Soil respiration is one of the largest and most important fluxes of carbon in terrestrial ecosystems. While eddy covariance methods are becoming widely used to measure nighttime total ecosystem respiration, the use of chambers placed over the soil is the most direct way of measuring respiration occurring within the soil and litter layers. Several decades of experience with chamber-based measurements have revealed most of the potential sources of error with this methodology. The objectives of this paper are to review several recently expressed concerns about uncertainties of chamber-based measurements of CO2 emissions from soils, to evaluate the direction and magnitude of these potential errors, and explain procedures that minimize these errors and biases. Disturbance of diffusion gradients cause underestimate of fluxes by less than 15% in most cases, and can be partially corrected for with curve fitting and/or can be minimized by using brief measurement periods. Underpressurization or overpressurization of the chamber caused by flow restrictions in air circulating designs can cause large errors, but can also be avoided with properly sized chamber vents and unrestricted flows. We found very small pressure differentials (±0.1 Pa) and modest (15%), inconsistent errors in flux estimates using our chamber design. Somewhat larger pressure differentials (±0.9 Pa) were observed under windy conditions, and the accuracy of chamber-based measurements made under such conditions needs more research. Spatial and temporal heterogeneity can be addressed with appropriate chamber sizes and numbers and frequency of sampling. For example, means of eight randomly chosen flux measurements from a population of 36 measurements made with 300 cm2 diameter chambers in tropical forests and pastures were within 25% of the full population mean 98% of the time and were within 10% of the full population mean 70% of the time. Finally, comparisons of chamber-based measurements with tower-based measurements require analysis of the scale of variation within the purported tower footprint. In a forest at Howland, ME, soil respiration rates differed by a factor of 2 between very poorly drained and well drained soils, but these differences were mostly fortuitously cancelled when spatially extrapolated over purported footprints of 600–2100 m length. While all of these potential sources of measurement error and sampling biases must be carefully considered, properly designed and deployed chambers provide a reliable means of accurately measuring soil respiration in terrestrial ecosystems.
Tag: carbon dioxide
Minimising artifacts and biases in chamber-based measurements of soil respiration
Soil respiration is one of the largest and most important fluxes of carbon in terrestrial ecosystems. While eddy covariance methods are becoming widely used to measure nighttime total ecosystem respiration the use of chambers placed over the soil is the most direct way of measuring respiration occurring within the soil and litter layers. Several decades of experience with chamber-based measurements have revealed most of the potential sources of error with this methodology. The objectives of this paper are to review several recently expressed concerns about uncertainties of chamber-based measurements of CO2 emissions from soils to evaluate the direction and magnitude of these potential errors and explain procedures that minimize these errors and biases. Disturbance of diffusion gradients cause underestimate of fluxes by less than 15% in most cases and can be partially corrected for with curve fitting and/or can be minimized by using brief measurement periods. Underpressurization or overpressurization of the chamber caused by flow restrictions in air circulating designs can cause large errors but can also be avoided with properly sized chamber vents and unrestricted flows. We found very small pressure differentials (±0.1 Pa) and modest (∼15%) inconsistent errors in flux estimates using our chamber design. Somewhat larger pressure differentials (±0.9 Pa) were observed under windy conditions and the accuracy of chamber-based measurements made under such conditions needs more research. Spatial and temporal heterogeneity can be addressed with appropriate chamber sizes and numbers and frequency of sampling. For example means of eight randomly chosen flux measurements from a population of 36 measurements made with 300 cm2 diameter chambers in tropical forests and pastures were within 25% of the full population mean 98% of the time and were within 10% of the full population mean 70% of the time. Finally comparisons of chamber-based measurements with tower-based measurements require analysis of the scale of variation within the purported tower footprint. In a forest at Howland ME soil respiration rates differed by a factor of 2 between very poorly drained and well drained soils but these differences were mostly fortuitously cancelled when spatially extrapolated over purported footprints of 600–2100 m length. While all of these potential sources of measurement error and sampling biases must be carefully considered properly designed and deployed chambers provide a reliable means of accurately measuring soil respiration in terrestrial ecosystems.
