Un modèle de croissance pour l’azobé, Lophira alata, au Gabon

Azobé, Lophira alata, is a major timber species in Central Africa classified as vulnerable into the IUCN red list. To date, despite numerous measures of increment, no growth model has been published for this species. This study aims to distinguish the effects between tree size and local competition on tree growth. A growth model was fitted for azobé, using data from four sites in Gabon. The growth model was designed to be useful for forest management that means it relied on variables that could be computed using forest inventory data. A lognormal growth model with a negative response to stand density and basal area has been selected. The relation between growth and size was unimodal with a maximum at 60 cm of diameter at breast height. A significant residual social status effect on growth has been found (with a slower growth for suppressed trees) while no residual site effect was found

A growth model for azobe, Lophira alata, in Gabon

Azobé, Lophira alata, is a major timber species in Central Africa classified as vulnerable into the IUCN red list. To date, despite numerous measures of increment, no growth model has been published for this species. This study aims to distinguish the effects between tree size and local competition on tree growth. A growth model was fitted for azobé, using data from four sites in Gabon. The growth model was designed to be useful for forest management that means it relied on variables that could be computed using forest inventory data. A lognormal growth model with a negative response to stand density and basal area has been selected. The relation between growth and size was unimodal with a maximum at 60 cm of diameter at breast height. A significant residual social status effect on growth has been found (with a slower growth for suppressed trees) while no residual site effect was found

A growth model for azobe, Lophira alata, in Gabon

Azobé, Lophira alata, is a major timber species in Central Africa classified as vulnerable into the IUCN red list. To date, despite numerous measures of increment, no growth model has been published for this species. This study aims to distinguish the effects between tree size and local competition on tree growth. A growth model was fitted for azobé, using data from four sites in Gabon. The growth model was designed to be useful for forest management that means it relied on variables that could be computed using forest inventory data. A lognormal growth model with a negative response to stand density and basal area has been selected. The relation between growth and size was unimodal with a maximum at 60 cm of diameter at breast height. A significant residual social status effect on growth has been found (with a slower growth for suppressed trees) while no residual site effect was found

Artificial infestations of Tapinanthus ogowensis (Engler) Danser (Loranthaceae) on three host species in the Logbessou Plateau (Douala, Cameroon)

In Cameroon today, Loranthaceae has become a major pest against which a great "battle" must be launched if food production in the country has to be maintained at a self-sufficient level. However, an effective battle against pests can only be achieved through a better understanding of their geographical distribution and biology. Eight Loranthaceae species (Globimetula braunii, Globimetula dinklagei, Globimetula opaca, Helixanthera mannii, Phragmanthera capitata, Tapinanthus globiferus, Tapinanthus ogowensis, and Tapinanthus preussii) have been identified in the Douala area. Among these species, T. ogowensis is the only one limited to a surface area of about eight hectares in the Logbessou plateau located in a direction of North-East from Douala (Latitude 03°40 -04°11' N, Longitude 09°16' -09°52' E, and at an altitude of 13 m). In this zone, the hemi-parasite infests only one host tree (Dacryodes edulis) in the orchards, gardens and agricultural plantations. The hemiparasite is however common and adapted to all the different ecological regions in the southern part Cameroon where it infests several host trees. In order to study the stages involved in the germination, fixation, as well as the initial stages involved in the development of the seedlings of T. ogowensis, three of the most frequent host species (D. edulis, Mangifera indica and Persea americana) on the plateau were artificially infected. The results revealed that the host species are sensitive to the parasite, T. ogowensis, at least during their early stages of growth and development. D. edulis is the most sensitive host species with a 22% yield of young seedlings as against 5 and 4% for P. americana and M. indica, respectively. This sensitivity of the mango tree to T. ogowensis had never been demonstrated before. The percentages of seeds germinating on the different host species however remained high; 96% on both D. edulis and M. indica and 93% on P. americana. It was also revealed that the development of the young seedlings of T. ogowensis is greatly influenced by the availability of light, a plausible reason why Loranthaceae occupies mainly the uppermost branches of the oldest trees found here

Using Model Analysis to Unveil Hidden Patterns in Tropical Forest Structures

peer reviewedWhen ordinating plots of tropical rain forests using stand-level structural attributes such as biomass, basal area and the number of trees in different size classes, two patterns often emerge: a gradient from poorly to highly stocked plots and high positive correlations between biomass, basal area and the number of large trees. These patterns are inherited from the demographics (growth, mortality and recruitment) and size allometry of trees and tend to obscure other patterns, such as site differences among plots, that would be more informative for inferring ecological processes. Using data from 133 rain forest plots at nine sites for which site differences are known, we aimed to filter out these patterns in forest structural attributes to unveil a hidden pattern. Using a null model framework, we generated the anticipated pattern inherited from individual allometric patterns. We then evaluated deviations between the data (observations) and predictions of the null model. Ordination of the deviations revealed site differences that were not evident in the ordination of observations. These sites differences could be related to different histories of large-scale forest disturbance. By filtering out patterns inherited from individuals, our model analysis provides more information on ecological processes

Integrated global assessment of the natural forest carbon potential

Forests are a substantial terrestrial carbon sink, but anthropogenic changes in land use and climate have considerably reduced the scale of this system 1. Remote-sensing estimates to quantify carbon losses from global forests 2–5 are characterized by considerable uncertainty and we lack a comprehensive ground-sourced evaluation to benchmark these estimates. Here we combine several ground-sourced 6 and satellite-derived approaches 2,7,8 to evaluate the scale of the global forest carbon potential outside agricultural and urban lands. Despite regional variation, the predictions demonstrated remarkable consistency at a global scale, with only a 12% difference between the ground-sourced and satellite-derived estimates. At present, global forest carbon storage is markedly under the natural potential, with a total deficit of 226 Gt (model range = 151–363 Gt) in areas with low human footprint. Most (61%, 139 Gt C) of this potential is in areas with existing forests, in which ecosystem protection can allow forests to recover to maturity. The remaining 39% (87 Gt C) of potential lies in regions in which forests have been removed or fragmented. Although forests cannot be a substitute for emissions reductions, our results support the idea 2,3,9 that the conservation, restoration and sustainable management of diverse forests offer valuable contributions to meeting global climate and biodiversity targets