The effects of commercial mechanised selective logging on a transect in lowland rainforest in the Lopé Reserve, Gabon

Seasonality and interindividual variation in mandrill feeding ecology revealed by stable isotope analyses of hair and blood

Mandrills are large-bodied terrestrial forest primates living in particularly large social groups of several hundred individuals. Following these groups in the wild to assess differences in diet over time as well as among individuals is demanding. We here use isotope analyses in blood and hair obtained during repeated captures of 43 identified free-ranging mandrills (Mandrillus sphinx) from Southern Gabon, to test how dietary variation relates to the season as well as an individual's age and sex. We measured the stable carbon (δ¹³ C‰) and nitrogen (δ¹⁵ N‰) isotope ratios in 46 blood and 214 hair section samples as well as from a small selection of mandrill foods (n = 24). We found some seasonal isotopic effects, with lower δ¹³ C values but higher δ¹⁵ N values observed during the highly competitive long dry season compared to the fruit-rich long rainy season. Variation in δ¹³ C was further predicted by individual age, with higher δ¹³ C values generally found in younger individuals suggesting that they may consume more high canopy fruit than older individuals, or that older individuals consume more low canopy foliage. The best predictor for δ¹⁵ N values was the interaction between age and sex, with mature and reproductively active males revealing the highest δ¹⁵ N values, despite the observation that males consume substantially less animal food items than females. We interpret high δ¹⁵ N values in these mature male mandrill blood and hair sections to be the result of nutritional stress associated with intense male-male competition, particularly during mating season. This is the first study showing isotopic evidence for nutritional stress in a free-ranging primate species and may spark further investigations into male mandrill diet and energy balance.

Looking beyond parks: the conservation value of unprotected areas for hornbills in Arunachal Pradesh, Eastern Himalaya

The loss of tropical forests and associated biodiversity is a global concern. Conservation efforts in tropical countries such as India have mostly focused on state-administered protected areas despite the existence of vast tracts of forest outside these areas. We studied hornbills (Bucerotidae), an ecologically important vertebrate group and a flagship for tropical forest conservation, to assess the importance of forests outside protected areas in Arunachal Pradesh, north-east India. We conducted a state-wide survey to record encounters with hornbills in seven protected areas, six state-managed reserved forests and six community-managed unclassed forests. We estimated the density of hornbills in one protected area, four reserved forests and two unclassed forests in eastern Arunachal Pradesh. The state-wide survey showed that the mean rate of encounter of rufous-necked hornbills Aceros nipalensis was four times higher in protected areas than in reserved forests and 22 times higher in protected areas than in unclassed forests. The mean rate of encounter of wreathed hornbills Rhyticeros undulatus was twice as high in protected areas as in reserved forests and eight times higher in protected areas than in unclassed forests. The densities of rufous-necked hornbill were higher inside protected areas, whereas the densities of great hornbill Buceros bicornis and wreathed hornbill were similar inside and outside protected areas. Key informant surveys revealed possible extirpation of some hornbill species at sites in two protected areas and three unclassed forests. These results highlight a paradoxical situation where individual populations of hornbills are being lost even in some legally protected habitat, whereas they continue to persist over most of the landscape. Better protection within protected areas and creative community-based conservation efforts elsewhere are necessary to maintain hornbill populations in this biodiversity-rich region.

Certified and uncertified logging concessions compared in Gabon: changes in stand structure, tree species, and biomass

