Forest Soil Carbon Stocks Research Articles

Linking Forest Vegetation and Soil Carbon Stock in Northwestern Russia

Research Highlights: It was found that both tree species and ground vegetation affected soil carbon stock in boreal forests. Carbon stocks in the mineral layers were related negatively to the C/N ratio in the organic horizon and pine proportion in the growing stock volume, and positively to the share of herbaceous plants and the proportion of spruce. Background and Objectives: Existing research showed the effects of tree species on soil carbon stocks in organic horizons, but these effects were less clear in mineral horizons. Little is known about the effects of ground vegetation on soil carbon stock. This study aims to identify associations between the forest vegetation composition and soil carbon stocks in northwestern Russia. Materials and Methods: Research data from 109 pine, spruce and birch forests of different Cajander’s and Sukachev’s types with different functional compositions of ground vegetation at autonomous positions are discussed in this paper. The V-test was used to assess the impact of vegetation on soil carbon stocks. Results: Variations in Carbon stocks in the mineral layers were associated with the soil types and vegetation composition. Carbic Albic Podzols accumulated the least amount of carbon in the mineral profile. Carbon stock in the mineral layers in pine forests was considerably lower than in spruce and birch forests. Spruce forests with the highest share of herbaceous plants were characterised by the highest carbon stocks in the mineral layers, while pine forests with dwarf shrubs and green mosses accumulated more carbon in the organic layers, but carbon stocks in the mineral layers here were the lowest. Conclusions: Differences in soil carbon stocks between and within northern and middle taiga in northwestern Russia were associated not only with soil types but also with the proportions of forest types dominated by different tree species and ground vegetation functional groups.

Effects of whole‐tree harvesting at thinning and subsequent compensatory nutrient additions on carbon sequestration and soil acidification in a boreal forest

AbstractResidues from forest harvesting operations may be utilized as a renewable energy source. However, the sustainability of this practice has been questioned due to the losses of nutrients and exchangeable base cations, which may impair the forest's carbon sequestration capacity and lead to soil acidification. We report the 18 year response of biomass growth, soil carbon stock and soil chemistry to whole‐tree harvest at thinning and associated compensatory measures in a Pinus sylvestris forest in northern Sweden. The whole‐tree harvest at thinning was combined with nutrient additions to compensate for the nutrient loss caused by extracting the residues. Four main treatments, stem‐only thinning, whole‐tree thinning, whole‐tree thinning with one‐time nitrogen fertilization and whole‐tree thinning with repeated nitrogen fertilization every third year were applied, with plots split for wood‐ash treatment. Eighteen years after the treatments, whole‐tree thinning that had removed 3.0 ± 0.2 Mg C/ha in residues had no effect on forest growth, soil carbon and nitrogen stocks or soil chemistry. Both nitrogen fertilization regimes increased biomass growth, but neither one resulted in a significant increase in soil carbon stock. Wood‐ash addition increased soil pH and exchangeable base cations, but did not affect carbon stock in biomass or soil. Our long‐term data suggest that utilizing harvesting residues for biofuel feedstocks is appropriate in this type of forest. Hence, any nitrogen and wood‐ash additions appear unnecessary as compensatory measures for the removal of harvesting residues, but nitrogen can be applied to increase forest growth following thinning.

Rates of dark CO2 fixation are driven by microbial biomass in a temperate forest soil

