Characterization of <Emphasis Type="Italic">Faidherbia albida</Emphasis> (Del.) A. Chev. population in agroforestry parklands in the highlands of Northern Ethiopia: impact of conservation,environmental factors and human disturbances

Concerns about sustainable management and conservation of multipurpose trees in their habitat have led to increased number of studies on the ecological characterization of their population. Such knowledge on Faidherbia albida, the most used tree in agroforestry parklands in Ethiopia, is limited. F. albida population was characterized in and compared between two agroforests having different conservation status in Northern Ethiopia. Population structural parameters along with environmental factors and human activities were assessed in 42 randomly installed plots using a transect method. Size class distribution was used to describe and analyze the species long-term population dynamics. Adult density was almost three times higher in Zongi agroforest (19.9 ± 2.9 trees ha^?1) where the species has been conserved and managed for longer time compared to Abraha-atsbeha agroforest (7.9 ± 2.5 trees ha^?1). The same trend was observed for tree morphological parameters which were significantly higher at Zongi than Abraha-atsbeha. However, size class distributions coefficient of skewness and the median diameter indicated a declining and vulnerable population at Zongi and an increasing population at Abraha-atsbeha. Species population characteristics were influenced by environmental factors such as altitude, stone cover, erosion severity, slope, and human-related disturbances including land use, fodder harvesting, distance away from the center of the village and proximity of household to the plots. The study confirms the impact of conservation, environmental factors and human disturbances on shaping F. albida population and recommends the consideration of the trade-offs between them to design effective conservation and management strategies to sustain F. albida agroforests.     

Carbon stocks in coffee agroforests and mixed dry tropical forests in the western highlands of Guatemala

Tree removal in Latin American coffee agroforestry systems has been widespread due to complex and interacting factors that include fluctuating international markets, government-supported agricultural policies, and climate change. Despite shade tree removal and land conversion risks, there is currently no widespread policy incentive encouraging the maintenance of shade trees for the benefit of carbon sequestration. In facilitation of such incentives, an understanding of the capacity of coffee agroforests to store carbon relative to tropical forests must be developed. Drawing on ecological inventories conducted in 2007 and 2010 in the Lake Atitlán region of Guatemala, this research examines the carbon pools of smallholder coffee agroforests (CAFs) as they compare to a mixed dry forest (MDF) system. Data from 61 plots, covering a total area of 2.24 ha, was used to assess the aboveground, coarse root, and soil carbon reservoirs of the two land-use systems. Results of this research demonstrate the total carbon stocks of CAFs to range from 74.0 to 259.0 Megagrams (Mg)?C ha^?1 with a mean of 127.6?±?6.6 (SE)?Mg?C ha^?1. The average carbon stocks of CAFs was significantly lower than estimated for the MDF (198.7?±?32.1?Mg?C?ha^?1); however, individual tree and soil pools were not significantly different suggesting that agroforest shade trees play an important role in facilitating carbon sequestration and soil conservation. This research demonstrates the need for conservation-based initiatives which recognize the carbon sequestration benefits of coffee agroforests alongside natural forest systems.     

The effects of management and plant diversity on carbon storage in coffee agroforestry systems in Costa Rica

Agroforestry systems can mitigate greenhouse gas (GHG) emissions, conserve biodiversity and generate income. Whereas the provision of ecosystem services by agroforestry is well documented, the functional relationships between species composition, diversity and carbon (C)-storage remain uncertain. This study aimed to analyze the effects of management (conventional vs. organic), woody plant diversity and plant composition on aboveground and belowground C-storage in coffee agroforestry systems. It was expected that organic farms would store more C, and that an increase in plant diversity would enhance C-storage due to complementarity effects. Additionally, it was expected that steep slopes decrease C-storage as a result of topsoil erosion. Woody plants were identified on 1?ha plots within 14 coffee farms (7 conventional and 7 organic). C-stocks in trees, coffee plants and roots were estimated from allometric equations. C-stocks in litter and topsoil (0?C25?cm) were estimated by sampling. On average, farms stored 93?±?29?Mg?C?ha^?1. Soil organic carbon accounted for 69?% of total C. Total C-stocks were 43?% higher on organic farms than on conventional farms (P?<?0.05). Conventional and organic farms differed in vegetation structure, but not in species diversity. It was found that the combined effect of farm type, species richness, species composition and slope explained 83?% of the variation in total C-storage across all farms (P?<?0.001). Coffee agroforestry in general and organic farms in particular may contribute to GHG mitigation and biodiversity conservation in a synergistic manner which has implications for the effective allocation of resources for conservation and climate change mitigation strategies in the agricultural sector.     

