–10 cm, 10–20 cm, and 20–30 cm depths were collected using soil core method. Soil physical and chemical properties and monthly variations in fine root dynamics (biomass distribution and decomposition) were analyzed. Fine root decomposition was studied by using the litterbag technique. Redundancy and correlation analyses were performed to evaluate the relationship between fine root dynamics, stands, and tree total basal area and soil properties. Both the fine root biomass and production of Q. leucotrichophora were significantly (P < 0.05) higher for oak without alder stands than oak mixed alder stands. Fine root biomass, production, and turnover rate of A. nepalensis were significantly (P < 0.05) higher than Q. leucotrichophora in oak mixed alder stands. Within the investigated soil profile, in all the sites, maximum fine root biomass and production were found in the upper (0–10 cm) soil depths. The analyses revealed clear differences in all the measured soil physical and chemical properties and fine root traits in oak mixed alder and oak without alder stands. The soil organic carbon (SOC), total nitrogen (TN) contents, and soil C and N stocks were significantly (P < 0.05) higher in oak mixed alder stands than oak without alder stands while opposite trends were found for soil pH and bulk density (BD). Present findings reveal that improvement of the soil properties under oak mixed alder stands was significantly higher than the oak without alder stands. Fine root decomposition for A. nepalensis was significantly faster than Q. leucotrichophora. Q. leucotrichophora fine roots in OMA stands decomposed at significantly faster rates compared to OWA stands. Additionally, the present study suggests that variation, in fine root dynamics across the forest stands was not only positively correlated to the soil physical and chemical properties but also highly dependent on the forest stand characteristics.
... establishment aids soil recovery, and may significantly benefit carbon sequestration(Bastin et al., 2019;Perks, Nagy, Meir, & Auld, 2010;Uri et al., 2017), lower grazing may reduce grassland species richness(Evans et al., 2015;Mitchell et al., 2017;Pakeman, Fielding, Everts, & Littlewood, 2019). The large impact of the location and type of woodland expansion on ecosystem service provision (such as on river baseflow,Nisbet et al., 2011) further complicates trade-offs, and highlights the importance of ensuring 'the right trees, are in the right place'(NCC, 2020). ...
Extreme rainfall and flood events are predicted to increase in frequency and severity as a consequence of anthropogenic climate change. In UK upland areas, historical over‐grazing and associated soil compaction have further exacerbated peak flood levels and flash‐flood risk along many river catchments. As a result, the reinstatement of upland woodland is increasingly seen as a key component of an integrated suite of options forming part of Natural Flood Management (NFM) associated with a “public money for public goods” approach to European agriculture. Nevertheless, understanding the impact of native woodland establishment on upland soil hydrology remains relatively poor. We compare physical and hydrological properties from the surface soils of establishing woodland and grazed pasture across four flood vulnerable upland headwater catchments in Dartmoor National Park, SW England. We show upland native woodland establishment is a viable soil recovery option, with a doubling of soil saturated hydraulic conductivity, increased “wetness threshold” and reduced surface soil compaction and bulk density within 15 years of establishment. Our study supports the establishment of native woodland as an effective tool to improve the hydrological functioning of soils in upland pastoral catchments and the provision of flash‐flood mitigation “ecosystem services”. We caution however, that land managers and policy makers must consider past and present management, soil type and catchment location when planning new NFM schemes if environmental benefits are to be maximised and “public money for public goods” are to be commensurate with outcomes. This article is protected by copyright. All rights reserved.
... We base our analysis of A. incana dynamics in the study reach entirely on growth performance estimates from lidar data. However, we used field measurements collected in 2007 and published data (Aosaar & Uri, 2008;Huss-Danell & Lundmark, 1988;Johansson, 2005;Krzaklewski, Pietrzykowski, & Wos, 2012;Uri et al., 2014Uri et al., , 2017Uri, Lohmus, Kiviste, & Aosaar, 2009;Wilson et al., 2018) to check that the lidar estimates were robust. For reasons of space economy, we present these data sets and their analysis in Data S1 (supplementary material) and summarize the results below. ...
Following a review of the European distribution, habitat requirements and life history characteristics of two riparian tree species, Alnus incana (L.) Moench (grey alder, a member of the Betulaceae family) and Populus nigra L. (black poplar, a member of the Salicaceae family), we explore their changing spatial distribution and topographic position within a 7 km, island braided reach of the Tagliamento River, Italy, where Populus nigra dominates the woody vegetation cover. Combining field observations and information extracted from aerial images, airborne lidar data and river flow time series for the period 1986–2017, we investigate (a) the changing spatial distribution of all (P . nigra ‐dominated) woody vegetation and of A . incana alone; (b) whether river bed topography can be associated with these changing spatial distributions and (c) we consider whether A . incana displays any particular characteristics in its spatial and topographic distribution that may indicate that it is complementing the physical engineering role of P . nigra . We show that A . incana predominantly grows in lines along channel, island and floodplain edges, bordering wooded areas dominated by P . nigra and that areas supporting A . incana are associated with the topographic development of the river bed. We conclude that A . incana appears to be acting as a complementary physical engineer to P . nigra , suggesting that similar complementary physical engineering of river beds may be achieved by species with different life history traits to influence landform development in other river environments.
... Arrows identifies that differences in chemical element content are significant (p < 0.05) according to Tukey's test and Dunnett's T3 correction phosphorous) during the afforestation of grasslands at a higher rate than in the more fertile Endostagnic Umbrisols. Many other studies have reported the role of grey alder afforestation in soil enrichment with nitrogen (Uri et al. 2014;Innangi et al. 2017;Morozov et al. 2018) and carbon (Uri et al. 2017). The changes in topsoil (0-10 cm) are caused by the accumulation of alder leaf litter and formation of easy decomposable and nitrogen-rich biomass (Innangi et al. 2017). ...
Background
Natural afforestation of former agricultural lands with alder species is common in Europe. Symbiotic nitrogen fixation by actinomycetes associated with alder species has been widely used for improvement of soil properties of abandoned agricultural lands, but relatively little is known of the interactions of these processes with soil type and chemical composition. We conducted a space-for time study with soil sampling under and outside grey alder tree canopies on two different soil groups to explore effects of colonisation of former agricultural lands by alder on soil properties.
Results
The results were analysed using analysis of variance. During the first 25 years after afforestation of former agricultural lands there was a significant increase in content of C tot , N tot , K ⁺ , Fe ³⁺ , Mn ²⁺ and available P in the topsoil (0–10 cm and 11–20 cm) of Dystric Arenosols soils, which are deficient in organic matter. Such trends were not evident in organic matter rich Endostagnic Umbrisols soils, in which exchangeable K ⁺ concentration decreased and exchangeable Fe ³⁺ and Al ³⁺ concentration increased.
Conclusions
The results show that the effects of grey alder on soil chemical properties depend on initial soil properties. The invasion of agricultural land by grey alder leads to spatial variability of soil chemical properties creating a mosaic pattern.