Soils substantially contribute to the terrestrial fluxes of CO2 to the atmosphere. Dark CO2 fixation, the microbial process by which pore space CO2 is reduced to organic matter, may recycle and trap some of the CO2 respired in soils before it can escape to the atmosphere. To evaluate its potential significance for global temperate forest soil carbon stocks, we quantified dark CO2 fixation rates in a temperate beech forest soil down to 1 m depth over a range of 2–20% (v:v) headspace CO2 concentrations, by tracing incorporation of a13C–CO2 label into microbial biomass carbon and soil organic matter. We found that fixation rates under a concentration of 2% CO2 decreased with depth from 0.86 to 0.06 μg C normalized to g(dw) soil−1 d−1. However, when dark CO2 fixation rates were normalized to soil microbial biomass carbon, no significant differences between depths were observed. Higher CO2 concentrations increased fixation rates, with a linear 2-fold increase between 2% and 10% CO2. Molecular analysis revealed the dominance of heterotrophs, along with the presence of autotrophs mainly employing the Calvin Benson Bassham (CBB) pathway followed by the reductive citric acid (rTCA) pathway. Although community composition varied with depth, the relative fraction of autotrophs determined by qPCR of RuBisCO (cbbL IA, cbbL IC) and ATP-citrate lyase (aclA) genes remained stable at approximately 0.5% of the total community. Dark CO2 fixed carbon accounted for up to 1.1% of microbial biomass carbon and up to 0.035% of soil organic carbon after 28 days. We estimated a fixation flux of 25 ± 7.2 g C m−2 yr−1 to 1 m depth for the Hainich forest soil under field conditions. Without this process, Hainich forest soil CO2 emissions would be 5.6% higher, recycling a fraction of carbon large enough to potentially affect carbon isotope signatures in SOC. If this is held for all temperate forest soils globally, the annual rate of dark CO2 fixation would be 0.26 ± 0.07 Pg C yr−1 to a depth of 1 m, without considering contributions from other biomes. In conclusion, microbial biomass carbon and CO2 concentration appear to be the main drivers of dark CO2 fixation in temperate forest soils, and dark CO2 fixation may maintain Hainich forest soil carbon stocks by moderating a significant fraction of soil CO2 emissions annually.

Rapid peat development beneath created, maturing mangrove forests: ecosystem changes across a 25-yr chronosequence.

Mangrove forests are among the world's most productive and carbon-rich ecosystems. Despite growing understanding of factors controlling mangrove forest soil carbon stocks, there is a need to advance understanding of the speed of peat development beneath maturing mangrove forests, especially in created and restored mangrove forests that are intended to compensate for ecosystem functions lost during mangrove forest conversion to other land uses. To better quantify the rate of soil organic matter development beneath created, maturing mangrove forests, we measured ecosystem changes across a 25-yr chronosequence. We compared ecosystem properties in created, maturing mangrove forests to adjacent natural mangrove forests. We also quantified site-specific changes that occurred between 2010 and 2016. Soil organic matter accumulated rapidly beneath maturing mangrove forests as sandy soils transitioned to organic-rich soils (peat). Within 25yr, a 20-cm deep peat layer developed. The time required for created mangrove forests to reach equivalency with natural mangrove forests was estimated as (1) <15yr for herbaceous and juvenile vegetation, (2) ~55yr for adult trees, (3) ~25yr for the upper soil layer (0-10cm), and (4) ~45-80yr for the lower soil layer (10-30cm). For soil elevation change, the created mangrove forests were equivalent to or surpassed natural mangrove forests within the first 5 yr. A comparison to chronosequence studies from other ecosystems indicates that the rate of soil organic matter accumulation beneath maturing mangrove forests may be among the fastest globally. In most peatland ecosystems, soil organic matter formation occurs slowly (over centuries, millennia); however, these results show that mangrove peat formation can occur within decades. Peat development, primarily due to subsurface root accumulation, enables mangrove forests to sequester carbon, adjust their elevation relative to sea level, and adapt to changing conditions at the dynamic land-ocean interface. In the face of climate change and rising sea levels, coastal managers are increasingly concerned with the longevity and functionality of coastal restoration efforts. Our results advance understanding of the pace of ecosystem development in created, maturing mangrove forests, which can improve predictions of mangrove forest responses to global change and ecosystem restoration.

