Forest Carbon Sink Research Articles

Above‐ground net primary productivity in regenerating seasonally dry tropical forest: Contributions of rainfall, forest age and soil

Abstract Identifying factors controlling forest productivity is critical to understanding forest‐climate change feedbacks, modelling vegetation dynamics and carbon finance schemes. However, little research has focused on productivity in regenerating tropical forests which are expanding in their fraction of global area have an order of magnitude larger carbon uptake rates relative to older forest. We examined above‐ground net primary productivity (ANPP) and its components (wood production and litterfall) over 10 years in forest plots that vary in successional age, soil characteristics and species composition using band dendrometers and litterfall traps in regenerating seasonally dry tropical forests in northwestern Costa Rica. We show that the components of ANPP are differentially driven by age and annual rainfall and that local soil variation is important. Total ANPP was explained by a combination of age, annual rainfall and soil variation. Wood production comprised 35% of ANPP on average across sites and years, and was explained by annual rainfall but not forest age. Conversely, litterfall increased with forest age and soil fertility yet was not affected by annual rainfall. In this region, edaphic variability is highly correlated with plant community composition. Thus, variation in ecosystem processes explained by soil may also be partially explained by species composition. These results suggest that future changes in annual rainfall can alter the secondary forest carbon sink, but this effect will be buffered by the litterfall flux which varies little among years. In determining the long‐term strength of the secondary forest carbon sink, both rainfall and forest age will be critical variables to track. We also conclude that detailed understanding of local site variation in soils and plant community may be required to accurately predict the impact of changing rainfall on forest carbon uptake. Synthesis. We show that in seasonally dry tropical forest, annual rainfall has a positive relationship with the growth of above‐ground woody tissues of trees and that droughts lead to significant reductions in above‐ground productivity. These results provide evidence for climate change—carbon cycle feedbacks in the seasonal tropics and highlight the value of longitudinal data on forest regeneration.

Forest carbon sink in the U.S. (1870–2012) driven by substitution of forest ecosystem service flows

Understanding the dynamics behind forest transitions, i.e., shifts from deforestation to forest recovery, is crucial for forest conservation and climate-change mitigation i.e., carbon (C) sequestration. We investigated the drivers of the forest transition in the United States, which was characterized by forest thickening despite surges in industrial wood extraction. We employ the concepts of Human Appropriation of Net Primary Productivity (HANPP) and Material and Energy Flow Analysis (MEFA) to quantitatively assess changes in major provisioning ecosystem services demanded from forests, i.e., industrial wood (comprising biomass used in products such as paper and pulp), grazing, and fuelwood, and analyse substitution processes from 1870-2012 at regional, sectoral, and national scales. The share of industrial wood in total annual forest biomass harvest increased from 23% to 84% over the time-period, while fuelwood and biomass grazed declined from 63% to 13%, and 14% to 3%, respectively. Reductions in demand for fuelwood and biomass grazed were enabled by shifts in feed and energy sources, consequently allowing for increases in both livestock numbers and energy use. Feed crops increased six-fold, alleviating grazing pressure on forest ecosystems, particularly in the Eastern states. Fossil fuels replaced fuelwood, especially in the residential sector. Between 1900-2012 the final energy mix increased seventeen-fold. Thus, the increase in biomass C stocks in U.S. forests was connected to substitution of forest ecosystem services with fossil fuel-based production systems, and with manifold increases in societal resource use and C dynamics. Such shifts need to be considered when assessing the positive environmental effects of forest transitions.

Assessment of Carbon Stock in Forest Biomass and Emission Reduction Potential in Malaysia