... For estimation of the soil nitrogen (N) pool as well as the soil nutrient status, samples for chemical analyses from twelve random points over each sample plot were taken from the upper 0-10, 10-20 and 20-30 cm soil layers with a soil corer to form a composite sample (Table 2) Uri, Kukumägi, Aosaar, Varik, Becker, Soosaar, et al. 2017). The content of soil nutrients, organic matter and soil pH were analysed in three replicates for each depth layer. ...
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.
... However, actual annual N release from root litter is larger than Table 6 reflects since annual fine root production (FRP) is a steady state process in soil. The production, dying and decomposition of fine roots in closed canopy forests are continuous long lasting processes and FRP ensuring steady state nutrient and carbon flux into the soil (Meyer et al. 2013;Uri et al. 2017a, Uri et al. 2017bVarik et al. 2015). ...
The decomposition of the leaf litter, fine roots (d < 2 mm) and coarser roots (2 ≤ d < 5 mm) of grey alder and silver birch, as well as of α-cellulose sheets using the litterbag method was studied in two experimental stands on Podzoluvisol soils in Southern Estonia. For both tree species, the coarser roots decomposed faster than the fine roots, (p < .05), tree species did not affect the decomposition rate of the roots (p > .5). The nitrogen (N) input to soil from aboveground litter was multiple times higher than the N flux from roots. The remaining relative ash-free mass of the leaves of grey alder and silver birch after three and a half years was similar. After 11 years the remaining relative ash-free mass of the fine and coarser roots of grey alder still accounted for around 10% of the initial value. For silver birch the remaining value was around 20% after 9 years. The litterbag method to underestimates in fertile soils the decomposition of organic matter and thus did not reflect the actual dynamics of decomposition.
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.
Peatbogs are important in global greenhouse gas budget estimates. The main aim of the work was to assess the amount of greenhouse gas emissions based on the Greenhouse Gas Emission Site Type (GEST) method and compare them with actual field measurements. The research was carried out in selected peatbog areas in the coastal zone of northern Poland. The proposed method allowed us to assess whether the restoration treatments carried out in peatbogs contributed to the emission of these gases. The results of this research using the GEST method indicate that, in the studied peatbog areas, the reduction in CO2 emissions was approximately 12%. These results were compared with actual measurements of greenhouse gas emissions made using the chamber method in 2018. The average CO2 emission for the entire peatbog was 16,338.7 t CO2-eq./yr. Comparing this result with the result obtained using the GEST method, it should be stated that it is lower by 2.464.1 t CO2-eq./year, which gives an approximately 13% overestimation of the result by the Gas Emission Site Type method.
This study aims to derive individual tree allometric equations for the above- and belowground biomass components of grey and common alder based on data sets obtained in Latvia. The species aboveground biomass data consisted of 81 trees collected in 27 forest stands. The belowground biomass data were obtained from 27 common alder and 28 grey alder trees sampled throughout Latvia. For grey and common alder, the root-to-shoot ratio decreased with increasing tree dimensions. Our analysis revealed that biomass functions currently used in the national forest inventory overestimate grey alder and underestimate common alder biomass stocks in Latvia. Our findings indicate that the existing local aboveground biomass equation has an overall satisfactory predictive ability compared to the derived equations in this study. The equations from southern Sweden underestimate biomass for mature trees and overestimate small tree biomass, suggesting that even in the hemiboreal region, the grey and common alder populations could have a different distribution of biomass allocated to various components. Model examinations indicated that the derived allometric functions for grey and common alder were unbiased and performed well within the data range and are the best available to substantially improve national estimates of carbon sequestration and biomass resources in Latvia.
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.
The present publication is a revised version of the PhD thesis “Methodology development for forest stand biomass and carbon stock estimates in Latvia”. Supervisors Dr.silv. Kaspars Liepiņš and Dr.silv. Andis Lazdiņš.Regardless the importance of the forestry sector in Latvia, the methodological basis for analysing the amount of biomass and sequestrated carbon in Latvia is still incomplete. Currently, one of the biggest drawbacks is that there are no approved and suitable biomass equations for common tree species in Latvia. Previous studies in Latvia on biomass and carbon assessment for common tree species are fragmented and limited to separate biomass fractions and several tree species. To estimate CO2 sequestration in aboveground and belowground woody biomass, accurate methods are required. This study is aimed to develop the methods for forest biomass and carbon stock assessment that are based on recommendations for national reporting.The material for study of aboveground and belowground tree biomass is collected in 124 forest stands. Three sample trees per stand have been harvested – in total 102 Scots pines, 81 Norway spruces, 105 birches and 84 European aspens, while stumps and roots of 37 Scots pines, 29 Norway spruces, 42 birches and 33 European aspens are lifted for belowground biomass studies. Accurate measurements of the stem basic density are needed to calculate total stem biomass. 14 366 stem wood and 4652 stem bark samples have been analysed to study the variation of within-the-stem basic density and to calculate the mean density of the stems.Our study approved that the basic density of stem bark significantly (p < 0.001) differs from stem wood density. The use of mean stem wood density values instead of whole stem density values leads to biased estimation of stem biomass (1.5–4.5% error depending on tree species). Examination of small root (diameter over 2 mm) biomass performed in our study to such an extent has not been done before. Within our study new equations for estimation of stem, branch, total aboveground and belowground biomass were developed for application in Latvian conditions for a wide range of tree dimensions. We found that the use of biomass equations applied for biomass estimation in Fennoscandia in our conditions are creating an 4.7–61.7% error depending on tree species and biomass component. Application of default values of biomass expansion factors and root to shoot ratios for temperate and boreal forests defined in IPCC guidelines creates an overestimation of 36.9% and an underestimation of 5.2%, respectively in comparison to methodology elaborated and recommended in this study. In accordance to the forest land definition used in national GHG reports, the total carbon stock in Latvia in year 2016 was 238.1 ±3.5 million tonnes.
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.
Silver birch (Betula pendula Roth.) is one of the main pioneer tree species occupying large areas of abandoned agricultural lands under natural succession in Estonia. We estimated aboveground biomass (AGB) dynamics during 17 growing seasons, and analysed soil nitrogen (N) and carbon (C) dynamics for 10 year period in a silver birch stand growing on former arable land. Main N fluxes were estimated and nitrogen budget for 10-year-old stand was compiled. The leafless AGB and stem mass of the stand at the age of 17-years were 94 and 76 Mg ha⁻¹ respectively. The current annual increment (CAI) of stemwood fluctuated, peaking at 10 Mg ha⁻¹ yr⁻¹ at the age of 15 years; the mean annual increment (MAI) fluctuated at around 4-5 Mg ha⁻¹. The annual leaf mass of the stand stabilised at around 3 Mg ha⁻¹ yr⁻¹. The stand density decreased from 11600 to 2700 trees ha⁻¹ in the 8- and 17-year-old stand, respectively. The largest fluxes in N budget were net nitrogen mineralization and gaseous N2-N emission. The estimated fluxes of N2O and N2 were 0.12 and 83 kg ha⁻¹ yr⁻¹, respectively; N leaching was negligible. Nitrogen retranslocation from senescing leaves was approximately 45 kg ha⁻¹, N was mainly retranslocated into stembark. The N content in the upper 0-10 cm soil layer increased significantly (145 kg ha⁻¹) from 2004 to 2014; soil C content remained stable. Both the woody biomass dynamics and the N cycling of the stand witness the potential for bioenergetics of such ecosystems. © 2016, Finnish Society of Forest Science. all rights reserved.