Fertilizer type and species composition affect leachate nutrient concentrations in coffee agroecosystems

Intensification of coffee (Coffea arabica) production is associated with increases in inorganic fertilizer application and decreases in species diversity. Both the use of organic fertilizers and the incorporation of trees on farms can, in theory, reduce nutrient loss in comparison with intensified practices. To test this, we measured nutrient concentrations in leachate at 15 and 100 cm depths on working farms. We examined (1) organically managed coffee agroforests (38 kg N ha^?1 year^?1; n = 4), (2) conventionally managed coffee agroforests (96 kg N ha^?1 year^?1; n = 4), and (3) one conventionally managed monoculture coffee farm in Costa Rica (300 kg N ha^?1 year^?1). Concentrations of nitrate (NO₃ ^?-N) and phosphate (PO₄ ^3?-P) were higher in the monoculture compared to agroforests at both depths. Nitrate concentrations were higher in conventional than organic agroforests at 15 cm only. Soil solutions collected under nitrogen (N)-fixing Erythrina poeppigiana had elevated NO₃ ^?-N concentrations at 15 cm compared to Musa acuminata (banana) or Coffea. Total soil N and carbon (C) were also higher under Erythrina. This research shows that both fertilizer type and species affect concentrations of N and P in leachate in coffee agroecosystems.     

Short-term changes in the soil carbon stocks of young oil palm-based agroforestry systems in the eastern Amazon

The current expansion of the oil palm (Elaeis guineensis Jacq.) in the Brazilian Amazon has mainly occurred within smallholder agricultural and degraded areas. Under the social and environmental scenarios associated with these areas, oil palm-based agroforestry systems represent a potentially sustainable method of expanding the crop. The capacity of such systems to store carbon (C) in the soil is an important ecosystem service that is currently not well understood. Here, we quantified the spatial variation of soil C stocks in young (2.5-year-old) oil palm-based agroforestry systems with contrasting species diversity (high vs. low); both systems were compared with a ~10-year-old forest regrowth site and a 9-year-old traditional agroforestry system. The oil palm-based agroforestry system consisted of series of double rows of oil palm and strips of various herbaceous, shrub, and tree species. The mean (±standard error) soil C stocks at 0–50 cm depth were significantly higher in the low (91.8 ± 3.1 Mg C ha^?1) and high (87.6 ± 3.3 Mg C ha^?1) species diversity oil palm-based agroforestry systems than in the forest regrowth (71.0 ± 2.4 Mg C ha^?1) and traditional agroforestry (68.4 ± 4.9 Mg C ha^?1) sites. In general, no clear spatial pattern of soil C stocks could be identified in the oil palm-based agroforestry systems. The significant difference in soil carbon between the oil palm area (under oil palm: 12.7 ± 2.3 Mg C ha^?1 and between oil palm: 10.6 ± 0.5 Mg C ha^?1) and the strip area (17.0 ± 1.4 Mg C ha^?1) at 0–5 cm depth very likely reflects the high input of organic fertilizer in the strip area of the high species diversity oil palm-based agroforestry system treatment. Overall, our results indicate a high level of early net accumulation of soil C in the oil palm-based agroforestry systems (6.6–8.3 Mg C ha^?1 year^?1) that likely reflects the combination of fire-free land preparation, organic fertilization, and the input of plant residues from pruning and weeding.     

