Quantitative and qualitative loss of tropical forests prompted international policy agendas to slow down forest loss through reducing emissions from deforestation and forest degradation (REDD)+, ensuring carbon offset payments to developing countries. So far, many African countries lack reliable forest carbon data and monitoring systems as required by REDD+. In this study, we estimate the carbon stocks of a naturally forested landscape unaffected by direct human impact. We used data collected from 34 plots randomly distributed across the Mount Birougou National Park (690 km2) in southern Gabon. We used tree-level data on species, diameter, height, species-specific wood density and carbon fraction as well as site-level data on dead wood, soil and litter carbon to calculate carbon content in aboveground, belowground, dead wood, soil and litter as 146, 28, 14, 186 and 7 Mg ha−1, respectively. Results may serve as a benchmark to assess ecosystem carbon loss/gain for the Massif du Chaillu in Gabon and the Republic of Congo, provide field data for remote sensing and also may contribute to establish national monitoring systems.ResumeLes pertes qualitatives et quantitatives de forêt tropicale ont poussé les calendriers politiques internationaux à ralentir la perte de forêts au moyen des mécanismes REDD+, qui garantissent le paiement compensatoire des émissions de carbone aux pays en développement. Jusqu'à présent, de nombreux pays africains ne disposent pas encore de données fiables sur le carbone forestier, pas plus que de systèmes de suivi exigés par les REDD+. Dans cet article, nous estimons les stocks de carbone d'un paysage de forêt naturelle non affecté par des impacts humains directs. Nous avons utilisé les données provenant de 34 parcelles réparties au hasard dans le Parc National du Mont Birougou (690 km²), dans le sud du Gabon. Nous avons utilisé trois niveaux de données pour les espèces, le diamètre, la hauteur et la densité spécifique du bois par espèce, et la fraction de carbone ainsi que des données au niveau du site sur le carbone du bois mort, du sol et de la litière pour calculer le contenu en carbone au-dessus du sol, en dessous, dans le bois mort, le sol et la litière, à savoir, respectivement, 146, 28, 14, 186 et 7 mg ha−1. Ces résultats peuvent servir de données de référence pour évaluer la perte ou le gain de carbone de l'écosystème pour le Massif du Chaillu, au Gabon, et en République du Congo, constituer des données de terrain pour la détection à distance et aussi contribuer à établir des systèmes de suivi au niveau national.

Holocene climate change caused disturbances of the Central African rainforest belt, with decrease in forest area during drier conditions followed by expansion during wetter periods. Today, human impact is a driver for forest degradation in the Congo Basin. For assessing the quality and quantity of forest degradation, information on biodiversity and carbon stocks from reference ecosystems is needed which (1) were not affected by Holocene climate change and (2) lack direct human impacts like logging or shifting cultivation. The Birougou Mountains in Gabon, which were devoid of direct human impact over the last centuries, may resemble such a reference ecosystem. This paper tests the hypothesis that the Birougou Mountains served as refugium for rainforest vegetation during periods of Holocene climate change. For 34 forest plots within the Birougou Mountains and 27 savannah plots within an adjacent forest savannah mosaic, we present stable carbon isotope data from current vegetation cover, organic inputs to soil organic carbon (SOC), bulk SOC and the humic acid fraction of SOC. Additionally, we estimated the mean age of the SOC humic acid fraction by 14 C dating. The data indicated a continuous forest cover in the Birougou Mountains since -at least -the Holocene climate optimum, but a change from forest to savannah vegetation in the forest savannah mosaic. Results confirm the forest of the Birougou Mountains as a refugium of rainforest vegetation and suitable reference for the natural potential regarding biodiversity and ecosystem carbon stocks.

The accurate prediction of the volume of standing trees is a prerequisite for planning and decision making in sustainable forest management. In Nepal, limited information on form factor (i.e. the ratio of the volume of a tree to the product of its basal area and height) is available for economically important tree species. Thus, current management plans consider a simple approximation for all species irrespective of their height and diameter, which hampers the estimation of a sustainable harvest rate. Therefore, this study elaborates the form factor for Sal (Shorea robusta), an economically valuable tree of Nepal based on a random selection of 100 individual trees representing a wide range of diameters between 10 and 100 cm. Diameter and bark thickness were measured at every 1-meter interval of the length of the stem and branches until the diameter reached 10 cm. The analysis allowed for the estimation of an average form factor for Sal wood with 0.407 over bark and 0.336 under bark, while the form factor for the stem was 0.335 over bark and 0.281 under bark. The results indicate an increasing form factor until 70 cm diameter and a decreasing value for larger diameters, because of the large crowns of the mature Sal trees. We conclude that the default form factor of Sal (0.5) used in management planning results in an overestimation of standing tree volume. Using form factor according to diameter classes will allow a more accurate prediction of the standing volume.

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The authors found some minus signs were omitted in Table 4 and the Equations (1) and (8), and have requested that the following changes be made to their paper [...]