Traditional agroforestry systems and biodiversity conservation in Benin (West Africa)

In the past, the conservation of biodiversity has been mostly understood in terms of the management of protected areas and natural forests, ignoring the possible role of farm areas and the ways through which rural communities have promoted biodiversity in their subsistence agricultural production systems. The present study focused on the floristic diversity within traditional agroforestry parkland systems around the Pendjari Biosphere Reserve in Benin and showed the diversity of tree species in the area as well as socio-economic factors which affect the practice of this farming system. We used questionnaires and interviewed a total of 118 households to collect data. Respondents were interviewed on their farms and during the interview; we inventoried the number of tree on the farm and determined the farm size. Twenty-one tree species belonging to 14 botanical families were recorded during the surveys and the average stand density of the woody component of farmlands was 7.97 ± 5.43 stems/ha. A number of both native and exotic tree species occurred in the parkland agroforestry systems with dominance of indigenous tree species. Species richness varied with the size of household where households with small land holding conserve more tree species in their field than households with large land holdings. 64% of households surveyed were making deliberate efforts to plant tree species on their farmlands. The most important reasons which determined household ambitions to conserve woody species on farmland were tree products contribution to food and medicine. Results also showed that respondents who noticed that trees were decreasing in the wild conserve more tree species on their farmlands. This research highlights the role of traditional agroforestry practices to support tree species richness and provides evidence of the farms’ role as biodiversity reservoirs.     

Conservation value of forest plantations for bird communities in western Kenya

Tree plantations of native and exotic species are frequently used to compensate for forest loss in the tropics. However, these plantations may support lower species diversity and different communities than natural forest. We therefore investigated bird communities in stands of natural forest, different types of tree plantations and secondary forest in Kakamega Forest, western Kenya. We compared birds differing in habitat specialisation, i.e. forest specialists, generalists, and visitors. We recorded significant differences in mean species richness and number of individuals among the different forest types. Stands of natural forest and plantations of indigenous tree species comprised more species and individuals than plantations of exotic tree species and secondary forest. This was caused by a significant decline of forest specialists and generalists from natural forest and indigenous plantations to exotic plantations and secondary forest. Species composition of the bird communities did not differ between natural forest stands and plantations of a mixture of indigenous tree species, but clearly changed between natural forest and plantations of single tree species. These findings demonstrate that natural forest areas are needed for the conservation of forest bird diversity, but that plantations with a mixture of indigenous tree species can have similarly high conservation value.     

Do Farm Characteristics Explain Differences in Tree Species Diversity among Western Kenyan Farms?

With the objective of planning diversification of on-farm tree species composition, a survey was conducted in western Kenya involving a complete tree census (trees were defined as all woody or ligneous plants, including shrubs and lianas) and collection of ethnobotanical information on 201 farms. Differences between farms in diversity of the 12 most frequent use-groups were analysed by species richness, Shannon, Simpson and Berger-Parker diversity indices, and Shannon evenness and equitability. A large range of values was detected among farms and use-groups. Multiple linear regression of diversity statistics on household characteristics indicated significant relationships. However, these relationships generally explained low percentages of variation (ranging 2-44%). The connection between household characteristics and use-group diversity allows targeting specific household types with lower diversity. Farm size had a positive relationship with diversity of most use-groups. However, accumulation curves revealed that the same area carried a larger abundance and diversity when it was composed of a greater number of smaller farms. If the pattern of further subdivision of farmland in the survey area continues and the same differences between smaller and larger farms prevail, then larger diversity per unit area can be expected. Because smaller farms contain smaller diversity, however, diversification with the aim of enhancing or stabilising productivity of individual farms may become an important priority in the survey area. The results presented allow for the identification of individual farms, use-groups, and household types for which diversification is more relevant, and at the same time allow for impact monitoring.     