Agroforestry species of the Bolivian Andes: an integrated assessment of ecological, economic and socio-cultural plant values

Agroforestry is a promising method for enhancing land-use sustainability in the Bolivian Andes. However, its benefits in terms of rural development are under-recognized due to gaps in understanding users?? perceptions while taking into consideration both local and global environmental goals. Our study aimed to narrow these gaps by developing an analytical framework for analyzing the site-specific socio-ecological factors and interactions related to local woody species and assessing their ecological, economic, and socio-cultural plant values in order to identify the most promising agroforestry species. The framework was then tested in an indigenous community at 2,760?C3,830?m?a.s.l., incorporating vegetation surveys, environmental studies, and interviews on plant functions. Ecological, economic, and socio-cultural values and the ecological apparency of plants were calculated, and detrended correspondence and principal component analyses helped to reveal the socio-ecological context of significant factors for plant distribution and uses. Results showed dominating seral woody species along an altitudinal gradient. Although shrubs were more ecologically apparent than trees, trees were perceived to be more valuable as the usefulness and cultural importance of species increased with plant height and timber availability. Phytosociological factors played a minor but still significant role in perceived usefulness. Schinus molle and Prosopis laevigata (<3,200?m a.s.l.), Polylepis subtusalbida (>3,200?m a.s.l.), and Baccharis dracunculifolia (both zones) were evaluated as most promising for agroforestry use. In conclusion, our analytical framework proved to be a valuable tool for context-specific agroforestry plant selection. Nonetheless, economic, technical, and socio-cultural limitations of cultivating native agroforestry species were revealed as well. Agroforestry science and practice should, therefore, focus on enhancing reproductive potentials of existing woody vegetation, as well as problem-oriented horizontal dialogues between indigenous, expert, and scientific actors.     

Floristic composition and management of cropland agroforest in southwestern Bangladesh

Cropland agroforest is an important production system in the southwest region of Bangladesh. This study focused on the floristic composition and management of existing cropland agroforests. A total of 313 cropland agroforests were surveyed and 83%respondents practiced pure agroforestry while the remaining 17% practiced agroforestry with fisheries. A total of 18 forest trees and 2 shrubs were recorded from 11 families and 59 species of agricultural crops were from 28 families. A higher proportion （79%） of cropland agroforests were occupied small land areas （0.12-0.80 ha）. About 63% of respondents planted trees for fruit production and 47%for timber production, and 35%of respondents engaged in commercial production （35%）. Swietenia macrophylla was the most prevalent species （relative prevalence 20.83） followed by Man-gifera indica （relative prevalence 15.57） and Cocos nucifera （relative prevalence 7.08）. Shorter spacing was used for timber and fuel wood species and wider spacing for fruit trees. A wide range of rotation periods, from 5 to 25 years, was observed for both cases. The use of chemical fertilizer was highest followed by cow dung and compost in cropland agroforests. Overall management practices of cropland agroforest in southwest Bangladesh were determined by the end product and local demand.     

Spatial and temporal trends in soil N-mineralization rates under the agroforestry systems in Bhabhar belt of Kumaun Himalaya,India