Growth, Productivity, Biomass and Carbon Stock in Eucalyptus saligna and Grevillea robusta Plantations in North Kivu, Democratic Republic of the Congo
Initiated by the World Wildlife Fund (WWF) more than a decade ago in North Kivu, single-species plantations of Eucalyptus saligna and Grevillea robusta constitute, with other village plantations, the current legal source of wood-energy for the communities bordering the Virunga National Park (PNVi). This study assesses the growth and productivity of these plantations in two sites with different soil and climatic conditions to predict their production over time. The study also assesses the carbon stock and long-term CO2 fixation in the biomass of the studied plantations to deduce their contribution to climate change mitigation. Non-destructive inventories were carried out during three consecutive years in 20 E. saligna and 12 G. robusta plantations in Sake and Kirumba. Analysis of the data revealed that both species have similar diametric growth while height growth and productivity were significantly higher in the E. saligna plantations. The productivity of E. saligna was also higher in Kirumba than in Sake, while that of G. robusta was higher in Sake than in Kirumba. The differences observed were mainly related to species, silviculture, altitude and concentration of bioavailable elements in the soils. The analysis of productivity evolution over time allowed us to determine optimal rotations at 8 and 12 years, respectively, for E. saligna and G. robusta plantations. The relationships between biomass or carbon stock and tree diameter were not different between the studied species but were significantly different at the stand level. If silviculture was standardized and plantations carefully monitored, carbon stock and long-term CO2 fixation would be higher in G. robusta plantations than in E. saligna plantations. These results indicate that while for productivity reasons E. saligna is the favoured species in wood-energy plantations to quickly meet the demand of the growing and disadvantaged population living in the vicinity of PNVi, carefully monitored G. robusta plantations could be more interesting in terms of carbon credits. To simultaneously optimise wood-energy production and carbon storage in the plantations initiated in North Kivu, E. saligna and G. robusta should be planted in mixture. In addition, species and site characteristics adapted silvicultural management practices must be applied to these plantations, which are very important for the region, its population and its park. Finally, the economic profitability as well as the sustainability of the plantations should be assessed in the longer term in North Kivu.
Deforestation and its potential disruption of the weather patterns of the Democratic Republic of the Congo: Insights from the Kahuzi-Biega National Park landscape
Key messages
- Regions surrounding the Kahuzi-Biega National Park (KBNP) and other areas of South Kivu Province in the eastern part of the Democratic Republic of the Congo have been losing their natural forests for decades.
- There is a positive correlation between deforestation and CO2 emissions. Our research shows that deforestation increases temperature and negatively impacts rainfall, although not significantly.
- Deforestation and its effects on the local climate are very likely to disrupt local agricultural practices and severely impact the unique biological diversity of the region.
- Understanding the important role of forests in regulating climate not only helps to develop appropriate climate change adaptation and mitigation strategies but also to attain better biodiversity conservation and food security, and to go beyond just carbon sequestration services.
Beyond reducing deforestation: impacts of conservation programs on household livelihoods
Understanding why forest conservation initiatives succeed or fail is essential to designing cost-effective programs at scale. In this study, we investigate direct and indirect impact mechanisms of a REDD+ project that was shown to be effective in reducing deforestation during the early years of its implementation in the Transamazon region, an area with historically high deforestation rates. Using counterfactual impact evaluation methods applied to survey and remote-sensing data, we assess the impact of the project over 2013-2019, i.e., from its first year until two years after its end. Based on the Theory of Change, we focus on land use and socioeconomic outcomes likely to have been affected by changes in deforestation brought about by the initiative. Our findings highlight that forest conservation came at the expense of pastures rather than cropland and that the project induced statistically greater agrobiodiversity on participating farms. Moreover, we find that the project encouraged the development of alternative livelihood activities that required less area for production and generated increased income. These results suggest that conservation programs, that combine payments conditional on forest conservation with technical assistance and support to farmers for the adoption of low-impact activities, can manage to slow down deforestation in the short term are likely to induce profound changes in production systems, which can be expected to have lasting effects.
How can process-based modeling improve peat CO2 and N2O emission factors for oil palm plantations?
Oil palm plantations on peat and associated drainage generate sizeable GHG emissions. Current IPCC default emission factors (EF) for oil palm on organic soil are based on a very limited number of observations from young plantations, thereby resulting in large uncertainties in emissions estimates. To explore the potential of process-based modeling to refine oil palm peat CO2 and N2O EFs, we simulated peat GHG emissions and biogeophysical variables over 30 years in plantations of Central Kalimantan, Indonesia. The DNDC model simulated well the magnitude of C inputs (litterfall and root mortality) and dynamics of annual heterotrophic respiration and peat decomposition N2O fluxes. The modeled peat onsite CO2-C EF was lower than the IPCC default (11 Mg C ha−1 yr−1) and decreased from 7.7 ± 0.4 Mg C ha−1 yr−1 in the first decade to 3.0 ± 0.2 and 1.8 ± 0.3 Mg C ha−1 yr−1 in the second and third decades of the rotation. The modeled N2O-N EF from peat decomposition was higher than the IPCC default (1.2 kg N ha−1 yr−1) and increased from 3.5 ± 0.3 kg N ha−1 yr−1 in the first decade to 4.7–4.6 ± 0.5 kg N ha−1 yr−1 in the following ones. Modeled fertilizer-induced N2O emissions were minimal and much less than 1.6% of N inputs recommended by the IPCC in wet climates regardless of soil type. Temporal variations in EFs were strongly linked to soil C:N ratio and soil mineral N content for CO2 and fertilizer-induced N2O emissions, and to precipitation, water table level and soil NH4+ content for peat decomposition N2O emissions. These results suggest that current IPCC EFs for oil palm on organic soil could over-estimate peat onsite CO2 emissions and underestimate peat decomposition N2O emissions and that temporal variation in emissions should be considered for further improvement of EFs.
