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1.
Our understanding of the processes influencing the storage and dynamics of carbon (C) in soils under semi-arid agroforestry systems in Sub-Saharan Africa (SSA) is limited. This study evaluated soil C pools in woodlot species of Albizia lebbeck (L.) Benth., Leucaena leucocephala (Lam.) de Wit, Melia azedarach (L.), and Gmelina arborea Roxb.; and in farmland and Ngitili, a traditional silvopastoral system in northwestern Tanzania. Soil organic carbon (SOC) was analyzed in the whole soil to 1 m depth and to 0.4 m in macroaggregates (2000–250 μm), microaggregates (250–53 μm), and silt and clay-sized aggregates (<53 μm) to provide information of C dynamics and stabilization in various land uses. Synchrotron-based C K-edge x-ray absorption near-edge structure (XANES) spectroscopy was also used to study the influence of these land use systems on the soil organic matter (SOM) chemistry to understand the mechanisms of soil C changes. Whole soil C stocks in woodlots (43–67 Mg C ha?1) were similar to those in the reserved Ngitili systems (50–59 Mg C ha?1), indicating the ability of the planted woodlots on degraded lands to restore SOC levels similar to the natural woodlands. SOC in the woodlots were found to be associated more with the micro and silt-and clay-sized aggregates than with macroaggregates, reflecting higher stability of SOC in the woodlot systems. The continuous addition of litter in the woodlots preserved recalcitrant aromatic C compounds in the silt and clay-sized aggregates as revealed by the XANES C K-edge spectra. Therefore establishment of woodlots in semi-arid regions in Tanzania appear to make significant contributions to the long-term SOC stabilization in soil fractions.  相似文献   

2.
No information is available about carbon (C) sequestration potentials in ecosystems on Andisols of the Chilean Patagonia. This study was undertaken to measure the size of C stocks in three predominant ecosystems: Pinus ponderosa-based silvopastoral systems (SPS), pine plantations (PPP) and natural pasture (PST), and examine how clover affect tree growth and stocks of soil C. The C contents of trees and pasture were determined by destructive sampling and dry combustion. Soil samples were taken at 0?C5, 5?C20, 20?C40?cm depths in order to determine soil C and N. For PPP and SPS total aboveground tree C was 38.4 and 53.1?kg tree?1 and belowground was 21.3 and 23.4?kg tree?1, respectively. Annual diameter increment at breast height was 1 and 2?cm in PPP and SPS, respectively, and was significantly higher in SPS. Trees in SPS, due to lower density and the presence of leguminous pasture, demonstrated enhanced growth and C sequestration. Soil organic C (SOC) stocks at 0?C40?cm depth were 193.76, 177.10 and 149.25?Mg?ha?1 in SPS, PST and PPP, respectively. The conversion of PPP to SPS and PST to PPP resulted in an increase of 44.51?Mg?ha?1 and a decrease of 27.85?Mg?ha?1 in SOC, respectively. Favorable microclimatic conditions in relation to air temperature and soil moisture were observed in SPS as well as a synergy between trees and pasture.  相似文献   

3.
This study quantified tree and soil C stocks and their response to different tree species and clay contents in improved fallows in eastern Zambia. From 2002 to 2003, soil, and destructively harvested two-year old tree, samples were analysed for C. There were significant differences (P < 0.05) in aboveground tree C stocks, and in net organic C (NOC) intake rates across coppicing tree species at Msekera and Kalunga. Aboveground C stocks ranged from 2.9 to 9.8 t ha-1, equivalent to NOC intakes of 0.8–4.9 t ha-1 year-1. SOC stocks in non-coppiced fallows at Kalichero and Msekera significantly differed (P < 0.05) across treatments. SOC stocks to 200 cm depth ranged from 64.7 t C ha-1 under non-coppicing fallows at Kalunga to 184.0 t ha-1 in 10-year-old coppicing fallows at Msekera. Therefore, tree and soil C stocks in improved fallows can be increased by planting selected tree species on soils with high clay content.  相似文献   

