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1.
Biofuels are considered as a climate-friendly energy alternative. However, their environmental sustainability is increasingly debated because of land competition with food production, negative carbon balances and impacts on biodiversity. Arid and semi-arid lands have been proposed as a more sustainable alternative without such impacts. In that context this paper evaluates the carbon balance of potential land conversion to Jatropha cultivation, biofuel production and use in arid and semi-arid areas. This evaluation includes the calculation of carbon debt created by these land conversions and calculation of the minimum Jatropha yield necessary to repay the respective carbon debts within 15 or 30 years.The carbon debts caused by conversion of arid and semi-arid lands to Jatropha vary largely as a function of the biomass carbon stocks of the land use types in these regions. Based on global ecosystem carbon mapping, cultivated lands and marginal areas (sparse shrubs, herbaceous and bare areas) show to have similar biomass carbon stocks (on average 4–8 t C ha−1) and together cover a total of 1.79 billion ha. Conversion of these lands might not cause a carbon debt, but still might have a negative impact on other sustainability dimensions (e.g. biodiversity or socio-economics). Jatropha establishment in shrubland (0.75 billion ha) would cause a carbon debt of 24–28 t C ha−1 on average (repayable within 30 year with yield of 3.5–3.9 t seed ha−1 yr−1). Land use change in the 1.15 billion ha of forested area under arid and semi-arid climates could cause a carbon debt between 70 and 118 t C ha−1. This debt requires 8.6–13.9 t seed production ha−1 yr−1 for repayment within 30 years. If repayment is required within 15 years, the necessary minimum yields almost double. Considering that 5 t seed ha−1 yr−1 is the current maximum Jatropha yield, conversion of forests cannot be repaid within one human generation. Repayment of carbon debt from shrubland conversions in 30 years is challenging, but feasible. Repayment in 15 year is currently not attainable.Based on this analysis the paper discusses the carbon mitigation potential of biofuels in arid and semi-arid environments.  相似文献   

2.
In the Ethiopian highlands, remarkable recovery of vegetation has been achieved using exclosures, protecting vegetation against livestock browsing and firewood harvesting. But these emerging forest resources require tools for sustainable use, implying knowledge on biomass stocks and growth. In this study we developed biomass functions estimating total, stem and branch biomass from diameter at stump height (DSH) and tree height (H) for an 11-year old exclosure in Tigray, Ethiopia. In a systematic grid of 55 plots, DSH and H of all trees and shrubs were recorded. 40 Acacia abyssinica trees were selected for destructive sampling. Allometric relationships using a natural log–log model were established between aboveground biomass, DSH and H. Models with only DSH were found best with R2 between 0.95 and 0.98. The functions were 10 fold cross-validated and R2_cv ranged from 0.94 to 0.97, indicating good model performance. The models were found well in range with those of other seasonal forests in East Africa. Total aboveground biomass was estimated 25.4 ton ha−1 with an annual production of 2.3 ton ha−1, allowing sustainable wood fuel use for 4 persons ha−1. The presented predictive functions help to harmonize between ecological and societal objectives and are as such a first step towards an integrated planning tool for exclosures.  相似文献   

3.
Shrubs play an important role in water-limited agro-silvo-pastoral systems by providing shelter and forage for livestock, for erosion control, to maintain biodiversity, diversifying the landscape, and above all, facilitating the regeneration of trees. Furthermore, the carbon sink capacity of shrubs could also help to mitigate the effects of climate change since they constitute a high proportion of total plant biomass. The contribution of two common extensive native shrub species (Cistus ladanifer L. and Retama sphaerocarpa (L.) Boiss.) to the carbon pool of Iberian dehesas (Mediterranean agro-silvo-pastoral systems) is analyzed through biomass models developed at both individual (biovolume depending) and community level (height and cover depending).The total amount of carbon stored in these shrubs, including above- and belowground biomass, ranges from 1.8 to 11.2 Mg C ha−1 (mean 6.8 Mg C ha−1) for communities of C. ladanifer and from 2.6 to 8.6 Mg C ha−1 (mean 4.5 Mg C ha−1) for R. sphaerocarpa. These quantities account for over 20–30% of the total plant biomass in the system. The potential for carbon sequestration of these shrubs in the studied system ranges 0.10–1.32 Mg C ha−1 year−1 and 0.25–1.25 Mg C ha−1 year−1 for the C. ladanifer and R. sphaerocarpa communities' respectively.  相似文献   