To access the process of nitrogen mineralization in soil, the buried-bag technique was used among traditional agroforestry systems in the Bhabhar belt of Kumaun Himalaya. The present study, determined the relationship between various parameters of N-mineralization with agroforestry systems, seasons and soil depths. Season and soil depth have significantly (p?<?0.001) affected the process of ammonification, nitrification and net N-mineralization. The soil ammonium-N pool was comparatively higher than the nitrate-N pool. Highest amount of ammonium and nitrate-N were recorded in the agri-horticulture (AH) system, and lowest in the agri-horti-silviculture (AHS) system. Among the systems, highest amount of inorganic-N (ammonium?+?nitrate) was recorded during rainy season while, lowest during winter season. The highest ammonification rate (6.47?±?1.47 mg kg^?1 month^?1) was observed in agri-silviculture system and lowest (5.67?±?1.68 mg kg^?1 month^?1) in AHS system, while nitrification value was maximum (2.53?±?0.40 mg kg^?1 month^?1) in AH system and minimum (2.23?±?0.37 mg kg^?1 month^?1) in AHS system. The values of net N-mineralization were ranged from 4.03?±?0.53 to 13.29?±?0.44 mg kg^?1 month^?1. The values of inorganic-N and net N-mineralization were significantly more (P?<?0.01) in the surface soil layer (0–20 cm) than the subsurface layers (20–40 cm and 40–60 cm). Nitrogen mineralization was negatively correlated with the soil pH and positively correlated with soil organic carbon and total soil nitrogen. Higher rate of N-mineralization in AHS system indicated rapid turnover of nitrogen due to soil management practices and suggested that the changes in agroforestry based land-use systems alter the process of net N-mineralization, nitrification and ammonification.

     

Differences in transpiration between a forest and an agroforestry tree species in the Sudanian belt

Average population growth in the African Sudanian belt is 3 % per year. This leads to a significant increase in cultivated areas at the expense of fallows and forests. For centuries, rural populations have been practicing agroforestry dominated by Vitellaria paradoxa parklands. We wanted to know whether agroforestry can improve local rainfall recycling as well as forest. We compared transpiration and its seasonal variations between Vitellaria paradoxa, the dominant species in fallows, and Isoberlinia doka, the dominant species in dry forests in the Sudanian belt. The fallow and dry forest we studied are located in northwestern Benin, where average annual rainfall is 1200 mm. Sap flow density (SFD) was measured by transient thermal dissipation, from which tree transpiration was deduced. Transpiration of five trees per species was estimated by taking into account the radial profile of SFD. The effect of the species and of the season on transpiration was tested with a generalized linear mixed model. Over the three-year study period, daily transpiration of the agroforestry trees, V. paradoxa (diameters 8–38 cm) ranged between 4.4 and 26.8 L day^?1 while that of the forest trees, I. doka, (diameters 20–38 cm) ranged from 9.8 to 92.6 L day^?1. Daily transpiration of V. paradoxa was significantly lower (15 %) in the dry season than in the rainy season, whereas daily transpiration by I. doka was significantly higher (13 %) in the dry season than in the rainy season. Our results indicate that the woody cover of agroforestry systems is less efficient in recycling local rainfall than forest cover, not only due to lower tree density but also to species composition.     

Carbon dynamics and stability between native Masson pine and exotic slash pine plantations in subtropical China

Afforestation and ecological restoration have often been carried out with fast-growing exotic tree species because of their high apparent growth and yield. Moreover, fast-growing forest plantations have become an important component of mitigation measures to offset greenhouse gas emissions. However, information on the long-term performance of exotic and fast-growing species is often lacking especially with respect to their vulnerability to disturbance compared to native species. We compared carbon (C) storage and C accumulation rates in vegetation (above- and belowground) and soil in 21-year-old exotic slash pine (Pinus elliottii Engelm.) and native Masson pine (Pinus massoniana Lamb.) plantations, as well as their responses to a severe ice storm in 2008. Our results showed that mean C storage was 116.77 ± 7.49 t C ha^?1 in slash pine plantation and 117.89 ± 8.27 t C ha^?1 in Masson pine plantation. The aboveground C increased at a rate of 2.18 t C ha^?1 year^?1 in Masson pine and 2.23 t C ha^?1 year^?1 in slash pine plantation, and there was no significant difference in C storage accumulation between the two plantation types. However, we observed significant differences in ice storm damage with nearly 7.5 % of aboveground biomass loss in slash pine plantation compared with only 0.3 % loss in Masson pine plantation. Our findings indicated that the native pine species was more resistant to ice storm because of their adaptive biological traits (tree shape, crown structure, and leaf surface area). Overall, the native pine species might be a safer choice for both afforestation and ecological restoration in our study region.     