Dataset on soil carbon dioxide fluxes from an incubation with tropical peat from three different land-uses in Jambi Sumatra Indonesia
Conversion of tropical peat swamp forests to increase and agricultural production has generated substantial peat carbon loss in the Asia-Pacific region. Different land-uses and management practices oxidize the tropical peat at diverse rates due mainly to different water table levels. In recent years, several studies have measured soil carbon dioxide emissions in-situ; however, only few studies have evaluated the effect of moisture on carbon dioxide fluxes in incubation experiments. Here, we present the dataset of an incubation performed with 360 intact peat cores from three different land-uses (i.e. 120 from intact peat swamp forest; 120 from drained logged peat forest; and 120 from oil palm plantation) collected on the peat dome of Jambi Sumatra Indonesia. Different moisture levels in the intact cores were set by either drying the intact peat cores for short period of time or by adding extra water before the incubation. Dynamic dark aerobic incubation in airtight containers coupled with carbon dioxide measurement with an infrared gas analyser and the gas fluxes was used to measure to gas fluxes. The average carbon dioxide fluxes were 5.38 ± 0.91, 4.15 ± 0.35 and 1.55 ± 0.13 µg CO2-C g−1 h−1 for the intact peat swamp forest, drained logged peat forest and oil palm plantation, respectively.
Root symbioses as belowground C pumps: a mitigation strategy against rising CO2 levels
Mycorrhizal and N-fixing root symbioses evolved at two points in the past when global CO2 was highest, consistent with the high demand these symbioses place on host C. Trees hosting both mycorrhiza and N-fixing bacteria are able to fix more atmospheric CO2 and grow at faster rates than non-symbiotic plants, or plants with only mycorrhiza. We argue that on the basis of this improved C capture, N-fixing trees act as C-pumps, sequestering C and locking it in biomass, thus, if properly managed, can contribute significantly towards the mitigation of rising CO2 levels.
Designing energy-efficient, economically sustainable and environmentally safe cropping system for the rainfed maize–fallow land of the Eastern Himalayas
Achieving a circular economic model in agriculture and meeting the food requirement of the growing population is a global challenge. The task is much more daunting in the Eastern Himalaya where low productive maize–fallow is a predominant production system. To enhance system productivity and energy use efficiency while maintaining environmental sustainability and economic profitability, therefore, energy-efficient, low carbon footprint (CF; CO2-e) and profitable short duration crops must be made an integral part of the maize fallow system. Thus, six cropping systems viz., maize–fallow, maize–French bean, maize–soybean, maize–black gram, maize–green gram, and maize–toria were evaluated for seven consecutive years (2011–2018) to assess their energy requirement and efficiency, carbon footprint (CF; CO2-e), economic returns and eco-efficiency. The results revealed that the maize–French bean system had the highest system productivity (11.4 Mg ha−1), energy productivity (17.9), energy profitability (15.9) and non-renewable energy use efficiency (9.97). The maize–French bean system had also the highest net profit (US$ 3764.5 ha−1) and benefit to cost ratio (2.54). The energy consumed under different inputs/activities across the cropping systems for chemical fertilizers, diesel and machinery ranged from 50.0–62.7%, 17.3–20.8% and 4.6–15.4%, respectively. The maize–fallow system had the highest CF (0.34 kg CO2 e per kg grain) while, the maize–French bean system had the lowest CF (0.19 kg CO2 e per kg grain). The maize–French bean system had also considerably increased eco-efficiency both in terms of energy use (US$ 0.23 MJ−1) and (US$ 1.78 per kg CO2 e) over maize–fallow system. Thus, the study has suggested that maize–French bean system is energy-efficient, economically viable and environmentally safer systems to utilize maize fallow and improve food security, may help in achieving green/circular economy.
Illegal logging, governance effectiveness and carbon dioxide emission in the timber-producing countries of Congo Basin and Asia
The empirical link between governance and illegal logging is widely accepted amongst scientist, although a minority still purports that illegal logging does not necessarily prevail because of poor governance. However, the nexus linking governance, illegal logging and carbon emission is not well enshrined in scientific literature. This paper seeks to review the literature on illegal logging and governance and empirically investigate the effect of illegal logging and governance effectiveness on carbon emission. Using panel dynamic ordinary least square method on data covering three Congo Basin timber-producing countries and three Asian timber-producing countries, this paper further investigates disaggregated effects between these two groups of countries. The empirical evidence underscores that Congo Basin timber-producing countries are characterised by increasing trend of illegal logging, poor governance effectiveness and corruption. Panel regression reveals a positive and significant impact of illegal logging, governance effectiveness and corruption on carbon emission. Asian producing countries depict a reducing trend in illegal logging and improvements in governance and corruption. There is a positive but not significant impact of illegal logging on carbon emission, and governance effectiveness reduces carbon emission. Thus, the dynamics of governance, illegal logging and carbon emission is not the same between timber-producing countries in Asia and Congo producing counties, thus suggesting the ability of institutions to curb illegal logging and enforce laws to reduce the effects of carbon emission. Multi-stakeholder consultations, government engagement, partnerships and training of control staff can help curb corruption. Legality checks should go beyond having legal documents to effectively check and control of timber concessions and small-scale logging.