4.
The ecological consequences of grassland afforestation in arid/semiarid sandy regions are not well known with respect to tree species and stand age. The present study quantifies the changes in above- and belowground carbon (C) stocks following afforestation in the southeastern Keerqin Sandy Lands with species of Mongolian pine and poplar. We studied 15-, 24-, and 30-year-old Mongolian pine plantations, 7-, 11-, and 15-year-old poplar plantations, and adjacent grasslands. The results show that total ecosystem C stocks increased following grassland afforestation. Aboveground C stocks increased at a rate of 2.75 Mg C ha−1 yr−1 in the poplar plantations, and 1.06 Mg C ha−1 yr−1 in the Mongolian pine plantations. Mineral soil C stocks decreased during the early stage of forest establishment, but recovered with increasing stand age. Root C stock increased significantly in the Mongolian pine plantations, but the poplar plantations showed no such increase relative to the grassland. Our results indicate that afforestation of the grassland in the southeastern Keerqin Sandy Lands would sequester more C than would continuous grassland. Tree species selection and stand developmental age should be considered in planning future afforestation projects.  相似文献   

5.
The pattern of carbon (C) allocation among the different pools is an important ecosystem structural feature, which can be modified as a result of changes in environmental conditions that can occur gradually (e.g., climatic change) or abruptly (e.g., management practices). This study quantified the C pools of plant biomass, litter and soil in an arid shrubland in Chile, comparing the natural condition (moderately disturbed by grazing) vs. the afforested condition (two-year-old plantation with Acacia saligna (Labill.) H.L. Wendl.), each represented by a 60 ha plot. To estimate plant biomass, allometric functions were constructed for the four dominant woody species, based on the volume according to their shape, which showed high correlation (R2 > 0.73). The soil was the largest C pool in both natural and afforested conditions (89% and 94%, respectively) and was significantly lower in the afforested than natural condition at all five soil depths. The natural condition had in total 36.5 ton (t) C ha−1 compared to 21.1 t C ha−1 in the afforested condition, mainly due to C loss during soil preparation, prior to plantation of A. saligna. These measurements serve as an important baseline to assess long-term effects of afforestation on ecosystem C pools.  相似文献   

6.
Agricultural mismanagement of irrigated drylands results in severe soil degradation. Afforestation is an option for ameliorating such degraded land. We evaluated the impact afforestation has on the topsoil (0-20 cm) of salinized degraded cropland in regards to salinity, aggregate stability, and soil organic carbon (SOC) stocks in Uzbekistan, Central Asia. The effects of tree plantations established under either furrow or drip irrigation were studied four years following afforestation and two years after irrigation ceased. For comparative study we also sampled fallow land, land with 80 years of tree growth, natural forest, desert ecosystems, and paddy rice fields. Initial furrow irrigation showed to be most effective in improving soil fertility after four years of afforestation; the respective plantations of Populus euphratica and Ulmus pumila showed significant levels of reduced soil salinity and increased aggregate stability and improved SOC stocks. The comparison of the long-term afforested land with the short-term equivalent suggested a C sequestration rate of 0.09-0.15 t C ha−1 year−1. The SOC stocks of the long-term afforestation site exceeded those of the native forest. Hence, a rehabilitation of salt-affected cropland is feasible following the conversion into occasionally irrigated tree plantations, although it takes decades to reach steady-state conditions.  相似文献   