Assessment of Organic Carbon Stocks in Forest Soils on a Regional Scale

Results of the comparison of organic carbon stocks in the automorphic and semihydromorphic forest soils are discussed. The database includes information on 289 soil profiles in the forest zone of European Russia. On the average, the total organic carbon pool (including forest litter) in semihydromorphic soils is three times higher than that in automorphic soils. The difference decreases with an increase in the thickness of the considered soil layer from 3.2 times for the layer of 0–30 cm to 2.6 times for the layer of 0–100 cm. The greatest difference in carbon stocks is noted for the organic horizons; in semihydromorphic soils, the carbon storage in them averages 73 ± 8.2 t C/ha; in automorphic soils, it is seven times smaller. The neglect of the contribution of semihydromorphic soils results in underestimation of the total soil organic carbon stock of the region. The degree of underestimation depends on the soil cover pattern of particular areas and on the thickness of the considered soil layer. Calculations made for Karelia show that the underestimation of organic carbon stocks in various landscapes ranges from 10 to 40%. For the total area of this republic, it is estimated at 22, 19, and 13% for the soil layers of 0–30, 0–50, and 0–100 cm, respectively. A comparative analysis of known pedotransfer functions for calculating soil bulk density shows that the best results (RMSE = 0.15; R2 = 0.36) for mineral horizons of forest soils in European Russia are provided by the pedotransfer function suggested by O.V. Chestnykh and D.G. Zamolodchikov.

Soil Carbon Sequestrations in Forest Soils in Relation to Parent Material and Soil Depth in South-Eastern Nigeria

There has been increased interest in soil organic carbon in recent times because of its role in carbon sequestration. Different parent materials affect soil properties and hence will influence how much carbon is sequestered by soil. The study was conducted in June 2019 to investigate soil carbon stock in forest soils with respect to their parent materials in three States in South-eastern Nigeria. Sampling was aided by the location map of the area and free soil survey method was used to locate sampling points. 0ne profile was dug in each location and described using the Food and Agricultural Organization guideline. A total of twelve soil samples were collected and analyzed for selected properties. Results showed that sand content was significantly higher in soils under coastal plain sands (851.96 g·kg−1) and was lowest in soils of Imo clay shale (605.60 g·kg−1). Clay content was higher in soils of Imo clay shale (277.34 g·kg−1) and was lowest in coastal plain sand (118.80 g·kg−1). Silt and clay had moderate variation in coastal plain sand (>15 ≤ 35%) and high variations in Asu River and Imo clay shale (CV > 35%). The soils studied were generally acidic with values ranging (3.52) in soils formed from coastal plain sand, followed by forest soils of Imo clay shale (3.64) and Asu river group (3.85). Soil organic carbon decreased with increase in soil depth in all soil parent materials studied. Mean values ranged from 6.14 g·kg−1 in soil underlain by coastal plain sand to 10.62 g·kg−1) in soils of Imo clay shale. Soil carbon sequestered under the three different parent materials ranged from 1575 - 4676.41 (g·cm−2). Also, soil depth had a notable impact on carbon sequestration with values ranging from 1529.42 - 4374.0541 (g·cm−2) and the thicker the horizon, the more carbon sequestered. Hence, the study concluded that more carbon is sequestered in the subsurface horizons of the soil pedons than in the epipedons.

Tropical forest soil carbon stocks do not increase despite 15 years of doubled litter inputs

Soil organic carbon (SOC) dynamics represent a persisting uncertainty in our understanding of the global carbon cycle. SOC storage is strongly linked to plant inputs via the formation of soil organic matter, but soil geochemistry also plays a critical role. In tropical soils with rapid SOC turnover, the association of organic matter with soil minerals is particularly important for stabilising SOC but projected increases in tropical forest productivity could trigger feedbacks that stimulate the release of stored SOC. Here, we demonstrate limited additional SOC storage after 13–15 years of experimentally doubled aboveground litter inputs in a lowland tropical forest. We combined biological, physical, and chemical methods to characterise SOC along a gradient of bioavailability. After 13 years of monthly litter addition treatments, most of the additional SOC was readily bioavailable and we observed no increase in mineral-associated SOC. Importantly, SOC with weak association to soil minerals declined in response to long-term litter addition, suggesting that increased plant inputs could modify the formation of organo-mineral complexes in tropical soils. Hence, we demonstrate the limited capacity of tropical soils to sequester additional C inputs and provide insights into potential underlying mechanisms.