There are few data on fine root biomass and morphology change in relation to stand age. Based on chronosequences for beech (9-140 years old), oak (11-140 years) and alder (4-76 years old) we aimed to examine how stand age affects fine root biomass and morphology. Soil cores from depths of 0-15 cm and 16-30 cm were used for the study. In contrast to previously published studies that suggested that maximum fine root biomass is reached at the canopy closure stage of stand development, we found almost linear increases of fine root biomass over stand age within the chronosequences. We did not observe any fine root biomass peak in the canopy closure stage. However, we found statistically significant increases of mean fine root biomass for the average individual tree in each chronosequence. Mean fine root biomass (0-30 cm) differed significantly among tree species chronosequences studied and was 4.32 Mg ha-1, 3.71 Mg ha-1 and 1.53 Mg ha-1, for beech, oak and alder stands, respectively. The highest fine root length, surface area, volume and number of fine root tips (0-30 cm soil depth), expressed on a stand area basis, occurred in beech stands, with medium values for oak stands and the lowest for alder stands. In the alder chronosequence all these values increased with stand age, in the beech chronosequence they decreased and in the oak chronosequence they increased until ca. 50 year old stands and then reached steady-state. Our study has proved statistically significant negative relationships between stand age and specific root length (SRL) in 0-30 cm soil depth for beech and oak chronosequences. Mean SRLs for each chronosequence were not significantly different among species for either soil depth studied. The results of this study indicate high fine root plasticity. Although only limited datasets are currently available, these data have provided valuable insight into fine root biomass and morphology of beech, oak and alder stands.
Commercial thinning is a common practice when growing even-aged stands in the Nordic countries. Thinning from below is carried out to harvest suppressed and part of the mid-sized trees that cannot successfully compete for resources and have become grown over by co-dominant and dominant trees. In five field experiments, we studied the effects of harvesting method on the nutrient amount of logging residues left at the site in thinning of Scots pine stands. Comparison was carried out between four harvesting methods representing different levels for forest-residue recovery: SOH (stem-only harvesting down to a diameter of 7 cm, SOH-E (stem-only harvesting down to a diameter of 2 cm),WTH (whole-tree harvesting including stems, tops and branches) and WTH-M (WTH and manual collection of those logging residues which were left in mechanical harvesting). In each experiment, logging residues were weighed and sampled for determination of their nutrient concentrations, and soil samples were taken from the surface peat layer (0-20 cm) for nutrient analyses. In SOH treatments, all residues and nutrients bound in the logging residues were left at the site. In WTH 28-67% and in WTH-M 4-20% of the nutrients remained at the site, with the figure depending on the experiment. The amounts of N (1%), P (1-4%), Ca (2-5%), and Mg (3-8%) bound in the logging residues in SOH were low in comparison to the corresponding amounts in the 0-20 cm peat layer. However, the amount of K in logging residues represented 10-26% and the amount of B 8-15% compared with the corresponding nutrients in peat. The amount of N, P, and K in logging residues after CTL harvesting was 39-86, 3-7, and 9-21 kg.ha-1, respectively. The corresponding figures after WTH were 15-36, 1-3, and 3-9 kg ha-1. We assume that WHT on peatland sites that are prone to K deficiency or already have a detected shortage may increase a risk for nutrient imbalances and growth loss in remaining tree stand.
INTRODUCTION Soil respiration (RS, Fig. 8.1) is the sum of an autotrophic component (RA) produced by roots and the associated rhizosphere (mycorrhizae and rhizosphere bacteria) and a heterotrophic component (RH) originating from soil micro-organisms that decompose the organic materials from both above-ground and below-ground litter (Bowden et al., 1993; Boone et al., 1998; Epron et al., 1999). Autotrophic respiration involves root carbohydrates and root exudates that have very low residence time in soil, while the heterotrophic component involves carbon compounds with a longer residence time, ranging from months to years for fresh litter and from years to centuries for old soil organic matter. All components are thought to be differently influenced by climatic conditions and site characteristics (Boone et al., 1998; Epron et al., 2001; Lavigne et al., 2004; Dilustro et al., 2005) and are thought to respond differently to elevated atmospheric CO2 or soil warming (Rustad et al., 2001; King et al., 2004; Pendall et al., 2004; Soe et al., 2004; Eliasson et al., 2005). Thus, separate estimations of these components are required for analyzing and modelling soil respiration and its response to climate or perturbation, for providing a better knowledge of carbon budgets of ecosystems and for improving carbon sequestration in soil (Hanson et al., 2000; Ryan and Law, 2005; Subke et al., 2006).
Young grey alder stands under 10 years of age that are growing on abandoned agricultural lands in Central Latvian lowlands were selected for this study. In the framework of the research the biomass of the trees was studied and an equation was developed for grey alder stands on abandoned agricultural lands. An allometric equation for the different biomass fractions of grey alder was developed. Tree biomass is characterised by a power model with a single independent variable (DBH), which also indirectly substitutes for the effect of the stand age. The model is adapted to each fraction by changing its ratio values. The determination coefficient of the model is high, varying from R 2 = 0.89 to R 2 = 0.94, and the confidence level of the model is 95%. The biomass of particular fractions is defined by a power regression, with the tree stem diameter at the height of 1.3 m used as an argument. In young grey alder stands on abandoned agricultural lands the majority, 64%, of root fractions is composed of coarse roots, followed by the stump fraction and fine roots, 28% and 8%, respectively. For aboveground biomass the largest fraction is stem, which constitutes 75% of the total aboveground biomass, while the share of branches is 25%.
We compared published estimates of the net fine root production (FRP) in forest sites to litterfall and aboveground net primary production (ANPP) to test whether annual rates of fine root and aboveground production vary together at global scales. We also compared FRP estimates to theoretical upper limits as defined by our previously published relationship between total root allocation (TRA, carbon allocated to FRP plus live-root respiration) and litterfall. Estimates of the carbon content of FRP in the total data set ranged from 25 to 820 g@?m^-^2@?yr^-^1 and were not correlated with annual litterfall of ANPP. Different methods used for estimating fine root production, however, showed contrasting results. Estimates derived using either sums of seasonal changes in fine root biomass (@'Sequential Core@' method) or differences between annual maximum and minimum fine root biomass (@'Maximum - Minimum@' method) were not correlated with either litterfall of ANPP. Sequential Core estimates were often high relative to predicted TRA values, whereas Maximum - Minimum estimates were generally <50% of TRA. The small number of FRP estimates derived from root-free cores (@'Ingrowth Core@' method) were not correlated with measures of aboveground production but were all well below predicted TRA values. In contrast to results of other methods, FRP estimates derived using ecosystem N budgets (@'N Budget@' method) were positively correlated with both litterfall and ANPP. Comparing FRP estimates based on N budgets with previous results of forest soil C budgets suggested that annual fine root production increases with aboveground production and that @?1/3 of TRA is used for production of fine roots.