The role of indigenous trees for the conservation of biocultural diversity in traditional agroforestry land use systems: The Bungoma case study: In-situ conservation of indigenous tree species

In order to precisely assess the role of agroforestry for the conservation of (agro-)biological diversity there is a need to adjust sampling methods used in plant sociology. This study is on the contribution of agroforestry land use to the in-situ conservation of indigenous trees within a typical East-African smallholder farming system in Western Kenya. A modified approach to measuring species richness and abundance is presented. The selection of tree-rich structures was done according to management patterns rather than considering syntaxonomic classifications from the vegetation science point of view. This approach, which is better suited to the strongly human-influenced vegetation of agroecosystems, employs between-management unit diversity measures to help evaluate abundance and constancy of species in particular management units. The predominant off-farm vegetation patterns are riverine forests, rocky hillsides, hedgerows, wooded grassland relicts, woodlands or colline forest relicts and tree groves whereas the noticeable tree-rich on-farm management units are homegardens, homesteads, life fences, coffee- and banana-groves and annual cropping fields. 98% out of all indigenous tree species known from Bungoma, occur in off-farm lands. 53% of the indigenous tree species occur in tree rich on-farm management units while 47% of the indigenous trees are dependent on the maintenance of off-farm lands. Hedgerows embody the most promising secondary vegetation structure that shows ample potential to accommodate a wide range of indigenous perennial species outside the natural vegetation formations. The pattern of distribution of various vegetation structures, and the mixture with diverse tree-based on-farm plots are interesting features in regard to floristic and eco-diversity on a landscape level. In this respect, three areas that show different population densities and distinct agro-historical conditions were compared. In regions of particular high population density the degree of association of various functional land use forms and woodland structures – each characterised by its own floristic make-up – is comparatively high. In contrast, in regions with less population but that were settled at a later date, one encounters fewer stands of woody plants with lower numbers of species. This revised version was published online in June 2006 with corrections to the Cover Date.     

A Comparison of the Utility and Agronomic Traits of Indigenous and Exotic Trees in the Mount Kenya Region

On-farm indigenous (Cordia africana) and exotic (Grevillea robusta) tree species were compared in terms of the quality of their utility and their agronomic traits in the Meru Central district of Kenya. These two species are the most common indigenous and exotic trees, respectively, among the recorded 117 trees on farms. Interviews with farmers and collected documents on tree felling and planting showed that farmers considered C. africana to be more useful than G. robusta. However, farmers wanted to plant more G. robusta than C. africana because the easily established and fast growing G. robusta has a higher short-term contribution to the household economy. The advantages of C. africana, however, should be redefined in terms of its long-term contribution to farmers; C. africana contributes to farming more effectively than does G. robusta. The lower growth performance and relative difficulty in the establishment of C. africana can be compensated for by its higher timber quality and coppicing ability.     

Effects of transformation processes on plant species richness and diversity in homegardens of the Nuba Mountains,Sudan

Traditional homegardens (HGs) are considered to harbor high levels of plant diversity and have been therefore characterized as sustainable agro-ecosystems suitable for on-farm (incl. circa situm) conservation of plant genetic resources. While the functional structure of traditional HGs is poorly understood specifically for semi-arid and arid regions, their plant species richness and diversity is increasingly threatened by recent and fast evolving agricultural transformation processes. This has been particularly claimed for traditional jubraka HG systems of Sudan. Therefore, sixty-one HGs in four villages of the Nuba Mountains, South-Kordofan Province, Sudan, were randomly selected, geographically recorded and plant richness and abundance determined and plant diversity parameters calculated. In addition, socio-economic household data were assessed by interviews and soil samples taken to allow a comprehensive analysis of putative factors affecting HG plant diversity across different villages, levels of commercialization and plant species composition based clusters. A total of 110 species from 35 plant families were grown in the HGs along with 71 ornamentals. Perennial species accounted for 57 % including 12 indigenous fruit tree (IFT) species and six exotic fruit tree species. Mean species richness of useful plant species (excluding ornamentals) per HG was 23 (range 6–46). On average, 41 % of the 23 species per HG were of exotic origin, however, with a large range (21–83 %) among locations. Mean diversity and evenness indices were 1.46 (range 0.49–2.42) and 0.48 (0.15–0.87), respectively. The level of commercialization of HGs only marginally affected species diversity measures although the species richness was significantly higher for commercial than subsistence HGs. Species richness was higher on lower (6.6–7.2) pH soils. IFT richness was highly variable, but non-significantly different across the four locations. Plant species richness and diversity was high in comparison with other HG systems in semi-arid regions. Cluster analysis was found to be a valuable tool to classify HGs and to extract homogeneous HG types with low, intermediate and high richness and diversity. In addition, the share of exotic and ornamental species in HGs indicated a trend towards the loss of traditional farming practices, particularly in areas with good market access. The data did not indicate the hypothesized loss of inter-specific diversity due to commercialization and species richness was numerically even higher for market-oriented HGs compared to subsistence ones.     

