南亚热带格木、马尾松幼龄人工纯林及其混交林生态系统碳氮储量

研究比较了南亚热带6年生格木(Erythrophleum fordii)、马尾松(Pinus massoniana)幼龄人工纯林及马尾松与格木混交林生态系统碳氮储量及其分配特征。结果表明,生态系统总碳储量依次为马尾松-格木混交林(137.75 t/hm2)格木纯林(134.07 t/hm2)马尾松纯林(131.10 t/hm2),总氮储量则为格木纯林(10.19 t/hm2)马尾松-格木混交林(8.68 t/hm2)马尾松纯林(7.01 t/hm2)。3种人工林生态系统碳氮库空间分布基本一致,绝大部分储存于0—100 cm土壤层,平均占生态系统总储量的81.49%和96.91%,其次为乔木层(分别占17.52%和2.69%),林下植被和凋落物层所占比例最小。林地土壤碳主要集中于表土层,其中0—30 cm土层平均碳储量为52.52 t/hm2,占土壤总碳储量(0—100 cm)的47.99%,土壤氮的分布则无明显规律。相比于纯林,与固氮树种混交的营林方式表现出更大的碳储存能力。3种幼龄人工林生态系统较低的地上与地下部分碳氮分配比,表明其仍具有较强的碳氮固持潜力。     

Reducing nutrient loss from farms through silvopastoral practices in coarse-textured soils of Florida,USA

Trees integrated into the range- and pasturelands of Florida could remove nutrients from deeper soil profiles that would otherwise be transported to water bodies and cause pollution. Soil nitrogen (N) and phosphorus (P) concentrations were monitored in three pastures: a treeless pasture of bahiagrass (Paspalum notatum); a pasture of bahiagrass under 20-year-old slash pine (Pinus elliotti) trees (silvopasture); and a pasture of native vegetation under pine trees (native silvopasture). Soil analysis from 10 profiles within each pasture showed that P concentrations were higher in treeless pasture (mean: 9.11 mg kg⁻¹ in the surface to 0.23 mg kg⁻¹ at 1.0 m depth) compared to silvopastures (mean: 2.51 and 0.087 mg kg⁻¹, respectively), and ammonium–N and nitrate–N concentrations were higher in the surface horizon of treeless pasture. The more extensive rooting zones of the combined stand of tree + forage may have caused higher nutrient uptake from silvopastures than treeless system. Further, compared to treeless system, soils under silvopasture showed higher P storage capacity. The results suggest that, compared to treeless pasture, silvopastoral association enhances nutrient retention in the system and thus reduces chances for nutrient transport to surface water. The study reflects the scope for applying ecological-engineering and ecosystem-restoration principles to silvopastoral-system design.     

Carbon sequestration potential of green roofs using mixed-sewage-sludge substrate in Chengdu World Modern Garden City

Green roofs which use sewage sludge to sequestrate urban carbon dioxide may represent a potential opportunity to evaluate carbon sequestration benefits for the urban development under increasing global climate change. In this study, green roofs composed of 6 small green segments with two different substrates, mixed-sewage-sludge substrate (MSSS, volume ratio of sewage sludge and local-natural soil 1:1), and local-natural soil (LNS), three different substrate depths (20 cm, 25 cm and 30 cm), and three types of native plants (Ligustrum vicaryi, Neottia auriculata, and Liriope spicata) in Chengdu City were established to determine carbon sequestration from July 2012 to July 2013 through assessment of the carbon storage and sequestration. Results show that the average carbon storage of MSSS and LNS on green roofs was respectively 13.15 kg C m⁻² and 8.58 kg C m⁻², and the average carbon sequestration followed the order of LNS (3.89 kg C m⁻² yr⁻¹) > MSSS (3.81 kg C m⁻² yr⁻¹). Thus MSSS could be considered as a potential material for carbon sequestration. The carbon storage and carbon sequestration by native plants on the green roofs followed the order of L. vicaryi > L. spicata > N. auriculata. The whole green roof had a mean carbon storage of 18.28 kg C m⁻² and average carbon sequestration of 6.47 kg C m⁻² yr⁻¹ in the combined biomass and substrate organic matter. The best green roof configuration was L. vicaryi together with MSSS substrate, with a middle-high level of carbon sequestration. It will be feasible and worthwhile to scale-up the adaptable green roof configurations in Chengdu World Modern Garden City.     