Community assessment of agroforestry opportunities in GaMothiba,South Africa

The sustainability of cocoa growing systems in the humid tropics is debatable. Socio-economic and technical data were obtained from 1,171 cocoa farmers and 1,638 cocoa plantations to assess the long-term dynamics of cocoa agroforests in central Cameroon since the beginning of the twentieth century. On-site, we estimated the age of the cocoa trees and measured their density in a sub-sample of 402 cocoa plantations. We inventoried associated woody species in 45 cocoa plantations from this sub-sample. Our results revealed a high Shannon index for the cocoa plantations (2.6) and showed that an average of 25 tree species per cocoa plantation had been planted with the cocoa trees at a density of 120 trees ha⁻¹. Surveys indicated that there had been no mineral fertilization. Nearly 70% of the cocoa agroforests were over 40 years old, and all farmers continuously regenerated their cocoa tree stands. Irrespective of the cocoa plantation age, the cocoa tree density remained over 1,000 plants ha⁻¹, and fermented dried cocoa yields were 255 kg ha⁻¹ on average. Cocoa agroforests occupied 60% of the cultivated area on farms and cocoa sales accounted for 75% of total farm income. Almost a third of the farmers were from the area and under 40 years old. In conclusion, our results show that the farmers’ agroforestry practices, in addition to the fact that the cocoa tree stands were continuously regenerated and passed down between generations of farmers, could explain the long-term dynamics of cocoa agroforests in central Cameroon.     

Seasonal changes in litter fall and its quality from three sub-tropical fruit tree species at Nelspruit, South Africa

Litter fall from upper storey trees in agroforestry systems contributes to nutrient cycling for the benefit of all components of the system besides serving as mulch. This study examined the seasonal changes in the quantity and quality of leaf litter fall from three sub-tropical fruit trees viz: avocado (Persea americana L.), mango (Mangifera indica L.) and litchi (Litchi chinensis L.) which have potential for use in agroforestry. Leaf litter production was estimated using nylon mesh litter traps erected over five randomly selected trees of each species in a completely randomised design. Litter quality was determined by analysing ash content and polyphenol, carbon, cellulose, lignin and nutrient concentrations over a 2?year period (2007?C2008). Total annual leaf litter production during the study period (dry matter basis) was 8.3, 6.3 and 5.6?t?ha^?1?year^?1 for litchi, mango and avocado, respectively. In both years, leaf litter fall was greatest during autumn and lowest during winter in all species. There were no significant differences in S, Ca, Mg and Mn concentrations in the leaf litter, but polyphenol, N, P and K concentrations differed significantly (P?<?0.05) between species. It was concluded that litter quality from all three tree species was low and would require appropriate management to improve its quality.     

The role of complex agroforestry systems in the conservation of forest tree diversity and structure in southeastern Ghana

The role of different agroforestry systems in the conservation of plant diversity and forest structure has not been directly compared in many agricultural dominated landscapes. In this study, we investigated tree diversity and forest structure in a complex agroforestry landscape traditionally grown for cocoa and mixed food crops and compared these to the natural forest in southeastern Ghana. The study was carried out using 36 25 m × 25 m plots. There was significant difference [95% Confidence Interval (95% CI)] in the native forest/non-crop tree species richness between the natural forest and the agroforest farmlands but species richness was similar between the cocoa and mixed food crops agroforests. The density of native forest/non-crop trees was significantly higher (P < 0.05) in the natural forest but similar between cocoa and mixed food crops agroforest. Similarly, the basal area of native forest/non-crop trees was significantly higher (P < 0.05) in the natural forest but comparable between cocoa and food crops agroforest. Of the 20 most abundant native forest/non-crop trees recorded, 12 of them showed significant responses (P < 0.05) to land use change with nine of the species significantly abundant in the natural forest relative to the agroforest systems. Eighteen native forest/non-crop trees species in the agroforestry systems were commonly recorded as being used; 100% of them being used as fuel wood with 83.3 and 77.8%, respectively, used as medicines and materials. The findings of this study suggests that although complex agroforestry systems are a poor substitute for the natural forest the heterogeneous mosaic landscape in which complex agroforestry forms part can be strategically managed to maximize the benefits of both sustainable agriculture production and conservation of plant diversity by acting as buffer between protected areas and intensively managed areas.     