A review of tree fodder production and utilization within smallholder agroforestry systems in Kenya

Although the biological advantages in terms of animal production and improved soil fertility of the use of herbaceous legumes have been well demonstrated in Kenya and elsewhere, adoption by small-scale farmers has often been disappointing. This has led to increased research into the use of both indigenous and exotic fodder trees. In common with conventional pasture legumes, tree fodders contain high levels of crude protein and minerals and many show high levels of digestibility. They are readily accepted by livestock and presumably because of their deep-root systems, they continue to produce well into the dry season. Antinutritive factors can be a problem, however, and polyphenolics, toxic amino acids, cyanogenic glycosides and alkaloids are found in many tree species. There are abundant niches on small farms where fodder trees can be grown without affecting crop production. Although detailed management recommendations are lacking, guidelines exist with regard to appropriate cutting heights and harvesting frequencies. In the Embu region, it has been estimated that three kg of fresh fodder of Calliandra calothyrsus has the same effect on milk production as one kg of commercial dairy meal. Up to about 500 trees (250 m of hedgerow) will produce enough fodder to supplement one dairy cow for a complete lactation. The tree fodder can either replace the concentrate without loss of yield, or it can complement it to produce more milk. It is being enthusiastically adopted by small-scale farmers, many of whom are starting to produce their own seed. Other tree species are now being studied in order to avoid over-reliance on a single fodder species. This revised version was published online in August 2006 with corrections to the Cover Date.     

Changes in plant species composition within a planted forest in a deciduous agroecosystem in Ghana

Plantations provide a micro-climate that can facilitate the regeneration of other forest species. Often exotic species have been tested for these kinds of functions. To determine the potential for indigenous trees as plantation species for their ability to foster forest species regeneration, this study was undertaken in a mixed indigenous plantation stand. Understories of the stand at 8?years of age were surveyed for plant diversity. The species richness increased by 24% per 1,000?m² between 2001 and 2008 and the number of families represented increased by 48%. The Shannon Diversity and Simpson Index values confirm a greater diversity 8?years after the plantation was established. The most abundant species in study plots were Chromolaena odorata and Cedrela odorata, which collectively represent about 54% of all species identified in the plots. The most species-rich families were Fabaceae and Euphorbiaceae representing 31% of the total species recorded. Asteraceae and Meliaceae were the two most dominant families, which collectively represent about 55% of all species identified in the plots. 47 forest tree species were found per 1,000?m² but those classified as ??saplings?? occurred in low densities. The 47 tree species included pioneer species such as Entandrophragma angolensis, Milicia excelsa, and Ceiba pentandra. Growth rates of planted species were differed, with half of the tested species having similar growth capacity to the exotic species. Generally, planted indigenous species enhanced habitats for other forest tree species in degraded sites. The observed growth of indigenous species, if planted and protected, shows that they may help in biodiversity recovery within agricultural landscapes.     

Comparing genetic diversity in agroforestry systems with natural forest: a case study of the important timber tree Vitex fischeri in central Kenya

It is possible that current tree domestication practices undertaken by farmers reduce the genetic base of tree resources on farms, raising concerns regarding the productivity, sustainability and conservation value of agroforestry ecosystems. Here, we assessed possible changes in genetic variation during domestication in the important and heavily utilised timber species, Vitex fischeri Gürke (syn. Vitex keniensis), by comparing geographically proximate forest and farm material in central Kenya. Employing RAPD analysis, a total of 104 polymorphic markers revealed by five arbitrary primers were scored in a total of 65 individuals, 32 from forest and 33 from farmland. Despite concerns of possible genetic erosion, forest and farm stands did not differ significantly in levels of genetic variation, with H values of 0.278 and 0.269, respectively. However, Mantel tests did reveal greater geographically related associative genetic structure among individuals in farm rather than forest material, with r _M values of 0.217 and 0.114, respectively. A more detailed analysis of structure suggested this could be due to local variation in origin of some on-farm trees. Implications of data for the genetic management of V. fischeri stands during farmer-led tree domestication activities are discussed. At present, there appears little reason to reject on-farm V. fischeri as a source of germplasm for future on-farm planting or for conservation purposes, although this situation may change and will require monitoring.     