Growth, production and carbon sequestration of silvopastoral systems with native timber species in the dry lowlands of Costa Rica

The multiple environmental issues of loss of forest cover due to cattle farming combined with pasture degradation leading to low levels of production, consequent extensification and therefore to more deforestation, are serious concerns in Costa Rica. To test the feasibility of countering these by combining a more productive pasture system with indigenous tree species, a silvopastoral experiment was established on a farm in the seasonally dry lowlands of Cañas, Guanacaste Province. A rapidly growing pasture species (Brachiaria brizantha) was tested against a traditional pasture dominated by Hyparrhenia rufa. Three indigenous tree species were established: Pithecellobium saman, Diphysa robinioides and Dalbergia retusa. Plots were grazed by cattle for 4 or 5 days with one to 2 month intervals between grazing episodes. After 51 months, D. robinioides was the fastest growing species, and P. saman the slowest, while B. brizantha produced three times the above ground and twice the below ground biomass as H. rufa, and trees had no effect upon grass yield. Contrary to competition theory, there was no effect of pasture species upon the two faster growing tree species. The carbon in above and below ground phytomass varied between 3.5 and 12.5 Mg C ha^?1 in treeless pasture controls and silvopastoral systems, respectively, and total soil organic carbon (TSOC) in the upper 0.6 m averaged 110 Mg ha^?1. B. brizantha appeared to stimulate tree root production, which in turn was highly correlated with TSOC, resulting in annual increments in TSOC of up to 9.9 Mg ha^?1 year^?1. These early results indicate the promising potential of this silvopastoral system for combining cattle production, and increasing tree cover and carbon sequestration.     

Seasonal abundance and activity of pill millipedes (Arthrosphaera magna) in mixed plantation and semi-evergreen forest of southern India

Seasonal occurrence and activity of endemic pill millipedes (Arthrosphaera magna) were examined in organically managed mixed plantation and semi-evergreen forest reserve in southwest India between November 1996 and September 1998. Abundance and biomass of millipedes were highest in both habitats during monsoon season. Soil moisture, conductivity, organic carbon, phosphate, potassium, calcium and magnesium were higher in plantation than in forest. Millipede abundance and biomass were about 12 and 7 times higher in plantation than in forest, respectively (P < 0.001). Their biomass increased during post-monsoon, summer and monsoon in the plantation (P < 0.001), but not in forest (P > 0.05). Millipede abundance and biomass were positively correlated with rainfall (P = 0.01). Besides rainfall, millipedes in plantation were positively correlated with soil moisture as well as temperature (P = 0.001). Among the associated fauna with pill millipedes, earthworms rank first followed by soil bugs in both habitats. Since pill millipedes are sensitive to narrow ecological changes, the organic farming strategies followed in mixed plantation and commonly practiced in South India seem not deleterious for the endangered pill millipedes Arthrosphaera and reduce the risk of local extinctions.     

Ecological Footprint: Refining the carbon Footprint calculation

Within the Ecological Footprint methodology, the carbon Footprint component is defined as the regenerative forest capacity required to sequester the anthropogenic carbon dioxide emissions that is not absorbed by oceans. A key parameter of the carbon Footprint is the Average Forest Carbon Sequestration (AFCS), which is calculated from the net carbon sequestration capacity of forests ecosystems.The aim of this paper is to increase the clarity and transparency of the Ecological Footprint by reviewing the rationale and methodology behind the carbon Footprint component, and updating a key factor in its calculation, the AFCS. Multiple calculation options have been set to capture different rates of carbon sequestration depending on the degree of human management of three types of forest considered (primary forests, other naturally regenerated forests and planted forests). Carbon emissions related to forest wildfires and soil as well as harvested wood product have been included for the first time in this update of the AFCS calculation. Overall, a AFCS value range of 0.73 ± 0.37 t C ha⁻¹ yr⁻¹ has been identified. The resulting carbon Footprint and Ecological Footprint values have then been evaluated based on this value range. Results confirm that human demand for ecosystem services is beyond the biosphere's natural capacity to provide them.     