We studied biomass production of two naturally originated grey alder (Alnus incana (L.) Moench)
stands having a mixture of birch and willow located in central Finland. One of the stands was
growing on a peatland site (Muhos) and the other on a mineral soil site (Juuka). The stands were
clear-cut and fertilization experiments were laid out with several treatments. At Muhos, the treatments
included nitrogen fertilisation with different amounts of wood ash and an unfertilized control.
At Juuka, the treatments included nitrogen fertilisation either with ash or with PK, and ash and
PK treatments alone and an unfertilized control. The sprouts at Muhos were grown for 17 years
and at Juuka for 20 years. At Juuka the stand was clear-cut second time at the age of 20 years and
grown for 8 years. The stands were measured several times and foliar samples were taken twice
during the study period. Clear-cutting increased stem number manifold. The stand density of
new coppiced forests after the clear-cutting decreased from 67 000–89 000 stems ha–1 at the age
of 3–6 years to 10 000–12 000 stems ha–1 at the age of 17–20 years. On neither site fertilization
affected biomass production of alders during the study period. Leafless above-ground biomass
was 52–57 Mg ha–1 after 17–20 years. Mean annual leafless above-ground biomass production
(MAI) increased with increase of rotation time. At the age of 17–20 years the MAI was 2.8–3.0
Mg ha a–1. At Muhos, ash increased foliar P and Ca concentrations, but decreased those of Mn.
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.
International agreements require countries to annually report on greenhouse gas emissions and removals. For the land-use sector, this includes estimating stock changes in various carbon pools. For carbon pools like mineral forest soil where a country-level statistical inventory based on measurements is very difficult, models are usually applied together with data from case studies. In this paper, we present a country-specific model together with case studies that aim at capturing major soil processes due to forestry activity. These processes include “hot moments”, e.g., disturbances that occur rarely but might result in relatively high emissions. The model only aims at developing a conservative estimate, rather than a central one, of net country-level carbon stock change with emissions overestimated and removals underestimated. The model is partially parameterised using paired sampling of soil organic carbon in the uppermost 30-cm layer, applying standard methods including those suggested by IPCC, in afforestations on former croplands and in artificial regenerations. Results show that soils of afforested croplands act as a sink, and carbon stock after regeneration might decrease due to disturbance by forest operations, but might also increase due to transfer of carbon from dead roots to soil depending on disturbance levels. The estimation at the country level, which involves additional considerations and data from the literature, suggests that overall, forest soils are a net sink in Hungary, but also that artificially limiting soil organic carbon changes estimation to the uppermost 30-cm layer as applied in the IPCC methodology might lead to artefacts.
In the Northern and Baltic countries, grey alder is a prospective tree species for short-rotation forestry. Hence, knowledge about the functioning of such forest ecosystems is critical in order to manage them in a sustainable and environmentally sound way. The 17-year-long continuous time series study is conducted in a grey alder plantation growing on abandoned agricultural land. The results of above- and below-ground biomass and production of the 17-year-old stand are compared to the earlier published respective data from the same stand at the ages of 5 and 10 years. The objectives of the current study were to assess (1) above-ground biomass (AGB) and production; (2) below-ground biomass: coarse root biomass (CRB), fine root biomass (FRB) and fine root production (FRP); (3) carbon (C) and nitrogen (N) accumulation dynamics in grey alder stand growing on former arable land. The main results of the 17-year-old stand were as follows: AGB 120.8 t ha−1; current annual increment of the stem mass 5.7 t ha year−1; calculated CRB 22.3 t ha−1; FRB 81 ± 10 g m−2; nodule biomass 31 ± 19 g m−2; fine root necromass 11 ± 2 g m−2; FRP 53 g DM m−2 year−1; fine root turnover rate 0.54 year−1; and fine root longevity 1.9 years. FRB was strongly correlated with the stand basal area and stem mass. Fine root efficiency was the highest at the age of 10 years; at the age of 17 years, it had slightly reduced. Grey alder stand significantly increased N and Corg content in topsoil. The role of fine roots for the sequestration of C is quite modest compared to leaf litter C flux.
The turbulent exchanges of CO2 and water vapour between an aggrading deciduous forest in the north-eastern United States (Harvard Forest) and the atmosphere were measured from 1990 to 1994 using the eddy covariance technique. We present a detailed description of the methods used and a rigorous evaluation of the precision and accuracy of these measurements. We partition the sources of error into three categories: (1) uniform systematic errors are constant and independent of measurement conditions (2) selective systematic errors result when the accuracy of the exchange measurement varies as a function of the physical environment, and (3) sampling uncertainty results when summing an incomplete data set to calculate long-term exchange.
Analysis of the surface energy budget indicates a uniform systematic error in the turbulent exchange measurements of -20 to 0%. A comparison of nocturnal eddy flux with chamber measurements indicates a selective systematic underestimation during calm (friction velocity < 0.17 m s−1) nocturnal periods. We describe an approach to correct for this error. The integrated carbon sequestration in 1994 was 2.1 t C ha−1 y−1 with a 90% confidence interval due to sampling uncertainty of ±0.3 t C ha−1 y−1 determined by Monte Carlo simulation. Sampling uncertainty may be reduced by estimating the flux as a function of the physical environment during periods when direct observations are unavailable, and by minimizing the length of intervals without flux data. These analyses lead us to place an overall uncertainty on the annual carbon sequestration in 1994 of -0.3 to +0.8 t C ha−1 y−1.
The effect of limited nitrogen (N) or water availability on fine root growth and turnover was examined in two deciduous species,
Alnus incana L. and Salix viminalis L., grown under three different regimes: (i) supply of N and water in amounts which would not hamper growth, (ii) limited
N supply and (iii) limited water supply. Plants were grown outdoors during three seasons in covered and buried lysimeters
placed in a stand structure and filled with quartz sand. Computer-controlled irrigation and fertilization were supplied through
drip tubes. Production and turnover of fine roots were estimated by combining minirhizotron observations and core sampling,
or by sequential core sampling. Annual turnover rates of fine roots <1 mm (5–6 year−1) and 1–2 mm (0.9–2.8 year−1) were not affected by changes in N or water availability. Fine root production (<1 mm) differed between Alnus and Salix, and between treatments in Salix; i.e., absolute length and biomass production increased in the order: water limited < unlimited < N limited. Few treatment
effects were detected for fine roots 1–2 mm. Proportionally more C was allocated to fine roots (≤2 mm) in N or water-limited
Salix; 2.7 and 2.3 times the allocation to fine roots in the unlimited regime, respectively. Estimated input to soil organic carbon
increased by ca. 20% at N limitation in Salix. However, future studies on fine root decomposition under various environmental conditions are required. Fine root growth
responses to N or water limitation were less pronounced in Alnus, thus indicating species differences caused by N-fixing capacity and slower initial growth in Alnus, or higher fine root plasticity in Salix. A similar seasonal growth pattern across species and treatments suggested the influence of outer stimuli, such as temperature
and light.
