Tropical Forests In Africa Research Articles

Les grands singes : qui sont-ils ? Sont-ils capables d’automédication ?

Six great ape species (chimpanzees, bonobos, Western gorillas, Eastern gorillas, Sumatran orangutans and Bornean orangutans) live in tropical forests of Africa and South-East Asia. Their habitat, severely threatened by deforestation, contains a vast chemical and biological diversity. During the last decade, we have isolated and identified novel pharmacologically active compounds from plants used by wild chimpanzees in Kibale National Park, Uganda. Our continuous observations over the last 12 years confirm that chimpanzees, when sick, may ingest plant material that are not generally eaten, supporting the existence of self-medication among great apes. Knowledge of great-ape diseases, and the medicinal resources of tropical forests, may be improved by preserving and studying our closest relatives in their natural habitat.

Allometric equations for biomass estimations in Cameroon and pan moist tropical equations including biomass data from Africa

Moist tropical forests in Africa and elsewhere store large amounts of carbon and need accurate allometric regressions for their estimation. In Africa the absence of species-specific or mixed-species allometric equations has lead to broad use of pan moist tropical equations to estimate tree biomass. This lack of information has raised many discussions on the accuracy of these data, since equations were derived from biomass collected outside Africa.Mixed-species regression equations with 71 sample trees using different input variables such as diameter, diameter and height, product of diameter and height, and wood density were developed to estimate total aboveground biomass and biomass of leaves and branches for a Cameroon forest. Our biomass data was added to 372 biomass data collected across different moist tropical forests in Asia and South America to develop new pan moist tropical allometric regressions. Species-specific and mixed-species height diameter regression models were also developed to estimate heights using 3833 trees.Using only diameter as input variable, the mixed-species regression model estimates the aboveground biomass of the study site with an average error of 7.4%. Adding height or wood density did not improve significantly the estimations. Using the three variables together improved the precision with an average error of 3.4%. For general allometric equations tree height was a good predictor variable. The best pan moist tropical equation was obtained when the three variables were added together followed by the one which includes diameter and height. This study provides height diameter relationships and wood density of 31 species. The pan moist tropical equation developed by Chave et al. (2005), estimates total aboveground biomass across different sites with an average error of 20.3% followed by equations developed in the present study with an average error of 29.5%.

The Social Life of the African Forest Yellow-Whiskered Greenbul Andropadus latirostris

A 10-year study of a population of A. latirostris showed that this greenbul behaved as a lek species in Northeastern Gaboon. Comparisons between A. latirostris and some neotropical Pipridae and Trochilidae are made, in order to establish ecological features common to lek species in tropical forests of Africa and South America.

Phylogenetics and cytology of a pantropical orchid genusPolystachya(Polystachyinae, Vandeae, Orchidaceae): Evidence from plastid DNA sequence data

AbstractThe pantropical orchid genusPolystachyais the subject of ongoing taxonomic work. We inferred phylogenetic relationships in the genus using 5.3 kb of plastid DNA, for 83 out of ca. 240 species and 12 out of 15 sections, as well as five outgroup species. We also collected ploidy data using chromosome counts and genome size estimates. Bayesian and parsimony trees were congruent with each other and well resolved.Polystachyaappears monophyletic based on current sampling, provided that the nameP. neobenthamiais used instead ofNeobenthamia gracilisfor that species. The current sectional classification does not define monophyletic groups, but the present study can be used as the basis for a future sectional classification. Areas postulated as Pleistocene refugia for wet tropical forests in Africa also form centres of diversity for the genus. Biogeographical analyses using DIVA and Lagrange show an early radiation in eastern Africa, followed by separate radiations in eastern and western Africa. Subsequent dispersal from western to eastern Africa has occurred at a much higher rate than from east to west. Dispersal to the Neotropics occurred more than once, and one lineage has spread recently and rapidly throughout the tropics. Polyploidy has occurred several times during the diversification of the genus, most notably in association with the recent pantropical dispersal.

The Afro‐Madagascan genus Warneckea (Melastomataceae): Molecular systematics and revised infrageneric classification

AbstractWarneckea consists of shrubs and small trees endemic to tropical forests in Africa, Madagascar, and Mauritius. Phylogenetic analyses of sequence data from the transcribed spacers of nuclear ribosomal DNA (ETS, ITS) indicate that W. sect. Carnosa Jacq.‐Fél. (1 sp., East Africa and Madagascar) is a divergent element that is best treated at subgeneric level. The analyses recovered three major lineages in W. subg. Warneckea, together forming a basal trichotomy. The three lineages represent W. sect. Strychnoidea (western and central Africa), sect. Warneckea (East Africa, Madagascar, Mauritius), and a third group with three West African species (W. fascicularis, W. guineensis, W. mangrovensis) comprising the newly proposed W. sect. Guineensea.

