Rapid expansion of natural rubber plantations in South-East Asia and other regions has greatly altered ecosystem based carbon (C) stocks with potential impacts on climate change mitigation and future C trading opportunities. Therefore, reliable estimations of carbon sequestration and emission at the landscape level after land cover transition from forest, swidden agriculture and other land use types are needed. We reviewed studies on C stocks and dynamics in rubber plantations considering the contribution of aboveground and belowground biomass, soil organic matter, collected latex and other minor components. C sequestration occurred after conversion of arable land to rubber plantations while C losses usually prevailed if forest was converted to rubber. These general trends strongly depended on local climate conditions and soil properties as well as on topography. Non-traditional planting of rubber under subtropical conditions with a dryer climate and at high elevations (300–1000 m above sea level) decreased the C sequestration potential of rubber. We show how rotation length, rubber clone, and management strategies like tapping frequency or planting density affect C stocks, discuss the uncertainties in C stock estimation and highlight improved approaches. An important conclusion is that upscaling of C stocks and dynamics under different climate scenarios and rotation lengths to a regional level requires the use of time averaged C stocks. Enhanced remote sensing techniques can greatly improve C stock estimates at the regional level, allowing for an accounting of the variability caused by terrain and plantation properties. A partial life cycle assessment of rubber production revealed greenhouse gas emissions as a minor contribution when compared to land use change effects on plant and soil C stocks and C accumulation in latex, wood products and seed oil. The review highlights scantily explored topics and proposes directions for future studies, which should decrease uncertainties in C estimates in rubber dominated landscapes.
Tag: Carbon sequestration
Rotational grass/clover for biogas integrated with grain production – A life cycle perspective
Rotational perennial grass/clover has multiple effects in cropping systems dominated by cereals. This study evaluated the environmental impact of rotational grass/clover ley for anaerobic digestion in a cer- eal-dominated grain production system in Sweden. Life cycle assessment (LCA) methodology was used to compare two scenarios: (i) a cropping system including only spring barley and winter wheat; and (ii) a cropping system including 2-year grass/clover ley in combination with spring barley and winter wheat. The functional unit was one tonne of grain. The two main functions of the grass/clover crop were to pro- vide feedstock for biogas production and to act as an organic fertiliser for allocation among the cereal crops in the rotation. Special consideration was given to nitrogen (N) management and the rotational effects of the grass/clover ley. In total, 73% of the N requirement of cereals in the ley scenario was met through symbiotic N fixation. Replacing diesel with biogas and mineral fertiliser with digested grass/clo- ver biomass (digestate) reduced the use of fossil fuels substantially, from 1480 MJ per tonne in the ref- erence scenario to 2900 MJ per tonne in the ley scenario. Potential eutrophication per tonne grain increased in the ley scenario, mainly owing to significantly higher ammonia emissions from spreading digestate and the larger area required for producing the same amount of grain. Potential acidification also increased when N mineral fertiliser was replaced by digestate. Crops relying on symbiotic N fixation are a promising feedstock for reducing the use of non-renewable energy in the production chain of farm-based bioenergy, but careful handling of the N-rich digestate is required. Replacing cereals intended for feed or food with bioenergy crops leads to indirect land use changes (iLUC) when the displaced crops must be produced elsewhere and the benefits obtained when biofuels replace fossil fuels may thereby be out- weighed. In this study, the iLUC factor assumed had a critical effect on global warming potential in the ley scenario. However, carbon sequestration and the higher yield potential of subsequent cereal crops can mitigate greenhouse gas emissions from iLUC to a varying extent. We recommend that crop sequences rather than single crops be considered when evaluating the environmental impact of production systems that include perennial legumes for food, feed and bioenergy.
