Plant biodiversity and vegetation structure in traditional cocoa forest gardens in southern Cameroon under different management

Floristic surveys were performed in 17 traditional cocoa forest gardens under different management regimes in the humid forest area of southern Cameroon, to assess the impact of intensification on plant biodiversity. This impact was evaluated by analyzing species richness, vegetation structure, carbon sequestration and above ground biomass. We hypothesize that: (a) plant (tree and herbs) species richness is negatively correlated to management intensity and (b) vegetational density predictably change with management intensity. Our results show that management as practiced in traditional cocoa forest gardens in southern Cameroon following a gradient of intensification from extensive cocoa forest gardens with high floristic diversity to intensive ones strongly impacts plant diversity, plant biomass and to some extend carbon storage with possible negative consequences on biodiversity. Great differences in species richness, species composition, and, for trees, diameter at breast height and basal area were evident among the five types of traditional cocoa forest garden systems investigated. In terms of plant species richness, we found a decreasing gradient of plant species numbers from extensive forest gardens to intensive ones. This study also highlights the importance of the Management Index for quantifying differences in the management; this index could be used to standardize certification procedures and assess conservation progress and success. Our findings support the idea that traditional cocoa forest gardens can help to protect many forest species, sustains smallholder production and offer more scope for conservation of biodiversity, at both species-level and landscape-level. Moreover, diverse traditional cocoa forest gardens may help in regulating pests and diseases and allow for efficient adaptation to changing socioeconomic conditions.     

Cocoa farms in the Mount Cameroon region: biological and cultural diversity in local livelihoods

A study was undertaken around Mt Cameroon to examine the role of biological and cultural diversity in the livelihood strategies of indigenous villagers and migrants to the region. Surveys of resources consumed and sold by 118 households were undertaken in five villages over the course of 1 year, the perspectives and practices of cocoa farmers documented, and useful tree species retained or planted on six cocoa farms mapped. Cocoa farms in this region generate more significant benefits for biodiversity conservation and local livelihoods than commercial plantations, but also place pressure on forest reserves and require chemical inputs. Roughly 50 tree species are commonly retained or planted on cocoa farms, primarily for timber or food, with many of these having high conservation value. Average tree density of non-cocoa trees was 15 trees per hectare, with tree densities higher, and a larger percentage of species used, on indigenous Bomboko farms than migrant farms. Both migrant and indigenous households rely on forest as a complement to farm income, but indigenous households do this to a far greater extent, while also making extensive use of fallow and home gardens. Indigenous households also derive roughly four times the income from wild and native species compared to migrants. While diversified cocoa farms contribute to conservation and livelihoods in the region, indigenous livelihoods grow from and require the conservation of a broader range of species and habitats, including natural forest.     

Conserving forest tree diversity in Guinée Forestière (Guinea,West Africa): the role of coffee-based agroforests

In the current deforestation context, agroforestry is increasingly considered in the tropical zone for its potential contribution to biodiversity conservation. In Guinée Forestière (Guinea, West Africa), coffee-based species rich agroforests are currently expanding on agricultural land around most villages. To assess the role these agroforests play with respect to biodiversity conservation, we compared their tree structure and diversity with those of a neighbouring natural forest. Eighty plots were sampled using a variable area transect method (60 plots distributed into 3 village agroforests, 20 natural forest plots). The structure of coffee-based agroforests showed obvious signs of farmers’ management: density of mature trees was significantly lower than in natural forest and most juvenile trees were eliminated and replaced by coffee trees. However, tree seedling density was not significantly different than in natural forest. Tree species richness and diversity were also lower than in natural forest but much higher than in any other agricultural or agroforestry land use system. These results are close to those obtained in the coffee-based agroforests of Central America, confirming that coffee-based agroforests retain many forest species that play a key role in the conservation of regional forest tree diversity.     