Allometric equations for biomass estimation of Enset (Ensete ventricosum) grown in indigenous agroforestry systems in the Rift Valley escarpment of southern-eastern Ethiopia

Enset (Ensete ventricosum), commonly known as false banana, is a large thick, single-stemmed, perennial herbaceous banana-like plant growing in the wild of sub-Sahara Africa, Madagascar and parts of Asia. In Ethiopia it has been domesticated and serves as a food plant. While the productivity and management of enset for food (pseudostem and corm) has been studied, little attention has been given to total biomass production and associated carbon sequestration. The objective of this study was to develop and evaluate allometric models for estimating above and belowground biomass and organic matter contents of enset grown in indigenous agroforestry systems in Rift Valley escarpment of south-eastern Ethiopia. Biomass harvesting of 40 plants was carried out at altitudes from 1900 to 2400 m.a.s.l. The mean plant dry weight was 9.4 ± 0.84 kg and organic matter content 94 %. Pseudostem biomass accounted for highest (64 %) of total biomass, followed by corm (24 %) and foliage (12 %). Basal diameter (d ₁₀) was the best predictor variable for total and all biomass components (Spearman r = 0.775–0.980, p < 0.01). The power model using d ₁₀ and height (H) (Y = 0.0007d ₁₀ ^2.571 H ^0.101; R ² = 0.91) was found to be the best performing model (highest ranking over six good-of-fit statistics) for predicting total biomass. Model performance decreased in the order pseudostem > corm > foliage biomass. The models presented can be used to accurately predict biomass and organic matter of enset in the agroforestry systems of Rift Valley escarpments Ethiopia.     

Species-specific responses to environmental stress on germination and juvenile growth of two Bolivian Andean agroforestry species

Integrating native trees in farmland can support soil, water and biodiversity conservation. This is particularly important in regions characterized by long periods of drought and soil erosion, such as the Bolivian Andes, where agroforestry with native woody species is rarely applied. Better knowledge on the effects of environmental stress on propagation and establishment of such native plants is needed to optimize their cultivation. In our study, we tested the effects of temperature and scarification on seed germination, and assessed seedling survival and juvenile growth of two potential agroforestry species (Prosopis laevigata var. andicola, Schinus molle) under diverse soil and water conditions. Temperatures above 30 °C accelerated germination, but they increased fungi infestation in the case of S. molle. The application of acid and mechanical scarification significantly improved the germination capacity of P. laevigata var. andicola. Medium to high moisture levels in sand provided the most favourable conditions for plant growth. S. molle was more sensitive to dry and P. laevigata var. andicola more vulnerable to water-saturated clay loam. Mulching enhanced the survival and growth of S. molle juveniles, but increased P. laevigata var. andicola’s growth in sand and dry soils only. Our results may facilitate guidance on improving propagation of these two potential agroforestry species under environmental stress conditions. More generally, our study shows that easily applicable treatments, such as mulching, can significantly improve the cultivation of native species, provided that their habitat requirements and limiting factors are well known. This highlights the relevance of identifying and closing such knowledge gaps for native trees and shrubs in order to promote their potential for use in agroforestry.     