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.
We describe a new and easy tech- nique for placing and lifting root meshes to estimate fine root production in forest ecosys- tems. The method improves upon previously proposed mesh placement techniques by using a sharp stainless steel blade and two thin stainless steel sheets to insert mesh more easily and accurately in the soil, and utilizing a narrow garden spade to lift the soil block containing the mesh. The proposed technique takes signifi- cantly less time than the widely used ingrowth core method, causes minimal disturbance to the soil, and requires only simple equipment. The detailed documentation of the method provided herein should improve estimations of fine root production in forest ecosystems.
It is recognized that human activities, such as fossil fuel burning, land-use change, and forest harvesting at a large scale, have resulted in the increase of greenhouse gases in the atmosphere since the onset of the industrial revolution. The increasing amounts of greenhouse gases, particularly CO2 in the atmosphere, is believed to have induced climate change and global warming. With the ability to remove CO2 from the atmosphere through photosynthesis, forests play a critical role in the carbon cycle and carbon sequestration at both global and local scales. It is necessary to understand the relationship between forest soil carbon dynamics and carbon sequestration capacity, and the impact of forest management practices on soil CO2 efflux for sustainable carbon management in forest ecosystems. This paper reviews a number of current issues related to (1) carbon allocation, (2) soil respiration, and (3) carbon sequestration in the forest ecosystems through forest management strategies. The contribution made by forests and forest management in sequestrating carbon to reduce the CO2 concentration level in the atmosphere is now well recognized. The overall carbon cycle, carbon allocation of the above- and belowground compartments of the forests, soil carbon storage and soil respiration in forest ecosystems and impacts of forest management practices on soil respiration are described. The potential influences of forest soils on the buildup of atmospheric carbon are reviewed.
Owing to its ability to produce large amounts of biomass in a short period of time, grey alder can be considered to be a prospective tree species for short-rotation forestry (SRF) in Eastern Europe and the Nordic countries. Relatively scanty data is available about grey alder yield and growth dynamics. Seven yield-tables from six countries and several pub-lished studies have been included in this review. The main aim of the review was to sum up and analyze published data; to evaluate the potential for biomass production and to summarize the existing relevant knowledge for giving recommendations about the optimal principles on managing alder stands. According to different yield-tables, the mean annual increment (MAI) of 20-year-old stands varied from 2.56 m 3 ha À1 to 4.75 m 3 ha À1 (dry matter). In favourable conditions, the growth of alder stands can be rapid and biomass production high. The highest woody biomass of annual production reported in literature amounts to 17 t ha À1 y À1 . A rotation length of 15.20 years is recommended by the majority of authors. The rotation period is longer in northern countries (Norway, Finland) than in southern countries. According to yield-tables, it coincides with the start of the decrease in MAI in most cases. Approximately 60 t ha À1 e90 t ha À1 of stemwood can be produced during one rotation. The density of the natural grey alder stand is typically very high. The optimal initial density of grey alder may not exceed 10,000 ha À1 in the case of plantations and the optimal number of trees per hectare before harvesting should range between 3000 ha À1 and 6000 ha À1 .
The dynamics of the above-ground biomass production of a grey alder plantation on abandoned farmland was investigated during 11 years after establishment. In the 12-year-old stand, the total biomass of the above-ground part of the stand was 68.8 t dry matter (DM) ha(-1) and the current annual production (CAP) was 14.0 t DM ha(-1) year(-1). The predicted mean annual increment (MAI) reached is maximum at the age of 16 years, which indicates bulk maturity (the stand age when CAI = MAI) and appropriate rotation time for obtaining maximum biomass production. In the case of short-rotation forestry, initial stand density should not be higher than 6500-6000 trees per hectare. Below-ground biomass accounted for 18 and 16 per cent of total stand biomass at a stand age of 5 and 10 years, respectively. The biomass of the nodules was estimated at 155 +/- 63 kg DM ha(-1) and the biomass of the fine roots was estimated at 870 +/- 130 kg DM ha(-1) in the 10-year-old grey alder stand. Of the fine roots, 80 per cent and almost all nodules were located in the upper 0-20 cm soil layer in both the 5-year-old and the 10-year-old stand. The value of leaf area index increased with stand age, ranging between 1.38 and 5.43 m(2) m(-2) during the development of the stand. Specific leaf area varied in different years from 11.1 to 13.5 m(2) kg(-1).
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.
Soil respiration (SR) constitutes the largest flux of CO(2) from terrestrial ecosystems to the atmosphere. However, there still exist considerable uncertainties as to its actual magnitude, as well as its spatial and interannual variability. Based on a reanalysis and synthesis of 80 site-years for 57 forests, plantations, savannas, shrublands and grasslands from boreal to tropical climates we present evidence that total annual SR is closely related to SR at mean annual soil temperature (SR(MAT)), irrespective of the type of ecosystem and biome. This is theoretically expected for non water-limited ecosystems within most of the globally occurring range of annual temperature variability and sensitivity (Q(10)). We further show that for seasonally dry sites where annual precipitation (P) is lower than potential evapotranspiration (PET), annual SR can be predicted from wet season SR(MAT) corrected for a factor related to P/PET. Our finding indicates that it can be sufficient to measure SR(MAT) for obtaining a well constrained estimate of its annual total. This should substantially increase our capacity for assessing the spatial distribution of soil CO(2) emissions across ecosystems, landscapes and regions, and thereby contribute to improving the spatial resolution of a major component of the global carbon cycle.
We estimated annual net ecosystem exchange (NEE) of a chronosequence of four Scots pine stands in southern Finland during years 2000–2002 using eddy covariance (EC). Net ecosystem productivity (NEP) was estimated using growth measurements and modelled mass losses of woody debris. The stands were 4, 12, 40 and 75 years old. The 4-year-old clearcut was a source of carbon throughout the year combining a low gross primary productivity (GPP) with a total ecosystem respiration (TER) similar to the forest stands. The annual NEE of the clearcut, measured by EC, was 386 g C m−2. Tree growth was negligible and the estimated NEP was −262 g C m−2 a−1. The annual GPPs at the other sites were close to each other (928−1072 g C m−2 a−1), but TER differed markedly, being greatest at the 12-year-old site (905 g C m−2 a−1) and smallest in the 75-year-old stand (616 g C m−2 a−1). Measurements of soil CO2 efflux showed that different rates of soil respiration largely explained the differences in TER. The NEE and NEP of the 12-year-old stand were close to zero. The forested stands were sinks of carbon. They had similar annual patterns of carbon exchange and half-hourly eddy fluxes were highly correlated, indicating similar responses to the environment. The NEE in the 40-year-old stand varied between −179 and –192 g C m−2 a−1, while NEP was between 214 and 242 g C m−2 a−1. The annual NEE of the 75-year-old stand was 323 g C m−2 and NEP was 252 g C m−2. This indicates that there was no reduction in carbon sink strength with stand age.