The invasive Yellow Crazy Ant and the decline of forest ant diversity in Indonesian cacao agroforests

Throughout the tropics, agroforests are often the only remaining habitat with a considerable tree cover. Agroforestry systems can support high numbers of species and are therefore frequently heralded as the future for tropical biodiversity conservation. However, anthropogenic habitat modification can facilitate species invasions that may suppress native fauna. We compared the ant fauna of lower canopy trees in natural rainforest sites with that of cacao trees in agroforests in Central Sulawesi, Indonesia in order to assess the effects of agroforestry on occurrence of the Yellow Crazy Ant Anoplolepis gracilipes, a common invasive species in the area, and its effects on overall ant richness. The agroforests differed in the type of shade-tree composition, tree density, canopy cover, and distance to the village. On average, 43% of the species in agroforests also occurred in the lower canopy of nearby primary forest and the number of forest ant species that occurred on cacao trees was not related to agroforestry characteristics. However, A. gracilipes was the most common non-forest ant species, and forest ant richness decreased significantly with the presence of this species. Our results indicate that agroforestry may have promoted the occurrence of A. gracilipes, possibly because tree management in agroforests negatively affects ant species that depend on trees for nesting and foraging, whereas A. gracilipes is a generalist when it comes to nesting sites and food preference. Thus, agroforestry management that includes the thinning of tree stands can facilitate ant invasions, thereby threatening the potential of cultivated land for the conservation of tropical ant diversity.     

Ecological outcomes of agroforests and restoration 15 years after planting

Large‐scale forest restoration relies on approaches that are cost‐effective and economically attractive to farmers, and in this context agroforestry systems may be a valuable option. Here, we compared ecological outcomes among (1) 12–15‐year‐old coffee agroforests established with several native shade trees, (2) 12–15‐year‐old high‐diversity restoration plantations, and (3) reference old‐growth forests, within a landscape restoration project in the Pontal do Paranapanema region, in the Atlantic Forest of southeastern Brazil. We compared the aboveground biomass, canopy cover, and abundance, richness, and composition of trees, and the regenerating saplings in the three forest types. In addition, we investigated the landscape drivers of natural regeneration in the restoration plantations and coffee agroforests. Reference forests had a higher abundance of trees and regenerating saplings, but had similar levels of species richness compared to coffee agroforests. High‐diversity agroforests and restoration plantations did not differ in tree abundance. However, compared to restoration plantations, agroforests showed higher abundance and species richness of regenerating saplings, a higher proportion of animal‐dispersed species, and higher canopy cover. The abundance of regenerating saplings declined with increasing density of coffee plants, thus indicating a potential trade‐off between productivity and ecological benefits. High‐diversity coffee agroforests provide a cost‐effective and ecologically viable alternative to high‐diversity native tree plantations for large‐scale forest restoration within agricultural landscapes managed by local communities, and should be included as part of the portfolio of reforestation options used to promote the global agenda on forest and landscape restoration.     

Shade Tree Diversity,Cocoa Pest Damage,Yield Compensating Inputs and Farmers' Net Returns in West Africa

Cocoa agroforests can significantly support biodiversity, yet intensification of farming practices is degrading agroforestry habitats and compromising ecosystem services such as biological pest control. Effective conservation strategies depend on the type of relationship between agricultural matrix, biodiversity and ecosystem services, but to date the shape of this relationship is unknown. We linked shade index calculated from eight vegetation variables, with insect pests and beneficial insects (ants, wasps and spiders) in 20 cocoa agroforests differing in woody and herbaceous vegetation diversity. We measured herbivory and predatory rates, and quantified resulting increases in cocoa yield and net returns. We found that number of spider webs and wasp nests significantly decreased with increasing density of exotic shade tree species. Greater species richness of native shade tree species was associated with a higher number of wasp nests and spider webs while species richness of understory plants did not have a strong impact on these beneficial species. Species richness of ants, wasp nests and spider webs peaked at higher levels of plant species richness. The number of herbivore species (mirid bugs and cocoa pod borers) and the rate of herbivory on cocoa pods decreased with increasing shade index. Shade index was negatively related to yield, with yield significantly higher at shade and herb covers<50%. However, higher inputs in the cocoa farms do not necessarily result in a higher net return. In conclusion, our study shows the importance of a diverse shade canopy in reducing damage caused by cocoa pests. It also highlights the importance of conservation initiatives in tropical agroforestry landscapes.     