Exploring the effects of dominant forest tree species, soil texture, altitude, and pHH2O on soil carbon stocks using generalized additive models

Data from forest inventories provide information on C stocks under various tree species. However, based on the literature, the effects of tree species can be insignificant due to variation caused by the influence of site-related factors. The aim of this study was to explore the effects of soil texture, pHH2O, elevation, and dominant tree species on soil carbon (C) stocks in forest soils of Poland using data mining. Data were obtained from 468 investigation sites, spread over the entire area of Poland, representing forest sites with five dominant tree species (Scots pine, Norway spruce, Silver fir, deciduous oak and European beech), different elevations (lowlands, uplands, and mountains) and variable soil texture. We analyzed the effects of these characteristics using generalized additive models (GAM). Total soil-profile (up to 100 cm) C stocks (on average 26 t ha−1 in the organic horizon and 66 t ha−1 in the mineral soil) in forest soils of Poland were slightly lower than those reported previously for European forests. Simple ANOVA results implied that soils of pine stands contained significantly less stored C than soil under the other coniferous species (spruce and fir) and under deciduous oak and beech. The GAM analysis enabled quantification of the overall contribution of variables to variation in C stocks, namely fine-fraction (FF; silt and clay) content (15%), pHH2O (13%), altitude (8%), and dominant tree species (3%). The FF content positively affected C stocks (up to 10 t C ha−1 particularly in sandy soils (80–100% sand). The effect of elevation was most evident in the organic horizon and 0–10 cm mineral layer, which resulted in an increase of ∼40 t C ha−1 from 300 to 1000 m above sea level. The GAM analysis also showed that in all horizons the C stocks were lowest in soil pHH2O range 4.5–5.5. Decreased pHH2O or increased pHH2O resulted in an increase of 10–40 t C ha−1 in C stocks. Tree species alone explained about 3% of variation in C stocks, but a large portion of the effects of pHH2O may be attributable to the dominant tree species.

Ecosystem carbon stocks and their temporal resilience in a semi-natural beech-dominated forest

Forest management, including setting aside non-intervention forests, is currently debated as a measure to efficiently mitigate climate change. Temperate, old-growth forests are rare and the long-term effect of setting aside forest reserves, e.g. for habitat conservation, on forest carbon stocks and carbon sequestration remains uncertain. In this study, we assessed the five principal forest carbon pools in a semi-natural, temperate forest in Denmark and evaluated the changes in biomass and dead wood carbon stocks over 20 years. We also benchmarked the current carbon stocks against those in managed beech-dominated forests in the same region. In the most recent inventory, carbon stocks totalled 395 Mg ha−1 of which 47% was in above-ground live biomass, 11% in below-ground biomass, 9% in dead wood, 2% in the forest floor, and 31% in the top 75 cm of the mineral soil. Compared to similar, but managed forests in the same region, carbon stocks in above- and below-ground biomass as well as in dead wood were notably larger. However, analyses of above- and below-ground biomass and dead wood carbon stocks showed remarkable stability during the past 20 years, despite major disturbances in terms of windthrows and various pathogens. Despite the overall stability of carbon stocks we observed some significant spatio-temporal changes. Notably, the observed dynamics illustrate a general retreat of Q. robur and increasing dominance of F. sylvatica under a small-scale disturbance regime. The forest floor and soil carbon stocks averaged 131 ± 4 Mg ha−1 and were very similar to those of managed beech-dominated forests, suggesting little potential for soil carbon sequestration from setting forests aside as unmanaged. Our study has implications for selection of adequate forest management strategies to efficiently mitigate climate change as it confirms the large and persistent carbon stocks in old-growth forests compared to managed forests, but offers no evidence of continued carbon sequestration in old-growth forests.