Development of utility and location indices for classifying agroforestry species: the case of Rwanda

In a study of farmer knowledge and experimentation of trees and tree cultivation, two categories of farmer consultants were identified, tree experts (n = 44) and control farmers (n = 70), via a two stage process of knowledge ranking and community interviews conducted in three communes in southern Rwanda in 1992. A detailed inventory of tree species was conducted revealing two key characteristics for on-farm trees: multiple utility and high locational flexibility. In order to logically organize the species inventory, two indices, a utility index (UI) and a locational flexibility index (LFI), were developed. The two indices were calculated for each species and then plotted as the axes on a bivariate grid. While few species had both high utility and flexibility indices, the majority that did were indigenous species long used in agroforestry systems (e.g., Euphorbia tirucalli, Vernonia amygdalina, Erythrina abyssinica, etc.). A few naturalized exotics introduced in the 1930s (e.g., Grevillea robusta, Eucalyptus camaldulensis, E. saligna, E. maideni, Cupressus lusitanica and Persea gratissima) were also appreciated for their multiple utility and locational flexibility. Farm sizes varied, averaging 1.27 ha among tree experts and 0.18 ha in the control group. The mean number of species cultivated was significantly higher on tree expert farms (P < 0.01). However, tree density was much lower on tree expert farms (731 trees · ha^–1) than on control farms (1,689 trees · ha^–1). Competitive species were found primarily on larger farms, whereas smaller farms were associated with species of greater UI and LFI. Farmers demonstrated deliberate and rational choices about which trees to plant in accordance with each species utility and flexibility in relation to land availability.     

Farmers’ Motivations to Plant and Manage On-Farm Trees in Ghana

Deforestation and forest degradation, especially in the agricultural landscapes, are serious threats to biodiversity conservation and sustainability of the timber industry. Planting trees on farms has been identified as having great potential to increase forest resources from agricultural landscapes. This paper examined farmers’ motivations and behaviour to engage in on-farm tree planting and management in Ghana by combining internal and external factors in a socio-psychological model. Data were collected from 156 smallholder farmers from five communities in two forest districts using a semi-structured questionnaire. Additional farm inventory data were collected from 33 farmers under two on-farm tree planting schemes. On-farm tree planting was perceived as providing income, access to personal timber for furniture, and access to loan facilities. Incentives such as provision of grants, farming inputs, capacity training, and access to markets for agricultural produce are factors that motivate on-farm tree planting in Ghana. The average standing volume of on-farm trees in the study area is 51.9 m³/ha which is almost twice the national average for the off-reserve areas in the semi-deciduous forests to which much of the study sites belong. Many farmers considered high financial costs and limited knowledge of appropriate techniques in managing planted on-farm trees as barriers to the development of tree stock on farms.     

Assessment of small mammal diversity in coffee agroforestry in the Western Ghats,India

Coffee agroforestry is a conservation strategy that has shown promise to support the diversity of bird, bat, and insect communities, but few studies have focused on non-volant mammals in coffee farms. We assessed mammal diversity within coffee agroforestry systems in Kodagu, India and investigated the impacts of the non-native shade tree species, Grevillea robusta, on mammal diversity. Twenty farms, with varying amounts of G. robusta planted within the coffee farm, were sampled throughout three rainfall zones during the 4-month study period. We captured six species of small mammals, with indirect methods yielding an additional five species, totaling 11 mammal species. Contrary to current ecological thought, we found that increased amounts of G. robusta did not have a negative impact on either abundance or richness of mammals. Small mammal abundances were higher at farms with greater amounts of herbaceous ground cover and larger, mature shade trees, while small mammal species richness was found to increase with an increase in tree species richness as well as greater amounts of herbaceous ground cover. Additionally, small mammal abundance was higher at coffee farms closer to forested areas. Based on these findings, we suggest the maintenance or cultivation of shade tree richness, mature shade trees, and herbaceous ground cover within coffee farms and preservation of forested areas within the landscape to enhance coffee agroforestry habitat for non-volant mammals. We hope that these habitat requirements will be incorporated into conservation strategies for the promotion of biodiversity within coffee agroforestry systems.     