Tree Spatial Structure,Host Composition and Resource Availability Influence Mirid Density or Black Pod Prevalence in Cacao Agroforests in Cameroon

Combining crop plants with other plant species in agro-ecosystems is one way to enhance ecological pest and disease regulation mechanisms. Resource availability and microclimatic variation mechanisms affect processes related to pest and pathogen life cycles. These mechanisms are supported both by empirical research and by epidemiological models, yet their relative importance in a real complex agro-ecosystem is still not known. Our aim was thus to assess the independent effects and the relative importance of different variables related to resource availability and microclimatic variation that explain pest and disease occurrence at the plot scale in real complex agro-ecosystems. The study was conducted in cacao (Theobroma cacao) agroforests in Cameroon, where cocoa production is mainly impacted by the mirid bug, Sahlbergella singularis, and black pod disease, caused by Phytophthora megakarya. Vegetation composition and spatial structure, resource availability and pest and disease occurrence were characterized in 20 real agroforest plots. Hierarchical partitioning was used to identify the causal variables that explain mirid density and black pod prevalence. The results of this study show that cacao agroforests can be differentiated on the basis of vegetation composition and spatial structure. This original approach revealed that mirid density decreased when a minimum number of randomly distributed forest trees were present compared with the aggregated distribution of forest trees, or when forest tree density was low. Moreover, a decrease in mirid density was also related to decreased availability of sensitive tissue, independently of the effect of forest tree structure. Contrary to expectations, black pod prevalence decreased with increasing cacao tree abundance. By revealing the effects of vegetation composition and spatial structure on mirids and black pod, this study opens new perspectives for the joint agro-ecological management of cacao pests and diseases at the plot scale, through the optimization of the spatial structure and composition of the vegetation.     

Biodiversity conservation in cocoa production landscapes: an overview

Cocoa agroforests that retain a floristically diverse and structurally complex shade canopy have the potential to harbour significant levels of biodiversity, yet few studies have documented the plant and animal species occurring within these systems or within landscapes dominated by cocoa production. In this special issue, we bring together nine studies from Latin America, Africa and Asia that document the contribution of cocoa agroforestry systems to biodiversity conservation, and explore how the design, management and location of these systems within the broader landscape influence their value as habitats, resources and biological corridors. Tree diversity within the cocoa production systems is variable, depending on management, cultural differences, location and farm history, among other factors. Animal diversity is typically highest in those cocoa agroforests that have high plant diversity, structurally complex canopies, and abundant surrounding forest cover. In general, both plant and animal diversity within cocoa agroforests is greater than those of other agricultural land uses, but lower than in the original forest habitat. There are several emerging threats to biodiversity conservation within cocoa production landscapes, including the loss of remaining forest cover, the simplification of cocoa shade canopies and the conversion of cocoa agroforestry systems to other agricultural land uses with lower biodiversity value. To counter these threats and conserve biodiversity over the long-term, land management should focus on conserving native forest habitat within cocoa production landscapes, maintaining or restoring floristically diverse and structurally complex shade canopies within cocoa agroforests, and retaining other types of on-farm tree cover to enhance landscape connectivity and habitat availability.     

<Emphasis Type="Italic">Cabruca</Emphasis> agroforests in southern Bahia,Brazil: tree component,management practices and tree species conservation

In southern Bahia, Brazil, cabrucas are the traditional agroforests in which cacao trees are planted under thinned-out native forests. To analyze the role of cabrucas in tree species conservation, we inventoried the non-cocoa trees in 1.0 ha plots of cabruca in 16 cocoa farms and compared our results with a similar survey undertaken in the early 1960s in the same region to analyze the long term changes. We also interviewed 160 cocoa farmers to investigate their preferences for species and the main practices used in managing shade trees. The cabrucas showed high levels of tree diversity for an agroforestry system (Shannon index ranging from 2.21 to 3.52) and also high variation in structure and composition among the different farms. Forest specialist trees accounted for most species (63.9%) in the survey and were among the species most preferred by the farmers, although we found evidence that some of these trees are gradually being replaced by other species. Our results indicate that cabrucas are poor substitutes for undisturbed forests in terms of tree species richness, but their presence in human-altered landscapes is of utmost importance to the conservation of forest tree species as they increase overall heterogeneity and may serve as ecological corridors, additional habitats, and buffer zones.     

