• Energy Research

Programs to provide alternative energy sources such as biogas improve indoor air quality and potentially reduce pressure on forests from fuelwood collection. This study tests whether biogas intervention is associated with higher forest biomass and forest regeneration in degraded forests in Chikkaballapur district in Southern India. Using propensity score matching, we find that forest plots in proximity to villages with biogas interventions (treatment) had greater forest biomass than comparable plots around villages without biogas (control). We also found significantly higher sapling abundance and diversity in treatment than control plots despite no significant difference in seedling abundances and diversity in treatment forests, suggesting that plants have a higher probability of reaching sapling stage. These results indicate the potential for alternative energy sources that reduce dependence on fuelwood to promote regeneration of degraded forests. However, forest regrowth is not uniform across treatments and is limited by soil nutrients and biased towards species that are light demanding, fire-resistant and can thrive in poor soil conditions.

Abstract. Deforestation and forest degradation in the tropics may substantially alter soil N-oxide emissions. It is particularly relevant to accurately quantify those changes to properly account for them in a REDD+ climate change mitigation scheme that provides financial incentives to reduce the emissions. With this study we provide updated land use (LU)-based emission rates (104 studies, 392 N2O and 111 NO case studies), we determine the trend and magnitude of flux changes with land-use change (LUC) using a meta-analysis approach (44 studies, 135 N2O and 37 NO cases) and evaluate biophysical drivers of N2O and NO emissions and emission changes for the tropics. The average N2O and NO emissions in intact upland tropical forest amounted to 2.0 ± 0.2 (n = 90) and 1.7 ± 0.5 (n = 36) kg N ha−1 yr−1, respectively. In agricultural soils annual N2O emissions were exponentially related to N fertilization rates and average water-filled pore space (WFPS) whereas in non-agricultural sites a Gaussian response to WFPS fit better with the observed NO and N2O emissions. The sum of soil N2O and NO fluxes and the ratio of N2O to NO increased exponentially and significantly with increasing nitrogen availability (expressed as NO3− / [NO3−+NH4+]) and WFPS, respectively; following the conceptual Hole-In-the-Pipe model. Nitrous and nitric oxide fluxes did not increase significantly overall as a result of LUC (Hedges's d of 0.11 ± 0.11 and 0.16 ± 0.19, respectively), however individual LUC trajectories or practices did. Nitrous oxide fluxes increased significantly after intact upland forest conversion to croplands (Hedges's d = 0.78 ± 0.24) and NO increased significantly following the conversion of low forest cover (secondary forest younger than 30 years, woodlands, shrublands) (Hedges's d of 0.44 ± 0.13). Forest conversion to fertilized systems significantly and highly raised both N2O and NO emission rates (Hedges's d of 1.03 ± 0.23 and 0.52 ± 0.09, respectively). Changes in nitrogen availability and WFPS were the main factors explaining changes in N2O emissions following LUC, therefore it is important that experimental designs monitor their spatio-temporal variation. Gaps in the literature on N oxide fluxes included geographical gaps (Africa, Oceania) and LU gaps (degraded forest, wetland (notably peat) forest, oil palm plantation and soy cultivation).

Forest conversion to oil palm and rubber plantations is a common land-use change in Jambi, Sumatra due to the high economic demand of forest border communities. The environmental effects of such conversions have raised global concerns due to the potential to increase nitrous oxide emissions (N2O) to the atmosphere. To quantify this effect, we conducted a series of monthly N2O flux measurements between July 2010 and August 2011 using a static chamber method in an undisturbed forest, a disturbed forest, a one year old rubber plantation, a twenty year old rubber plantation and an eight year old oil palm plantation. All plantations belonged to smallholders and were usually not fertilized. In order to understand the effect of management intensification on N2O fluxes, we applied nitrogen (N) as urea (33.3 kg N ha-1) in the oil palm plantation in April 2011 and monitored the emissions intensively until 28 days after fertilizer application. Nitrous oxide consumption was significant in these weathered soils, accounting for 30% of recorded flux data, although 17% of the negative fluxes fell below detection limits. Most of these happened in the oil palm plantation and undisturbed forest. Annual N2O emission rates amounted to 1.73 ± 0.48, 1.22 ± 0.27, 1.34 ± 0.36, 1.02 ± 0.27 and 1.04 ± 0.39 kg N ha-1 y-1 in the undisturbed forest, disturbed forest, one year old rubber plantation, twenty year old rubber plantation and oil palm plantation, respectively. Forest disturbance and conversion to rubber and oil palm plantation did not significantly affect annual N2O emission rates. However in the oil palm plantation, the amount of N emitted as N2O was high (3.1 ± 1.2% of the fertilizer N applied), so at a typical fertilizer application rate of 141 kg N ha-1 y-1, annual emissions would have amounted to 4.4 ± 1.6 kg N ha-1 y-1, more than twice the emission rate in the undisturbed forest. Dry mass and nitrogen mass in standing litter, distance to the nearest termite nest, rainfall on the day of measurement and air temperature were the key factors that predicted annual N2O fluxes across the land-use change transitions.