Malaysia has a large extent of forest cover that plays a crucial role in storing biomass carbon and enhancing carbon sink (carbon sequestration) and reducing atmospheric greenhouse gas emissions, which helps to reduce the negative impacts of global climate change. This article estimates the economic value of forest carbon stock and carbon value per hectare of forested area based on the price of removing per ton CO2eq in USD from 1990 to 2050. The economic value of biomass carbon stored in the forests is estimated at nearly USD 51 billion in 2020 and approximately USD 41 billion in 2050, whereas carbon value per hectare forest area is estimated at USD 2885 in 2020 and USD 2388 in 2050. If the BAU scenario of forest loss (converting forests to other land use) continues, the projected estimation of carbon stock and its economic value might fall until 2050 unless further initiatives on proper planning of forest management and ambitious policy implementation are taken. Instead, Malaysia’s CO2 emission growth started to fall after 2010 due to rising forest carbon sink of 282 million tons between 2011 and 2016, indicating a huge potential of Malaysian forests for future climate change mitigation. The estimated and projected value of carbon stock in Malaysian forest biomass, annual growth of forest carbon, forest carbon density and carbon sink would be useful for the better understanding of enhancing carbon sink by avoiding deforestation, sustainable forest management, forest conservation and protection, accurate reporting of national carbon inventories and policy-making decisions. The findings of this study could also be useful in meeting emission reduction targets and policy implementation related to climate change mitigation in Malaysia.

Interspecific Soil Water Partitioning as a Driver of Increased Productivity in a Diverse Mixed Mediterranean Forest

AbstractIt has been assumed that mixing of species with high physiological diversity reduces competition over water and light resources, compared to single‐species forests. Although several mechanisms to explain this observation have been proposed, quantification of these effects is lacking. Here we studied water‐use dynamics for five tree species in a mature, mixed, evergreen, and Mediterranean forest. We use empirical measurements of key tree structural attributes including root distribution, through DNA barcoding and soil cores, tree height and biomass along with measurements of species‐specific water use for two years. These measurements at the tree‐scale were used to parameterize an ecosystem model of coupled water, carbon and energy fluxes (Regional Hydro Ecologic Simulation System, RHESSys). Site‐scale empirical measurements showed contrasting diurnal and seasonal transpiration and sap flow curves across tree species, with year‐round activity in angiosperms, and mostly wet season‐activity in gymnosperms. Water‐use patterns matched the rooting depth patterns, with the deep‐ and shallow‐rooted Ceratonia and Cupressus, showing year‐round and seasonal behaviors, respectively. RHESSys estimates of species‐specific and stand‐scale transpiration, biomass and productivity across 20 years of climate variation showed substantial differences between mixed and monoculture scenarios. Stand‐scale annual net primary productivity and transpiration increased by 20–70 g C m−1 yr−1 and 40–80 mm yr−1, respectively, for mixed stands relative to average fluxes aggregated across monocultures. Model results, collaborated by field data provide evidence for niche partitioning of the soil water resource among co‐habiting tree species, and demonstrate that this mechanism can facilitate higher productivity and an enhanced forest carbon sink especially in semi‐arid regions.

A review and prospect of global bamboo forest carbon sink research based on CiteSpace

As climate warming further worsens, the studies of bamboo forest carbon sink have gradually evolved into one of the important branches of carbon sink research field. With the employment of CiteSpace software, a literature review was conducted of researches on bamboo forest carbon sink included in the Web of Science Core Collection for analysis and prospects into the future. The results showed that a) with close attention drawn from more and more researchers, bamboo forest carbon sink research is embracing a rapid development; b) with the close cooperation among authors, substantial progress has been achieved in this field with a collection of research papers published, forming a strong core author group while the core institutions have shown obvious geographical agglomeration with great contributions made to this field; c) the existing studies mainly focus on the discussion of bamboo forest carbon storage, bamboo forest carbon sequestration capacity, management methods, bamboo products carbon storage, and the effects of bamboo forests on the promotion of carbon storage and farmers’ income and it has been concluded that bamboo forests have a high level of carbon storage, the carbon sequestration capacity of bamboo forests is significantly higher than that of other forests, management methods have a significant impact on on the promotion of the carbon sequestration capacity of bamboo forest, bamboo products have great potential for substitution and emission reduction and bamboo forests have the double effect on the promotion of carbon sink and farmers’ income; d) the change of research keywords is a reflection of the efforts to cope with the global climate change and promote the sustainable management of bamboo forests by improving the carbon sequestration capacity. In the future, it is necessary to enhance the influence of bamboo forest carbon sinks and encourage countermeasure researches on practical issues to give full play to the double effect of bamboo forest carbon sinks on the reduction of emissions and the promotion of farmers’ income. [Ch, 2 fig. 2 tab. 39 ref.]