The contribution of cacao agroforests to the conservation of lower canopy ant and beetle diversity in Indonesia

The ongoing destruction of tropical rainforests has increased the interest in the potential value of tropical agroforests for the conservation of biodiversity. Traditional, shaded agroforests may support high levels of biodiversity, for some groups even approaching that of undisturbed tropical forests. However, it is unclear to what extent forest fauna is represented in this diversity and how management affects forest fauna in agroforests. We studied lower canopy ant and beetle fauna in cacao agroforests and forests in Central Sulawesi, Indonesia, a region dominated by cacao agroforestry. We compared ant and beetle species richness and composition in forests and cacao agroforests and studied the impact of two aspects of management intensification (the decrease in shade tree diversity and in shade canopy cover) on ant and beetle diversity. The agroforests had three types of shade that represented a decrease in tree diversity (high, intermediate and low diversity). Species richness of ants and beetles in the canopies of the cacao trees was similar to that found in lower canopy forest trees. However, the composition of ant and beetle communities differed greatly between the agroforest and forest sites. Forest beetles suffered profoundly from the conversion to agroforests: only 12.5% of the beetle species recorded in the forest sites were also found in the agroforests and those species made up only 5% of all beetles collected from cacao. In contrast, forest ants were well represented in agroforests, with 75% of all species encountered in the forest sites also occurring on cacao. The reduction of shade tree diversity had no negative effect on ants and beetles on cacao trees. Beetle abundances and non-forest ant species richness even increased with decreasing shade tree diversity. Thinning of the shade canopy was related to a decrease in richness of forest ant species on cacao trees but not of beetles. The contrasting responses of ants and beetles to shade tree management emphasize that conservation plans that focus on one taxonomic group may not work for others. Overall ant and beetle diversity can remain high in shaded agroforests but the conservation of forest ants and beetles in particular depends primarily on the protection of natural forests, which for forest ants can be complemented by the conservation of adjacent shaded cacao agroforests.     

Breakdown of the species-area relationship in exotic but not in native forest patches

We studied the pattern of bird species richness in native and exotic forest patches in Hungary. We hypothesized that species-area relationship will depend on forest naturalness, and on the habitat specialization of bird species. Therefore, we expected strong species-area relationship in native forest patches and forest bird species, and weaker relationship in exotic forest patches containing generalist species. We censused breeding passerine bird communities three times in 13 forest patches with only native tree species, and 14 with only exotic trees in Eastern Hungary in 2003. Although most bird species (92%) of the total of 41 species occurred in both exotic and native forests, the species-area relationship was significant for forest specialist, but not for generalist species in the native forests. No relationship between bird species and area was found for either species group in the forest with exotic tree species. The comparison of native versus exotic forest patches of similar sizes revealed that only large (>100 ha) native forests harbor higher bird species richness than exotic forests for the forest specialist bird species. There is no difference between small and medium forest patches and in richness of generalist species. Thus, the species-area relationship may diminish in archipelago of exotic habitat patches and/or for habitat generalist species; this result supports the warning that the extension of exotic habitats have been significantly contributing to the decline of natural community patterns.     