7.
Allometric equations and community biomass stocks are presented for Guiera senegalensis J.F. Gmel (Gs) and Piliostigma reticulatum (DC.) Hochst (Pr) – two native shrub species in the Sahel. These shrubs are of interest because they dominate semi-arid sub-Sahalien Africa but have been largely overlooked as a key biomass component and regulator of ecosystem composition and function in this landscape. In Year 1, best predictors of aboveground biomass were height and number of stems (Gs) and crown diameter (Pr); and for belowground biomass were height and basal diameter (Gs) and basal diameter (Pr). In Year 2, height and crown diameter were the best predictors of aboveground biomass (R2 = 0.90 for Gs and 0.87 for Pr), whereas basal diameter and number of stems (Gs) and basal diameter (Pr) were best predictors of belowground biomass. Peak-season biomass estimates ranged from 0.44 to 4.58 ton ha?1 (mean = 2.38 ton ha?1) in the Gs sites and from 0.33 to 7.38 ton ha?1 (mean = 3.71 ton ha?1) in the Pr communities. Both species exhibited unusually large root:shoot ratios (4.5:1 for Gs and 10.2:1 for Pr). Although models differ between years, allometric relationships provide reasonable biomass estimates for Gs and Pr.  相似文献   

8.
In this article we evaluate the potential use of Cladonia foliacea tissue N content, C:N ratio, and phosphomonoesterase (PME) activity as biomarkers of N deposition by means of a field experiment. In order to do this, we continuously added NH4NO3 to a semi-arid shrubland at four rates: 0, 10, 20 and 50 kg N ha−1 yr−1 starting in October 2007. Tissue N content and C:N ratios, considered as N stress indicators, significantly increased and decreased, respectively, after 1.5 years. The response found suggests N saturation above 20 kg N ha−1 yr−1. After 2.5 years, extracellular PME activity increased with 20 kg N ha−1 yr−1 and this was attributed to an induced nutritional (N to P) imbalance. Above this threshold, PME significantly decreased as a consequence of the physiological stress caused by extra N. Effects on PME were dependent on the soil properties (pH and Ca and Mg availability) experienced by C. foliacea. PME response suggests a critical load of ∼26.4 kg N ha−1 yr−1 (20 kg N ha−1 yr−1 + background) for this lichen. Further tissue chemistry and PME evaluations in C. foliacea and soil surveys conducted along wide N deposition gradients will confirm the potential use of this species as a biomonitor of N pollution and the importance of soil properties on its ability to respond to atmospheric reactive N.  相似文献   

9.
Two experiments were conducted in southern Kordofan State to determine the influence of Acacia senegal L., Balanites aegyptiaca L. and Azadirachta indica L. on millet (Pennisetum typhoides) yield, soil quality and to monitor decomposition and nutrients release from tree litters. Yield under A. indica (174.83 kg ha−1) and B. aegyptiaca (173.09 kg ha−1) were significantly higher than the control (121.43 kg ha−1). The lowest yield (111.04 kg ha−1) was recorded under A. senegal. Straw dry matter under B. aegyptiaca (1161.5 kg ha−1) and A. indica (857.8 kg ha−1) was significantly higher than both under A. senegal (321.8 kg ha−1) and the control (454.8 kg ha−1). Trees varied in their capacity to induce changes in soil properties whereas effects on soil N were not substantial. A. indica had a decomposition rate (0.6283 week−1) 2.0 times higher than that of B. aegyptiaca (0.2057 week−1) and A. senegal (0.267 week−1). The highest rate of P and K release from A. indica and B. aegyptiaca litters has resulted in significant accumulation in the soil indicating these tree litters are potential sources for these elements. The capacity of trees to improve soil fertility could offer an alternative management system for improved cultivation of field crops.  相似文献   

10.
Annual/perennial and tall/short plant species differentially dominate early to late successional shortgrass steppe communities. Plant species can have different ratios of above-/below-ground biomass distributions and this can be modified by precipitation and grazing. We compared grazing effects on aboveground production and root biomass in early- and mid-seral fields and undisturbed shortgrass steppe. Production averaged across four years and grazed and ungrazed treatments were 246, 134, and 102 g m−2 yr−1 for the early-, mid-seral, and native sites, respectively, while root biomass averaged 358, 560, and 981 g m−2, respectively. Early- and mid-seral communities provided complimentary forage supplies but at the cost of root biomass. Grazing increased, decreased, or had no effect on aboveground production in early-, mid-seral, and native communities, and had no effect on roots in any. Grazing had some negative effects on early spring forage species, but not in the annual dominated early-seral community. Dominant species increased with grazing in native communities with a long evolutionary history of grazing by large herbivores, but had no effects on the same species in mid-seral communities. Effects of grazing in native communities in a region cannot necessarily be used to predict effects at other seral stages.  相似文献   