4.
Scarcity of simple and reliable methods of estimating soil organic carbon (SOC) turnover and lack of data from long-term experiments make it difficult to estimate attainable soil C sequestration in tropical improved fallows. Testing and validating existing and widely used SOC models would help to determine attainable C storage in fallows. The Rothamsted C (RothC) model, therefore, was tested using empirical data from improved fallows at Msekera in eastern Zambia. This study (i) determined the effects of nitrogen fixing tree (NFT) species on aboveground organic C inputs to the soil and SOC stocks, (ii) estimated annual net organic C inputs to the soil using the RothC, and (iii) tested the performance of RothC model using empirical data from improved fallows. Soil samples (0–20 cm) were collected from coppicing and non-coppicing fallow experiments in October 2002 for determination of SOC by LECO CHN-1000 analyser. Data on surface litter, maize and weed biomasses, and on weather, were supplied by the Zambia/ICRAF Agroforestry Project. Measured SOC stocks to 20 cm depth ranged from 32.2 to 37.8 t ha−1 in coppicing fallows and 29.5 to 30.1 t ha−1 in non-coppicing fallows compared to 22.2–26.2 t ha−1 in maize monoculture systems. Coppicing fallows accumulated more SOC (680–1150 g m−2 year−1) than non-coppicing fallows (410–789 g m−2 year−1). While treatments with NFTs accumulated more SOC than NFT-free systems, SOC stocks increased with increasing tree biomass production and tree rotation. For food security and C sequestration, coppicing fallows are a potentially viable option.  相似文献   

5.
Tree removal in Latin American coffee agroforestry systems has been widespread due to complex and interacting factors that include fluctuating international markets, government-supported agricultural policies, and climate change. Despite shade tree removal and land conversion risks, there is currently no widespread policy incentive encouraging the maintenance of shade trees for the benefit of carbon sequestration. In facilitation of such incentives, an understanding of the capacity of coffee agroforests to store carbon relative to tropical forests must be developed. Drawing on ecological inventories conducted in 2007 and 2010 in the Lake Atitlán region of Guatemala, this research examines the carbon pools of smallholder coffee agroforests (CAFs) as they compare to a mixed dry forest (MDF) system. Data from 61 plots, covering a total area of 2.24 ha, was used to assess the aboveground, coarse root, and soil carbon reservoirs of the two land-use systems. Results of this research demonstrate the total carbon stocks of CAFs to range from 74.0 to 259.0 Megagrams (Mg)?C ha?1 with a mean of 127.6?±?6.6 (SE)?Mg?C ha?1. The average carbon stocks of CAFs was significantly lower than estimated for the MDF (198.7?±?32.1?Mg?C?ha?1); however, individual tree and soil pools were not significantly different suggesting that agroforest shade trees play an important role in facilitating carbon sequestration and soil conservation. This research demonstrates the need for conservation-based initiatives which recognize the carbon sequestration benefits of coffee agroforests alongside natural forest systems.  相似文献   

6.
We compared soil organic carbon (SOC) stocks and stability under two widely distributed tree species in the Mediterranean region: Scots pine (Pinus sylvestris L.) and Pyrenean oak (Quercus pyrenaica Willd.) at their ecotone. We hypothesised that soils under Scots pine store more SOC and that tree species composition controls the amount and biochemical composition of organic matter inputs, but does not influence physico-chemical stabilization of SOC. At three locations in Central Spain, we assessed SOC stocks in the forest floor and down to 50 cm in the mineral in pure and mixed stands of Pyrenean oak and Scots pine, as well as litterfall inputs over approximately 3 years at two sites. The relative SOC stability in the topsoil (0-10 cm) was determined through size-fractionation (53 μm) into mineral-associated and particulate organic matter and through KMnO4-reactive C and soil C:N ratio.Scots pine soils stored 95-140 Mg ha−1 of C (forest floor plus 50 cm mineral soil), roughly the double than Pyrenean oak soils (40-80 Mg ha−1 of C), with stocks closely correlated to litterfall rates. Differences were most pronounced in the forest floor and uppermost 10 cm of the mineral soil, but remained evident in the deeper layers. Biochemical indicators of soil organic matter suggested that biochemical recalcitrance of soil organic matter was higher under pine than under oak, contributing as well to a greater SOC storage under pine. Differences in SOC stocks between tree species were mainly due to the particulate organic matter (not associated to mineral particles). Forest conversion from Pyrenean oak to Scots pine may contribute to enhance soil C sequestration, but only in form of mineral-unprotected soil organic matter.  相似文献   