Potential of indigenous multistrata agroforests for maintaining native floristic diversity in the south-eastern Rift Valley escarpment, Ethiopia

Most studies undertaken in the field of agroforestry have focussed on system design, soil fertility management, and system interactions. Less emphasis has been placed on biodiversity aspects. The aim of this study is to investigate the potential of indigenous, multistrata agroforests for maintaining native woody species diversity in the south-eastern Rift Valley escarpment, Ethiopia. A total of 60 farms, representing three agroforest types (enset-AF, enset-coffee-AF and fruit-coffee-AF), were randomly selected along altitudinal gradients. Enset (Ensete ventricosum) is a perennial, herbaceous monocarpic banana-like plant which serves as a food plant in Ethiopia. The three agroforests are results of the domestication of natural forests and intensification of the landuse systems centuries ago. Sample-based assessment protocols were employed to place sample quadrats and to measure all individuals in the quadrats. A total of 58 woody species, belonging to 49 genera and 30 families, was recorded. Of all woody species identified, 86% were native. The highest proportion of native woody species was recorded in enset-AF (92%), followed by enset-coffee-AF (89%) and fruit-coffee-AF (82%). Among native tree species, Millettia ferruginea and Cordia africana were the most widespread. In all, 22 native woody species were recorded as of interest for conservation, acccording to IUCN Red lists and local criteria. Among them, Pygeum africanum and Rhus glutinosa were categorised as vulnerable in the wild, and in need of conservation priority. The introduction of non-native fruit trees in agroforests can be a threat to maintenance of native woody species. Management strategies favoring enset and coffee will also put other native tree species at risk. A smaller number of native woody species was recorded in fruit-coffee-AF, but a higher mean basal area and stem number. The mean basal area and stem number ranged from 5.4?±?0.5 to 11.7?±?1.0?m^2?ha^?1 and 625?±?84 to 1,505?±?142 stems?ha^?1, respectively. Altitude explained 68 and 71% of the variation in species richness and abundance, respectively. Finally, it is concluded that recognition of the indigenous agroforestry system as an option for maintaining native woody species should be given more attention, to counteract the local threat of these species from the wild.     

The effect of land use systems on tree diversity: farmer preference and species composition of cocoa-based agroecosystems in Ghana

Traditionally, most cocoa farms are established by removing the forest understorey and thinning the forest canopy so that cocoa seedlings can grow into productive trees by utilising the forest rent of the newly cleared area and the shade provided by the remaining trees. With the introduction of new hybrid cocoa varieties, there is a gradual shift towards the elimination of shade trees in the cocoa landscape. Farmers have found it necessary to eliminate forest tree species to effect high performance of these new varieties and as a result large areas of forested land are being lost, thereby posing a threat to biodiversity A study was carried out in Atwima, a major cocoa farming district in the Ashanti region of Ghana, to assess the impact of cocoa cultivation on tree diversity. The study also investigated farmers’ preferences for tree species retained on cocoa farms as well as their traditional knowledge on tree species and their effect on cocoa cultivation. The assessment consisted of identification and enumeration of all tree species with diameter at breast height greater than or equal to 10 cm, and was carried out on one-hectare plots of: (a) Active Cocoa Farms (ACF), stratified into (i) Mature Cocoa Forest (MCF) and (ii) Young Replanted Cocoa (YRC); (b) Fallow land (FL), and (c) Natural Forest (NF). A total of four one-hectare plots replicated five times (or 20 ha) were enumerated. Tree diversity was more strongly influenced by landuse type than age of cocoa farm. Fallow lands contained a higher tree diversity followed by natural forest, with the active cocoa farms, both mature and young, containing the lowest variety of species. However, stem count was highest in the natural forest followed by FL and ACF. Generally, stem counts of important tree species, as well as those classified as either endangered or vulnerable, were extremely low in the landscape (0–2 per hectare), indicating a critical potential for conservation and rejuvenation. Farmers’ preference for trees on cocoa farms was based on their usefulness. Three categories of trees emerged from their classification of trees on cocoa farms: (i) naturally occurring trees that are very useful; (ii) naturally occurring species of minor economic use; and (iii) naturally occurring tree species that are aggressive or incompatible with cocoa. Multistrata cocoa farms are a potential niche for conservation, but given the current trends in cocoa replanting, future conservation strategies will have to focus on identified targeted species which are of conservation concern, as well as those that are of value to farmers.     

