Resilient secondary tropical forests? Although deforestation is rampant across the tropics, forest has a strong capacity to regrow on abandoned lands. These “secondary” forests may increasingly play important roles in biodiversity conservation, climate change mitigation, and landscape restoration. Poorter et al . analyzed the patterns of recovery in forest attributes (related to soil, plant functioning, structure, and diversity) in 77 secondary forest sites in the Americas and West Africa. They found that different attributes recovered at different rates, with soil recovering in less than a decade and species diversity and biomass recovering in little more than a century. The authors discuss how these findings can be applied in efforts to promote forest restoration. —AMS

Global patterns of regional (gamma) plant diversity are relatively well known, but whether these patterns hold for local communities, and the dependence on spatial grain, remain controversial. Using data on 170,272 georeferenced local plant assemblages, we created global maps of alpha diversity (local species richness) for vascular plants at three different spatial grains, for forests and non-forests. We show that alpha diversity is consistently high across grains in some regions (for example, Andean-Amazonian foothills), but regional ‘scaling anomalies’ (deviations from the positive correlation) exist elsewhere, particularly in Eurasian temperate forests with disproportionally higher fine-grained richness and many African tropical forests with disproportionally higher coarse-grained richness. The influence of different climatic, topographic and biogeographical variables on alpha diversity also varies across grains. Our multi-grain maps return a nuanced understanding of vascular plant biodiversity patterns that complements classic maps of biodiversity hotspots and will improve predictions of global change effects on biodiversity.

As 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.

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In addition to bioenergy production, Acacia magium, a fast growing species, plays a major role in climate change mitigation through carbon sequestration from the atmosphere. The objective of this study was to improve estimates of aboveground biomass of 3, 7 and 11 years old stands of Acacia mangium set up through natural regeneration at Anguédédou in Côte d'Ivoire. Tree measurements were done in circular plots of 615 m 2 located at the center of each stand. 24 trees of circumference at breast height (cbh) between 31 and 116 cm were felled, weighed and measured. Multiple linear regressions were used to develop allometric equations linking aboveground biomass of trees to cbh and/or height. The carbon stock and sequestration capacity of each stand was assessed using these predictive models. The average cbh was 39.4 cm, 73.5 cm and 91.4 cm respectively for 3, 7 and 11 years old stands with a density ranging between 845 trees•ha −1 and 553 trees•ha −1 . The allometric equations for biomass estimation were Btotal aboveground = exp(−3.455 + 2.081 × ln(C)), Btrunk = exp (−5.153 + 1.681 × ln(C) + 1.056 × ln(H)), Bbranches = exp(−2.005 + 0.498 × ln(C 2 × H)), Bleaves = exp(−2.415 + 1.339 × ln(C)). Total height had no influence on total and leaf biomass but increased precision of trunk and branch biomass.The carbon sequestration capacity of aboveground biomass was highest in Acacia mangium stand of 7 years old with 45.14 teqCO 2 •ha −1 •year −1 and lowest in the 3-year stand with 33.90 teqCO 2 •ha −1 •year −1 .

For monitoring and reporting forest carbon stocks and fluxes, many countries in the tropics and subtropics rely on default values of forest aboveground biomass (AGB) from the Intergovernmental Panel on Climate Change (IPCC) Guidelines for National Greenhouse Gas (GHG) Inventories. Default IPCC forest AGB values originated from 2006, and are relatively crude estimates of average values per continent and ecological zone. The 2006 default values were based on limited plot data available at the time, methods for their derivation were not fully clear, and no distinction between successional stages was made. As part of the 2019 Refinement to the 2006 IPCC Guidelines for GHG Inventories, we updated the default AGB values for tropical and subtropical forests based on AGB data from >25,000 plots in natural forests and a global AGB map where no plot data were available. We calculated refined AGB default values per continent, ecological zone, and successional stage, and provided a measure of uncertainty. AGB in tropical and subtropical forests varies by an order of magnitude across continents, ecological zones, and successional stage. Our refined default values generally reflect the climatic gradients in the tropics, with more AGB in wetter areas. AGB is generally higher in old-growth than in secondary forests, and higher in older secondary (regrowth >20 years old and degraded/logged forests) than in young secondary forests (≤20 years old). While refined default values for tropical old-growth forest are largely similar to the previous 2006 default values, the new default values are 4.0 to 7.7-fold lower for young secondary forests. Thus, the refined values will strongly alter estimated carbon stocks and fluxes, and emphasize the critical importance of old-growth forest conservation. We provide a reproducible approach to facilitate future refinements and encourage targeted efforts to establish permanent plots in areas with data gaps.

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Question: Does shifting cultivation contribute to plant diversity in an Afrotropical semi‐deciduous forest lacking large‐scale natural disturbance? Location: Sanaimbo forest, Côte d'Ivoire (Ivory Coast). Methods: We surveyed species assemblages, structural attributes of diversity, and life‐history traits along a 30‐year chronosequence of abandoned fields, comparatively to old‐growth and selectively logged forest stands. Results: Patterns of species assemblages strongly changed with fallow area age, with respect to species'light requirements, suggesting niche partitioning along the successional gradient. Species richness, diversity and equitability were all increasing along this gradient. There were clear shifts in life‐history traits spectra as the forest recovered, especially regarding leaf shape, lifespan and hairiness, diaspore dispersal, seed size, resprouting capacity, and life forms. Early colonization by the invasive Chromolaena odorata did not appear to impair secondary succession. Soil type influenced old‐growth forest vegetation but not fallow vegetation. After 30 years of forest regrowth, plant communities exhibited endemism rates similar to those of ancient forests. Conclusions: Shifting cultivation appears to be a sustainable land use when small‐sized fields are embedded in a forest matrix and when agriculture lasts only one to few years, preserves remnant trees, excludes fire and keeps several years between two clearing episodes. It may even contribute to the high biodiversity maintenance at the whole forest scale, by conserving the successional mosaic. However, conservation of old‐growth forest patches is required for a number of climax tree species.