Soil C:P Ratio along Elevational Gradients in Picea schrenkiana Forest of Tianshan Mountains

Forest soils potentially store a large pool of carbon and phosphorus. A deep understanding of the total carbon and phosphorus stock in forest soils is vital in the assessment of the nutrients dynamics in forest ecosystems. This study examined the effects of elevation, soil depth, and climatic variables, specifically mean annual temperature (MAT) and mean annual precipitation (MAP), on soil carbon and organic phosphorus in Schrenk's spruce (Picea schrenkiana) forest at Tianshan Mountains. Results showed that soil organic carbon (SOC) significantly increased while organic phosphorus decreased with elevation. Interestingly, carbon increased faster with increasing elevation in the alluvial horizon than in the leached horizon, demonstrating the important role of deep soils in carbon sequestration potential. SOC concentration decreased with soil depth, whereas phosphorus concentration initially decreased and then increased. SOC had no significant relationships with MAT and MAP, whereas phosphorus concentration decreased with MAT. Similar to the impacts of MAT and MAP on SOC, these two climatic variables also exerted no significant influence on C:P ratio.

Continental‐scale nitrogen pollution is shifting forest mycorrhizal associations and soil carbon stocks

Most tree roots on Earth form a symbiosis with either ecto- or arbuscular mycorrhizal fungi. Nitrogen fertilization is hypothesized to favor arbuscular mycorrhizal tree species at the expense of ectomycorrhizal species due to differences in fungal nitrogen acquisition strategies, and this may alter soil carbon balance, as differences in forest mycorrhizal associations are linked to differences in soil carbon pools. Combining nitrogen deposition data with continental-scale US forest data, we show that nitrogen pollution is spatially associated with a decline in ectomycorrhizal vs. arbuscular mycorrhizal trees. Furthermore, nitrogen deposition has contrasting effects on arbuscular vs. ectomycorrhizal demographic processes, favoring arbuscular mycorrhizal trees at the expense of ectomycorrhizal trees, and is spatially correlated with reduced soil carbon stocks. This implies future changes in nitrogen deposition may alter the capacity of forests to sequester carbon and offset climate change via interactions with the forest microbiome.

The effects of forest thinning on soil carbon stocks and dynamics: A meta-analysis

Forest thinning is widely used in forest management activities and has complex effects on underground carbon processes. Although many case studies have been done, how forest thinning affects soil carbon stocks and dynamics remains unclear, especially at different recovery stage. Here, we synthesized the results from 53 peer-reviewed publications and conducted a meta-analysis to evaluate the general responses of 10 variables related to forest soil carbon stocks and dynamics to forest thinning management. Overall, we did not find remarkable effects of thinning on soil moisture, fine root biomass and soil carbon stocks (including soil total carbon, soil organic carbon and microbial biomass carbon). However, thinning resulted in a significant reduction in litterfall production (−23.7%), while significantly increasing soil temperature (+8.7%) and soil respiration (+29.4%) in general. In particular, the effect of forest thinning on soil respiration was significant in light (thinning intensity <33%) to moderate (33–67% of thinning intensity) thinning. In the early stage of recovery (≤2 yr after thinning), this effect was also significant. Thinning significantly increased soil respiration in both broadleaved (+35.6%) and mixed forests (+9.3%) but not in coniferous forest due to the difference of litterfall quality. These results provide a synthetic review of the effects of forest thinning on soil carbon stocks and dynamics and may help to improve forest management strategies.

A Canadian upland forest soil profile and carbon stocks database.