There is a general agreement that forest ecosystems in the Northern Hemisphere function as significant sinks for atmospheric
CO2; however, their magnitude and distribution remain large uncertainties. In this paper, we report the carbon (C) stock and
its change of vegetation, forest floor detritus, and mineral soil, annual net biomass increment and litterfall production,
and respiration of vegetation and soils between 1992 to 1994, for three temperate forest ecosystems, birch (Betula platyphylla) forest, oak (Quercus liaotungensis) forest and pine (Pinus tabulaeformis) plantation in Mt. Dongling, Beijing, China. We then evaluate the C budgets of these forest ecosystems. Our results indicated
that total C density (organic C per hectare) of these forests ranged from 250 to 300 t C ha−1, of which 35–54 t C ha−1 from vegetation biomass C and 209–244 t C ha−1 from soil organic C (1 m depth, including forest floor detritus). Biomass C of all three forests showed a net increase, with
1.33–3.55 t C ha−1 a−1 during the study period. Litterfall production, vegetation autotrophic respiration, and soil heterotrophic respiration were
estimated at 1.63–2.34, 2.19–6.93, and 1.81–3.49 t C ha−1 a−1, respectively. Ecosystem gross primary production fluctuated between 5.39 and 12.82 t C ha−1 a−1, about half of which (46%–59%, 3.20–5.89 t C ha−1 a−1) was converted to net primary production. Our results suggested that pine forest fixed C of 4.08 t ha−1 a−1, whereas secondary forests (birch and oak forest) were nearly in balance in CO2 exchange between the atmosphere and ecosystems.
Over two-thirds of terrestrial carbon is stored belowground and a significant amount of atmospheric CO2 is respired by roots and microbes in soils. For this analysis, soil respiration (Rs) data were assembled from 31 AmeriFlux and CarboEurope sites representing deciduous broadleaf, evergreen needleleaf, grasslands, mixed deciduous/evergreen and woodland/savanna ecosystem types. Lowest to highest rates of soil respiration averaged over the growing season were grassland and woodland/savanna < deciduous broadleaf forests < evergreen needleleaf, mixed deciduous/evergreen forests with growing season soil respiration significantly different between forested and non-forested biomes (p < 0.001). Timing of peak respiration rates during the growing season varied from March/April in grasslands to July–September for all other biomes. Biomes with overall strongest relationship between soil respiration and soil temperature were from the deciduous and mixed forests (R
2 ≥ 0.65). Maximum soil respiration was weakly related to maximum fine root biomass (R
2 = 0.28) and positively related to the previous years’ annual litterfall (R
2 = 0.46). Published rates of annual soil respiration were linearly related to LAI and fine root carbon (R
2 = 0.48, 0.47), as well as net primary production (NPP) (R
2 = 0.44). At 10 sites, maximum growing season Rs was weakly correlated with annual GPP estimated from eddy covariance towersites (R
2 = 0.29; p < 0.05), and annual soil respiration and total growing season Rs were not correlated with annual GPP (p > 0.1). Yet, previous studies indicate correlations on shorter time scales within site (e.g., weekly, monthly). Estimates of annual GPP from the Biome-BGC model were strongly correlated with observed annual estimates of soil respiration for six sites (R
2 = 0.84; p < 0.01). Correlations from observations of Rs with NPP, LAI, fine root biomass and litterfall relate above and belowground inputs to labile pools that are available for decomposition. Our results suggest that simple empirical relationships with temperature and/or moisture that may be robust at individual sites may not be adequate to characterize soil CO2 effluxes across space and time, agreeing with other multi-site studies. Information is needed on the timing and phenological controls of substrate availability (e.g., fine roots, LAI) and inputs (e.g., root turnover, litterfall) to improve our ability to accurately quantify the relationships between soil CO2 effluxes and carbon substrate storage.
The global environment is constantly changing and our planet is getting warmer at an unprecedented rate. The study of the carbon cycle, and soil respiration, is a very active area of research internationally because of its relationship to climate change. It is crucial for our understanding of ecosystem functions from plot levels to global scales. Although a great deal of literature on soil respiration has been accumulated in the past several years, the material has not yet been synthesized into one place until now. This book synthesizes the already published research findings and presents the fundamentals of this subject. Including information on global carbon cycling, climate changes, ecosystem productivity, crop production, and soil fertility, this book will be of interest to scientists, researchers, and students across many disciplines. * A key reference for the scientific community on global climate change, ecosystem studies, and soil ecology * Describes the myriad ways that soils respire and how this activity influences the environment * Covers a breadth of topics ranging from methodology to comparative analyses of different ecosystem types * The first existing "treatise" on the subject.
Biomass from woody crops is regarded as a future major source of renewable energy. Wood production therefore has to be enhanced to meet the energy needs of an increasing population. This can be reached by using fast-growing tree species. Grey alder (Alnus incana (L.) Moench.) is an indigenous and fast-growing species, which is well adapted to the harsh climate of northern Europe, and could complement other biomass-oriented species used today. This study aimed to assess the potential for wood production and carbon (C) sequestration in biomass and soil of grey alder plantations under north European conditions. The estimates were based on literature data on above- and below ground biomass production, including fine roots, biomass allocation patterns and litter decomposition. By applying logistic functions on production figures and adding an estimated breeding response, grey alder would be able to produce on average 6–7 Mg ha−1 yr−1 of above ground woody biomass during a rotation up to 25 years. This would significantly contribute to increased biomass availability in the Nordic and Baltic countries when applied on agricultural land. By assuming that grey alder will mostly be used on areas suitable for the species, e.g. sites with harsh climate or moist conditions, an estimate of 560,000 ha of newly abandoned agricultural land will be available. Thus, afforestation of those areas with grey alder would result in a total annual increase of aboveground woody biomass of 3.7 Tg, corresponding to 69,000 TJ yr−1. Grey alder would also be an efficient C sink when used on newly abandoned agricultural land. Using the same areas as for biomass the annual C sequestration in biomass and soil would reach 2.6 Tg C. These figures show that grey alder has a potential to be a significant contributor for increasing biomass supply and capture C in northern Europe.
Key message
The estimates of fine root production by net sheet method were not affected by the net material or the aperture size, but flexible nets are preferable to avoid an underestimation.