11.
Species-specific allometric models were developed to predict aboveground biomass (AGB) of eight woody species in the Borana rangelands, Ethiopia. The 23 equations developed (8 species; three biomass components: total aboveground, stem and branches) fit the data well to predict total AGB and by components for each of the species (r2 > 0.70; p < 0.001). The AGB of tree shaped species (e.g., Acacia bussei and Acacia etabaica) were significantly predicted from a single predictor (circumference of the stem at ankle height), with a high coefficient of determination (r2 > 0.95; p < 0.001). In contrast, the AGB of bushy shrubs (e.g., Acacia oerfota) was more effectively predicted by using the canopy volume (r2 = 0.84; p < 0.001). Shrubs with a tall stem and an umbrella-like canopy structure (e.g., Acacia mellifera) were most accurately predicted by a combination of both circumference of the stem at ankle height and canopy volume (r2 = 0.95; p < 0.001). Hence, our species-specific allometric models could accurately estimate their woody aboveground biomass in a semi-arid savanna ecosystem of southern Ethiopia. These equations will help in future carbon-trade discussions in times of climate change and CO2 emission concerns and mitigation strategies.  相似文献   

12.
中亚热带山区土地利用变化对土壤有机碳储量和质量的影响   总被引：13，自引：0，他引：13  
杨玉盛  谢锦升  盛浩  陈光水  李旭 《地理学报》2007,62(11):1123-1131
通过对中亚热带山区天然林、人工林(用材林和经济林)、次生林、果园和坡耕地等7 种典型土地利用方式的土壤有机碳储量及质量的研究, 结果表明: 中亚热带山区天然林转变 为其他土地利用类型后, 土壤有机碳储量下降了25.6%~51.2%, 而表层0~20 cm 土壤有机碳 储量下降了45.1%~74.8%, 比底层土壤有机碳对土地利用变化的响应更为敏感。土壤轻组有机碳储量(0~60 cm) 下降了52.2%~84.2%, 轻组有机碳占总有机碳比例从13.3%降到3.0% ~10.7%, 比土壤总有机碳对土地利用变化更为敏感。天然林转变为其他土地利用类型后土壤 有机碳损失巨大的原因主要与凋落物归还数量及质量, 水土流失和经营措施对土壤(特别是表层土壤) 的扰动引起土壤有机质加速分解等因素有关。坡耕地人为干扰最严重, 土壤有机 碳下降幅度最大。中亚热带山区土地利用变化引起土壤有机碳储量下降幅度高于全球平均水平, 主要与区域降水和地貌条件有关。因此, 保护山区脆弱生态环境, 加强天然林保护和植 被恢复, 合理营造人工林, 减少耕作, 对山区土壤碳吸存、减缓大气CO2 浓度升高和气候变化以及促进山区可持续开发的生态服务功能发展都具有重要意义。  相似文献   

13.
《Polar Science》2014,8(2):166-182
The larch forests on the permafrost in northeastern Mongolia are located at the southern limit of the Siberian taiga forest, which is one of the key regions for evaluating climate change effects and responses of the forest to climate change. We conducted long-term monitoring of seasonal and interannual variations in hydrometeorological elements, energy, and carbon exchange in a larch forest (48°15′24′′N, 106°51′3′′E, altitude: 1338 m) in northeastern Mongolia from 2010 to 2012. The annual air temperature and precipitation ranged from −0.13 °C to −1.2 °C and from 230 mm to 317 mm. The permafrost was found at a depth of 3 m. The dominant component of the energy budget was the sensible heat flux (H) from October to May (H/available energy [Ra] = 0.46; latent heat flux [LE]/Ra = 0.15), while it was the LE from June to September (H/Ra = 0.28, LE/Ra = 0.52). The annual net ecosystem exchange (NEE), gross primary production (GPP), and ecosystem respiration (RE) were −131 to −257 gC m−2 y−1, 681–703 gC m−2 y−1, and 423–571 gC m−2 y−1, respectively. There was a remarkable response of LE and NEE to both vapor pressure deficit and surface soil water content.  相似文献   

