Lianas are increasing in many forests and show higher stem turnover rates and different chemical profiles compared with trees. However, liana deadwood decomposition dynamics have been overlooked. We redress this omission and hypothesize that liana wood decomposes faster than tree wood due to its larger vessels and higher nutrient content than trees, resulting in greater activity of both microbial and invertebrate decomposers. We tested this hypothesis in a common-garden decomposition experiment with deadwood of two size classes (2.5 and 4 cm diameter) belonging to 12 liana and 12 tree species in tropical China. Liana wood decomposed 28.6% faster than tree wood in the presence of invertebrates for large diameter but showed no significant difference for the smaller diameter. Initial contents of nitrogen, calcium, potassium and hemicellulose were higher for liana than tree wood. Likewise, liana bark had higher potassium and lignin contents than tree bark. The microbial contribution to decomposition based on mesh size exclusion of invertebrates, across lianas and trees, was similar. The presence of invertebrates more than doubled the decomposition rates for both lianas and trees. Overall, lianas decompose faster than trees, at least for larger diameter deadwood, and therefore may promote forest carbon and nutrient turnover rates.
Tag: Carbon cycle
Priority research questions in global peatland science
Peatlands are among Earth’s largest terrestrial carbon stores and are crucial for climate regulation, biodiversity conservation, and water security. Yet peatlands worldwide are deteriorating under pressures from climate change and human disturbance. Strategic, globally coordinated research is urgently needed to protect, restore and manage peatlands so they can continue to deliver essential ecosystem services. To meet this challenge, here we present a global research prioritisation for peatland science, based on a two-stage online survey and expert voting exercise involving 467 participants from 54 countries. We identify 50 priority research questions spanning carbon dynamics, climate impacts, restoration and management, technological innovation, and community and policy engagement. These questions provide a community-informed agenda to guide peatland research over the next decade. Addressing them will help close critical knowledge gaps, strengthen evidence-based decision making, and support the role of peatlands in achieving global climate and biodiversity goals.
The importance of tropical tree-ring chronologies for global change research
Tropical forests are vital to global carbon and water cycles, yet the effects of climate change on these systems remain poorly understood due to limited long-term data. This study compiles 492 tropical tree-ring chronologies to assess their potential in reconstructing climate variability and understanding the climate sensitivity of woody productivity. The analysis reveals that while tree-ring studies have expanded rapidly, they remain biased toward high-elevation and drier regions, with significant gaps in wetter climates and among angiosperms. The strongest climate signals are found in cooler, drier sites. Species-distribution modeling identifies untapped regions for future research. These findings highlight the value of tropical dendrochronology in global change science, offering insights into climate extremes, vegetation dynamics, and model validation.
Sensitivity of Above-Ground Biomass Estimates to Height-Diameter Modelling in Mixed-Species West African Woodlands
It has been suggested that above-ground biomass (AGB) inventories should include tree height (H), in addition to diameter (D). As H is a difficult variable to measure, H-D models are commonly used to predict H. We tested a number of approaches for H-D modelling, including additive terms which increased the complexity of the model, and observed how differences in tree-level predictions of H propagated to plot-level AGB estimations. We were especially interested in detecting whether the choice of method can lead to bias. The compared approaches listed in the order of increasing complexity were: (B0) AGB estimations from D-only; (B1) involving also H obtained from a fixed-effects H-D model; (B2) involving also species; (B3) including also between-plot variability as random effects; and (B4) involving multilevel nested random effects for grouping plots in clusters. In light of the results, the modelling approach affected the AGB estimation significantly in some cases, although differences were negligible for some of the alternatives. The most important differences were found between including H or not in the AGB estimation. We observed that AGB predictions without H information were very sensitive to the environmental stress parameter (E), which can induce a critical bias. Regarding the H-D modelling, the most relevant effect was found when species was included as an additive term. We presented a two-step methodology, which succeeded in identifying the species for which the general H-D relation was relevant to modify. Based on the results, our final choice was the single-level mixed-effects model (B3), which accounts for the species but also for the plot random effects reflecting site-specific factors such as soil properties and degree of disturbance.
Carbon balance in rubber (Hevea brasiliensis) plantations: A review on uncertainties at plot and landscape level
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.
Minimizing 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.
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.
The effects of invertebrates on wood decomposition across the world
Invertebrates and microorganisms are important but climate-dependent agents of wood decomposition globally. In this meta-analysis, we investigated what drives the invertebrate effect on wood decomposition worldwide. Globally, we found wood decomposition rates were on average approximately 40% higher when invertebrates were present compared to when they were excluded. This effect was most pronounced in the tropics, owing mainly to the activities of termites. The invertebrate effect was stronger for woody debris without bark as well as for that of larger diameter, possibly reflecting bark- and diameter-mediated differences in fungal colonisation or activity rates relative to those of invertebrates. Our meta-analysis shows similar overall invertebrate effect sizes on decomposition of woody debris derived from angiosperms and gymnosperms globally. Our results suggest the existence of critical interactions between microorganism colonisation and the invertebrate contribution to wood decomposition. To improve biogeochemical models, a better quantification of invertebrate contributions to wood decomposition is needed.
Climate seasonality limits leaf carbon assimilation and wood productivity in tropical forests
The seasonal climate drivers of the carbon cycle in tropical forests remain poorly known although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combination of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measurements and 35 litter productivity measurements) their associated canopy photosynthetic capacity (enhanced vegetation index EVI) and climate we ask how carbon assimilation and aboveground allocation are related to climate seasonality in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rainfall is < 2000ĝ€-mmĝ€-yrĝ'1 (water-limited forests) and to radiation otherwise (light-limited forests). On the other hand independent of climate limitations wood productivity and litterfall are driven by seasonal variation in precipitation and evapotranspiration respectively. Consequently light-limited forests present an asynchronism between canopy photosynthetic capacity and wood productivity. First-order control by precipitation likely indicates a decrease in tropical forest productivity in a drier climate in water-limited forest and in current light-limited forest with future rainfall < 2000ĝ€-mmĝ€-yrĝ'1. Author(s) 2016.
Effect of rewetting degraded peatlands on carbon fluxes: a meta-analysis
Numerous studies claim that rewetting interventions reduce CO2 and increase CH4 fluxes. To verify the claim, we conducted a systematic review and meta-analysis of the effects of rewetting on CO2 and CH4 fluxes and dissolved organic carbon (DOC). We identified 28 primary articles eligible for meta-analysis, from which we calculated 48 effect sizes for CO2 emissions, 67 effect sizes for CH4 emissions, and 5 effect sizes for DOC. We found that rewetting significantly decreased CO2 fluxes, with temperate zones showing the highest Hedges’ g effect size (−0.798 ± 0.229), followed by tropical (−0.338 ± 0.269) and boreal (−0.209 ± 0.372) zones. Meanwhile, rewetting increased CH4 fluxes, with the highest Hedges’ g effect size shown in temperate zones (1.108 ± 0.144), followed by boreal (0.805 ± 0.183) and tropical (0.096 ± 0.284) zones. In addition, based on yearly monitoring after rewetting, the CH4 emissions effect size increased significantly over the first 4 years (r2 = 0.853). Overall, the rewetting intervention reduced CO2 emissions by −1.43 ± 0.35 Mg CO2–C ha−1 year−1, increased CH4 emissions by 0.033 ± 0.003 Mg CH4–C ha−1 year−1, and had no significant impact on DOC. To improve the precision and reduce the bias of rewetting effect size quantification, it is recommended to conduct more experimental studies with extended monitoring periods using larger sample sizes and apply the before-after control-impact study design, especially in boreal and tropical climate zones.