Canopy conductance and gas exchange of a Japanese cypress forest after rainfall‐induced wetness

AbstractIncreased stomatal conductance of the dry leaves right after wetness ended was reported before, while few studies paid attention to this phenomenon in canopy scale and its contribution to the forest carbon sink function. Therefore, we observed the continuous change of canopy wetness and ecosystem fluxes after wetness ended by using wetness sensors and eddy covariance method for a Japanese cypress forest (Chamaecyparis obtuse Sieb. Et Zucc.) in the Asian monsoon area. Larger gc (canopy conductance) were found in the relationships with both vapor pressure deficit and Rn (net radiation) during the first several hours after wetness ended. The results for λE (latent heat flux) were similar to that of gc in spring and summer. Net ecosystem exchange (NEE) in the relationships with Rn at different stages after wetness ended did not show clear difference except in spring. Nevertheless, annual summed‐up NEE showed that the average CO2 uptake at the first several hours after wetness ended was larger than the usual dry period. These results suggest that the improved stomatal opening at the first several hours after wetness ended plays a significant role in the canopy‐scale gas exchange processes.

Integrated remote sensing and model approach for impact assessment of future climate change on the carbon budget of global forest ecosystems

At present, global warming is an indisputable fact, and more and more attention has been paid to the impacts of climate warming on global ecological environments. Forests play increasing significant roles in regulating global carbon balance and mitigating climate change. Therefore, to understand the response mechanisms of the carbon budget of global forest ecosystems to future climate change, an improved version of the FORest ecosystem Carbon budget model for CHiNa (FORCCHN) and future Representative Concentration Pathway (RCP) scenario RCP4.5 and RCP8.5 were applied in this study. The results demonstrated that the global forest ecosystems will play a major role in the carbon sink under the future two climate change scenarios. In particular, the average carbon budget of global forest ecosystems under RCP4.5 scenario was estimated to be 0.017 kg(C)·m−2·yr−1 from 2007 to 2100. The future carbon sink areas of global forest ecosystems will increase significantly. Under RCP4.5 and RCP8.5 climate scenarios, the carbon sink areas of global forest ecosystems during 2026–2100 would be significantly been expanded than those in 2007–2025, with increases of 83.16–87.26% and 23.53–29.70%, respectively. The impacts of future climate change on carbon budget of global forest ecosystems will significantly vary between different regions. The carbon budget of forests will be enhanced in the northern hemisphere and significantly weakened in the southern hemisphere under the future two climate change scenarios. The carbon sink regions of global forests will be mainly distributed in the middle and high latitudes of the northern hemisphere. In particular, the forests' carbon budget in northeastern and central Asia, northern Europe and western North America will increase by 40% ~ 80%. However, the carbon budget of forests will decrease by 20% ~ 40% in the most regions of the southern hemisphere. In northern South America and central Africa, the forests' carbon budget will be reduced by more than 40%. In the future, in some areas of southern hemisphere, where the forests' carbon budget was predicted to be reduced, some measures for improving forest carbon sink, such as strengthening forest tending, enforcing prohibiting deforestation laws and scientific forest management, and so on, should be implemented to ensure immediate mitigation and adaptation to climate change.

Setting the forest reference levels in the European Union: overview and challenges

BackgroundThe contribution of EU forests to climate change mitigation in 2021–2025 is assessed through the Forest Reference Levels (FRLs). The FRL is a projected country-level benchmark of net greenhouse gas emissions against which the future net emissions will be compared. The FRL models the hypothetical development of EU forest carbon sink if the historical management practices were continued, taking into account age dynamics. The Member States’ FRLs have been recently adopted by the European Commission with the delegated Regulation (EU) 2021/268 amending the Regulation (EU) 2018/841. Considering the complexity of interactions between forest growth, management and carbon fluxes, there is a need to understand uncertainties linked to the FRL determination.ResultsWe assessed the methodologies behind the modelled FRLs and evaluated the foreseen impact of continuation of management practices and age dynamics on the near-future EU27 + UK forest carbon sink. Most of the countries implemented robust modelling approaches for simulating management practices and age dynamics within the FRL framework, but faced several challenges in ensuring consistency with historical estimates. We discuss that the projected 16% increase in harvest in 2021–2025 compared to 2000–2009, mostly attributed to age dynamics, is associated to a decline of 18% of forest sink (26% for living biomass only).ConclusionsWe conclude that the FRL exercise was challenging but improved the modelling capacity and data availability at country scale. The present study contributes to increase the transparency of the implementation of forest-related EU policies and provides evidence-based support to future policy development.