Forest management certification is assumed to promote sustainable forest management, but there is little field-based evidence to support this claim. To help fill this gap, we compared a Forest Stewardship Council (FSC)-certified with an adjacent uncertified, conventionally logged concession (CL) in Gabon on the basis of logging damage, above-ground biomass (AGB), and tree species diversity and composition. Before logging, we marked, mapped, and measured all trees >10 cm dbh in 20 and twelve 1-ha permanent plots in the FSC and CL areas, respectively. Soil and tree damage due to felling, skidding, and road-related activities was then assessed 2-3 months after the 508 ha FSC study area and the 200 ha CL study area were selectively logged at respective intensities of 5.7 m(3)/ha (0.39 trees/ha) and 11.4 m(3)/ha (0.76 trees/ha). For each tree felled, averages of 9.1 and 20.9 other trees were damaged in the FSC and CL plots, respectively; when expressed as the impacts per timber volume extracted, the values did not differ between the two treatments. Skid trails covered 2.9 % more of the CL surface, but skid trail length per unit timber volume extracted was not greater. Logging roads were wider in the CL than FSC site and disturbed 4.7 % more of the surface. Overall, logging caused declines in AGB of 7.1 and 13.4 % at the FSC and CL sites, respectively. Changes in tree species composition were small but greater for the CL site. Based on these findings and in light of the pseudoreplicated study design with less-than perfect counterfactual, we cautiously conclude that certification yields environmental benefits even after accounting for differences in logging intensities.

Spatial patterns of tree recruitment in East African tropical forests that have lost their vertebrate seed dispersers

The direct removal of adult trees by logging affects tree recruitment in tropical rain forests. However, secondary effects of logging, such as loss of vertebrate seed dispersers may also affect tree recruitment. We studied the recruitment and spatial distribution of five tree species namely Balanites wilsoniana, Celtis zenkeri, Chrysophyllum albidum, Cordia millenii and Ricinodendron heudelotii in Kibale, Budongo and Mabira Forests in Uganda. These forests have been subjected to varying degrees of disturbance leading to changes in their vertebrate seed dispersers. Vertebrate frugivores of the five tree species were identified. Three 1-ha plots were established around adult trees of the same five species in each forest and the distance from the juveniles to the nearest adult conspecific was measured to generate a recruitment curve. Frugivore visitation rates were high in the less disturbed Budongo and Kibale (2.2 and 1.6 individuals h−1 respectively) compared with the highly disturbed Mabira (0.9 individuals h−1). In the frugivore-impoverished forest, 70–90% of juveniles established beneath adult conspecifics, whereas in the less-disturbed forests juveniles were established up to 80 m from adult conspecifics. Shade-tolerant species capable of recruiting beneath adult conspecifics appeared to maintain their populations without dispersal. Consequently, disturbances leading to significant loss of vertebrates may alter tree recruitment and spatial distribution with consequences for long-term population viability of shade-intolerant tropical trees.

The threat to primates and other mammals from the bushmeat trade in Africa, and how this threat could be diminished

The threat that the bushmeat trade presents to primates and other taxa was assessed from the literature, including data from markets, village hunting studies and logging concessions in Central and West Africa. In many cases the numbers of both common and protected species of primate being killed throughout the region are thought to be unsustainable. This is also the case for other taxa involved in the bushmeat trade, which crosses geographic, cultural and economic boundaries. A suite of measures must be considered to mitigate the effects of this trade, and these measures will have to recognize the local, regional and national socio-economic importance of the trade if they are to result in long-term conservation success.

Influence of Timber Extraction Routes on Central African Small-Mammal Communities, Forest Structure, and Tree Diversity

Despite increasing pressure to harvest timber from African tropical forests, the short- and long-term ecological effects of qualitative and quantitative variation in extraction practices rarely have been examined. At a site in the southwestern Central African Republic, we surveyed rodent and tree communities and vegetation structure in unlogged forest and along skid trails and secondary and primary access roads at 12 and 19 years after logging. The most important source of variation among transects was the type of logging road: primary and secondary access roads showed the greatest change and skid trails the least. An intercorrelated suite of changes occurred along the margins of the roads, including changes in rodent community composition, increases in rodent abundance and diversity, changes in the height distribution of rodent abundance, increases in understory foliage density, and decreases in sapling density and tree species richness. Ecological changes along the secondary roads were nearly as strong as those along primary roads, despite the fact that secondary roads had been abandoned immediately after logging, whereas primary roads had been traveled up to the time of the research. Continuing edge-induced effects along graded road margins at between 12 and 19 years after logging were indicated by differences in tree species composition, sapling and tree densities, and understory density. Our results support conclusions of increased disturbance to rainforest communities with increasingly destructive road construction techniques and suggest that canopy damage rather than stem damage is the most appropriate measure of logging damage. Although minimizing the length of access roads is important in reducing ecological effects, it should not be achieved at the expense of increased canopy damage. Rodent communities appear to be an easily measured indicator of these ecological changes and may be responsive to landscape-level changes in forest cover and degradation.