Quantification and assessment of changes in ecosystem service in the Three-River Headwaters Region,China as a result of climate variability and land cover change

Rapid and periodic assessment of the impact of land cover change and climate variability on ecosystem services at regional levels is essential to understanding services and sustainability of ecosystems. This study focused on quantifying and assessing the changes in multiple ecosystem services in the Three-River Headwaters Region (TRHR), China in 2000–2012. Based on the widely used biophysical models including Integrated Valuation of Ecosystem Services and Trade-Offs (InVEST), Revised Wind Erosion Equation (RWSQ), and Carnegie-Ames-Stanford Approach (CASA) models, this study assessed the historical flow of regulating services, including soil conservation, water yield, and carbon sequestration, and provisioning service food provision. The soil conservation function of ecosystem was slightly enhanced as a whole, and water yield increased sharply, with both the soil conservation and water yield showing an increasing spatial homogenization. The net primary productivity (NPP) and food production increased substantially from 2000 to 2012. Ecosystem services are closely and complexly interlinked. The correlation analyses indicated a trade-off between the water yield and carbon sequestration, however, a synergy between soil conservation and carbon sequestration. Congruence between the three different ecosystem provisioning services, including pasture, meat, and grain, was found. There was also a synergy between food production and ecosystem carbon sequestration in the TRHR. Climatic variability and vegetation restoration are important for the ecosystem services flow. Correlation analyses showed that the increase in precipitation significantly enhanced the water yield (P < 0.01) and soil erosion (P < 0.01), while the temperature increase influenced positively the NPP (P < 0.1). The experience of ecological rehabilitation and the change in key ecosystem services in the TRHR exemplified the positive effects of environmental policies and the necessity of adopting an adaptive management approach. Thus the ecological construction and policy making should take climate variability into account, and facilitate synergies on multiple ecosystem services in order to maximize human well-being and preserve its natural ecosystems.     

Carbon profiles of typical forest types across Europe assessed with CO2FIX

This paper presents for 16 typical forest types across Europe a standard carbon sequestration profile. The study was carried out with the model CO2FIX which was parameterised with local yield table data and additional required parameters. CO2FIX quantifies the carbon of the forest ecosystem–soil–wood products chain at the stand level. To avoid misleading results annual net sequestration rates are not presented here, because these strongly fluctuate in time. Therefore, only its advancing mean is presented as a more reliable indicator. This avoids a great deal of uncertainty for policy makers. The variation between forest types is large, but mean sequestration rates mostly peak after some 38 years (with a net source lasting up to 15 years after afforestation) at an average value of 2.98 Mg C ha⁻¹ per year (ranging between forest types from 4.1 to 1.15). After 200 years, the net sequestration rate saturates to a value of 0.8 Mg C ha⁻¹ per year (ranging from 1.4 to 0.13). The long-term mean carbon stock in tree biomass and products amounts on average to 114 Mg C ha⁻¹ (ranging from 52 to 196).     

Extinction thresholds and negative responses of Afrotropical ant-following birds to forest cover loss in oil palm and agroforestry landscapes

Afrotropical ant-following birds are vulnerable to forest loss and disturbance, but critical habitat thresholds regarding their abundance and species richness in human-dominated landscapes, including industrial oil palm plantations, have never been assessed. We measured forest cover through Landsat imagery and recorded species richness and relative abundance of 20 ant-following birds in 48 plots of 1-km², covering three landscapes of Southwest Cameroon: Korup National Park, smallholder agroforestry areas (with farms embedded in forest), and an industrial oil palm plantation. We evaluated differences in encounter frequency and species richness among landscapes, and the presence of critical thresholds through enhanced adaptive regression through hinges. All species were detected in Korup National Park and the agroforestry landscape, which had similar forest cover (>85%). Only nine species were found in the oil palm plantation (forest cover = 10.3 ± 3.3%). At the 1-km² scale, the number of species and bird encounters were comparable in agroforests and the protected area: mean species richness ranged from 12.2 ± 0.6 in the park and 12.2 ± 0.6 in the agroforestry matrix to 1.0 ± 0.4 in the industrial oil palm plantation; whereas encounters decreased from 34.4 ± 3.2 to 26.1 ± 2.9 and 1.3 ± 0.4, respectively. Bird encounters decreased linearly with decreasing forest cover, down to an extinction threshold identified at 24% forest cover. Species richness declined linearly by ca. one species per 7.4% forest cover lost. We identified an extinction threshold at 52% forest cover for the most sensitive species (Criniger chloronotus, Dicrurus atripennis, and Neocossyphus poensis). Our results show that substantial proportions of forests are required to sustain complete ant-following bird assemblages in Afrotropical landscapes and confirm the high sensitivity of this bird guild to deforestation after industrial oil palm development. Securing both forest biodiversity and food production in an Afrotropical production landscape may be best attained through a combination of protected areas and wildlife-friendly agroforestry.     