"A Canadian upland forest soil profile and carbon stocks database" was compiled in phases over a period of 10years to address various questions related to modeling upland forest soil carbon in a national forest carbon accounting model. For 3,253 pedons, the SITES table contains estimates for soil organic carbon stocks (Mg/ha) in organic horizons and mineral horizons to a 100-cm depth, soil taxonomy, leading tree species, mean annual temperature, annual precipitation, province or territory, terrestrial ecozone, and latitude and longitude, with an assessment of the quality of information about location. The PROFILES table contains profile data (16,167 records by horizon) used to estimate the carbon stocks that appear in the SITES table, plus additional soil chemical and physical data, where provided by the data source. The exceptions to this are estimates for soil carbon stocks based on Canadian National Forest Inventory data (NFI [2006] in REFERENCES table), where data were collected by depth increment rather than horizon and, therefore, total soil carbon stocks were calculated separately before being entered into the SITES table. Data in the PROFILES table include the carbon stock estimate for each horizon (corrected for coarse fragment content), and the data used to calculate the carbon stock estimate, such as horizon thickness, bulk density, and percent organic carbon. The PROFILES table also contains data, when reported by the source, for percent carbonate carbon, pH, percent total nitrogen, particle size distribution (percent sand, silt, clay), texture class, exchangeable cations, cation and total exchange capacity, and percent Fe and Al. An additional table provides references (REFERENCES table) for the source data. Earlier versions of the database were used to develop national soil carbon modeling categories based on differences in carbon stocks linked to soil taxonomy and to examine the potential of using soil taxonomy and leading tree species to improve accuracy in modeled predictions. The current database is being used to develop soil carbon model parameters linked to soil taxonomy and leading tree species and, by various governmental and nongovernmental organizations, to improve digital mapping of ecosite types and soil properties regionally, nationally, and internationally. © Her Majesty the Queen in Right of Canada, 2018. Information contained in this publication or product may be reproduced, in part or in whole, and by any means, for personal or public non-commercial purposes, without charge or further permission, unless otherwise specified. You are asked to: exercise due diligence in ensuring the accuracy of the materials reproduced; indicate the complete title of the materials reproduced, and the name of the author organization; indicate that the reproduction is a copy of an official work that is published by Natural Resources Canada (NRCan) and that the reproduction has not been produced in affiliation with, or with the endorsement of, NRCan. Commercial reproduction and distribution is prohibited except with written permission from NRCan. For more information, contact NRCan at copyright.droitdauteur@nrcan-rncan.gc.ca.

Soil organic carbon stocks and related soil properties in a primary Picea abies (L.) Karst. volcanic-mountain forest

Although many published studies have evaluated soil organic carbon (SOC) stocks in forest soils, none have yet focused on primary (i.e., unlogged) spruce (Picea spp.) forests on volcanic rocks. Previous research in the Călimani volcanic mountain range, Romania, revealed a close relationship between soil morphology and the canopy disturbance history of a primary spruce (Picea abies L. Karst.) forest in the area. Here, six representative soil profiles were chosen from a large pedological study to test the hypothesis that the different disturbance regimes of the study plots had significant effects on SOC stocks. We used a combination of traditional soil core and excavation methods, modified for soil sampling and SOC stock estimations by horizons. In addition, chemical soil properties such as pH and the contents of Al, Fe, and Si in selected extracts (oxalate-extracted Alo, Feo, and Sio, pyrophosphate-extracted Alp and Fep) were determined to detect diagnostic properties of the soils.Total SOC stocks in the organic horizons plus mineral soil to the 0.5 m depth ranged from 18.2 to 32.0 kg C m−2. In the 0–0.5 m depth, the SOC stocks were significantly positively correlated with the severity of the maximum-recorded canopy disturbance. The SOC contents in mineral soil down to the 1.0 m depth were positively correlated with the contents of Alp + Fep, especially in the subsoil horizons. A strong positive correlation was found between pHKCl, Sio contents, Alp − Alo contents, and the Alo/Feo ratio. The soils were classified as Podzols and Andosols.Our results indicate that in primary spruce-dominated forests on volcanic rocks, the regime of high-severity natural canopy disturbances may have positive effects on SOC accumulation in the mineral soil. The Alo/Feo ratio may be a potentially useful proxy for the relative degree of leaching and podzolization in these soils.