7.
Agroforestry is an ancient practice widespread throughout Africa. However, the influence of Sahelian agroforestry systems on carbon storage in soil and biomass remains poorly understood. We evaluated the carbon storage potential of three agroforestry systems (fallow, parkland and rangeland) and five tree species (Faidherbia albida, Acacia raddiana, Neocarya macrophylla, Balanites aegyptiaca and Euphorbia balsamifera) growing on three different soils (clay, sandy loam and sandy) in the Niayes zone, Senegal. We calculated tree biomass carbon stocks using allometric equations and measured soil organic carbon (SOC) stocks at four depths (0–20, 20–50, 50–80 and 80–100 cm). F. albida and A. raddiana stored the highest amount of carbon in their biomass. Total biomass carbon stocks were greater in the fallow (40 Mg C ha?1) than in parkland (36 Mg C ha?1) and rangeland (29 Mg C ha?1). More SOC was stored in the clay soil than in the sandy loam and sandy soils. On average across soil texture, SOC stocks were greater in fallow (59 Mg C ha?1) than in rangeland (30 Mg C ha?1) and parkland (15 Mg C ha?1). Overall, the total amount of carbon stored in the soil + plant compartments was the highest in fallow (103 Mg C ha?1) followed by rangeland (68 Mg C ha?1) and parkland (52 Mg C ha?1). We conclude that in the Niayes zones of Senegal, fallow establishment should be encouraged and implemented on degraded lands to increase carbon storage and restore soil fertility.  相似文献   

8.
Little is known on soil organic carbon (SOC) stocks in karst areas worldwide, although many of them have seen long-term application of agroforestry systems with a potential for carbon sequestration. Therefore, our study aimed to assess landscape-level SOC concentration and stock in the Silica Plateau, a part of the Slovak Karst Biosphere Reserve located in the Western Carpathians (Slovakia) with a centuries-long agroforestry record. The most represented local soil units are Chromi-Rendzic Leptosols and Chromic Cambisols with clayey loam texture, C/N ratio 9–12, and $ {\text{pH}}_{{{\text{H}}_{2} {\text{O}}}} $ 6.6–6.2 in their organo-mineral surface horizons. Mull surface humus form prevails under mixed forest stands dominated by hornbeam (Carpinus betulus L.), oak (Quercus petraea L.), and beech (Fagus sylvatica L.). A total of 2,700 soil samples were collected from 150 soil pits. Both SOC concentrations and stocks were determined for the 0–60?cm mineral soil layer. Soil stoniness was accounted for by means of electrical resistivity tomography. According to the analysis of covariance, cropland SOC concentration (0.026?g?g?1) is significantly lower compared to forestland (0.040?g?g?1) and pastureland (0.041?g?g?1) (P?<?0.01). During the period of 130?years after forest clearing, cropland SOC stock has been reduced at an exponential decay rate of ca 0.002?year?1, while the SOC stock in pastureland has increased following land use change from cropland by approximately 30% during the same period of time. Irrespective of land use history, overall SOC stock is high reaching on average 207.4?Mg?ha?1, out of which 66% are stored within 0–30?cm and 34% within 30–60?cm soil layers.  相似文献   