Impact of cocoa farming on vegetation in an agricultural landscape in Ghana

Cocoa production occurs almost wholly within areas identified as biodiversity hotspots in West Africa and it has been noted as a major contributor to deforestation at the forest‐agriculture interface. This study investigated the impact of cocoa farming on vegetation in relation to three land‐use types of increasing cocoa production intensity from remnant native forest through shaded to unshaded cocoa farmlands in Ghana. The study used transects and forty‐two 25 m × 25 m vegetation plots. The overall noncocoa plant species richness decreased significantly (95% CI) from the remnant native forest through shaded to the unshaded cocoa farmlands. Significant differences (P ≤ 0.05) were also found in the mean density and basal area of noncocoa plants per hectare with the remnant native forest recording the highest values and the unshaded cocoa farmlands the lowest. The relative density of about 44.7% out of the 41 most abundant plant species declined in cocoa farmlands. The results of this study showed that cocoa farming could result in a drastic forest plant species loss with subsequent recruitment of nonforest species, forest plant species population decline as well as changes in the structural characteristics of the vegetation. This impact increases with increasing cocoa production intensity.     

Litter-dwelling ants as bioindicators to gauge the sustainability of small arboreal monocultures embedded in the Amazonian rainforest

One of the greatest threats to biodiversity and the sustainable functioning of ecosystems is the clearing of forests for agriculture. Because litter-dwelling ants are very good bioindicators of man-made disturbance, we used them to compare monospecific plantations of acacia trees, cocoa trees, rubber trees and pine trees with the surrounding Neotropical rainforest (in contrast to previous studies on forest fragments embedded in industrial monocultures). Although the global level of species turnover was weak, species richness decreased along a gradient from the forest (including a treefall gap) to the tree plantations among which the highest number of species was noted for the cocoa trees, which are known to be a good compromise between agriculture and conservation. Species composition was significantly different between natural habitats and the plantations that, in turn, were different from each other. Compared to the forest, alterations in the ant communities were (1) highest for the acacia and rubber trees, (2) intermediate for the cocoa trees, and, (3) surprisingly, far lower for the pine trees, likely due to very abundant litter. Functional traits only separated the rubber tree plantation from the other habitats due to the higher presence of exotic and leaf-cutting ants. This study shows that small monospecific stands are likely sustainable when embedded in the rainforest and that environmentally-friendly strategies can be planned accordingly.     

Water transport of native and exotic tree species in relation to xylem anatomical characteristics in low subtropical China

Aims Exotic fast-growing tree species have been commonly planted as pioneer species to facilitate ecological restoration in South China. Their growth and resource utilization behavior related to intrinsic physiology and structural properties have profound influences on forest ecosystem. However, the contrastive research focusing on water utilization features along with xylem anatomical properties between native and exotic species is scarce in South China. The objective of this study is to investigate the sapwood anatomical characteristics and water utilization conditions of native and exotic fast-growing species, and to elucidate the relationship between sap-flux density and conduit features.Methods We measured sap-flux density, conduit length, diameter and density of four native species (Schima superba, Michelia macclurei, Castanopsis hystrix and Castanopsis fissa) and four exotic species (Eucalyptus citriodora, Eucalyptus urophylla × grandis, Acacia auriculaeformis and Acacia mangium). Sap flux density was measured based on the Granier's thermal dissipation probe method. The whole-tree water transport was quantified by multiplying sap-flux density by sapwood area. The measurements of conduit characteristics were conducted by using segregation and slice method.Important findings Sapwood area increased with the growing diameter at breast height (DBH) as a power function. Native species had a larger water-conducting tissue area than exotic species at the same DBH value when trees grew to a size with a certain value of DBH. The conduit diameter of exotic species was significantly larger than that of native species. Conversely, native species, such as S. superba and M. macclurei, had longer conduit length and higher conduit density than other tree species. Based on a physiological interpretation of the measured conduit characteristics, native tree species developed a safe water transport system while exotic fast-growing tree species come into being an efficient system instead. Water transport increased with the growing DBH as a power function, and the exponent for native species (1.60) was higher than that for exotic species (1.22). Under the combined impact of sap-flux density and sapwood area, native species presented a larger water transport at a larger DBH value, indicating that growth advantage of exotic fast-growing species might weaken as DBH increased.     