Improving intra‐ and inter‐annual GPP predictions by using individual tree inventories and leaf growth dynamics

Abstract Carbon sequestration is a key ecosystem service provided by forests. Inventory data based on individual trees are considered to be the most accurate method for estimating forest productivity. However, the estimations of forest photosynthesis from inventory data remain understudied, particularly when considering the growth and development of individual trees under the background of global change. Here, we used the leaf growth process with phenology and non‐structural carbohydrates (NSC) storage to revise an individual‐tree‐based carbon model, FORCCHN. This model couples leaf development and biomass to quantify gross primary productivity (GPP) in the forests, where growth is decoupled from photosynthesis in daily step. The model was initialized with inventory‐based forest data rather than the more widely used satellite‐based data. We tested the model against measured above‐ground woody biomass, growth of leaf biomass, daily gross ecosystem exchange (GEE) and yearly GEE at five representative forest sites in the Northern Hemisphere. We also compared the results from the original model and the revised model at five forest sites. Including leaf growth dynamics and inventory‐based initialization improved the predicted performance (r2) of GPP by an average of 33%. Synthesis and applications. Our results suggest that the appropriate vegetation data sources (i.e. inventory or satellite selection) and the effective predictions of the growth process should be considered when developing future carbon cycle models and forest carbon estimation options. Applying and improving such carbon models to evaluate carbon sequestration is an important part of forest carbon sink management.

Spatially explicit changes in forest biomass carbon of China over the past 4 decades: Coupling long-term inventory and remote sensing data

Quantification of the spatial pattern of forest carbon (C) sinks in high resolution is helpful to reveal the factors that affect the C cycle and provides valuable information for developing sustainable forest management policies. Here we developed a method using the data of long-term forest inventories (1977–2018) and spatially-explicit remotely sensed information from land-use maps and the Normalized Difference Vegetation Index (NDVI) datasets, to estimate the spatial and temporal variation of forest biomass C in China. At first, we calculated forest biomass C stocks using the refined Continuous Biomass Expansion Factor (CBEF) model with parameters for each forest type based on eight national forest inventories. Secondly, based on multi-temporal land-use remote sensing and national forest inventory datasets, we obtained forest coverage datasets with high resolution (1 km*1 km). Thirdly, we downscaled the forest biomass C density using the calibrated forest coverage maps and the maximum NDVI values derived from GIMMS-NDVI3g imagery. Our results showed that China's forest functioned as a C sink of 3777.73 Tg C, and the C density of forest stands increased from 35.41 Mg C ha−1 during 1977–1981 to 43.95 Mg C ha−1 during 2014–2018. In addition, the validation results for most of the provinces based on published inventory estimates during the eight periods showed that the forest area at the pixel scale was successfully calibrated. From this, we produced the maps with a finer resolution for a series of spatially continuous forest biomass carbon density distribution and carbon sinks. Notably eight major forest projects have accounted for 44%–51% of the forest C stocks added in China from 1977 to 2018. Our research provides new insights for understanding and monitoring the spatiotemporal variations in of forest biomass and key information to support the development of new afforestation policies moving forward.

Forest Carbon Sink Evaluation – An Important Contribution for Carbon Neutrality

Forest carbon sink refers to the carbon storage in nature, including the process, activity and mechanism of removing carbon dioxide from the air. Forest carbon sinks play a very important role in reducing the concentration of greenhouse gases in the atmosphere and slowing down the global warming process. Fujian Province is one of the key forest areas in southeast China. It has a mild climate, abundant rainfall, superior natural conditions, and abundant forest resources. According to the National Forest Resources Continuous Inventory Statistics, the Fujian forest coverage rate reached 66.8% in 2018 and has kept the No. 1 ranking in China for the past 40 consecutive years. The potential of forest carbon sink resources is considerable. This article first analyzes forest carbon sinks and their advantages, and then studies the development of forest carbon sinks in Fujian Province, and carries out quantitative estimation. Finally, relevant suggestions for the development of forest carbon sinks are given.