9.
Carbon (C) sequestration potential was quantified for five tree species, commonly used in tree-based intercropping (TBI) and for conventional agricultural systems in southern Ontario, Canada. In the 25-year-old TBI system, hybrid poplar (Populus deltoides × Populus nigra clone DN-177), Norway spruce (Picae abies), red oak (Quercus rubra), black walnut (Juglans nigra), and white cedar (Thuja occidentalis) were intercropped with soybean (Glycine max). In the conventional agricultural system, soybean was grown as a sole crop. Above- and belowground tree C Content, soil organic C, soil respiration, litterfall and litter decomposition were quantified for each tree species in each system. Total C pools for hybrid poplar, white cedar, red oak, black walnut, Norway spruce and a soybean sole-cropping system were 113.4, 99.4, 99.2, 91.5, 91.3, and 71.1 t C ha?1, respectively at a tree density of 111 trees ha?1, including mean tree C content and soil organic C stocks. Net C flux for hybrid poplar, white cedar, red oak, black walnut, Norway spruce and soybean sole-crop were 2.1, 1.4, 0.8, 1.8, 1.6 and ?1.2 t C ha?1 year?1, respectively. Results presented suggest greater atmospheric CO2 sequestration potential for all five tree species when compared to a conventional agricultural system.  相似文献   

10.
Forest soil organic carbon (SOC) and forest floor carbon (FFC) stocks are highly variable. The sampling effort required to assess SOC and FFC stocks is therefore large, resulting in limited sampling and poor estimates of the size, spatial distribution, and changes in SOC and FFC stocks in many countries. Forest SOC and FFC stocks are influenced by tree species. Therefore, quantification of the effect of tree species on carbon stocks combined with spatial information on tree species distribution could improve insight into the spatial distribution of forest carbon stocks.We present a study on the effect of tree species on FFC and SOC stock for a forest in the Netherlands and evaluate how this information could be used for inventory improvement. We assessed FFC and SOC stocks in stands of beech (Fagus sylvatica), Douglas fir (Pseudotsuga menziesii), Scots pine (Pinus sylvestris), oak (Quercus robur) and larch (Larix kaempferi).FFC and SOC stocks differed between a number of species. FFC stocks varied between 11.1 Mg C ha−1 (beech) and 29.6 Mg C ha−1 (larch). SOC stocks varied between 53.3 Mg C ha−1 (beech) and 97.1 Mg C ha−1 (larch). At managed locations, carbon stocks were lower than at unmanaged locations. The Dutch carbon inventory currently overestimates FFC stocks. Differences in carbon stocks between conifer and broadleaf forests were significant enough to consider them relevant for the Dutch system for carbon inventory.  相似文献   

11.
Ecosystem-level assessments of carbon (C) stocks of agroforestry systems are scarce. We quantified the ecosystem-level C stocks of one agroforestry-based oil palm production system (AFSP) and one agroforestry-based oil palm and cacao production system (AFSP+C) in eastern Amazonia. We quantified the stocks of C in four pools: aboveground live biomass, litter, roots, and soil. We evaluated the distribution of litter, roots, and soil C stocks in the oil palm management zones and in the area planted with cacao and other agroforestry species. The ecosystem-C stock was higher in AFSP+C (116.7 ± 1.5 Mg C ha?1) than in AFSP (99.1 ± 3.1 Mg C ha?1). The total litter-C stock was higher in AFSP+C (3.27 ± 0.01 Mg C ha?1) than in AFSP (2.26 ± 0.06 Mg C ha?1). Total root and soil C stocks (0–30 cm) did not differ between agroforestry systems. Ecosystem-C stocks varied between agroforestry systems due to differences in both aboveground and belowground stocks. In general, the belowground-C stocks varied spatially in response to the management in the oil palm and non-oil palm strips; these results have important implications for the monitoring of ecosystem-level C dynamics and the refinement of soil management.  相似文献   