Forests without primates: primate/plant codependency

Detailed studies of primates and fruiting trees have illustrated that these groups of organisms are involved in a very complex set of interactions, with primates relying on fruiting trees as important food resources and fruiting trees relying on frugivores for seed dispersal. Human activities that influence either primate seed dispersal or fruit production have the potential of having unanticipated effects on the other interactants. Here we evaluate what is known and what we still need to learn to evaluate the long-term consequences of disrupting the interactions between primates and tropical forest trees. We do this by first assessing the potential importance of primates at dispersing the seeds of tropical forest trees. Second, we consider possible consequences of hunting primates on recruitment in tropical tree communities. Third, we address the converse by considering the impacts of decreasing resource availability for primates through either logging or through the extraction of nontimber forest products. Finally, we provide a case study from Kibale National Park, Uganda, that contrasts seedling recruitment in 20 forest fragments in which primate seed dispersers have been dramatically reduced with seedling recruitment in areas that have an intact frugivore community. In comparison to the intact forest, the fragments had lower seedling density and fewer species of seedlings. Furthermore, a greater proportion of the seedlings were from small-seeded species that might not require primates for their dispersal, since they probably can be dispersed by small birds. All of these considerations suggest that disrupting the complex interactions between primates and fruiting trees can potentially have negative and possibly cascading effects on ecosystem processes.

Habitat alteration and the conservation of African primates: case study of Kibale National Park, Uganda

Tropical forests and the animals they support are being threatened by accelerating rates of forest conversion and degradation. In a continually fluctuating sociopolitical world, it is often impossible to protect areas from such conversion until the political environment is suitable to pursue conservation goals, by which time, the forests have often been converted to other uses. This reality suggests a need for inquiry into which primate species can persist after different types of disturbances and how quickly primate communities can recover from disturbance. Here we examine the persistence of primate populations in disturbed habitats by providing a case study of patterns of primate abundance in areas of Kibale National Park (766 km2), Uganda, that have been modified by different types and intensities of human activities, primarily commercial logging and agricultural clearing. Distributional surveys at 24 sites and detailed line-transect censuses at six sites demonstrate that primate populations in Kibale are often high and suggest that patterns of population change associated with disturbance are complex. Analysis of the land use coverage of Kibale reveals that abandoned farms (10.3%) and degraded forest (8.7%) now cover 146 km2. Unfortunately, we do not know what proportion of the farms were established on areas that were forest versus grassland. However, if the areas that are now abandoned farms were all once forested, this means that 79 km2 of forest has been lost. Based on density estimates from nearby sites, this would represent a loss of 52,612 monkeys and 200 chimpanzees. Populations would also have been affected by the degradation of the 66 km2 (8.7%) of forest. These estimates of the potential reductions in the primate populations that could have resulted from forest clearing and degradation illustrate the importance of protecting land. A review of the literature illustrates that the biomass of primates found within Kibale is very high in comparison to other locations and thus illustrates the importance of Kibale to regional conservation.

Tree species diversity in commercially logged bornean rainforest

The effects of commercial logging on tree diversity in tropical rainforest are largely unknown. In this study, selectively logged tropical rainforest in Indonesian Borneo is shown to contain high tree species richness, despite severe structural damage. Plots logged 8 years before sampling contained fewer species of trees greater than 20 centimeters in diameter than did similar-sized unlogged plots. However, in samples of the same numbers of trees (requiring a 50 percent larger area), logged forest contained as many tree species as unlogged forest. These findings warrant reassessment of the conservation potential of large tracts of commercially logged tropical rainforest.