Abstract
The estimation of the fine root production is important for understanding the mechanisms of carbon cycling in ecosystems. The recently developed net sheet method allows the measurement of fine root production in forest ecosystems. The simplicity of this innovative technique reduces labor costs and causes little soil disturbance during installation. However, the protocols and methods are still poorly developed; for example, the effects of net material, mesh aperture size and firmness on the results remain unknown. Therefore, we measured the number and dry mass of fine roots grown through net sheets in forest soils to determine the effect of the net quality and type (polyamide, polyethylene, polyethylene terephthalate, stainless steel), mesh aperture size (2 and 4 mm) and firmness (firm and flexible) on the results. The study was conducted in managed and unmanaged Japanese cedar forests in Japan and in a mixed dipterocarp forest in Malaysia. No effect of net material or mesh aperture size on the number of roots grown through the net sheets or on root production was observed. A smaller number of roots grew through the firm type of nets than that of the flexible nets in the managed Japanese cedar and mixed dipterocarp forests. These results suggest that fine root production is not affected by the material of the net sheets or the mesh aperture size, but flexible nets are preferable to avoid an underestimation of fine root production.
Standing crop, rates of production, mortality, decomposition, and nitrogen dynamics of two size classes of fine roots (0-05 mm and 0.5-3.0 mm diameter) were estimated for 1 yr in a 53-yr-old red pine (Pinus resinosa Ait.) plantation and in an adjacent 80-yr-old mixed hardwood stand in north-central Massachusetts. Dry matter of live fine roots was higher in the hardwoods (mean = 6.1 Mg/ha; annual range 3.6-8.6 Mg/ha) than in the plantation (mean = 5.1 Mg/ha; annual range 2.5-7.8 Mg/ha.) Dead root mass was similar in the hardwoods (mean = 4.4 Mg/ha) and the plantation (mean = 4.0 Mg/ha). Nitrogen standing crop of live roots in the hardwoods was higher than in the plantation (mean = 65 kg/ha and 42 kg/ha, respectively). Net fine root production was estimated from changes in standing crop. Production estimates ranged from 4.1 to 11.4 Mg@?ha^-^1@?yr^-^1 in the hardwoods and from 3.2 to 10.9 Mg@?ha^-^1@?yr^-^1 in the plantation, depending on the assumptions made in the calculations. Concurrent estimates of total nitrogen requirement for this production ranged from 73 to 184 kg@?ha^-^1@?yr^-^1 in the hardwoods and from 44 to 122 kg@?ha^-^1@?yr^-^1 in the plantation. Decomposition, measured as mass loss from buried cloth bags, was @?20% in 0.4-mm mesh bags and as high as 47% in 3-mm mesh bags after 1 yr. Integrating production and nitrogen requirements with estimates of decomposition rates and nitrogen mineralization for these ecosystems suggested that the lower estimates of production are more accurate.
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.
Abstract We present results from two years’ net ecosystem flux measurements above a boreal forest in central Sweden. Fluxes were measured with an eddy correlation system based on a sonic anemometer and a closed path CO2 and H2O gas analyser. The measurements show that the forest acted as a source during this period, and that the annual balance is highly sensitive to changes in temperature. The accumulated flux of carbon dioxide during the full two-year period was in the range 480–1600 g CO2 m–2. The broad range is caused by uncertainty regarding assessment of the night-time fluxes. Although annual mean temperature remained close to normal, the results are partly explained by higher than normal respiration, due to abnormal temperature distribution and reduced soil moisture during one growing season. The finding that a closed forest can be a source of carbon over such a long period as two years contrasts sharply with the common belief that forests are always carbon sinks.
There has been renewed interest in the issue of growing trees to sequester carbon following the Kyoto Protocol in 1997. It is a complex issue, raising many questions. In this paper, the author offers answers to some of the questions commonly asked in the UK. These questions concern: (1) the basic rationale for growing trees to sequester carbon (does it make sense?); (2) the size of the reservoirs, sinks and sources of carbon in the UK (how important are the forests?); (3) effects of species, site and management (which is most effective at storing carbon?); (4) areas and numbers of trees needed to offset fossil fuel emissions (how many trees need to be planted per person or per car?); and (5) the monetary value of the carbon stored (what is it worth?). The answers given are taken mostly from published literature.
Degenerated and nonproductive forest soils having a very low content of nitrogen and organic material can probably be restored by cultivation of nitrogen-fixing plants such as Alnus spp. The effects of liming and N fertilization on enhancement of early growth and biomass production of Alnusincana (L.) Moench were studied in northern Sweden. Survival was over 90% in all treatments. During the 1st year, root growth was more rapid than shoot growth, reflecting acclimation of the nursery grown plants to the field conditions. In the following 5 years, the height increase and the production of leaf litter biomass and leaf litter nitrogen were significantly higher in limed than in unlimed alders. N–P–K fertilization also had a positive effect, while N alone had a negative effect. During the 6th year, limed alders, at a spacing of 1.5 × 1.5 m, produced 440–710 kg leaf litter ha−1 containing 11–17 kg Nha−1. Unlimed alders produced 50–250 kg leaf litter ha−1 containing 1–6 kg Nha−1. Therefore, the simple and inexpensive treatment of liming at planting considerably enhanced the growth and production of leaf litter nitrogen by A. incana at the site.
The self-thinning rule (the —3/2 power rule) has been used frequently to describe the competition-regulated relationship between size and density in plant populations. Because the parameters of the self-thinning rule and principles are easily derived, the application of this rule to tree stands could simplify the development of stand density management guides. This paper briefly examines the structure and development of the few existing stand density management guides which are based on the self-thinning rule. The self-thinning rule is then applied to seven existing data sets to develop a guide for red alder (Alnus rubra Bong.). The self-thinning line for red alder has a slope of -1.5 and a (y-intercept (average stem volume) of 3.3 m3 (1.175 × 102 ft3). The density unit is stems ha−1. The other two lines on the density management diagram, the line of imminent competition mortality and the lower thinning limit, are placed at relative densities of 55 and 30%. The relative-density values for crown closure, mortality and the lower thinning limit correspond to those for other species. It was not possible to use a seedling alder study to determine the intercept of the self-thinning line for trees.
Forest development following stand-replacing disturbance influences a variety of ecosystem processes including carbon exchange with the atmosphere. On a series of ponderosa pine (Pinius ponderosa var. Laws.) stands ranging from 9 to> 300 years in central Oregon, USA, we used biological measurements to estimate carbon storage in vegetation and soil pools, net primary productivity (NPP) and net ecosystem productivity (NEP) to examine variation with stand age. Measurements were made on plots representing four age classes with three replications: initiation (I, 9–23 years), young (Y, 56–89 years), mature (M, 95–106 years), and old (O, 190–316 years) stands typical of the forest type in the region. Net ecosystem productivity was lowest in the I stands (−124 g C m−2 yr−1), moderate in Y stands (118 g C m−2 yr−1), highest in M stands (170 g C m−2 yr−1), and low in the O stands (35 g C m−2 yr−1). Net primary productivity followed similar trends, but did not decline as much in the O stands. The ratio of fine root to foliage carbon was highest in the I stands, which is likely necessary for establishment in the semiarid environment, where forests are subject to drought during the growing season (300–800 mm precipitation per year). Carbon storage in live mass was the highest in the O stands (mean 17.6 kg C m−2). Total ecosystem carbon storage and the fraction of ecosystem carbon in aboveground wood mass increased rapidly until 150–200 years, and did not decline in older stands. Forest inventory data on 950 ponderosa pine plots in Oregon show that the greatest proportion of plots exist in stands ∼ 100 years old, indicating that a majority of stands are approaching maximum carbon storage and net carbon uptake. Our data suggests that NEP averages ∼ 70 g C m−2 year−1 for ponderosa pine forests in Oregon. About 85% of the total carbon storage in biomass on the survey plots exists in stands greater than 100 years, which has implications for managing forests for carbon sequestration. To investigate variation in carbon storage and fluxes with disturbance, simulation with process models requires a dynamic parameterization for biomass allocation that depends on stand age, and should include a representation of competition between multiple plant functional types for space, water, and nutrients.
