Tag: carbon sinks
Relationship between carbon stocks and tree species diversity in a humid Guinean savanna landscape in northern Sierra Leone
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.
Effects of Prosopis juliflora Invasions on land use/cover change in South Afar region, Northeast Ethiopia
Prosopis juliflora(henceforth referred as Prosopis) plant is an invasive species affecting the health of rangelands in Afar region of Ethiopia. The study aims to assess (1) the effects of Prosopisinvasion on land use land cover (henceforth referred to LULC), and (2) extent of vegetation cover changes. We used a combination of remote sensing data and field observations to analyze the effects Prosopisinvasion on land use/ land cover dynamics and changes (LULCC) for the patterns and dynamics of land-use/cover changes for 31 years from 1986 to2017 in the arid and semi-arid of Sothern Afar rangelands, Ethiopia. The overall accuracy for 1986, 2000, and 2017 were 81.4%, 82.3%, and 84.9% with Kappa statistics of 0.77, 0.79, and 0.82 respectively. InAmibara district, farmlands, water bodies, land under Prosopis, and grassland areas were increased during 1986-2017 by 1879 ha (10.8%), 1197 ha (55.6%), 3132 ha (99.0 %), and 31,039 ha (22.0 %), respectively. However, bare lands and woodlands areas were decreased by 1239 ha (56.7 %) and 36,065 ha (49.9 %), respectively. In Awash Fentale district, changes in land use/land cover types showed positive trends for farmlands, water bodies, Prosopis, and grazing lands by 4258 ha (81.4 %), 1035 ha (97.4 %), 2335 ha (97.0 %), and 18,187 ha (25.8 %) respectively in the same period. However, bare lands and woodland areas decreased by 59.78 ha (59.8 %) and 51 ha (50.9 %), respectively. If the present change continues, pastoralists grazing lands will be lost.
Carbon sequestration in tropical agroforestry systems
Removing atmospheric carbon (C) and storing it in the terrestrial biosphere is one of the options, which have been proposed to compensate greenhouse gas (GHG) emissions. Agricultural lands are believed to be a major potential sink and could absorb large quantities of C if trees are reintroduced to these systems and judiciously managed together with crops and/or animals. Thus, the importance of agroforestry as a land-use system is receiving wider recognition not only in terms of agricultural sustainability but also in issues related to climate change. The objective of this paper was to analyse C storage data in some tropical agroforestry systems and to discuss the role they can play in reducing the concentration of CO2 in the atmosphere. The Csequestration potential of agroforestry systems is estimated between 12 and 228Mgha-1 with amedian value of 95Mgha-1. Therefore, based on the earth’s area that is suitable for the practice (585-1215 × 106 ha), 1.1-2.2 Pg C could be stored in the terrestrial ecosystems over the next 50 years. Long rotation systems such as agroforests, homegardens and boundary plantings can sequester sizeable quantities of C in plant biomass and in long-lasting wood products. Soil C sequestration constitutes another realistic option achievable in many agroforestry systems. In conclusion, the potential of agroforestry for CO2 mitigation is well recognised. However, there are a number of shortcomings that need to be emphasised. These include the uncertainties related to future shifts in global climate, land-use and land cover, the poor performance of trees and crops on substandard soils and dry environments, pests and diseases such as nematodes. In addition, more efforts are needed to improve methods for estimating C stocks and trace gas balances such as nitrous oxide (N2O) and methane (CH4) to determine net benefits of agroforestry on the atmosphere
Aboveground carbon stocks in oil palm plantations and the threshold for carbon-neutral vegetation conversion on mineral soils
The carbon (C) footprint of palm-oil production is needed to judge emissions from potential biofuel use. Relevance includes wider sustainable palm oil debates. Within life cycle analysis, aboveground C debt is incurred if the vegetation replaced had a higher C stock than oil palm plantations. Our study included 25 plantations across Indonesia, in a stratified study design representing the range of conditions in which oil palm is grown. From allometric equations for palm biomass and observed growth rates, we estimated the time-averaged aboveground C stock for 25-year rotations and 95%-confidence intervals to be 42.07 (42.04-42.10) Mg C ha-1 for plantations managed by company on mineral soil, 40.03 (39.75-40.30) Mg C ha-1 for plantations managed by company on peat, and 37.76 (37.42-38.09) Mg C ha-1 for smallholder oil palm on mineral soils. Oil palm can be established C debt-free on mineral soils with aboveground C stocks below these values; neutrality of mineral soil C pools was documented in a parallel study. Acknowledging variation in shoot:root ratios, the types of vegetation that can be converted debt-free to oil palm include grasslands and shrub, but not monocultural rubber plantations, rubber agroforest, and similar secondary or logged-over forests of higher C stock.
Reducing uncertainty in the use of allometric biomass equations for predicting above-ground tree biomass in mixed secondary forests
Estimates of forest biomass are needed for tracking changes in C stocks, as well as for other purposes. A common method for estimating forest biomass is through use of allometric equations which relate the biomass of individual trees to easily obtainable non-destructive measurements, such as diameter. A common form is B=aDb for biomass B, diameter D and parameters a and b. Field data collected in Sumatra and compared with previously published data show that the values of a and b vary between sites. This variation is likely to be the major source of uncertainty if biomass estimates are produced using equations that are not calibrated for individual sites. However, calibration by collection of B and D data for each site is unrealistic, requiring destructive measures. Methods of choosing values for a and b are, therefore, proposed that do not require destructive measurements. The parameter b can be estimated from the site-specific relationship between height (H) and diameter, H=kDc as b=2+c. The parameter a can be estimated from the average wood density (ρ) at the site as a=rρ, where r is expected to be relatively stable across sites. The allometric equation proposed is therefore B=rρD2+c.