Increasing carbon storage in intact African tropical forests

The response of terrestrial vegetation to a globally changing environment is central to predictions of future levels of atmospheric carbon dioxide. The role of tropical forests is critical because they are carbon-dense and highly productive. Inventory plots across Amazonia show that old-growth forests have increased in carbon storage over recent decades, but the response of one-third of the world's tropical forests in Africa is largely unknown owing to an absence of spatially extensive observation networks. Here we report data from a ten-country network of long-term monitoring plots in African tropical forests. We find that across 79 plots (163 ha) above-ground carbon storage in live trees increased by 0.63 Mg C ha(-1) yr(-1) between 1968 and 2007 (95% confidence interval (CI), 0.22-0.94; mean interval, 1987-96). Extrapolation to unmeasured forest components (live roots, small trees, necromass) and scaling to the continent implies a total increase in carbon storage in African tropical forest trees of 0.34 Pg C yr(-1) (CI, 0.15-0.43). These reported changes in carbon storage are similar to those reported for Amazonian forests per unit area, providing evidence that increasing carbon storage in old-growth forests is a pan-tropical phenomenon. Indeed, combining all standardized inventory data from this study and from tropical America and Asia together yields a comparable figure of 0.49 Mg C ha(-1) yr(-1) (n = 156; 562 ha; CI, 0.29-0.66; mean interval, 1987-97). This indicates a carbon sink of 1.3 Pg C yr(-1) (CI, 0.8-1.6) across all tropical forests during recent decades. Taxon-specific analyses of African inventory and other data suggest that widespread changes in resource availability, such as increasing atmospheric carbon dioxide concentrations, may be the cause of the increase in carbon stocks, as some theory and models predict.

Aggregated seed dispersal by wreathed hornbills at a roost site in a moist evergreen forest of Thailand

AbstractHornbills (Bucerotidae) are widely regarded as important seed dispersers in tropical forests in Africa and Asia. We investigated how the roosting behavior of wreathed hornbills (Aceros undulatus) influences seed deposition and seedling survival at a roost site in a moist evergreen forest of Khao Yai National Park, Thailand. Fallen fruits and seeds were collected in traps that were placed around a roosting site for 14 months, and seedlings were monitored in adjacent quadrats for 3 years. Seedfall and seedlings of species represented in the hornbill diet occurred at significantly higher densities in the traps and quadrats located beneath the crown of the roosting tree than in those located beyond the crown. With the exception of Cinnamomum subavenium, the seeds and seedlings of most diet species rarely survived beyond the first year. The quality of hornbill dispersal to this roosting site may be poor due to the highly concentrated seedfall, which results in high seed and seedling mortality. However, the number of seeds deposited by each hornbill each day at roosting sites is relatively low. Wreathed hornbills are primarily scatter dispersers during the day and probably serve as agents of seed dispersal in the moist evergreen forest of Khao Yai.

Managing the tropical landscape: a comparison of the effects of logging and forest conversion to agriculture on ants, birds, and lepidoptera

Most tropical forest will not be conserved, but instead will be used in some way, most often for logging, agriculture, or both. Management of tropical forest landscapes for diversity depends upon an understanding of how many and which species can persist in different types of managed ecosystems. I compared the effects of logging and conversion of forest to agriculture or pasture on ant, bird, and lepidoptera species richness by combining data from 34 studies from tropical forests in Africa, Asia, and the Americas. Forest conversion to agriculture or pasture decreased the species richness of ants and of animals overall, whereas logging did not decrease species richness overall or of ants, birds or lepidoptera. After sites were abandoned, the diversity of logged sites did not change over time. In contrast, the diversity of old fields increased with time. Ants, birds, and lepidoptera responded similarly to forest clearance or disturbance, whether it be for logging or conversion to agriculture or pasture. In terms of faunal diversity, selective logging appears to have much less impact on faunal diversity than does forest conversion, both initially and after sites are abandoned.

State and change in carbon pools in the forests of tropical Africa

To improve estimates of the state and change in C pools due to changes in land use in tropical forests of Africa, we combined spatially explicit estimates of biomass C density, obtained by modelling in a geographical information system (GIS), with new data on the area of forests (woody formations with a minimum of 10% crown cover) reported at subnational units for 1980 and 1990 by the Food and Agriculture Organization (FAO). Estimates of the biomass C densities for grass/shrub savannas were also included using a simple model based on precipitation. The total C pool in above– and below–ground forests and grass/shrub savannas of Africa for 1980 was 50.8 Pg (1015g), with aboveground forest biomass accounting for 75% of the total, below–ground forest biomass for 21%, and grass/shrub savannas for 4%. Area weighted mean biomass C densities were about 180 Mg ha–1 for lowland moist forests, 82 Mg ha–1 for all forests, and 6 Mg ha–1 for grass savannas. The total change in the aboveground forest C pool for the decade 1980–90 due to changes in land cover and use was estimated to be a decrease of 6.6 Pg C. Of this total, 43% was due to deforestation and 57% due to biomass reduction by other human activities. Six countries, mostly in central Africa, accounted for more than 73% of the total change in the C pool. The difference between state and change of C pool estimates made at the subnational scale and those made at the national scale proved to be insignificant across the region as a whole (2% for pools and – 1% for change in pool) but potentially important to individual countries (from + 36% to – 39% for pools and from + 43% to – 57% for change in pool). The differences between the two approaches may reflect a better match of the areas being deforested with the biomass C density of forests being cleared.