Does tree species composition affect soil CO<Subscript>2</Subscript> emission and soil organic carbon storage in plantations?

Key message

Mixed tree plantations are potential silvicultural systems to increase soil carbon storage through altering litter and root inputs and soil physiochemical properties.

Abstract

Afforestation and reforestation are major strategies for global climate change mitigation. Different tree species composition can induce diverse changes in soil CO₂ emission and soil carbon sequestration in tree plantation. This study employed three plantations of monoculture and mixed Pinus yunnanensis and Eucalyptus globulus to estimate the effect of tree species composition on soil CO₂ emission and soil organic carbon storage in subtropical China. We found that tree species composition had a significant effect on the soil CO₂ emission and soil organic carbon storage. Soil CO₂ emission was lower in the mixed plantation than in the P. yunnanensis plantation, whereas it was higher than in the E. globulus plantation. Differences in soil CO₂ emission among the three plantations were determined by leaf litterfall mass, fine root biomass, soil available nitrogen, pH, soil bulk density, and soil C:N ratio. Soil organic carbon storage was 34.5 and 23.2 % higher in the mixed plantation than in the P. yunnanensis and E. globulus plantations, respectively. Higher soil organic carbon stock in the mixed plantation was attributed to lower C/N ratio of leaf litter and soil, greater fine root biomass and soil organic carbon content, and lower soil CO₂ emission. We conclude that mixed tree plantation can enhance soil carbon sequestration, but can decrease or increase soil CO₂ emission through altering litter and root inputs and soil physiochemical properties.

     

Variation in soil properties under different land uses and attitudinal gradients in soils of the Indian Himalayas

We studied the interaction effects of 8-different land uses systems viz., forestry (T₁), silvopastoral (T₂), horticulture (T₃), agrihorticulture (T₄), agrisilviculture (T₅), agrihortisilviculture (T₆) > grassland (T₇) and agriculture (T₈) in 2-altitudinal gradient for three consecutive soil layers of up to 1 m deep from sub-montane to low hill sub-tropical zone of Western Himalayas in Himachal Pradesh State of India. All the land uses under agroforestry practices viz., agrisilviculture, silvopastoral, agrihorticulture and agrihortisilviculture showed significantly enhanced values of pH, organic carbon (OC %), available N, P, K and exchangeable Ca, Mg and available S than agriculture land use. A maximum value of soil carbon (1.08%) was observed in forest land use followed by silvopastoral, horticulture, agrihorticulture, agrisilviculture, agrihortisilviculture, grassland and agriculture, respectively. Overall highest values of available N, P and K were observed under forest land use and silvopastoral among agroforestry systems. Available N, P, and K declined with increasing altitude. Exchangeable Mg followed the trend T₇ > T₂ > T₅ > T₁ > T₆ > T₃ > T₄ > T₈ and available Sulphur as T₇ > T₃ > T₂ > T₆ > T₅ > T₄ > T₈ > T_1, respectively. The value of exchangeable Ca and available S increased with increasing altitude. From the study it can be concluded that tree based land use systems of subtropical zone of the Himalayan region are more sustainable and environment friendly than agriculture and grassland use systems. Hence, they need to be conserved and promoted on large scale. The outcome of this paper will be helpful in convincing the farmers for adoptions of agroforestry practices in large scale.     