12.
An accurate characterization of tree carbon (TC), forest floor carbon (FFC) and soil organic carbon (SOC) in tropical forest plantations is important to estimate their contribution to global carbon stocks. This information, however, is poor and fragmented. Carbon contents were assessed in patula pine (Pinus patula) and teak (Tectona grandis) stands in tropical forest plantations of different development stages in combination with inventory assessments and soil survey information. Growth models were used to associate TOC to tree normal diameter (D) with average basal area and total tree height (HT), with D and HT parameters that can be used in 6–26 years old patula pine and teak in commercial tropical forests as indicators of carbon stocks. The information was obtained from individual trees in different development stages in 54 patula pine plots and 42 teak plots. The obtained TC was 99.6 Mg ha−1 in patula pine and 85.7 Mg ha−1 in teak forests. FFC was 2.3 and 1.2 Mg ha−1, SOC in the surface layer (0–25 cm) was 92.6 and 35.8 Mg ha−1, 76.1 and 19 Mg ha−1 in deep layers (25–50 cm) in patula pine and teak, respectively. Carbon storage in trees was similar between patula pine and teak plantations, but patula pine had higher levels of forest floor carbon and soil organic carbon. Carbon storage in trees represents 37 and 60% of the total carbon content in patula pine and teak plantations, respectively. Even so, the remaining percentage corresponds to SOC, whereas FFC content is less than 1%. In summary, differences in carbon stocks between patula pine and teak trees were not significant, but the distribution of carbon differed between the plantation types. The low FFC does not explain the SOC stocks; however, current variability of SOC stocks could be related to variation in land use history.  相似文献   

13.
《Southern Forests》2013,75(3):235-245
Global sustainable development goals include reducing greenhouse gas emissions from land-use change and maintaining biodiversity. Many studies have examined carbon stocks and tree species diversity, but few have studied the humid Guinean savanna ecosystem. This study focuses on a humid savanna landscape in northern Sierra Leone, aiming to assess carbon stocks and tree species diversity and compare their relationships in different vegetation types. We surveyed 160 sample plots (0.1 ha) in the field for tree species, aboveground carbon (AGC) and soil organic carbon (SOC). In total, 90 tree species were identified in the field. Gmelina arborea, an exotic tree species common in the foothills of the Kuru Hills Forest Reserve, and Combretum glutinosum, Pterocarpus erinaceous and Terminaria glaucescens, which are typical savanna trees, were the most common species. At landscape level, the mean AGC stock was 29.4 Mg C ha?1 (SD 21.3) and mean topsoil (0–20 cm depth) SOC stock was 42.2 Mg C ha?1 (SD 20.6). Mean tree species richness and Shannon index per plot were 7 (SD 4) and 1.6 (SD 0.6), respectively. Forests and woodlands had significantly higher mean AGC and tree species richness than bushland, wooded grassland or cropland (p < 0.05). In the forest and bushland, a small number of large diameter trees covered a large portion of the total AGC stocks. Furthermore, a moderate linear correlation was observed between AGC and tree species richness (r = 0.475, p < 0.001) and AGC and Shannon index (r = 0.375, p < 0.05). The correlation between AGC and SOC was weak (r = 0.17, p < 0.05). The results emphasise the role of forests and woodlands and large diameter trees in retaining AGC stocks and tree species diversity in the savanna ecosystem.  相似文献   