Quantification of carbon stock and tree diversity of homegardens in a dry zone area of Moneragala District, Sri Lanka
Homegarden agroforestry systems are suggested to hold a large potential for climate change mitigation and adaptation. This is due to their multifunctional role in providing income, food and ecosystem services while decreasing pressure on natural forests and hence saving and storing carbon. In this paper, above-ground biomass carbon and tree species diversity of trees was quantified in homegardens around two villages in the dry south-eastern part of Moneragala district of Sri Lanka. A total of 45 dry zone homegardens were sampled on size, diameter at breast height, tree height and species diversity. Using allometric equations, we find a mean above-ground biomass stock of 13 mega grams of carbon per hectare (Mg C ha1) with a large range among homegardens (1–56 Mg C ha1, n = 45) due to a variation of tree diversity and composition between individual homegardens. Mean above-ground carbon stock per unit area was higher in small homegardens (0.2 ha, 26 Mg C ha1, n = 11) and statistically different compared to medium (0.4–0.8 ha, 9 Mg C ha1, n = 27) and large (1.0–1.2 ha, 8 Mg C ha1, n = 7) homegardens. In total, 4,278 trees were sampled and 70 tree species identified and recorded. The Shannon Wiener index were used to evaluate diversity per homegarden and ranged from 0.76 to 3.01 with a mean value of 2.05 ± 0.07 indicating a medium evenly distributed diversity of sampled tree species. The results show a vast heterogeneity in terms of carbon stock and tree diversity within the less studied dry zone homegardens; results that contribute to more knowledge of their expansion potential as well as climate mitigation and adaptation potential. The results are also useful for whether homegardens should be considered to be included as an activity to enhance natural forest cover within Sri Lanka’s newly commenced UN-REDD National Programme.
Facilitating agroforestation of landscapes for sustainable benefits: Tradeoffs between carbon stocks and local development benefits in Indonesia according to the FALLOW model
Although Indonesia has no shortage of land area that lost its forest cover before 1990 and has become the global leader in land-use based greenhouse gas emissions, the widespread expectation that the afforestation/reforestation approach to Clean Development Mechanisms (A/R CDM) could lead to sustainable development benefits has not so far materialized. The main challenges to implementation of the current A/R CDM mechanisms are in (1) the definition of forest and its institutional implications, (2) the projectization that is embedded in the definition of CDM, (3) non-linear baselines related to forest transitions that complicate attribution, (4) inherent lack of synergy with other development activities and (5) high transaction costs and temporary nature of credits. In possible new international regimes that aim to include all relevant changes in land-use based emissions, a more outcome-based programmatic approach may partially replace the project cycle assessments of CDM. However, there will still be a need to assess the combination of factors and policies that can be expected to enhance terrestrial carbon storage through voluntary land-use decisions, by a combination of reduced emissions and enhanced storage. Tradeoffs usually exist between local livelihoods and carbon storage, but assessment of the opportunity costs of C sequestration requires analysis at the landscape and community scale at scenario level, including local adjustment and optimization. We explored such scenarios for a number of cases in Indonesia that range from a forest margin to a degraded lands setting. FALLOW model applications were set up for 4 landscapes in Indonesia (15-98% forest cover, 1-55% grassland, 17-51personskm-2) to test the internal consistency of the hypothesis that farmer-led development of tree-based land-use systems in response to accessible markets, legal tenure arrangements, availability of reliable technical information and local investment can convert degraded forest lands at low public cost and form an attractive alternative to project-based interventions with detailed prescriptions and planning. The calculated (non-linear) baselines for carbon stocks varied from an average trend of -0.26 to +0.23MgCha-1year-1 over a 25 year period of assessment, equivalent to a net sequestration of -0.95 to 0.84tCO2ha-1year-1 The highest value for predicted additional carbon storage in the wider landscape did not coincide with the best results for local livelihoods, but in each of the case studies the results for a `programmatic’ removal of constraints to profitable smallholder tree-based production systems was more attractive than a `prescribed’ tree planting in designated project areas. These results support the design of international modalities for an outcome-based approach to enhancing carbon storage with local flexibility in implementation.
Optimal measurement strategies for aboveground tree biomass in agricultural landscapes
Robust and cost effective methods for estimating aboveground biomass of trees on farms are necessary to understand the significance of this carbon pool, identify climate change mitigation opportunities and support smallholder farmers’ ability to capitalize on the emerging green economy. Using a dataset of 72 destructively sampled trees and 855 non-destructively sampled trees, we identified methodologically and economically efficient strategies to construct allometric equations and measure on-farm tree biomass. We found that robust biomass estimates can be obtained from measuring diameter at breast height (DBH) alone. Inclusion of tree height, specific wood density, and/or crown area in the allometric equation changed the biomass estimates by only 1.3 %, though these additional variables improved precision by reducing the error from 7.8 % to between 4.8 and 7.0 %. Research accuracy-to-cost trade-offs can be optimized by building equations based on destructive measurements of trees that span stem diameters found in the landscape; equations based on only small or large diameter trees result in poor estimates. Given (1) the resources required to measure additional dendrometric parameters in the field (2) the potential to introduce measurement errors that can propagate through estimates at farm and landscape scales, and (3) the need to quickly increase the amount of data available at low cost, we recommend that allometric equations for trees on farms be based solely on DBH and that the sampling strategy capture the range of tree sizes found in the landscape and future indirect quantification should focus on diameter at breast height as a predictor of biomass to save resources.
Life cycle assessment: Biochar as a greenhouse gas sink?
[No abstract available]