Estimating water–food–ecosystem trade-offs for the global negative emission scenario (IPCC-RCP2.6)

Negative emission technologies such as bioenergy with carbon capture and storage (BECCS) are regarded as an option to achieve the climatic target of the Paris Agreement. However, our understanding of the realistic sustainable feasibility of the global lands for BECCS remains uncertain. In this study, we assess the impact of BECCS deployment scenarios on the land systems including land use, water resources, and ecosystem services. Specifically, we assess three land-use scenarios to achieve the total amount of 3.3 GtC year−1 (annual negative emission level required for IPCC-RCP 2.6) emission reduction by growing bioenergy crops which requires huge use of global agricultural and forest lands and water. Our study shows that (1) vast conversion of food cropland into rainfed bio-crop cultivation yields a considerable loss of food production that may not be tolerable considering the population increase in the future. (2) When irrigation is applied to bio-crop production, the bioenergy crop productivity is enhanced. This suppresses the necessary area for bio-crop production to half, and saves the land for agricultural productions. However, water consumption is doubled and this may exacerbate global water stress. (3) If conversion of forest land for bioenergy crop cultivation is allowed without protecting the natural forests, large areas of tropical forest could be used for bioenergy crop production. Forest biomass and soil carbon stocks are reduced, implying degradation of the climate regulation and other ecosystem services. These results suggest that without a careful consideration of the land use for bioenergy crop production, a large-scale implementation of BECCS could negatively impact food, water and ecosystem services that are supporting fundamental human sustainability.

Labile and stabile soil organic carbon fractions in surface horizons of mountain soils – relationships with vegetation and altitude

Global and local climate changes could disturb carbon sequestration and carbon stocks in forest soils. Thus, it is important to characterize the stability of soil organic matter and the dynamics of soil organic carbon (SOC) fractions in forest ecosystems. This study had two aims: (1) to evaluate the effects of altitude and vegetation on the content of labile and stabile forms of organic carbon in the mountain soils; and (2) to assess the impact of the properties of soil organic matter on the SOC pools under changing environmental conditions. The studies were conducted in the Karkonosze Mountains (SW Poland, Central Europe). The content of the most labile fraction of carbon (dissolved organic carbon, DOC) decreases with altitude, but the content of fulvic acids (FA), clearly increases in the zone above 1000 m asl, while the stabile fraction (humins, non-hydrolyzing carbon) significantly decreases. A higher contribution of stabile forms was found in soils under coniferous forests (Norway spruce), while a smaller - under deciduous forests (European beech) and on grasslands. The expected climate change and the ongoing land use transformations in the zone above 1000 m asl may lead to a substantial increase in the stable humus fraction (mainly of a non-hydrolyzing carbon) and an increase in the SOC pools, even if humus acids are characterized by a lower maturity and greater mobility favorable to soil podzolization. In the lower zone (below 1000 m asl), a decrease in the most stable humus forms can be expected, accompanied by an increase of DOC contribution, which will result in a reduction in SOC pools. Overall, the expected prevailing (spatial) effect is a decreasing contribution of the most stable humus fractions, which will be associated with a reduction in the SOC pools in medium-high mountains of temperate zone of Central Europe.

Changes in physical properties and carbon stocks of gray forest soils in the southern part of Moscow region during postagrogenic evolution

Changes in carbon stocks and physical properties of gray forest soils during their postagrogenic evolution have been studied in the succession chronosequence comprising an arable, lands abandoned 6, 15, and 30 years ago; and a secondary deciduous forest (Experimental Field Station of the Institute of Physicochemical and Biological Problems of Soil Science, Russian Academy of Sciences, Pushchino, Moscow region). It is found that carbon stocks in the upper 60-cm soil layer gain with increasing period of abandonment, from 6.17 kg C/m2 on the arable land to 8.81 kg C/m2 in the forest soil, which represents the final stage of postagrogenic succession. The most intensive carbon accumulation occurs in the upper layer of the former plow (0- to 10-cm) horizon. It is shown that the self-restoration of gray forest soils is accompanied by a reliable decrease of bulk density in the upper 10-cm layer from 1.31 ± 0.01 g/cm3 on the arable to 0.97 ± 0.02 g/cm3 in the forest. In the former plow horizon of the arable–abandoned land–forest succession series, the portion of macroaggregates increases from 73.6 to 88.5%; the mean weighted diameter of aggregates, by 1.6 times; and the coefficient of aggregation, by 3.8 times. Thus, the removal of lands from agricultural use results in a gradual restoration of their natural structure, improvement of soil agronomical properties, and carbon sequestration in the upper part of the soil profile.