Conservation and the Development of National Parks in the Humid Tropics of Africa

The diverse humid forests of tropical Africa are on the verge of destruction and the few protected areas are also under threat from illegal land and resource use. The conservation history of these forests dates from about 85 years ago but game and forest reserves have not protected the ecosystems. The humid lowland forests have always been perceived as lacking any potential for tourism and are known to have valuable resources. Thus, few of the humid lowland forests were protected after the major conservation initiatives of 1933 and 1961. Increasing con- cern for the protection of lowland humid forests led to several large national parks being created in the years 1966-74 but few were established in the most threatened forests of West Africa and none in East Africa. The high cost of national park development and the unlikely possibility of tourism has led to biosphere reserves being favoured and it is suggested that these are likely to be more successful than national parks. Specialized forms of tourism are successful in the montane forests however, and the future of national parks in these areas would seem to be assured. The high cost of protecting and managing national parks suggests that unless inter- national financial aid is available, those that have already been established may have an uncertain future. It is proposed that only one large national park is required in each country within the lowland humid forests and that biosphere reserves are more appropriate for other conserved areas in these

Evolutionary Ecology of Afrotropical and Neotropical Vultures in Forests

Several species of vultures are commonly found in neotropical forests, but none has occupied the forested regions of the Old World. It is suggested that a greater abundance of food for large scavenging animals may exist in New World forests because of their higher mammalian biomass and the complexity of their invertebrate communities. Cathartid vultures are highly efficient at searching for food and may be the major scavengers of large mammal carcasses in the neotropical forest. RESUMEN. Se encuentran varias especies de buitres en bosques neotropicales, pero ninguno ha ocupado regiones boscosas en el Viejo Mundo. Se sugiere que la mayor abundancia de comida para animales carroneros, existente en los bosques del Nuevo Mundo se deberia a su mayor biomasa de mamiferos y a la complejidad de su comunidad de invertebrados. Los buitres de la familia Cathartidae son muy eficientes buscando comida y pueden ser los mayores carroneros de carcasas de mamiferos grandes en los bosques neotropicales. Vultures differ from other meat eating birds in that they virtually never kill their prey, but obtain almost all food by scavenging from dead animals. This method of feeding has been exploited by two groups of birds, the New World vultures and the Old World vultures, which are quite unrelated. The 1 5 species of vultures that are found in Africa, Asia and southern Europe are classified in the family Accipitridae together with the eagles and hawks to which they are obviously closely related (Brown and Amadon 1968). The seven species of New World vultures, however, appear to show affinities to the storks, family Ciconiidae (Ligon 1967; Feduccia 1980); these Cathartid vultures are usually placed for convenience as a suborder within the Falconiformes (Brown and Amadon 1968), although it is widely recognized that they do not belong there (Voous 1973). Despite their different ancestry, the two groups of modern vultures are extremely similar in superficial appearance. They are textbook examples of convergent evolution. Both groups have a similar diversity of species, and share many aspects of plumage pattern and a common dependence on soaring flight. In contrast, the habitats occupied by these two vulture groups are markedly different in one respect. The Old World vultures are confined to open habitats such as savannas, grasslands, and semideserts, and none of these species is found in any of the forested areas of Africa or Asia. Among the New World vultures, the two species of condors (Gymnogyps californianus and Vultur gryphus) live in mountainous areas. The five smaller Cathartid vultures, however, have centers of distribution in the neotropical forest region and several species live in dense forest conditions. In this review I consider some possible reasons why neotropical forests are able to support several species of vultures, whereas the tropical forests of Africa and Asia support none; this implies that the scavenger food chains in the two regions of forest may differ significantly. I first briefly consider the evolutionary history of the two vulture groups, and then consider the potential size of the food supply for scavenging animals in forested areas, the potential competition among scavengers for this resource, and finally the comparative efficiency of vultures at locating food. Little information is available about the ecology of any of the Cathartid vultures in forested regions; thus many of these considerations are tentative, and much of what follows is speculation. EVOLUTIONARY HISTORY OF VULTURES The fossil record of both vulture groups is comparatively good (Brodkorb 1964; Rich 1983). Thus, we know that although today the New World vultures and the Old World vultures are clearly separated geographically, they did not develop in isolation; fossil New World species have been found in the Old World, and similarly fossil Old World species have been found in the New World. Ten Old World species from four genera have been discovered from the