Natural durability of wood of ten native species from northeastern Mexico

Thorn scrub vegetation in Mexico is distributed over 50 million ha, where native tree species are the source of forage, timber, firewood and charcoal. Research describing wood durability of species from this vegetation type has not been fully determined, nor classified according to international standards. Thus, the aim of this study was to determine and classify the natural durability of ten woody species. Their natural durability was determined according to the European Pre-Norm 807, the loss of dynamic modulus of elasticity (MOEdyn) (MPa) was determined and wood mass loss (g) after being exposed to Trametes versicolor and Coniophora puteana fungi. Wood durability was classified according to the European Norm 350-1. Highly significant differences (p<0.001) were found between the durability of woody species. The more durable species with lower MOEdyn lost were Condalia hookeri (57.5%±0.6%), Havardia pallens (58.2%±0.4%) and Acacia schaffneri (58.9%±6.3%). Species with lower mass loss after exposed to Coniophora puteana were Ebenopsis ebano (6.3%±1.9%), Condalia hookeri (8.6%±2.3%) and Cordia boissieri (11.8%±2.3%). E. ebano (7.1%±2.4%), Condalia hookeri (8.2%±2.5%) and Cordia boissieri (11.5%±3.1%) showed the lower mass lost after exposed to T. versicolor. According to European Norm 350-1, three woody species were classified as very durable and durable species.     

Woody biomass on farms and in the landscapes of Rwanda

Scattered trees and woodlots are a prominent feature of agricultural landscapes of Rwanda. However, little is known about their characteristics and their contribution to farmers’ wood needs. Here, we present the results of a survey of (a) the abundance, composition, and size of trees and woodlots in the low, medium and high altitude regions of Rwanda, (b) total woody biomass and biomass for fuelwood at farm and landscape levels, and (c) opportunities for their sustainable use. Scattered trees occurred in all landscapes at minimum densities ranging from 20 to 167 trees ha^?1. Of the 56 tree genera recorded, a handful of tree species dominated, with the ten most common species accounting for over 70 % of all trees recorded. Most of them provided fuelwood, fruit and timber to farm owners. Woodlots occurred on about 40 % of the survey farms and consisted for 90 % of eucalyptus coppice. Woody biomass dry weight of scattered trees on agricultural landscape was 0.7 t ha^?1 in low altitude region (LAR), 3 t ha^?1 in medium altitude region (MAR), and 1 t ha^?1 in high altitude region (HAR). Dry weight woody biomass in woodlots (<0.5 ha) was the highest in MAR (221 t ha^?1), followed by that in HAR (205 t ha^?1) and least in LAR (96 t ha^?1). About 80 % of total woody biomass in trees and woodlots on farmland was useable biomass for fuelwood, indicating that the production of fuelwood on agricultural land was important. Woody biomass on agricultural land was higher than that in forest plantations, and was potentially sufficient to reduce the gap between fuelwood supply and demand when the entire agricultural area was taken into account. In order to achieve this on agricultural land, while contributing to food security and environmental conservation as well, smallholder farmers must be provided with incentives to grow woodlots and to adopt agroforestry systems, thereby considering the trade-offs with agricultural production. Strategies to encourage smallholder farmers to increase the use of agroforestry have to account for the farmers’ ecological and socioeconomic conditions.     

Structure and regeneration status of Komto Afromontane moist forest, East Wollega Zone, west Ethiopia

We conducted a study in Komto Forest in East Wollega Zone, Oromia National Regional State, West Ethiopia for determining vegetation structure and regeneration status in this forest. We systematically sampled 53 quadrats (20 m × 20 m) along line transects radiating from the peak of Komto Mountain in eight directions. Vegetation parameters such as DBH, height, seedling and sapling density of woody species, and location and altitude of each quadrat were recorded. In total, 103 woody plant species of 87 genera and 45 families were identified. Analysis of selected tree species revealed different population structures. Generally, the forest was dominated by small trees and shrubs characteristic of secondary regeneration. Observations on the regeneration of the forest indicated that there are woody species that require urgent conservation measures. Based on the results of this study, we recommend detailed ecological studies of various environmental factors such as soil type and properties, and ethnobotanical studies to explore indigenous knowledge on uses of plants.     