Changes in energy and livestock systems largely explain the forest transition in Austria (1830–1910)

Achieving a global forest transition, that is a shift from deforestation to reforestation, is important for climate-change mitigation. Forest transitions are enabled by socioecological processes, including land displacement, agricultural intensification and woodfuel substitution for other energy, but their respective contributions remain poorly understood. Here, by means of a scenario approach we quantify the importance of enabling conditions of the forest transition in Austria between 1830 and 1910 and their overall emissions implications, including the forest carbon sink potential in the hypothetical absence of wood use. We combine historical databases on land use, biomass production and energy use and an empirical dynamic forest growth model to develop five hypothetical counterfactual scenarios. The scenarios assume food and energy consumption in the absence of woodfuel substitution, food imports and three variations of agricultural intensification and assess effects on forest change and carbon balances. We find that the absence of any of the enabling conditions would have completely depleted forest biomass by 1910. Livestock efficiency gains and woodfuel substitution, two rarely discussed drivers of forest change, were equally important as yield increase and land displacement. The cumulative forest sink potential in the absence of any wood extraction throughout the period was found to be about twice the forest carbon stock in 1830. All counterfactual scenarios led to increasing overall emissions, “no woodfuel substitution” being closest to the historical trend. Our work lays the ground for a new typology of forest transitions according to the socioecological processes that enable them.

Distinct storage mechanisms of soil organic carbon in coniferous forest and evergreen broadleaf forest in tropical China

The impact of human activities on soil carbon (C) storage in tropical forests has aroused wide concern during the past decades, because these ecosystems play a key role in ameliorating global climate change. However, there remain uncertainties about how land-use history alters soil organic carbon (SOC) stability and storage in different forests. In this study, we measured the C content and mass distributions of soil aggregates, density fractions, mineral-bound C and microbial biomass C in the organic horizon, 0-10 cm and 10-20 cm soil layers in coniferous forest and evergreen broadleaf forest at Dinghushan Biosphere Reserve in tropical China. The broadleaf forest had larger SOC stocks than the coniferous forest, but the proportion of SOC stored in different density fractions at 0-10 cm soils was similar between forest types, while a greater proportion of SOC was stored in microaggregates in the coniferous forest. Most of the SOC was held as light fraction C in the organic horizon in the coniferous forest, whereas the concentrations of mineral-bound C were higher in the broadleaf forest. These findings indicate clear differences in the protection of SOC between broadleaf and coniferous forests growing on the same soil type. We propose that historic conversion of broadleaf forest to coniferous forest has reduced soil C sequestration capacity by altering the diversity and quality of plant inputs to the soil, which in turn affected macroaggregate formation, soil chemical properties and microbial biomass. Our results thus demonstrate that changes in forest tree species composition could have long-lasting effects on soil structure and carbon storage, providing crucial evidence for policy decisions on forest carbon sink management.

Changes in net ecosystem exchange of CO2 in Arctic and their relationships with climate change during 2002–2017

Arctic warming leads to permafrost degradation, which can increase ecosystem respiration and release more greenhouse gas into the atmosphere. Meanwhile, climate warming also promotes the plant growth and increases carbon assimilation. Presently, it is largely unknown about the carbon budget and their responses to climate change in the Arctic regions. In this study, to investigate the seasonal and annual net ecosystem carbon exchange (NEE), we collected 71 observation stations for net ecosystem exchange (NEE) of CO2 in the high latitude permafrost regions during 2002–2017. The results showed that the annual NEE was −8.2 ± 4.1 g CO2 m−2 d−1 for forest, −3.3 ± 2.6 g CO2 m−2 d−1 for shrub, −4.8 ± 4.1 g CO2 m−2 d−1 for grassland, −3.6 ± 3.0 g CO2 m−2 d−1 for wetland and 0.02 ± 0.62 g CO2 m−2 d−1 for tundra, respectively. From 2002 to 2017, the CO2 emissions of grassland (carbon source) showed a decreasing trend, and the CO2 assimilation of shrub and forest (carbon sink) has been increased. The wetland and tundra are shifting from carbon sources to sinks. There were great variations in temperature sensitivities (Q10) of NEE in different seasons, with larger values in winter and lower values in summer. These findings indicate that the Arctic terrestrial ecosystem presently acts as a carbon sink, while there is a possibility that future warming, especially the warming in winter, may decrease the carbon sink of the Arctic terrestrial ecosystem.