14.
Carbon pools in two Quercus petraea (sessile oak) dominated chronosequences under different forest management (high forest and coppice with standards) were investigated. The objective was to study temporal carbon dynamics, in particular carbon sequestration in the soil and woody biomass production, in common forest management systems in eastern Austria along with stand development. The chronosequence approach was used to substitute time-for-space to enable coverage of a full rotation period in each system. Carbon content was determined in the following compartments: aboveground biomass, litter, soil to a depth of 50 cm, living root biomass and decomposing residues in the mineral soil horizons. Biomass carbon pools, except fine roots and residues, were estimated using species-specific allometric functions. Total carbon pools were on average 143 Mg ha−1 in the high forest stand (HF) and 213 Mg ha−1 in the coppice with standards stand (CS). The mean share of the total organic carbon pool (TOC) which is soil organic carbon (SOC) differs only marginally between HF (43.4%) and CS (42.1%), indicating the dominance of site factors, particularly climate, in controlling this ratio. While there was no significant change in O-layer and SOC stores over stand development, we found clear relationships between living biomass (aboveground and belowground) pools and C:N ratio in topsoil horizons with stand age. SOC pools seem to be very stable and an impact of silvicultural interventions was not detected with the applied method. Rapid decomposition and mineralization of litter, indicated by low O-horizon pools with wide C:N ratios of residual woody debris at the end of the vegetation period, suggests high rates of turnover in this fraction. CS, in contrast to HF benefits from rapid resprouting after coppicing and hence seems less vulnerable to conditions of low rainfall and drying topsoil.  相似文献   

15.
In all, 48 sites of subalpine coniferous forest that had undergone natural regeneration for 5-310 years were selected as study locations in the Southwest China. We compared species richness (S), plant diversity (Shannon-Wiener index, H′; Margalef index, R), and above- and below-ground ecosystem carbon (C) pools of six plant communities along a chronosequence of vegetation restoration, and we also examined evidence for a functional relationship between plant diversity and C storage. Our results showed that above-ground C increased significantly (over 52-fold), mainly due to the increase of C in aboveground living plants and surface litter. Soil organic carbon (SOC) content increased from the herb community type (dominated by Deyeuxia scabrescens, P1) to mixed forest type (dominated by Betula spp. and Abies faxoniana, P4), which constituted the main C pool of the system (63-89%), but decreased thereafter (communities P5-P6). The mean C stock in the whole ecosystem - trees, litter layer and mineral soil - ranged from 105 to 730 Mg C ha−1 and was especially high in the spruce forest community type (dominated by Picea purpurea, P6). On the other hand, the relationships between C stocks (soil, aboveground) and mean annual temperature or altitude were generally weak (P > 0.05). Moreover, we did not detect a relationship between S and aboveground C storage, while we found a significant negative relationship between H′, R and aboveground C storage. In addition, our experiment demonstrated that total root biomass and litter C/N ratio were significant functional traits influencing SOC, while S, R, and H′ had little effect. Path analysis also revealed that litter C/N ratio predominantly regulated SOC through changes in the quantity of microorganisms and soil invertase enzyme activity.  相似文献   