Potential impacts of climate warming on active soil organic carbon contents along natural altitudinal forest transect of Changbai Mountain

Understanding soil carbon fractions and their responses to the global warming is important for improving soil carbon management of natural altitudinal forest ecosystem. In this study, the contents of soil total organic carbon (SOC), soil labile organic carbon (LOC), and microbial biomass carbon (MBC) in soil upper layers (0–20 cm) were measured along a natural altitudinal transect in the north slope of Changbai Mountain. The results showed that under natural conditions the contents of SOC and LOC were largest in Betula ermanii forest (altitude 1996 m), moderate in spruce-fir forest (altitude 1350 m), and smallest in Korean pine mixed broad-leaf tree forest (altitude 740 m). MBC contents in different forest ecosystems decreased in the order of Betula ermanii forest, Korean pine mixed broad-leaf tree forest, and dark coniferous forest. In addition, the responses of SOC, LOC, and MBC to soil warming were conducted by relocating intact soil cores from high- to low-elevation forests for one year. As expected, the soil core relocation caused significant increase in soil temperature but made no significant effect on soil moisture. After one year incubation, soil relocation significantly decreased SOC contents, whereas the contents of LOC, MBC, and the ratios of LOC to SOC and MBC to SOC increased.     

Variability of soil carbon sequestration capability and microbial activity of different types of salt marsh soils at Chongming Dongtan

Variations in the soil carbon sequestration capability of different types of salt marsh soils at Chongming Dongtan and its influencing factors were studied by analyzing the soil organic carbon (SOC) content, organic matter input and microbial activities. The results indicated that the total SOC content at Area A (southeast of Dongtan, sandy soil with Phragmites communis) was only 46.11% of that of Area B (northeast of Dongtan, clay soil with mixed P. communis and Spartina alterniflora) (P = 0.000 < 0.05), but their organic matter input per year was almost identical. These findings implied that Area B had a lower output of SOC. The microbial biomass at Area A was 3.83 times greater than that at Area B (P = 0.049 < 0.05); the soil catalase and invertase activities at Area A, which were related to carbon metabolism, were 60.31% (P = 0.006 < 0.05) and 34.33% (P = 0.021 < 0.05) higher than at Area B, respectively; and the soil respiration at Area A was also higher than at Area B. These findings implied that the microbial activities at Area A were greater than those at Area B, and therefore the carbon metabolism was rapid, resulting in increased SOC output at Area A. Increased water content and salinity in the clay soil at Area B may inhibit the microbial activities, thereby reducing the decomposition of the organic matter and enhancing carbon sequestration. In addition, some artificial measures for controlling spread of S. alterniflora at Area B (mowing/digging and tillage (M + D); mowing/digging and tillage/waterlogging (M + D + W)) were found to generally improve the microbial activity of soil, thereby increasing SOC output. However, when the two different physical controlling modes were compared, the SOC and microbial activities of the soil subjected to the M + D + W treatment were relatively high and low, respectively, due to waterlogging restraining the microbial metabolism. These findings indicated that the difference in microbial activities was the important factor leading to variability in the SOC sequestration capability between Areas A and B. Additionally, with the exception of soil texture and vegetation types, environmental conditions and artificial turbulence also influenced microbial activities of soil, and hence SOC output and organic carbon sequestration capability.     

Forest carbon storage along the north-south transect of eastern China: Spatial patterns,allocation, and influencing factors

Forests play an important role in sequestrating atmospheric CO₂; therefore, understanding the spatial variations and controlling mechanisms of forest carbon (C) storage is important. In this study, we collected data on forest C storage along a north-south transect of eastern China from literature published between 2004 and 2014. The collected data, which were from over 2000 plots, allowed us to explore the latitudinal patterns in forest C storage. The results showed that vegetation C storage decreased with increasing latitude, while soil C storage increased. This spatial pattern of vegetation C storage was more apparent for mature forests (forest age > 80 years). Furthermore, latitudinal patterns in forest C storage, both in vegetation and in soil, became stronger with increasing statistical scale, increasing from plot scale to latitudinal scale (2–5°). However, total forest C storage (vegetation + soil) had no apparent latitudinal pattern. Interestingly, the allocation ratios of forest C storage between vegetation and soil had a negative logarithmic relationship with latitude. These results suggest that in eastern China, climatic factors control latitudinal patterns in the forest C storage of vegetation and soil, albeit in different ways (positive for vegetation and negative for soil), and also control the allocation ratios of forest C storage between vegetation and soil. Furthermore, the latitudinal patterns of forest C storage were opposite for vegetation and soil, resulting from the different climatic controlling mechanism.     