Boreal forest soil carbon fluxes one year after a wildfire: Effects of burn severity and management.

The extreme 2018hot drought that affected central and northern Europe led to the worst wildfire season in Sweden in over a century. The Ljusdal fire complex, the largest area burnt that year (8995ha), offered a rare opportunity to quantify the combined impacts of wildfire and post-fire management on Scandinavian boreal forests. We present chamber measurements of soil CO2 and CH4 fluxes, soil microclimate and nutrient content from five Pinus sylvestris sites for the first growing season after the fire. We analysed the effects of three factors on forest soils: burn severity, salvage-logging and stand age. None of these caused significant differences in soil CH4 uptake. Soil respiration, however, declined significantly after a high-severity fire (complete tree mortality) but not after a low-severity fire (no tree mortality), despite substantial losses of the organic layer. Tree root respiration is thus key in determining post-fire soil CO2 emissions and may benefit, along with heterotrophic respiration, from the nutrient pulse after a low-severity fire. Salvage-logging after a high-severity fire had no significant effects on soil carbon fluxes, microclimate or nutrient content compared with leaving the dead trees standing, although differences are expected to emerge in the long term. In contrast, the impact of stand age was substantial: a young burnt stand experienced more extreme microclimate, lower soil nutrient supply and significantly lower soil respiration than a mature burnt stand, due to a thinner organic layer and the decade-long effects of a previous clear-cut and soil scarification. Disturbance history and burn severity are, therefore, important factors for predicting changes in the boreal forest carbon sink after wildfires. The presented short-term effects and ongoing monitoring will provide essential information for sustainable management strategies in response to the increasing risk of wildfire.

Carbon stock and sink economic values of forest ecosystem in the forest industry region of Heilongjiang Province, China

The values of forest carbon stock (CSV) and carbon sink (COV) are important topics in the global carbon cycle. We quantitatively analyzed the factors affecting changes in both for forest ecosystem in 2000−2015. With multiple linear stepwise regression analysis, we obtained the factors that had a significant impact on changes of CSV and COV, and then the impacts of these variables on CSV and COV were used for further quantitative analysis using the vector autoregressive model. Our results indicated that both stand age and afforestation area positively affect CSV and COV; however, the forest enterprise gross output value negatively affects CSV. Stand age has the largest long-term cumulative impact on CSV and COV, reaching 40.4% and 9.8%, respectively. The impact of enterprise gross output value and afforestation area on CSV and COV is the smallest, reaching 4.0% and 0.3%, respectively.

Author Correction: Disturbance suppresses the aboveground carbon sink in North American boreal forests

Author Correction: Disturbance suppresses the aboveground carbon sink in North American boreal forests

Opportunities for forest sector emissions reductions: a state-level analysis.