16.
Tree growth, biomass productivity, litterfall mass and nutrient content, changes in soil chemical properties and understory forest succession were evaluated over a 8.5-year period in single- and mixed-species (50 : 50) plantations of two N2-fixing species, Casuarina equisetifolia and Leucaena leucocephala, and a non-fixing species, Eucalyptus robusta. At the optimal harvest age for maximum biomass production (4 years), total aboveground biomass ranged from 63 Mg ha−1 in the Eucalyptus monoculture to 124 Mg ha−1 in the Casuarina/Leucaena mixture, and was generally greater in the mixed-species than in single-species treatments due to increased productivity of the N-fixing species in the mixed stands. Total litterfall varied from 5.3 to 10.0 Mg ha−1 year−1 among treatments, or between 5.9% and 13.2% of net primary production. Litterfall production and rates of nutrient return for N, P, K, Ca and Mg were generally highest for Leucaena, intermediate for Casuarina and lowest for Eucalyptus. These rates were usually higher in the mixed-species than in monospecific stands due to differences in biomass productivity, but varied considerably depending on their species composition. Total system carbon and nutrient pools (in biomass plus soils to 40-cm depth) for N, P, K, Ca, Mg, Mn at four years were consistently greater in the plantation treatments than in the unplanted control plots. Relative to the single-species plantations, these system pools were generally larger in the mixed-species plantations for C (−10% to +10%), N (+17% to +50%), P (−1% to +63%), K (−19% to +46%), Ca (−10% to +48%), Mg (+5% to +57%) and Mn (+19% to +86%). Whole-tree harvests at four years would result in substantial system carbon and nutrient losses, although these estimated losses would not exceed the estimated gains realized during the four-year period of tree growth at this site. At 7.5 years, soil organic matter and effective cation exchange capacity were reduced in all plantation treatments relative to the control. Changes in soil nutrient content from 0 to 7.5 years were highly variable and not significantly different among treatments, although stands containing Leucaena generally showed higher rates of nitrogen and phosphorus accretion in soils than those with Eucalyptus and/or Casuarina. Natural regeneration of secondary forest tree and shrub species increased over time in all plantation treatments. A total of 24 native or naturalized forest species were recorded in the plantations at 8.5 years. Woody species abundance at this age was significantly greater beneath Casuarina than either Eucalyptus or the Eucalyptus/Leucaena mixed stands. Species richness and diversity, however, were greatest beneath stands containing Eucalyptus and/or Leucaena than in stands with Casuarina.  相似文献   

17.
Forest soil carbon(C) is an important component of the global C cycle. However, the mechanism by which tree species influence soil organic C(SOC) pool composition and mineralization is poorly understood. To understand the effect of tree species on soil C cycling, we assessed total, labile, and recalcitrant SOC pools, SOC chemical composition by ~(13) C nuclear magnetic resonance spectroscopy, and SOC mineralization in four monoculture plantations. Labile and recalcitrant SOC pools in surface(0–10 cm) and deep(40–60 cm) soils in the four forests contained similar content. In contrast, these SOC pools exhibited differences in the subsurface soil(from 10 to20 cm and from 20 to 40 cm). The alkyl C and O-alkyl C intensities of SOC were higher in Schima superba and Michelia macclurei forests than in Cunninghamia lanceolata and Pinus massoniana forests. In surface soil, S.superba and M. macclurei forests exhibited higher SOC mineralization rates than did P. massoniana and C.lanceolata forests. The slope of the straight line between C_(60) and labile SOC was steeper than that between C_(60) and total SOC. Our results suggest that roots affected the composition of SOC pools. Labile SOC pools also affected SOC mineralization to a greater extent than total SOC pools.  相似文献   

18.
The effect of forest conservation on the organic carbon (C) stock of temperate forest soils is hardly investigated. Coarse woody debris (CWD) represents an important C reservoir in unmanaged forests and potential source of C input to soils. Here, we compared aboveground CWD and soil C stocks at the stand level of three unmanaged and three adjacent managed forests in different geological and climatic regions of Bavaria, Germany. CWD accumulated over 40–100 years and yielded C stocks of 11 Mg C ha?1 in the unmanaged spruce forest and 23 and 30 Mg C ha?1 in the two unmanaged beech–oak forests. C stocks of the organic layer were smaller in the beech–oak forests (8 and 19 Mg C ha?1) and greater in the spruce forest (36 Mg C ha?1) than the C stock of CWD. Elevated aboveground CWD stocks did not coincide with greater C stocks in the organic layers and the mineral soils of the unmanaged forests. However, radiocarbon signatures of the O e and O a horizons differed among unmanaged and managed beech–oak forests. We attributed these differences to partly faster turnover of organic C, stimulated by greater CWD input in the unmanaged forest. Alternatively, the slower turnover of organic C in the managed forests resulted from lower litter quality following thinning or different tree species composition. Radiocarbon signatures of water-extractable dissolved organic carbon (DOC) from the top mineral soils point to CWD as potent DOC source. Our results suggest that 40–100 years of forest protection is too short to generate significant changes in C stocks and radiocarbon signatures of forest soils at the stand level.  相似文献   