Alternative pathways of liana communities in the forests of northwestern Argentina

Liana dynamics in secondary and mature forests are well known in tropical areas dominated by native tree species. Outside the tropics and in secondary forests invaded by exotic species, knowledge is scarce. In this study, we compare liana communities between secondary and mature forests dominated by native species in a subtropical montane area of Sierra de San Javier, Tucuman, Argentina. Additionally, we evaluate changes of liana communities in secondary forests with increasing densities of Ligustrum lucidum and Morus alba, two of the most invasive exotic trees of the area. We surveyed liana species richness and density in three 30-year secondary patches, four 60-year secondary patches, and four mature patches dominated by native tree species, to analyze changes in liana communities with forest age. Within each patch, we sampled 10–25 20 × 20 m quadrats. Additionally, we surveyed liana density and species richness in secondary forest patches with different densities of L. lucidum and M. alba. In native-dominated forests, liana species richness increased and showed a tendency of increasing basal area from 30-year secondary forests to mature forests. Liana density was highly variable, and most of the species were shared between native-dominated secondary and mature forests. Liana density and species richness decreased with L. lucidum density, whereas in secondary forests highly dominated by M. alba, lianas increased in density. Overall, lianas followed different pathways influenced by native forest succession and exotic tree invasions.     

Allelopathy: a tool for weed management in forest restoration

Forest restoration uses active management to re-establish natural forest habitat after disturbance. However, competition from early successional species, often aggressively invasive exotic plant species, can inhibit tree establishment and forest regeneration. Ideally, restoration ecologists can plant native tree species that not only establish and grow rapidly, but also suppress exotic competitors. Allelopathy may be a key mechanism by which some native trees could reduce the abundance and impact of exotic species. Allelopathy is a recognized tool for weed management in agriculture and agroforestry, but few studies have considered how allelopathic interactions may aid restoration. Here we introduce the “Homeland Security” hypothesis, which posits that some naïve exotic species may be particularly sensitive to allelochemicals produced by native species, providing a tool to reduce the growth and impacts of invasive exotic species on reforestation. This article explores how exploiting allelopathy in native species could improve restoration success and the re-establishment of natural successional dynamics. We review the evidence for allelopathy in agroforestry systems, and consider its relevance for reforestation. We then illustrate the potential for this approach with a case study of tropical forest restoration in Panama. C₄ grasses heavily invade deforested areas in the Panama Canal watershed, especially Saccharum spontaneum L. We measured the effect of leaf litter from 17 potential restoration tree species on the growth of invasive C₄ grasses. We found that leaf litter from legume trees had a greater inhibitory effect on performance of S. spontaneum than did litter from non-legume trees. However, allelopathic effects varied greatly among species within tree functional groups. Further evaluation of intra- and inter-specific interactions will help to improve our selection of restoration species.     

Effect of native and exotic leaf litter on macroinvertebrate communities and decomposition in a western Montana stream

Invasion by exotic trees into riparian areas has the potential to impact terrestrial and aquatic systems. To test the effect of different streamside tree species on the aquatic food web in a stream in Montana, we compared decomposition rates of leaf litter and invertebrate assemblages associated with the leaf litter of the exotic Acer platanoides and the dominant native Populus trichocarpa trees. Macroinvertebrate family richness, evenness, and diversity increased with days of aquatic processing; however, there was no effect of leaf species. Leaves of the A. platanoides were associated with 70% greater density of macroinvertebrates of the family Nemouridae. This family consists primarily of detritivores and had the greatest overall density and frequency of occurrence relative to other macroinvertebrate families. The density of a family of predatory macroinvertebrates (Rhyacophilidae) was also generally (73%) greater in association with A. platanoides than P. trichocarpa leaves. The density of Ephemerellidae and Rhyacophilidae increased over time. In contrast to studies comparing leaves of exotic vs. native trees, we observed no difference in leaf decomposition rates; however, the amount of leaf inputs are likely to differ between native and invaded forests. The results indicate that replacement of native riparian trees with exotics affected the most common family of macroinvertebrates and possibly a common family of predatory macroinvertebrates (Rhyacophilidae), which may affect the detrital food web.     