Afforestation of savannah with cocoa agroforestry systems: a small-farmer innovation in central Cameroon

Cocoa cultivation is generally considered to foster deforestation. Contrary to this view, in the forest–savannah interface area in Cameroon, farmers have planted cocoa agroforestry systems on Imperata cylindrica grasslands, a soil-climate zone generally considered unsuitable for cocoa cultivation. We undertook a survey to understand the agricultural and ecological bases of this innovation. Age, cropping history and marketable cocoa yield were assessed in a sample of 157 cocoa plantations established on grasslands and 182 cocoa plantations established in gallery forests. In a sub-sample of 47 grassland cocoa plantations, we inventoried tree species associated with cocoa trees and measured soil organic matter levels. Marketable cocoa yields were similar for the two types of cocoa plantations, regardless of their age: 321?kg?ha^?1 in cocoa plantations on grasslands and 354?kg?ha^?1 in cocoa plantations in gallery forests. Two strategies were used by farmers to eliminate I. cylindrica prior to the establishment of cocoa plantations, i.e., cropping oil palms in dense stands and planting annual crops. Farmers then planted cocoa trees and fruit tree species, while preserving specific forest trees. The fruit tree and forest tree densities respectively averaged 223 and 68 trees?ha^?1 in plantations under 10?years old, and 44 and 27 trees?ha^?1 in plantations over 40?years old, whereas the cocoa tree density remained stable at 1,315 trees?ha^?1. The Shannon–Weaver index increased from 1.97 to 2.26 over the same period although the difference was not statistically significant. The soil organic matter level was 3.13?% in old cocoa plantations, as compared to 1.7?% in grasslands. In conclusion, our results show that the occupation of grasslands by cocoa agroforestry systems is both an important example of ecological intensification and a significant farmer innovation in the history of cocoa growing.     

Can the shrub Chromolaena odorata (Asteraceae) be considered as improving soil biology and plant nutrient availability?

This paper attempts to provide a new perception of the weed Chromolaena odorata (Asteraceae) which is considered as a plague in agriculture or as a soil fertility indicator. The study was conducted in the forest-savanna transition zone of C?te d??Ivoire and aimed to compare soil biological activity and plant nutrient availability under three well-represented vegetation features, including C. odorata lands (ChrO), shrub savannas (ShrS), and grass savannas (GraS). Each of these vegetation features included five plot replicates (50?m?×?50?m size) distributed in the landscape. Soil chemical parameters such as pH, organic matter, soluble phosphorus, exchangeable bases, and biological parameters such as abundance and diversity of earthworms, and soil enzymatic activities were investigated. Composite soil samples were collected and analyzed for chemical and microbial parameters while earthworms were sampled using the Tropical Soil Biology and Fertility 25?×?25?×?30?cm soil monolith method. A principal component analysis showed a clear demarcation between C. odorata plots and the savanna ones. Soluble P and exchangeable bases were significantly higher under ChrO than under both savannas. Earthworm density was twice higher under ChrO (433.3?±?90.8?ind?m^?2) than under ShrS (173.9?±?61.5?ind?m^?2) and GraS (176.0?±?40.6?ind?m^?2) and this was accounted for by the abundance of detritivores and polyhumics. Acid and alkaline phosphatase activities under ChrO (2.9?±?0.2 and 2.5?±?0.3???mol pNP?g^?1 soil?h^?1, respectively) were twice higher than under both savannas. Based on the fact that ChrO and ShrS were located on similar soil types and had the same topographic position, we concluded that the establishment of C. odorata in a savanna land and its subsequent high biomass and quality-litter production were mostly the reasons of the improvement in soil biology and plant nutrient availability. Between-savanna comparison showed that ShrS, with higher CEC and exchangeable bases, was somewhat more fertile than GraS, probably because of a better soil physical status. In view of the agronomic potentials of the shrub C. odorata, it may be taken as a basis for improved fallow in Africa.