We studied greenhouse gas (GHG) fluxes in two differently loaded riparian Alnus incana-dominated forests in agricultural landscapes of southern Estonia: a 33-year-old stand in Porijõgi, in which the uphill agricultural activities had been abandoned since the middle of the 1990s, and a 50-year-old stand in Viiratsi, which still receives polluted lateral flow from uphill fields fertilized with pig slurry. In Porijõgi, closed-chamber based sampling lasted from October 2001 to October 2009, whereas in Viiratsi the sampling period was from November 2003 to October 2009. Both temporal and spatial variations in all GHG gas fluxes were remarkable. Local differences in GHG fluxes between micro-sites (“Edge”, “Dry” and “Wet” in Porijõgi, and “Wet”, “Slope” and “Dry” in Viiratsi) were sometimes greater than those between sites. Median values of GHG fluxes from both sites over the whole study period and all microsites did not differ significantly, being 45 and 42 mg CO2–C m−2 h−1, 8 and 0.5 μg CH4–C m−2 h−1, 1.0 and 2.1 mg N2–N m−2 h−1, and 5 and 9 μg N2O–N m−2 h−1, in Porijõgi and Viiratsi, respectively. The N2:N2O ratio in Viiratsi (40–1200) was lower than in Porijõgi (10–7600). The median values-based estimation of the Global Warming Potential of CH4 and N2O was 19 and 185 kg CO2 equivalents (eq) ha−1 yr−1 in Porijõgi and −14 and 336 kg CO2 eq ha−1 yr−1 in Viiratsi, respectively. A significant Spearman rank correlation was found between the mean monthly air temperature and CO2, CH4 and N2 fluxes in Porijõgi, and N2O flux in Viiratsi, and between the monthly precipitation and CH4 fluxes in both study sites. Higher groundwater level significantly increases CH4 emission and decreases CO2 and N2O emission, whereas higher soil temperature significantly increases N2O, CH4 and N2 emission values. In Porijõgi, GHG emissions did not display any discernable trend, whereas in Viiratsi a significant increase in CO2, N2, and N2O emissions has been found. This may be a result of the age of the grey alder stand, but may also be caused by the long-term nutrient load of this riparian alder stand, which indicates a need for the management of similar heavily loaded riparian alder stands.
The effect of stand age on soil respiration and its components was studied in a first rotation Sitka spruce chronosequence composed of 10-, 15-, 31-, and 47-year-old stands established on wet mineral gley in central Ireland. For each stand age, three forest stands with similar characteristics of soil type and site preparation were used. There were no significant differences in total soil respiration among sites of the same age, except for the case of a 15-year-old stand that had lower soil respiration rates due to its higher productivity. Soil respiration initially decreased with stand age, but levelled out in the older stands. The youngest stands had significantly higher respiration rates than more mature sites. Annual soil respiration rates were modelled by means of temperature-derived functions. The average Q10 value obtained treating all the stands together was 3.8. Annual soil respiration rates were 991, 686, 556, and 564 g C m−2 for the 10-, 15-, 31-, and 47-year-old stands, respectively. We used the trenching approach to separate soil respiration components. Heterotrophic respiration paralleled soil organic carbon dynamics over the chronosequence, decreasing with stand age to slightly increase in the oldest stand as a result of accumulated aboveground litter and root inputs. Root respiration showed a decreasing trend with stand age, which was explained by a decrease in fine root biomass over the chronosequence, but not by nitrogen concentration of fine roots. The decrease in the relative contribution of autotrophic respiration to total soil CO2 efflux from 59.3% in the youngest stand to 49.7% in the oldest stand was explained by the higher activity of the root system in younger stands. Our results show that stand age should be considered if simple temperature-based models to predict annual soil respiration in afforestation sites are to be used.
Forest age, which is affected by stand-replacing ecosystem disturbances (such as forest fires, harvesting, or insects), plays a distinguishing role in determining the distribution of carbon (C) pools and fluxes in different forested ecosystems. In this synthesis, net primary productivity (NPP), net ecosystem productivity (NEP), and five pools of C (living biomass, coarse woody debris, organic soil horizons, soil, and total ecosystem) are summarized by age class for tropical, temperate, and boreal forest biomes. Estimates of variability in NPP, NEP, and C pools are provided for each biome-age class combination and the sources of variability are discussed. Aggregated biome-level estimates of NPP and NEP were higher in intermediate-aged forests (e.g., 30–120 years), while older forests (e.g., >120 years) were generally less productive. The mean NEP in the youngest forests (0–10 years) was negative (source to the atmosphere) in both boreal and temperate biomes (−0.1 and –1.9 Mg C ha−1 yr−1, respectively). Forest age is a highly significant source of variability in NEP at the biome scale; for example, mean temperate forest NEP was −1.9, 4.5, 2.4, 1.9 and 1.7 Mg C ha−1 yr−1 across five age classes (0–10, 11–30, 31–70, 71–120, 121–200 years, respectively). In general, median NPP and NEP are strongly correlated (R2=0.83) across all biomes and age classes, with the exception of the youngest temperate forests. Using the information gained from calculating the summary statistics for NPP and NEP, we calculated heterotrophic soil respiration (Rh) for each age class in each biome. The mean Rh was high in the youngest temperate age class (9.7 Mg C ha−1 yr−1) and declined with age, implying that forest ecosystem respiration peaks when forests are young, not old. With notable exceptions, carbon pool sizes increased with age in all biomes, including soil C. Age trends in C cycling and storage are very apparent in all three biomes and it is clear that a better understanding of how forest age and disturbance history interact will greatly improve our fundamental knowledge of the terrestrial C cycle.
Nitrogen-fixing tree species have larger effects on forest soils than other species, and these effects include consistent
increases in soil organic matter and carbon (C). Across 19 case studies, an increase of 1 g N was associated with an increase
of 12 to 15 g C. Few studies have examined the mechanisms behind the accumulation of soil C; documented processes include
reduced decomposition of older, stabilized soil C, increased rates of formation of stabilized soil C, and higher rates of
input of C in detritus. The influences of N-fixing trees on stabilized soil C may not derive directly from the increased supply
of N, as fertilization with inorganic N did not alter soil C. More experimentation is needed on the influence of N-fixing
trees on the soil biotic community, as the soil microbes and invertebrates may hold the key to the influence of N-fixation
on soil C.