Carbon stock in planted woodlots at Kongowe, Kibaha, Tanzania
Forest degradation due to extraction of wood for fuelwood and charcoal production or agricultural expansion is one of the main sources of carbon dioxide (CO2) emissions in Africa. Woodlots can offset CO2 emissions while sustainably meeting the wood demand of local communities. However, the amount and dynamics of carbon (C) stored in soils in coastal area woodlots and the contribution of this practice to climate change mitigation is largely unexplored. This study evaluated wood biomass and C stocks in woodlots, forest reserves and farmland with Acacia crassicarpa Benth., Acacia mangium Wild., and Acacia auriculiformis Benth. to determine their ability to sequester soil C and offsetting CO2 emissions. Woodlots of fast-growing Acacia spp. produced wood (30 to 62 Mg C/ha), which may meet the household fuelwood demand for up to 10 to 20 years and offset up to 31 Mg C/ha of C emissions. Moreover, these species stored soil organic carbon (SOC) (58 Mg C/ha), which was similar to levels in the native forests; demonstrating climate change mitigation capacity. The effects of tree species on SOC was confined to the top 40 cm with native forest consistently recording the highest values. This improvement was attributed to litter and root turnover, C leaching and mixing of SOC by microorganisms, and increased recalcitrant form of SOC with depth. Because of the sandy soil texture in the study site, most of SOC stocks (up to 70% in the bulk soil and 50% in fractionated soils) were in the labile fractions and prone to degradation. Of the tested woodlot species, A. auriculiformis showed the highest promise to produce wood and improve SOC because of higher survival. Our results showed that woodlots systems utilizing the fast growing tree species hold high promise to mitigate atmospheric CO2 increase through on-farm wood supply to alleviate harvesting pressure and accumulation of SOC in the soil
Assessing C-stock dynamics at the landscape level
•UpscalingUpscalingissues: from plot to issues: from plot to landscapelandscape•Study area Study area ––forest transitionforest transitionInformation resolution Information resolution ––CC–stock .stock dynamics dynamics••Spatial resolution Spatial resolution ––land use/cover land use/cover •Temporal resolution Temporal resolution ––CC–stock stock dynamics dynamic
The potential of using Agroforestry as a win-win solution to climate change mitigation and adaptation and meeting food security challenges in Southern Africa
Some of the most profound and direct impacts of climate change in southern Africa over years have been droughts, fluctuations in annual rainfall, extreme temperatures and floods. These have resulted in low and unstable food production, especially maize which is the staple food in most Southern African countries. Furthermore, research suggests that 30% of threatened plant species will be critically endangered or extinct due to drought, thus further worsening food availability, accessibility and stability in the region. Drought is therefore is assumed to be the major obstacle to the achievement of food security in Southern Africa. Agroforestry is emerging as the promising option to sustain agricultural productivity and livelihoods of farmers. We discussed the need for further selection and releasing new tree germplasm with superior capacity to adapt to the changing climatic and ecological conditions in the region. Innovative mechanisms to further enhance the contribution of agroforestry to climate change mitigation and adaptation are examined.
Alternatives to Slash-and-Burn in Brazil: summary report and synthesis of phase II
The conversion of primary forest to other land uses in the Amazon threatens biodiversity and releases carbon into the atmosphere but makes economic development and poverty reduction possible. Small-scale farmers practising slash-and-burn cultivation account for a significant proportion of tropical deforestation. However, the conditions necessary for increased productivity of alternative land use systems (LUS) to improve farmer welfare and simultaneously reduce deforestation are not well understood. This research attempted to determine the environmental consequences of different LUS, whether these consequences could be mitigated with appropriate technological, policy and institutional changes and what sorts of tradeoffs existed among the different social objectives facing policy makers. The research programme implemented during Phase II of ASB’s project in Brazil was designed to better understand how the Government of Brazil, national and international research organizations and donor agencies can balance global environmental objectives with economic development and poverty reduction. The key question can be summarized as: can intensifying land use within forest and on cleared land simultaneously reduce deforestation and reduce poverty
Carbon offsets for conservation and development in Indonesia?
The logic of the Clean Development Mechanism (CDM) and other such ‘carbon (C) offsets’ rests on the notion that the opportunity cost of reducing C emissions is lower in developing countries, creating opportunities for mutually beneficial C trading. While the CDM may offer significant gross financial benefits, there has been little analysis of the opportunity costs of foregone resource exploitation and development opportunities. In addition to assessing the potential for net benefits, this paper also considers the practical implications for design and implementation of C offsets for forest conservation and agro forestation in Indonesia. Virtually nothing is known about these administrative factors, and their associated costs, which can also play a decisive role in feasibility of C, offset schemes. Data are from field studies in the lowlands of the Indonesian island of Sumatra, where forests and derived land uses are broadly representative of the lowland humid tropical rainforest systems of insular South-East Asia. These data are the basis for assessing the trade-offs between natural forest protection for C sequestration and conversion to other land uses to meet national development objectives that directly affect people’s livelihoods. Carbon stocks are analyzed in terms of ‘time-averaged’ C, an indicator developed for this project. Opportunity costs of land-use alternatives are estimated using standard techniques for economic assessment of investment projects in developing countries. The study finds that imputed timber values are a significant share of the opportunity costs of forest conservation, even for conservative estimates of timber prices. The question of compensating for these foregone values raises complex questions regarding the political economy of Indonesia, since property rights over these resources are highly contentious. These controversies over property rights are also examined within the context of recurrent smoke pollution from land fires in Indonesia, that (among other problems) contribute to greenhouse gas emissions. This smoke is symptomatic of deeper political and institutional problems that raise questions about the permanence of C storage through land-use practices in Indonesia. In comparison to forest conservation, C offsets through agro forestation seem more feasible in Indonesia because property rights over timber from planted trees would be easier to establish and enforce than property rights over timber from natural forests. Although results in this paper look promising, there is still much to be learned about implementation costs, even for the ‘easier’ case of agro forestation.