Afforestation effects on vegetation structure and diversity of grasslands in southern Brazil: The first years

We evaluated the effects of afforestation on the composition and structure of southern Brazilian subtropical grasslands directly beneath tree plantations, in pastures, and in permanent protection areas near watercourses. Cover of plants was registered in 120 plots of 1 m² in grasslands located at two distances from small watercourses in pasture and eucalypt plantation areas within a livestock ranching landscape. Livestock density is reduced in plantation areas. Species composition beneath tree plantations was significantly different from both pasture and nearby permanent protection areas. Permanent protection areas near plantations were also compositionally different from pastures. Eucalypt plantation was the environment type where ruderals were most abundant. Growth form cover distribution in pasture areas showed a consistent pattern, with graminous herbs being the most common growth form followed by prostrate herbs, prostrate subshrubs, and standing subshrubs. In plantation areas, the dominance of the graminoid herb growth form increased markedly, as well as standing herbs. These increases occurred mainly at the expense of prostrate herbs and subshrubs, which were significantly reduced. Plot-level species density was significantly affected by distance from watercourse and, more importantly, was significantly influenced by the interaction between management regime and distance to watercourse. It was reduced in eucalypt plantations relative to permanent protected areas. Current management of eucalypt plantations in southern Brazil produce unsuitable conditions for grassland species to thrive within plantations. Livestock densities <1.0 animal unit ha^?1 in eucalypt plantations undermines the ability of surrounding permanent protection areas to act as ecological networks for biodiversity conservation.     

Soil water utilization characteristics of Haloxylon ammodendron plantation with different age during summer

Haloxylon ammodendron is one of the main shrubs that were used in desertification control project in China. Large area (2700 km²) of H. ammodendron plantation, especially more than 10 years plantation, has degraded outside Minqin oasis, northwest China. It is hard for H. ammodendron plantation to utilize ground water deeper than 20 m and to use precipitation with only mean annual 116.2 mm and uneven distribution in growing season. Thus, soil water might be the main water source of H. ammodendron plantation. Moreover, following H. ammodendron grows up, more soil water will be needed. In this study, it is hypothesized that H. ammodendron plantation would utilize deeper soil water as its age increased. Water use characteristics of different ages of H. ammodendron plantation (2 years, 5 years, 10 years, 20 years and 30 years) were examined by stable oxygen isotope technology outside Minqin oasis in July 2009. The δ¹⁸O values of water in H. ammodendron xylem, six different depths of soil (20 cm, 30 cm, 50 cm, 100 cm, 150 cm and 200 cm), rain and ground water (replaced by well water) were compared to determine major water source of H. ammodendron plantation. Meanwhile, the density, height, length and width of individuals were measured, and soil water contents were examined at the six depths in these plantation. The results showed that in 5 years H. ammodendron plantation, soil water content in 50 cm was significantly lower than moving sand dune and other ages, and soil water content in 100–200 cm was lower than moving sand dune and 2 years H. ammodendron plantation. The main depth that H. ammodendron used soil water increased as the age increased; 2 years H. ammodendron mainly used 50–200 cm soil water; 5 years H. ammodendron used 100–200 cm soil water and started to use ground water; 10 years H. ammodendron used 150–200 cm soil water and ground water, plant density of H. ammodendron declined and soil water content recovered gradually; 20 years and 30 years H. ammodendron mainly used ground water. Therefore, excessive consumption to soil water of high plant density might be one of the reasons for the degradation of H. ammodendron plantation. The critical age of H. ammodendron plantation is 5 years outside Minqin oasis because it consumed excessive soil water. If the density of 5 years H. ammodendron plantation was not decreased by selective cutting at present, it would degrade as the stand age increased later. It is suggested that initial density of new H. ammodendron plantation outside Minqin oasis must be reduced to slow down its consumption of soil water in future, and then the stability of H. ammodendron plantation could be sustained for a longer time.     

