• Energy Research

Abstract Wood density is a critical control on tree biomass, so poor understanding of its spatial variation can lead to large and systematic errors in forest biomass estimates and carbon maps. The need to understand how and why wood density varies is especially critical in tropical America where forests have exceptional species diversity and spatial turnover in composition. As tree identity and forest composition are challenging to estimate remotely, ground surveys are essential to know the wood density of trees, whether measured directly or inferred from their identity. Here, we assemble an extensive dataset of variation in wood density across the most forested and tree-diverse continent, examine how it relates to spatial and environmental variables, and use these relationships to predict spatial variation in wood density over tropical and sub-tropical South America. Our analysis refines previously identified east-west Amazon gradients in wood density, improves them by revealing fine-scale variation, and extends predictions into Andean, dry, and Atlantic forests. The results halve biomass prediction errors compared to a naïve scenario with no knowledge of spatial variation in wood density. Our findings will help improve remote sensing-based estimates of aboveground biomass carbon stocks across tropical South America.

This study presents for the first time in Venezuela a joint analysis of deforestation and forest degradation processes, including its effects on carbon emissions. The Caparo Forest Reserve, located in the Western Plains ecoregion, in one of the national hot spots of deforestation, served as a case study using three different periods: 1990–2000, 2000–2010 and 2010–2015. In the context of the United Nations Framework Convention on Climate Change (UNFCCC) framework, the Practice Guidance for Land Use, Land-Use Change and Forestry from the Intergovernmental Panel on Climate Change (IPCC) was followed. These guidelines combine the activity data for the estimation of deforestation and degradation rates, in this case using open access Landsat imagery in conjunction with the TerraAmazon system with the emission factors, and these based on aboveground biomass (AGB) estimations using field data from permanent plots monitored during the study period. Deforestation was responsible of a net loss of −53,461 ha, while close to −3667 ha were classified as degraded forests during the 1990–2000 decade (−4.9% annual deforestation rate). An estimated area of −36,447 ha and −515 ha between 2000 and 2010 was affected by both processes (−4.3% annual forest loss), and −8111 ha and −737 ha between 2010 and 2015 (−3.2% per year). These processes were responsible for an estimated equivalent in carbon emissions of 2.21 ± 0.32 (SEM—Standard Error of the Mean) Mt CO2 year−1 (1990–2000), 1.56 ± 0.19 Mt CO2per year between 2000 and 2010, while 0.80 ± 0.11 Mt CO2 year−1 during the 2010–2015 period. Between 92.9% and 98.63% (mean 94.9%) of these emissions came from deforestation, and between 1.37% and 7.79% (mean 5.1%) from forest degradation. Using available data, at national scale, deforestation and forest degradation in Caparo represented, on average, 0.49% of the total CO2 emissions and about 1.79% of land use change related emissions for the same period in Venezuela. Finally, we briefly outline a set of elements so these results can serve as a baseline for the potential establishment of a Reducing Emissions from Deforestation and Forest Degradation (REDD+) strategy in the area.

AbstractMost of the planet's diversity is concentrated in the tropics, which includes many regions undergoing rapid climate change. Yet, while climate‐induced biodiversity changes are widely documented elsewhere, few studies have addressed this issue for lowland tropical ecosystems. Here we investigate whether the floristic and functional composition of intact lowland Amazonian forests have been changing by evaluating records from 106 long‐term inventory plots spanning 30 years. We analyse three traits that have been hypothesized to respond to different environmental drivers (increase in moisture stress and atmospheric CO2 concentrations): maximum tree size, biogeographic water‐deficit affiliation and wood density. Tree communities have become increasingly dominated by large‐statured taxa, but to date there has been no detectable change in mean wood density or water deficit affiliation at the community level, despite most forest plots having experienced an intensification of the dry season. However, among newly recruited trees, dry‐affiliated genera have become more abundant, while the mortality of wet‐affiliated genera has increased in those plots where the dry season has intensified most. Thus, a slow shift to a more dry‐affiliated Amazonia is underway, with changes in compositional dynamics (recruits and mortality) consistent with climate‐change drivers, but yet to significantly impact whole‐community composition. The Amazon observational record suggests that the increase in atmospheric CO2 is driving a shift within tree communities to large‐statured species and that climate changes to date will impact forest composition, but long generation times of tropical trees mean that biodiversity change is lagging behind climate change.

AbstractAs countries advance in greenhouse gas (GHG) accounting for climate change mitigation, consistent estimates of aboveground net biomass change (∆AGB) are needed. Countries with limited forest monitoring capabilities in the tropics and subtropics rely on IPCC 2006 default ∆AGB rates, which are values per ecological zone, per continent. Similarly, research into forest biomass change at a large scale also makes use of these rates. IPCC 2006 default rates come from a handful of studies, provide no uncertainty indications and do not distinguish between older secondary forests and old‐growth forests. As part of the 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories, we incorporate ∆AGB data available from 2006 onwards, comprising 176 chronosequences in secondary forests and 536 permanent plots in old‐growth and managed/logged forests located in 42 countries in Africa, North and South America and Asia. We generated ∆AGB rate estimates for younger secondary forests (≤20 years), older secondary forests (>20 years and up to 100 years) and old‐growth forests, and accounted for uncertainties in our estimates. In tropical rainforests, for which data availability was the highest, our ∆AGB rate estimates ranged from 3.4 (Asia) to 7.6 (Africa) Mg ha−1 year−1 in younger secondary forests, from 2.3 (North and South America) to 3.5 (Africa) Mg ha−1 year−1 in older secondary forests, and 0.7 (Asia) to 1.3 (Africa) Mg ha−1 year−1 in old‐growth forests. We provide a rigorous and traceable refinement of the IPCC 2006 default rates in tropical and subtropical ecological zones, and identify which areas require more research on ∆AGB. In this respect, this study should be considered as an important step towards quantifying the role of tropical and subtropical forests as carbon sinks with higher accuracy; our new rates can be used for large‐scale GHG accounting by governmental bodies, nongovernmental organizations and in scientific research.