Carbon stocks in Indonesian homegarden systems: can smallholder systems be targeted for increased carbon storage?
Homegardens are a common smallholder agroforestry system in Indonesia and throughout the tropics. These species-rich, tree-based systems produce non-wood and wood products for both home use and market sale. Due to their high biomass,these systems simultaneously offer potential for carbon (C) storage. While small size limits the amount of C stored by individualsmallholder agroforestry systems, on a per area basis these systems can storage as much C as some secondary forests. In aggre-gate, smallholder homegarden agroforestry systems can contribute signi®cantly to a region’s carbon budget while simultaneouslyenhancing smallholder livelihoods. A ®eld study in Lampung, Indonesia indicates that homegardens with an average age of 13years store 35.3 Mg C ha±1in their above-ground biomass, which is on par with the C stocks reported for similar-aged secondaryforests in the same area. However, to compare accurately the C stocks of different land-use systems a scale is required thatadjusts C stocks of the systems’ ages and rotation lengths to a common base. The time-averaged C stock, which is half the Cstock at the maximum rotation length, serves this purpose. Our projections reveal that, depending on management options, thetime-averaged above-ground C stocks of homegarden systems could vary from 30 to 123 Mg C ha±1. These projected time-aver-aged above-ground C stocks of homegardens are substantially higher than those of Imperata-cassava systems (2.2 Mg C ha±1),which is an extensive vegetation type in the study area. If homegarden systems and other smallholder tree-based systems were toexpand in currently degraded and underutilized lands, such as Imperata grasslands, the C sequestration potential would be about80 Mg C ha±1, with considerable variation depending on species composition and management practices. Clear opportunity existsto induce management that leads to higher C stocks at the systems level. However, incentive mechanisms are needed that assuresmallholders will bene®t from selecting management practices that favor higher C stocks.
Mapping of soil organic carbon stocks for spatially explicit assessments of climate change mitigation potential
Current methods for assessing soil organic carbon (SOC) stocks are generally not well suited for understanding variations in SOC stocks in landscapes. This is due to the tedious and time-consuming nature of the sampling methods most commonly used to collect bulk density cores, which limits repeatability across large areas, particularly where information is needed on the spatial dynamics of SOC stocks at scales relevant to management and for spatially explicit targeting of climate change mitigation options. In the current study, approaches were explored for (i) field-based estimates of SOC stocks and (ii) mapping of SOC stocks at moderate to high resolution on the basis of data from four widely contrasting ecosystems in East Africa. Estimated SOC stocks for 0–30 cm depth varied both within and between sites, with site averages ranging from 2 to 8 kg m2. The differences in SOC stocks were determined in part by rainfall, but more importantly by sand content. Results also indicate that managing soil erosion is a key strategy for reducing SOC loss and hence in mitigation of climate change in these landscapes. Further, maps were developed on the basis of satellite image reflectance data with multiple R-squared values of 0.65 for the independent validation data set, showing variations in SOC stocks across these landscapes. These maps allow for spatially explicit targeting of potential climate change mitigation efforts through soil carbon sequestration, which is one option for climate change mitigation and adaptation. Further, the maps can be used to monitor the impacts of such mitigation efforts over time.
Soil fertility, small-farm intensification and the environment in Africa
In order to eradicate hunger, malnutrition, poverty and environmental degradation in subsaharan Africa, policies that favour smallholder rural development need to be formulated. This paper focuses on two key factors; a) the reversal of soil fertility depletion ad the fundamental biophysical constraint to food security; and b) the intensification and diversification of small-holder farming by growing trees and plants that produce high valued products as a key to poverty eradication. The paper proposes ten main components necessary for the achievement of the mentioned objectives. These components are discussed with special reference to eastern and southern Africa.