14.
We used biodegradable dissolved organic carbon (BDOC) incubations, specific ultraviolet absorbance (SUVA254, indicator of aromatic carbon content) and laboratory experiments to determine the bioavailability and chemical composition of dissolved organic matter (DOM) leached from fresh leaves and litter aged on a seasonally dry floodplain for 2, 4, and 6 months. Our objective was to elucidate how litter age and solar radiation affect the bacterial utilization of DOM released from floodplain leaf litter when inundated. Leachate percent BDOC ranged from 22 to 47% for three different leaf species and significantly decreased (p < 0.05) with increasing litter age. However, total BDOC (mg C L−1) was unrelated to litter age. Bacterial utilization of DOM leachate collected from litter aged on the floodplain for four and six months significantly increased following 48 h of irradiation for all species but there was no difference for leachate from fresh and two month old litter. The photo-mediated increase in percent BDOC was concomitant with a decrease in aromatic carbon content, as SUVA254 values decreased on average 9 ± 6% for light exposure experiments. Our findings demonstrate that sunlight moderates the degradation of plant litter in the terrestrial environment through the photo-mediated shift in DOM composition and its bioavailability in streams.  相似文献   

15.
Mean tree biomass and soil carbon (C) densities for 39 map sheet grids (1° lat. × 1.5° long.) covering the Acacia woodland savannah region of Sudan (10–16° N; 21–36° E) are presented. Data from the National Forest Inventory of Sudan, Harmonized World Soil Database and FAO Local Climate Estimator were used to calculate C densities, mean annual precipitation (MAP) and mean annual temperature (MAT). Above-ground biomass C and soil organic carbon (SOC, 1 m) densities averaged 112 and 5453 g C m−2, respectively. Below-ground biomass C densities, estimated using root shoot ratios, averaged 33 g C m−2. Biomass C densities and MAP increased southwards across the region while SOC densities were lowest in the centre of the region and increased westwards and eastwards. Both above-ground biomass C and SOC densities were significantly (p < 0.05) correlated with MAP (rs = 0.84 and rs = 0.34, respectively) but showed non-significant correlations with MAT (rs = −0.22 and rs = 0.24, respectively). SOC densities were significantly correlated with biomass C densities (rs = 0.34). The results indicated substantial under stocking of trees and depletion of SOC, and potential for C sequestration. Up-to-date regional and integrated soil and forest inventories are required for planning improved land-use management and restoration.  相似文献   

16.
Carbon stocks and carbon accumulation in the earth's drylands have gained increasing attention. The winter-cold deserts of Middle Asia, i.e. in Kazakhstan, Uzbekistan, and Turkmenistan, cover an area of 2.5 million km2. Within these deserts, the two Saxaul species White Saxaul (Haloxylon persicum Bunge ex Boiss. & Buhse) and Black Saxaul (Haloxylon aphyllum (Minkw.) Iljin) are dominant woody species with a potential distribution area of about 500,000 km2. From the 1950s until today, the Saxaul vegetation has been degraded through logging and over-grazing. In this paper, we estimate the current and potential living above ground and below ground biomass of the Saxaul vegetation and its carbon stock. The living above ground biomass ranges between 1.5 t/ha and 3 t/ha. The potential carbon stocks above ground and below ground amount to 29.4–52.1 million t and 22–81.4 million t, respectively. Today, only 11%–28% of the potential biomass and carbon stock have remained. The carbon stock of the Saxaul vegetation is low compared to other ecosystems of the earth, but restoration and conservation of Saxaul vegetation is one way to sequester carbon through vegetation for Uzbekistan and Turkmenistan, which do not have much other woody vegetation.  相似文献   