19.
A study was conducted to assess carbon stocks in various forms and land-use types and reliably estimate the impact of land use on C stocks in the Nam Yao sub-watershed (19°05'10"N, 100°37'02"E), Thailand. The carbon stocks of aboveground, soil organic and fine root within primary forest, reforestation and agricultural land were estimated through field data collection. Results revealed that the amount of total carbon stock of forests (357.62 ± 28.51 Mg·ha-1, simplified expression of Mg (carbon)·ha-1) was significantly greater (P＜ 0.05) than the reforestation (195.25 ±14.38 Mg·ha-1) and the agricultural land (103.10±18.24 Mg·ha-1). Soil organic carbon in the forests (196.24 ±22.81 Mg·ha-1) was also significantly greater (P＜ 0.05) than the reforestation (146.83± 7.22 Mg·ha-1) and the agricultural land (95.09 ± 14.18 Mg·ha-1). The differences in carbon stocks across land-use types are the primary consequence of variations in the vegetation biomass and the soil organic matter. Fine root carbon was a small fraction of carbon stocks in all land-use types. Most of the soil organic carbon and fine root carbon content was found in the upper 40-cm layer and decreased with soil depth. The aboveground carbon(soil organic carbon: fine root carbon ratios (ABGC: SOC: FRC), was 5:8:1, 2:8:1, and 3:50:1 for the forest, reforestation and agricultural land, respectively. These results indicate that a relatively large proportion of the C loss is due to forest conversion to agricultural land. However, the C can be effectively recaptured through reforestation where high levels of C are stored in biomass as carbon sinks, facilitating carbon dioxide mitigation.  相似文献   

20.
This paper presents a synthesis of experiments conducted in a tropical tree plantation established in 2001 and consisting of 22 plots of 45 m × 45 m with either one, three or six native tree species. We examined the changes in carbon (C) pools (trees, herbaceous vegetation, litter, coarse woody debris (CWD), and mineral topsoil at 0-10 cm depth) and fluxes (decomposition of CWD and litter, as well as soil respiration) both through time and among diversity levels. Between 2001 and 2009 the aboveground C pools increased, driven by trees. Across diversity levels, the mean observed aboveground C pool was 7.9 ± 2.5 Mg ha−1 in 2006 and 20.4 ± 7.4 Mg ha−1 in 2009, a 158% increase. There was no significant diversity effect on the observed aboveground C pool, but we found a significant decrease in the topsoil C pool, with a mean value of 34.5 ± 2.4 Mg ha−1 in 2001 and of 25.7 ± 5.7 Mg ha−1 in 2009 (F1,36 = 52.12, p < 0.001). Assuming that the biomass C pool in 2001 was negligible (<1 Mg ha−1), then the plantation gained in C, on average, ∼20 and lost ∼9 Mg ha−1 in biomass and soil respectively, for an overall gain of ∼11 Mg ha−1 over 8 years. Across the entire data set, we uncovered significant effects of diversity on CWD decomposition (diversity: F2,393 = 15.93, p < 0.001) and soil respiration (monocultures vs mixtures: t = 15.35, df = 11, p < 0.05) and a marginally significant time × diversity interaction on the loss of total C from the mineral topsoil pool (see above). Monthly CWD decomposition was significantly faster in monocultures (35.0 ± 24.1%) compared with triplets (31.3 ± 21.0%) and six-species mixtures (31.9 ± 26.8%), while soil respiration was higher in monocultures than in mixtures (t = 15.35, df = 11, p < 0.001). Path analyses showed that, as diversity increases, the links among the C pools and fluxes strengthen significantly. Our results demonstrate that tree diversity influences the processes governing the changes in C pools and fluxes following establishment of a tree plantation on a former pasture. We conclude that the choice of tree mixtures for afforestation in the tropics can have a marked influence on C pools and dynamics.  相似文献   

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