Plinio Sist 10,88 | Bonaventure Sonke 60 | J. Daniel Soto 21 | Cintia Rodrigues de Souza 24 | Juliana Stropp 89 | Martin J. P. Sullivan 35 | Ben Swanepoel 34 | Hans ter Steege 25,90 | John Terborgh 91,92 | Nicolas Texier 93 | Takeshi Toma 94 | Renato Valencia 95 | Luis Valenzuela 75 | Leandro Valle Ferreira 96 | Fernando Cornejo Valverde 97 | Tinde R. Van Andel 25 | Rodolfo Vasque 77 | Hans Verbeeck 61 | Pandi Vivek 22 | Abstract Aim:Large tropical trees form the interface between ground and airborne observations, offering a unique opportunity to capture forest properties remotely and to investigate their variations on broad scales. However, despite rapid development of metrics to characterize the forest canopy from remotely sensed data, a gap remains between aerial and field inventories. To close this gap, we propose a new pan-tropical model to predict plot-level forest structure properties and biomass from only the largest trees.Location: Pan-tropical.Time period: Early 21st century. Major taxa studied: Woody plants.Methods: Using a dataset of 867 plots distributed among 118 sites across the tropics, we tested the prediction of the quadratic mean diameter, basal area, Lorey's height, community wood density and aboveground biomass (AGB) from the ith largest trees. Results:Measuring the largest trees in tropical forests enables unbiased predictions of plot-and site-level forest structure. The 20 largest trees per hectare predicted quadratic mean diameter, basal area, Lorey's height, community wood density and AGB with 12, 16, 4, 4 and 17.7% of relative error, respectively. Most of the remaining error in biomass prediction is driven by differences in the proportion of total biomass held in medium-sized trees (50-70 cm diameter at breast height), which shows some continental dependency, with American tropical forests presenting the highest proportion of total biomass in these intermediate-diameter classes relative to other continents. Main conclusions:Our approach provides new information on tropical forest structure and can be used to generate accurate field estimates of tropical forest carbon stocks to support the calibration and validation of current and forthcoming space missions. It will reduce the cost of field inventories and contribute to scientific understanding of tropical forest ecosystems and response to climate change. K E Y W O R D Scarbon, climate change, forest structure, large trees, pan-tropical, REDD+, tropical forest ecology

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Dans la foulée de la réforme agraire de 1969, le gouvernement péruvien lança un programme de reboisement dans les Andes. Plus de 20 000 ha furent ainsi boisés en pins dans la région de Cajamarca, dont 8 500 ha dans la coopérative agraire de Granja Porcon. Destinés alors à approvision- ner les paysans en bois et à développer l’ac- tivité économique locale, à enrayer la dégra- dation des sols et des forêts naturelles rési- duelles, ces boisements sont aujourd’hui sollicités pour leur contribution au stockage du carbone. Cette recherche vise à comparer la capacité de séquestration de carbone des pâturages et des plantations de Pinus patula de haute altitude (3 250-3 450 m). À cette fin, deux approches ont été combi- nées : l’échantillonnage des sols (couches holorganiques et 0-100 cm) et de la végéta- tion dans les deux formations végétales (pâturages et boisements de Pinus patula âgés de 17 à 26 ans), sur cambisols déve- loppés sur matériaux volcaniques ; l’établis- sement d’un modèle de croissance de type peuplement, couvrant une plus grande diversité d’âges, de sylvicultures et de ferti- lités. Après vingt ans, la différence entre le carbone stocké dans les écosystèmes fores- tiers et les produits ligneux, d’une part, et en pâturages, d’autre part, s’élève à 154 t/ha, soit environ 7,7 t/ha/an. Cette différence s’explique très largement par la contribution des parties aériennes des arbres. Le reboi- sement en Pinus patula tend à réduire les stocks de carbone du sol par rapport aux for- mations prairiales correspondantes. La réduction est significative (α £ 0,05) dans les 40 premiers centimètres du sol mais la dynamique temporelle suggère que cet effet est temporaire. Le modèle de croissance montre que le stockage de carbone dans les parties aériennes des arbres augmente avec l’âge et la densité des peuplements, ainsi qu’avec la fertilité du site. Il permet aussi d’évaluer la contribution des éclaircies à environ 23 % de la quantité de carbone associée aux parties aériennes des arbres pour une sylviculture classique.

& Key message Under similar site conditions, leaf litter decomposition beneath Central African rainforests was largely driven by average leaf litter quality. Although significant, the additional variability related to litter mixing and to the decomposition environment was limited. & Context Under given site conditions, litter decomposition is expected to mainly depend on its average quality. However, the additional impacts of litter diversity as well as of the local decomposition environment remain rather inconclusive. & Aims This study investigates the litter mixture effects on decomposition and home-field advantage for two emblematic old growth forest types of the Congo Basin: the Scorodophloeus zenkeri Harms mixed forests and the evergreen Gilbertiodendron dewevrei (De Wild.) J. Léonard monodominant forests. & Methods Based on a litterbag experiment, variations in leaf litter mass loss were measured from the eight most important tree species under mixed and monodominant forests and for all possible two-species combinations. & Results Remaining mass was largely explained (90%) by a multivariate measure of initial litter quality including 11 functional traits, which performed better than any single leaf litter trait. For the litter mixtures, the average deviation from expectation based on simple additive effects ranged from slightly synergistic (+ 2.56%) to slightly antagonistic (− 0.86%) after 1 and 6 months, respectively. Mixture identity and chemical dissimilarity contributed to explaining the mixing effects, yet the effect of chemical dissimilarity at the whole mixture level was only detected through an interaction with incubation time. In addition, the initial decomposition rates of S. zenkeri and G. dewevrei were accelerated under their own forest type. & Conclusion In agreement with the "home-field advantage" theory, our results highlighted that the functional composition of the host forest did have an indirect impact on decomposition. In addition, leaf litter decomposition was mainly controlled by average litter quality, which in turn was closely related to a multivariate measure of green leaf quality. This suggests that increased knowledge of tree species leaf traits in tropical forests would greatly help in better understanding the litter decomposition dynamics.

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