Exotic vascular plant invasiveness and forest invasibility in urban boreal forest types

The riverine forests of the northern city of Edmonton, Alberta, Canada display strong resilience to disturbance and are similar in species composition to southern boreal mixedwood forest types. This study addressed questions such as, how easily do exotic species become established in urban boreal forests (species invasiveness) and do urban boreal forest structural characteristics such as, native species richness, abundance, and vertical vegetation layers, confer resistance to exotic species establishment and spread (community invasibility)? Eighty-four forest stands were sampled and species composition and mean percent cover analyzed using ordination methods. Results showed that exotic tree/shrub types were of the most concern for invasion to urban boreal forests and that exotic species type, native habitat and propagule supply may be good indicators of invasive potential. Native forest structure appeared to confer a level of resistance to exotic species and medium to high disturbance intensity was associated with exotic species growth and spread without a corresponding loss in native species richness. Results provided large-scale evidence that diverse communities are less vulnerable to exotic species invasion, and that intermediate disturbance intensity supports species coexistence. From a management perspective, the retention of native species and native forest structure in urban forests is favored to minimize the impact of exotic species introductions, protect natural succession patterns, and minimize the spread of exotic species.     

Restoration of Tropical Moist Forests on Bauxite-Mined Lands in the Brazilian Amazon

We evaluated forest structure and composition in 9- to 13-year-old stands established on a bauxite-mined site at Trombetas (Pará), Brazil, using four different reforestation techniques following initial site preparation and topsoil replacement. These techniques included reliance on natural forest regeneration, mixed commercial species plantings of mostly exotic timber trees, direct seeding with mostly native early successional tree species, and mixed native species plantings of more than 70 tree species (the current operational restoration treatment at this site). Replicated fixed-radius plots in each treatment and in undisturbed primary forest were used to quantify the canopy and understory structure and the abundance and diversity of all vascular plant species. Treatment comparisons considered regeneration density, species richness and diversity for all floristic categories, and, for trees and shrubs, the relative contribution of initial planting and subsequent regeneration from soil seed banks and seed inputs from nearby primary forests. With the possible exception of the stands of mixed commercial species, which were superior to all others in terms of tree basal-area development but relatively poor in species richness, all treatments were structurally and floristically diverse, with a high probability of long-term restoration success. Of these, the mixed native species plantings appeared to be at least risk of arrested succession due to the dominance of a broader range of tree species of different successional stages or expected life spans. In all treatments, several locally important families of primary forest trees (Annonaceae, Chrysobalanaceae, Lauraceae, Palmae and Sapotaceae) were markedly underrepresented due to a combination of poor survival of initial plantings and limitations on seed dispersal from the surrounding primary forest.     

Regeneration of indigenous trees in Mgahinga Gorilla National Park, Uganda

This study examines the regeneration of indigenous tree species in the formerly encroached area in Mgahinga Gorilla National Park (MGNP), south‐western Uganda. Before gazetting in 1992, MGNP had basically been agricultural land for well over 50 years. The distribution of exotic vegetation was established using a Geographical Positioning System receiver and indigenous vegetation was sampled by establishment of quadrats along transect lines. Observations indicated that approximately 2% of the old cropland was covered by exotic woodlots. Black wattle (Acacia mearnsii) and Eucalyptus trees were found to be the most widely distributed and Pinus patula the least distributed species in the park. Species numbers of indigenous trees (n = 26) were high in the old cropland, compared with twelve species observed in exotic woodlots. The natural forest supported the highest (75%) stem density and the lowest (4%) stem density was recorded in exotic woodlots. Seedling class (< 2 cm, d.b.h.) accounted for the majority of juveniles, with the lowest stem density (1350 seedlings ha^?1) recorded in exotic woodlots compared with 6609 seedlings ha^?1 in the old cropland and 24,625 seedlings ha^?1 in the natural forest. The levels of tree diversity and stocking characteristics recorded under the exotic species suggest that a low diverse community of native species may exploit this environment.