Effects of rest grazing on organic carbon storage in Stipa Baicalensis steppe in Inner Mongolia

In order to evaluate the potential effects of rest grazing on organic carbon storage on the Stipa baicalensis steppe in Inner Mongolia, compared the S. baicalensis steppes after rest grazing for 3 years, 6 years, and 9 years, using potassium dichromate heating method, this study analyzed the organic carbon storage of plant and soil in the steppes among different periods of rest grazing. The results indicated that as the rest grazing years prolonged, the biomass included above-ground parts, litters and underground plant parts(roots) of the plant communities all increased, meanwhile the carbon content of the biomass increased with the rest grazing years prolonged. For the zero rest grazing (RG0) steppe and the steppes after a rest grazing of 3 years (RG3a), 6 years (RG6a), 9 years (RG9a), the carbon storage in above-ground parts of plant communities were 42.60 g C/m², 66.33 g C/m², 83.46 g C/m², 100.29 g C/m² respectively; the carbon storage of litters were 7.85 g C/m², 9.12 g C/m², 9.18 g C/m², 11.54 g C/m² separately; the carbon storage of underground plant parts (0–100 cm) were 281.40 g C/m², 576.38 g C/m², 745.33 g C/m², 1279.61 g C/m² respectively; and the carbon storage in 0–100 cm soil were 22991.14 g C/m², 24687.75 g C/m², 26564.86 g C/m²,33041.55 g C/m². The results suggested that as the rest grazing years prolonged, the organic carbon storage in plant communities and soil increased. The carbon storage of underground plant parts and soil organic carbon mainly concentrated in 0–40 cm soil. After rest grazing for 3 years, 6 years, and 9 years, the increased soil organic carbon were as the 81.14%, 85.84%, and 89.46% of the total increased carbon; From the perspective of carbon sequestration cost, the total cost of RG3a, RG6a and RG9a were 2903.40 RMB/hm², 5806.80 RMB/hm², and 8710.20 RMB/hm². The cost reduced with the extension of rest grazing years, 0.17 RMB/kg C, 0.16 RMB/kg C, 0.09 RMB/kg C for RG3a, RG6a and RG9a respectively. From the growth characteristics of grassland plants, the spring was one of the two avoid grazing periods, timely rest grazing could effectively restore and update grassland vegetation, and was beneficial to the sustainable use of grassland. From the available data, the organic carbon storage of RG9a was the highest, while the cost of carbon sequestration was the lowest. Therefore, spring rest grazing should be encouraged to continue for it was proved to be a very efficient grassland use measures.     

Soil macrofauna as indicators of soil quality and land use impacts in smallholder agroecosystems of western Nicaragua

The tropical dry forest region along the western slope of Central America represents a biodiverse and fragile area that is under increasing pressure from agricultural production, thus threatening the provision of ecosystem services, the integrity of these landscapes, and the rural communities who depend on them. To address this issue, we evaluated the influence of common agricultural management practices (cropping and livestock systems) vs. the Quesungual slash-and-mulch agroforestry system (QSMAS) on diverse parameters of soil quality and function. We then used this information to identify soil invertebrate bioindicators that represent key aspects of soil quality (chemical fertility, physical properties, aggregate morphology, and biological functioning). In February of 2011 soil sampling was conducted on six hillside farms near the town of Somotillo in western Nicaragua to assess soil properties and the abundance and diversity of soil macrofauna within four management systems: (1) QSMAS, based on maize production, (2) traditional maize cropping system with few trees (TC), (3) silvopastoral system with low tree density (SP), and (4) secondary forest (SF), used as a reference. The conversion of forest to agriculture demonstrated the greatest impact of management in this study. For example, SF presented significantly higher diversity of soil invertebrate taxonomic groups than either TC or SP (P < 0.03), and demonstrated the lowest level of soil compaction, significantly less than SP (P < 0.05). Additionally, SF demonstrated the highest value of soil quality according to a synthetic indicator that integrates chemical, physical and biological aspects of soil quality. Although overall soil quality under QSMAS was lower than SF, this system demonstrated the highest abundance (number of individuals) of soil macrofauna, and appeared to at least partially mitigate the negative consequences of forest conversion on soil functioning. Using the Indicator Value Index, which ranks species according to their specificity and fidelity across sites, along with farmer consultation we found seven indicator taxa of soil quality that could greatly facilitate future evaluation of land management impacts by farmers and technicians in the region. We suggest that the methodology applied is robust and adaptable to diverse agroecological contexts and would allow for more rapid responses to evolving land use issues as they arise.     