17.
We developed an approach using remote sensing and modeling, applicable to Algerian forest inventory, for estimating the volume of timber in Aleppo pine stands. We used ordinary linear regression (OLR) and reduced major axis (RMA) regression to assess an operational model to map stand volume from satellite images. Our analysis was supported by measurements from 151 sample plots and spectral values from remote sensing imagery. Fifteen candidate models were tested through the Akaike Information Criterion to assess their predictive power. For the 2009 Landsat TM image, we found that the best models for both regression methods used the NDVI as the independent variable. The RMSEs were 20.3% (16.10 m3 ha−1) and 22.5% (17.83 m3 ha−1), respectively, for OLR and RMA. We chose the RMA regression models because they had realistic standard deviation values for the estimated volumes, and they gave lower RMSEs in volume classes over 40 m3 ha−1. Our method gave similar results for two other images, which demonstrated that our approach was robust when applied to data from a different year (2006 Landsat TM), but from the same sensor, and also to data from a different sensor (2005 Alsat-1).  相似文献   

18.
Changes in soil texture, bulk density, pH, concentrations and stocks of OC, N, P and K before and after conversion of a 6-year-old Acacia senegal plantation to other land management systems (LMS) were investigated, after three cropping seasons, in the drylands of western Sudan. LMS included pure and intercropped sorghum (PS), roselle (PR) and grasses (PG) with A. senegal at high- and low-tree densities (HD 433 and LD 266 trees ha?1). Significant changes included increase in coarse sand and a decrease in fine sand under pure and intercropped systems at LD; decrease in clay contents in PS and PR; an increase in clay ratio in all pure crops and HD + R; a decrease in aggregated mean concentrations of OC, N and P under all LMS by 42%, 68% and 45%, respectively; increase in soil pH under all LMS; a depletion of aggregated mean stocks of OC, N, P and K in all LMS by 38%, 30%, 52% 13%, respectively. The study established that wholesale tree clearance constitutes a major cause of soil degradation, and tree inputs and cycling of nutrients are of major importance to soil fertility in the study area.  相似文献   

19.
《Polar Science》2014,8(2):146-155
The Boreal black spruce forest is highly susceptible to wildfire, and postfire changes in soil temperature and substrates have the potential to shift large areas of such an ecosystem from a net sink to a net source of carbon. In this paper, we examine CO2 exchange rates (e.g., NPP and Re) in juniper haircap moss (Polytrichum juniperinum) and microbial respiration in no-vegetation conditions using an automated chamber system in a five-year burned black spruce forest in interior Alaska during the fall season of 2009. Mean ± standard deviation microbial respiration and NEP (net ecosystem productivity) of juniper haircap moss were 0.27 ± 0.13 and 0.28 ± 0.38 gCO2/m2/hr, respectively. CO2 exchange rates and microbial respiration showed temporal variations following fluctuation in air temperature during the fall season, suggesting the temperature sensitivity of juniper haircap moss and soil microbes after fire. During the 45-day fall period, mean NEP of P. juniperinum moss was 0.49 ± 0.28 MgC/ha following the five-year-old forest fire. On the other hand, simulated microbial respiration normalized to a 10 °C temperature might be stimulated by as much as 0.40 ± 0.23 MgC/ha. These findings demonstrate that the fire-pioneer species juniper haircap moss is a net C sink in the burned black spruce forest of interior Alaska.  相似文献   

20.
The Royal Belum forest reserve is one of the oldest tropical rainforests in the world and it is one of the largest virgin forest reserves in Malaysia. However, not many studies have been conducted to understand the ecology of this forest. In this study we estimated the aboveground biomass (AGB) of the forest using diameter at breast height (DBH) and height of trees (h ), tree species and hemispherical photographs of tree canopy. We estimated AGB using five allometric equations. Our results demonstrated that the AGB given by the one tree species specific allometric equation does not show any significant differences from the values given by the non‐tree species specific allometric equations at tree and plot levels. The AGB of Intsia bijuga species, Koompassia malaccensis species and Shorea genera were comparatively higher, owing to their greater wood density, DBH and h. This has added importance because some of these species are categorized as threatened species. Our results demonstrated that mean AGB values in this forest (293.16 t ha‐1) are the highest compared to some studies of other areas in Malaysia, tropical Africa and tropical Bazilian Amazonia, implying that the Royal Belum forest reserve, is an important carbon reservoir.  相似文献   

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