Household tree holdings: A case study in Mutoko communal area, Zimbabwe

Tree holdings at homesteads and in homefields were investigated for two villages in Zimbabwe. Of the households, 90% owned at least one exotic tree. Trees were concentrated at homesteads and conserved indigenous trees tended to be edible fruit trees. Female heads of households (divorcees and widows) had fewer trees than households headed by men. Households with longer period of residence at a site had increased the proportion of indigenous fruit trees compared to non-fruit trees. Wealth status showed no relationship to tree holdings. The considerable tree planting and tree conservation activity around homesteads and in homefields has the effect of replacing non-fruit indigenous trees with exotic and indigenous fruit trees. Agroforestry research, extension and development should focus more on current practices, concentrate more on trees that farmers favour (such as fruit trees) and take into account differences among households. This revised version was published online in June 2006 with corrections to the Cover Date.     

Biodiversity field trials to inform reforestation and natural resource management strategies along the African Great Green Wall in Senegal

Forest restoration is carried out with varying objectives in mind, one of which is biodiversity conservation. The present study examines the extent by which tree biodiversity could potentially be maximized in the context of the pan-African Great Green Wall for the Sahara and the Sahel Initiative (GGW). Towards this end, ten indigenous tree species were selected for study in the Ferlo region in Northern Senegal based on previous ethnobotanical studies in the zone. The species included Acacia senegal, Acacia nilotica, Acacia tortilis subsp. raddiana, Acacia seyal, Adansonia digitata, Balanites aegyptiaca, Dalbergia melanoxylon, Sclerocarya birrea, Tamarindus indica and Ziziphus mauritiana. Germination experiments were first performed in the laboratory on seed lots from Senegal, Burkina Faso, Kenya, and South Africa prior to in situ sapling production in the nursery in Northern Senegal situated along the GGW. A split plot field design was employed and the effects of seed provenance (two per species) and the addition of organic fertilizer at the timing of planting were determined. Over the course of the 2 year experimental period, the newly planted trees, in addition to the naturally regenerating woody vegetation and herbaceous grasses were monitored in the fenced-in experimental field plot. Of the ten species, only B. aegyptiaca, A. tortilis subsp. raddiana, and S. birrea exhibited moderate survival rates. The effects of provenance and fertilizer addition were sporadic and species-dependent. Natural regeneration of woody species was abundant albeit characterized by low biodiversity whereas herbaceous grass species showed extensive biodiversity, especially under tree canopies as compared to open areas.     

Colonisation of native and exotic conifers by indigenous bark beetles (Coleoptera: Scolytinae) in France

Planting exotic conifers offers indigenous forest insects an opportunity to extend their host range and eventually to become significant pests. Knowing the ecological and evolutionary modalities driving the colonisation of exotic tree species by indigenous insects is thus of primary importance. We compared the bark beetle communities (Coleoptera: Curculionidae, Scolytinae) associated with both native and introduced conifers in France. The aim of our study was to estimate the influence of both host- and insect-related factors on the beetles’ likelihood to shift onto new hosts. We considered the influence of host origin (i.e. native vs. exotic), host tree species identity, tree bark thickness and tree taxonomic proximity, as well as insects’ host specificity. A field inventory using trap trees was carried out in two regions in France (Limousin and Jura) during two consecutive years (2006 and 2007) on three European native conifer species [Norway spruce (Picea abies); Scots pine (Pinus sylvestris) and European Silver-fir (Abies alba)] and five North American [Sitka spruce (Picea sitchensis); Eastern white pine (Pinus strobus); Grand fir (Abies grandis); Douglas fir (Pseudotsuga menziesii) and Western red cedar (Thuja plicata)]. A total of 18 indigenous and 2 exotic bark beetle species were collected. All exotic conifer species were colonised by indigenous bark beetle species and no significant difference was observed of the cumulated species richness of the latter between native and exotic tree species (13 vs. 14, P < 0.05). The ability of indigenous bark beetles to shift onto exotic conifers appeared to strongly depend on host species (significantly structuring bark beetle assemblages), the presence of phylogenetically related native conifer species and that of similar resources, in combination with insect host specificity. Host tree species status (native or exotic) also seemed to be involved, but its effect did not seem as essential as that of the previous factors. These findings are discussed in terms of adaptation, plasticity and practical aspects of forest management.     