Distribution characteristics and factors influencing the ecosystem in western Hubei

Western Hubei is the most concentrated area of forest resources in Hubei Province, and the knowledge of the distribution characteristics of ecosystem carbon density is important to understand the regional characteristics of carbon density and its mechanism of formation. Carbon density and factors influencing different layers in the ecosystem were studied by using field data. The average carbon density of ecosystems in western Hubei was 159.05 t/hm²; the carbon density of different forest types in descending order was Abies fargesii forests (362.25 t/hm²), mixed broadleaf-conifer forests (154.13 t/hm²), broad-leaved forests (146.09 t/hm²), and coniferous forests (135.76 t/hm²), and ecosystem carbon density increased with increasing age. The carbon density of the arborous layer, shrub layer, and soil layer of A. fargesii forests was significant higher than that of the other forests (P < 0.05), indicating the carbon storage per unit area of A. fargesii forests, which grow at higher elevations, was the greatest. The carbon density in arborous layers of broad-leaved forests, mixed broadleaf-conifer forests, and coniferous forests was 39.29 t/hm², 48.99 t/hm², and 48.39 t/hm², respectively. Those of the soil layer were 102.96 t/hm², 100.97 t/hm², and 82.37 t/hm², respectively, and there were no significant differences among them. Among the three forest types, carbon density in the litter layer was greater than that of the shrub layer, which indicated the litter layer plays an important role in carbon storage. The carbon density of mixed broadleaf-conifer forests was greatest, excluding A. fargesii forests, in medium (58.71 t/hm²) and mature forests (79.66 t/hm²). Thus, the carbon sink of mixed broadleaf-conifer forests had more potential than the others at the medium and mature forest stage. The soil layer carbon density in different forests constituted 60.67—70.48% of the entire ecosystem, and was 1.70—2.62 times greater than that of the arborous layer. There are many factors influencing ecosystem carbon density, which result from the interaction of environmental and topographical factors. The main explanatory variables of carbon density of the region were altitude, precipitation, and canopy density. The vegetation and soil layer carbon density increased as altitude increased, and the rate of change for every vertical 100 m was 1.3 t/hm² and 1.9 t/hm², respectively (P < 0.05). Although the annual average precipitation only affected the carbon density of the vegetation, it increased to 4 t/hm² (P < 0.01) when average precipitation was >100 mm.     

Effects of grassland conversion to cropland and forest on soil organic carbon and dissolved organic carbon in the farming-pastoral ecotone of Inner Mongolia

Effects of grassland conversion to cropland and forest on soil organic carbon (SOC), dissolved organic carbon (DOC) in the farming-pastoral ecotone of Inner Mongolia were investigated by direct field sampling. SOC content and DOC content in soil decreased after grassland were shifted to forest or cropland, in the sequence of grassland soil > forest soil > cropland soil. SOC stock declined by 18% after grassland shifted from to forest. Reclamation of cropland for 10 years, 15 years and 20 years lost SOC in 0–30 cm soil layer, by 34%, 14% and 18%, respectively, compared with that of grassland. DOC in 3 soil layers was within 21.1–26.5 mg/L in grassland, 12.1–14.6 mg/L in forest soil, and 8.0–14.0 mg/L in cropland soil. Correlation analysis indicated that SOC content and DOC content were positively dependent on total nitrogen content (p < 0.05), but negatively on bulk density or land use type (p < 0.05). DOC was positively correlated SOC (p < 0.01). Moreover, SOC content could be quantitatively described by a linear combination of land use types (p = 0.000, r² = 0.712), and DOC content by a linear combination of two soil-related variables, land use types and SOC (p = 0.000, r² = 0.861).