AbstractKey messageWe compiled 2,458 biomass equations from 168 destructive sampling studies in Indonesia. Unpublished academic theses contributed the largest share of the biomass equations. The availability of the biomass equations was skewed to certain regions, forest types, and species. Further research is necessary to fill the data gaps in emission factors and to enhance the implementation of climate change mitigation projects and programs.ContextLocally derived allometric equations contribute to reducing the uncertainty in the estimation of biomass, which may be useful in the implementation of climate change mitigation projects and programs in the forestry sector. Many regional and global efforts are underway to compile allometric equations.AimsThe present study compiles the available allometric equations in Indonesia and evaluates their adequacy in estimating biomass in the different types of forest across the archipelago.MethodsA systematic survey of the scientific literature was conducted to compile the biomass equations, including ISI publications, national journals, conference proceedings, scientific reports, and academic theses. The data collected were overlaid on a land use/land cover map to assess the spatial distribution with respect to different regions and land cover types. The validation of the equations for selected forest types was carried out using independent destructive sampling data.ResultsA total of 2,458 biomass equations from 168 destructive sampling studies were compiled. Unpublished academic theses contributed the majority of the biomass equations. Twenty-one habitat types and 65 species were studied in detail. Diameter was the most widely used single predictor in all allometric equations. The cumulative number of individual trees cut was 5,207. The islands of Java, Kalimantan, and Sumatra were the most studied, while other regions were underexplored or unexplored. More than half of the biomass equations were for just seven species. The majority of the studies were carried out in plantation forests and secondary forests, while primary forests remain largely understudied. Validation using independent data showed that the allometric models for peat swamp forest had lower error departure, while the models for lowland dipterocarp forest had higher error departure.ConclusionAlthough biomass studies are a major research activity in Indonesia due to its high forest cover, the majority of such activities are limited to certain regions, forest types, and species. More research is required to cover underrepresented regions, forest types, particular growth forms, and very large tree diameter classes.

AbstractQuantifying and understanding the small‐scale variability of nitrous oxide (N2O) and carbon dioxide (CO2) emission are essential for reporting accurate ecosystem greenhouse gas budgets. The objective of this study was to evaluate the spatial pattern of soil CO2 and N2O emissions and their relation to topography in a tropical montane forest. We measured fluxes of N2O and CO2 from 810 sampling locations across valley bottom, midslope, and ridgetop positions under controlled laboratory conditions. We further calculated the minimum number of samples necessary to provide best estimates of soil N2O and CO2 fluxes at the plot level. Topography exhibited a major influence on N2O emissions, with soils at midslope position emitting significantly less than at ridgetops and valley bottoms, but no consistent effect of topography on soil CO2 emissions was found. The high spatial variation of N2O and CO2 fluxes was further increased by changes in vegetation and soil properties resulting from human disturbance associated with charcoal production. Soil N2O and CO2 fluxes showed no spatial pattern at the plot level, with “hot spots” strongly contributing to the total emissions (10% of the soil cores represented 73 and 50% of the total N2O and CO2 emissions, respectively). Thus, a large number of samples are needed to obtain robust estimates of N2O and CO2 fluxes. Our results highlight the complex biogeochemical cycling in tropical montane forests, and the need to carefully address it in research experiments to robustly estimate soil CO2 and N2O fluxes at the ecosystem scale.

Abstract. The Agriculture, Forestry and Other Land Use (AFOLU) sector contributes with ca. 20–25 % of global anthropogenic emissions (2010), making it a key component of any climate change mitigation strategy. AFOLU estimates, however, remain highly uncertain, jeopardizing the mitigation effectiveness of this sector. Comparisons of global AFOLU emissions have shown divergences of up to 25 %, urging for improved understanding of the reasons behind these differences. Here we compare a variety of AFOLU emission datasets and estimates given in the Fifth Assessment Report for the tropics (2000–2005) to identify plausible explanations for the differences in (i) aggregated gross AFOLU emissions, and (ii) disaggregated emissions by sources and gases (CO2, CH4, N2O). We also aim to (iii) identify countries with low agreement among AFOLU datasets to navigate research efforts. The datasets are FAOSTAT (Food and Agriculture Organization of the United Nations, Statistics Division), EDGAR (Emissions Database for Global Atmospheric Research), the newly developed AFOLU “Hotspots”, “Houghton”, “Baccini”, and EPA (US Environmental Protection Agency) datasets. Aggregated gross emissions were similar for all databases for the AFOLU sector: 8.2 (5.5–12.2), 8.4, and 8.0 Pg CO2 eq. yr−1 (for Hotspots, FAOSTAT, and EDGAR respectively), forests reached 6.0 (3.8–10), 5.9, 5.9, and 5.4 Pg CO2 eq. yr−1 (Hotspots, FAOSTAT, EDGAR, and Houghton), and agricultural sectors were with 1.9 (1.5–2.5), 2.5, 2.1, and 2.0 Pg CO2 eq. yr−1 (Hotspots, FAOSTAT, EDGAR, and EPA). However, this agreement was lost when disaggregating the emissions by sources, continents, and gases, particularly for the forest sector, with fire leading the differences. Agricultural emissions were more homogeneous, especially from livestock, while those from croplands were the most diverse. CO2 showed the largest differences among the datasets. Cropland soils and enteric fermentation led to the smaller N2O and CH4 differences. Disagreements are explained by differences in conceptual frameworks (carbon-only vs. multi-gas assessments, definitions, land use vs. land cover, etc.), in methods (tiers, scales, compliance with Intergovernmental Panel on Climate Change (IPCC) guidelines, legacies, etc.) and in assumptions (carbon neutrality of certain emissions, instantaneous emissions release, etc.) which call for more complete and transparent documentation for all the available datasets. An enhanced dialogue between the carbon (CO2) and the AFOLU (multi-gas) communities is needed to reduce discrepancies of land use estimates.