Identifying important biophysical and social determinants of on-farm tree growing in subsistence-based traditional agroforestry systems

Many expert-designed agroforestry projects enunciated in 1970s around the world, particularly in the developing countries, had uneven success due to inadequate adoption or abandonment after adoption. There are many empirical studies on factors affecting on-farm tree cultivation mainly where expert-designed agroforestry programmes were introduced but lacking in case of traditional agroforestry. Moreover, the concern to identify key factors influencing on-farm tree growing is gaining importance. The present study identifies key factors in on-farm tree growing based on investigation of traditional agroforestry using logistic regression approach. The study is based on household survey of 401 households located in Indian Western Himalaya. The factors affecting on-farm tree growing were grouped into: biophysical (included land use and infrastructural aspects) and social. Models predicting on-farm tree growing for each category were developed and key factors affecting on-farm tree growing in the respective category were identified. A composite model was also developed by combining biophysical and social factors. In the present study, farm size, agroclimatic zone, soil fertility, mobility and importance of tree for future generations respectively were the key factors which influenced tree growing. In contrast to many previous studies which considered either biophysical or social factors, the composite model in the present study reveals that both biophysical and social factors are simultaneously important in motivating the farmers to grow trees on their farms in traditional agroforestry. Moreover, the present study open vistas for using farmers’ experience and knowledge of adoption of agroforestry to stimulate on-farm tree growing. The wider implication of the study is that biophysical as well as social variables should be considered together in designing suitable agroforestry systems in various parts of the world.     

Relationship between carbon stocks and tree species diversity in a humid Guinean savanna landscape in northern Sierra Leone

Global sustainable development goals include reducing greenhouse gas emissions from land-use change and maintaining biodiversity. Many studies have examined carbon stocks and tree species diversity, but few have studied the humid Guinean savanna ecosystem. This study focuses on a humid savanna landscape in northern Sierra Leone, aiming to assess carbon stocks and tree species diversity and compare their relationships in different vegetation types. We surveyed 160 sample plots (0.1 ha) in the field for tree species, aboveground carbon (AGC) and soil organic carbon (SOC). In total, 90 tree species were identified in the field. Gmelina arborea, an exotic tree species common in the foothills of the Kuru Hills Forest Reserve, and Combretum glutinosum, Pterocarpus erinaceous and Terminaria glaucescens, which are typical savanna trees, were the most common species. At landscape level, the mean AGC stock was 29.4 Mg C ha^?1 (SD 21.3) and mean topsoil (0–20 cm depth) SOC stock was 42.2 Mg C ha^?1 (SD 20.6). Mean tree species richness and Shannon index per plot were 7 (SD 4) and 1.6 (SD 0.6), respectively. Forests and woodlands had significantly higher mean AGC and tree species richness than bushland, wooded grassland or cropland (p < 0.05). In the forest and bushland, a small number of large diameter trees covered a large portion of the total AGC stocks. Furthermore, a moderate linear correlation was observed between AGC and tree species richness (r = 0.475, p < 0.001) and AGC and Shannon index (r = 0.375, p < 0.05). The correlation between AGC and SOC was weak (r = 0.17, p < 0.05). The results emphasise the role of forests and woodlands and large diameter trees in retaining AGC stocks and tree species diversity in the savanna ecosystem.     

Partial cutting as a conservation alternative for oak (Quercus spp.) forest—Response of bryophytes and lichens on dead wood

Semi-open oak-rich forests may support many species adapted to large trees and coarse woody debris. Currently many oak-rich forests in northern Europe have more or less closed canopies due to lack of natural and cultural disturbances. In these forests, conservation oriented partial harvesting of biofuel may restore a desired forest structure and light regime that potentially may favour many species that have declined during the last century. We quantified effects of such cutting on lichens and bryophytes living on dead wood in southern Sweden, using a design with paired cutting and control plots (each 1 ha) in 15 forests. In each plot we surveyed the same five logs and three stumps before and after harvest (25% of the tree basal area removed). The epixylic species composition shifted towards a flora typical for dryer dead wood. The mean species number of lichens per stump increased (clear effect) and the mean number of bryophytes per stump decreased (nearly significantly) due to harvesting. The species composition, but not species richness, on logs was affected. No increases or decreases in species of conservation concern could be detected. Since the overall negative effects were weak, we suggest that partial harvesting of dense oak forests is compatible with maintenance of the diversity of lichens and bryophytes on dead wood. However, the amount of such forest harvested needs to be carefully assessed in relation to demands of other taxa.