Potential changes in Czech forest soil carbon stocks under different climate change scenarios

Abstract Detailed inventory data (n=3930) of the soil organic carbon up to 30 cm depth have been used to estimate the forest soil’s carbon content in altitudinal vegetation zones that are occurring in the Czech Republic. The effect of global warming represented by the use of different emission scenarios on the soil organic carbon content was investigated. Using the most pessimistic climatic model, scenario losses in C from the Czech Republic forest soils or central Europe, eventually, could be as high as 13% of the current forest soil’s carbon stock.

Carbon and nitrogen stocks in Norwegian forest soils — the importance of soil formation, climate, and vegetation type for organic matter accumulation

Relationships between soil C and N stocks and soil formation, climate, and vegetation were investigated in a gridded database connected to the National Forest Inventory in Norway. For mineral soil orders, C and N stocks were estimated to be 11.1–19.3 kg C·m−2 and 0.41–0.78 kg N·m−2, respectively, declining in the following order: Gleysols &gt; Podzols &gt; Brunisols &gt; Regosols. Organic peat-type soils stored, on average, 31.3 kg C·m−2 and 1.10 kg N·m−2, whereas shallow Organic folisols stored, on average, 10.2 kg C·m−2 and 0.34 kg N·m−2. For Norway’s 120 000 km2 of forest, the total of soil C stocks was estimated to be 1.83 Gt C, with a 95% CI of 1.71–1.95 Gt C. Podzolic soils comprise the largest soil group and store approximately 50% of the forest soil C. Sixty percent of the soil C stock in Podzolic soils was stored in the mineral soil, increasing with temperature and precipitation. Poorly drained soil types store approximately 47% of the total forest soil C in Norway. Soils with water saturation have large C stocks mainly in the forest floor, suggesting that they are more susceptible to forest management and environmental change. Soil C stocks under pine and spruce forests were similar, although pine forests had larger C stocks in the forest floor, while spruce forests had the highest C stocks in the mineral soil compartment. C stocks in the forest floor increase from dry to moist ground vegetation, while ground vegetation nutrient classes reflect better the C and N stocks in the mineral soil.

Underestimation of boreal forest soil carbon stocks related to soil classification and drainage

Soil organic carbon (C), accumulated over millennia, comprise more than half of the C stored in boreal and temperate forest landscapes. We used the Norwegian national forest inventory and soil survey network (n = 719, no deep organic soils) to explore the validity of a deterministic model representation of this pool (Yasso07). We statistically compared simulated and measured soil C stocks and related differences (measured – simulated) to site factors (drainage, topography, climate, vegetation, C-to-N ratio, and soil classification). Median C stocks were 5.0 kg C·m−2 (model) and 14.5 kg C·m−2 (measurements). Soil C differences related to site factors (r2 of 0.16 to 0.37). For Brunisols, Gleysols, and wet Organic soils, differences related primarily to topographic wetness. For Regosols, Podzols, and Dystric Eluviated Brunisols, they related to climate, profile depth, and, in some cases, drainage class and site index. We argue that soil moisture regimes in our study area overrule tree productivity effects in the determination of soil C stocks and present conditions for soil formation that the model cannot (and does not explicitly) account for. These are processes such as humification and podsolization that involve eluviation and illuviation of dissolved organic C (DOC) with sesquioxides to form spodic B horizons and carbon enrichment due to hampered decomposition in frequently anoxic conditions.