The forest sector can play a significant role in climate change mitigation. We evaluated forest sector carbon trends and potential mitigation scenarios in Vermont using a systems-based modeling framework that accounts for net emissions from all forest sector components. These components comprise (1) the forest ecosystem, including land-use change, (2) harvested wood products (HWP), and (3) substitution effects associated with using renewable wood-based products and fuels in place of more emission-intensive materials and fossil fuel-based energy. We assessed baseline carbon trends from 1995 through 2050 using a business as usual (BAU) scenario. Emission reductions associated with different forest management and HWP scenarios were evaluated relative to the BAU scenario from 2020 to 2050. We estimated uncertainty for each forest sector component and used a Monte Carlo approach to estimate the distribution of cumulative total mitigation for each scenario relative to baseline. Our analysis indicates that the strength of the forest sector carbon sink in Vermont has been declining and will continue to decline over coming decades under the BAU scenario. However, several scenarios evaluated here could be effective in reducing emissions and enhancing carbon uptake. Shifting HWP to longer-lived commodities resulted in a 14% reduction in net cumulative emissions by 2050, the largest reduction of all scenarios. A scenario that combined extending harvest rotations, utilizing additional harvest residues for bioenergy, and increasing forest productivity resulted in a 12% reduction in net cumulative emissions. Shifting commodities from pulp and paper to bioenergy showed a 7.3% reduction in emissions. In contrast, shortening rotations to increase harvests for bioenergy use resulted in a 5.5% increase in emissions. In summary, model simulations suggest that net emissions could be reduced by up to 14% relative to BAU, depending on the management and HWP-use scenario. Combining multiple scenarios could further enhance reductions. However, realizing the full climate mitigation potential of these forests may be challenging due to socioeconomic barriers to implementation, as well as alternative management objectives that must be considered along with carbon sequestration.

Disturbance suppresses the aboveground carbon sink in North American boreal forests

Climate change is altering vegetation and disturbance dynamics in boreal ecosystems. However, the aggregate impact of these changes on boreal carbon budgets is not well understood. Here we combined multiple satellite datasets to estimate annual stocks and changes in aboveground biomass (AGB) across boreal northwestern North America. From 1984 to 2014, the 2.82 × 106 km2 study region gained 434 ± 176 Tg of AGB. Fires resulted in losses of 789 ± 48 Tg, which were mostly compensated by post-fire recovery of 642 ± 86 Tg. Timber harvests contributed to losses of 74 ± 5 Tg, which were partly offset by post-harvest recovery of 32 ± 9 Tg. Earth system models overestimated AGB accumulation by a factor of 3 (+1,519 ± 171 Tg), which suggests that these models overestimate the terrestrial carbon sink in boreal ecosystems and highlights the need to improve representation of fire and other disturbance processes in these models. Disturbance regimes from fire, drought, harvest and insects will probably intensify in the future and under climate change. Despite partial offsets from regrowth, disturbance from fire and harvest reduces carbon uptake and storage in boreal forests, impacting the strength of this carbon sink.

Variations of carbon allocation and turnover time across tropical forests

AbstractAimThe carbon sink in tropical forests is a highly uncertain component of the global carbon budget. An understanding of the processes controlling this sink requires better quantification of carbon allocation, stocks and turnover times.LocationTropical forests.Time period2010–2017.Major taxa studiedTropical forest ecosystem.MethodsWe develop a novel data assimilation system using satellite‐based annual above‐ground biomass derived from L‐band vegetation optical depth with 25 km × 25 km grid spacing, together with leaf area, to constrain the 25 km × 25 km carbon allocation patterns of net primary productivity (NPP) into the wood, leaf and root pools, and their turnover times. Our average data‐driven estimates of these variables are broadly consistent with independent ground‐based estimates of NPP allocation and wood turnover from forest inventory plots.ResultsIn tropical forest, on average, the NPP allocation into wood (0.30 ± 0.04) is significantly higher than that into leaves (0.24 ± 0.07). From the wet to dry tropics, forest NPP allocation into both wood and leaves declines slightly. The turnover times of forest leaf pools exhibit little spatial variation, whereas the turnover times of wood pools in Africa (median and interquartile range: years) are slightly longer than those in South America ( years) and Southeast Asia ( years). Our datasets reveal emergent trade‐offs across climatic and vegetation gradients between growth and life span/turnover for both wood and leaves. The spatial gradients of NPP allocation to wood/leaves are associated with canopy height, adjusted by climate condition and nutrient acquisition. The spatial gradients of wood and leaf turnover times are influenced mainly by climate and leaf characteristics.Main conclusionsOur data‐driven estimates of carbon allocation and turnover times provide a basis for more detailed exploration of these mechanisms in field studies. This highlights that improved model representation of carbon allocation and turnover is necessary for more accurate prediction of future carbon dynamics.