Domestication potential of Marula (Sclerocarya birrea subsp caffra) in South Africa and Namibia: 2. Phenotypic variation in nut and kernel traits

As part of a wider study characterizing tree-to-tree variation in fruit traits as a pre-requisite for cultivar development, fruits were collected from each of 63 marula (Sclerocarya birrea) trees in Bushbuckridge, South Africa and from 55 trees from the North Central Region of Namibia. The nuts were removed from the fruit flesh, and the kernels extracted, counted and weighed individually to determine the patterns of dry matter partitioning among the nut components (shell and kernel) of different trees. Mean nut, shell and kernel mass were not significantly different between the two countries. Between sites in South Africa there were highly significant differences in mean nut mass, shell mass, kernel mass and kernel number. In Namibia, there were highly significant differences between geographic areas in mean shell mass, kernel mass and kernel number, but not in nut mass. These differences had considerable impacts on shell:kernel ratios (8.0 - 15.4). In South Africa, mean kernel mass was significantly greater in fruits from farmers fields (0.42 g) than from communal land (0.30 g) or natural woodland (0.32 g). Within all sites, in both South Africa and Namibia, there was highly significant and continuous variation between individual trees in nut mass (South Africa = 2.3 - 7.1 g; Namibia = 2.7 - 6.4 g) and kernel mass (South Africa = 0.09 - 0.55 g; Namibia = 0.01 - 0.92 g). The small and valuable kernels constitute a small part of the nut (Namibia = 6.1- 11.1%; South Africa = 7.6 - 10.7%). There can be 4 kernels per nut, but even within the fruits of the same tree, kernel number can vary between 0-4, suggesting variation in pollination success, in addition to genetic variation. The nuts and kernels of the Namibian trees were compared with the fruits from one superior tree (Namibian Wonder: nuts = 10.9 g; kernels = 1.1 g). Oil content (%) and oil yield (g/fruit) also differed significantly between trees (44.7 - 72.3% and 8.0 - 53.0 g/fruit). The percentage frequency distribution of kernel mass was skewed from trees in farmers fields in South Africa and in some sites in Namibia, suggesting a level of anthropogenic selection. It is concluded that there is great potential for the development of cultivars for kernel traits, but there is also a need to determine how to increase the proportion of nuts with four kernels, perhaps through improved pollination success.     

Domestication potential of Marula (<Emphasis Type="Italic">Sclerocarya birrea</Emphasis> subsp. <Emphasis Type="Italic">caffra</Emphasis>) in South Africa and Namibia: 3. Multiple trait selection

An understanding of the inter-relationships between the traits characterising tree-to-tree variation in fruits and kernels is fundamental to the development of selected cultivars based on multiple trait selection. Using data from previously characterised marula (Sclerocarya birrea) trees in Bushbuckridge, South Africa and North Central Region of Namibia, this study examines the relationships between the different traits (fruit pulp, flesh/juice mass, and nut shell and kernel mass) as a means to determine the opportunities to develop cultivars. Strong and highly significant relationships were found between fruit mass and pulp mass in trees from South Africa and Namibia, indicating that size is a good predictor of fruit pulp production. However, fruit size is not a good predictor of nut or kernel production, as there were weak relationships between fruit and nut and/or kernel mass, which varied between sites and landuses. Generally, the relationships between fruit mass and kernel mass were weaker than between fruit mass and nut mass. Relationships between kernel mass and shell mass were generally weak. The lack of strong relationships between fruit and kernel mass does, however, imply that there are opportunities to identify trees with either big fruits/small nuts for pulp production, or trees with large kernels in relatively small fruits for kernel oil production. However, within fruits from the same tree, nuts could contain 0–4 kernels, indicating that even in trees with an inherent propensity for large kernels, improved pollination may be required to maximise kernel mass through an increase in kernel number. Finally, the relationships between percentage kernel oil content and the measured morphological traits were also very weak. The conclusions of these results are that there is merit in identifying different combinations of traits for the selection of trees producing either pulp or kernels. Consequently, fruit and kernel ‘ideotypes’ are presented as guides to the selection of elite trees for cultivar development. These results have important implications for the domestication of the species as a producer of fruits or kernels for food/beverages or cosmetic oils.     

Domestication of Irvingia gabonensis: 3. Phenotypic variation of fruits andkernels in a Nigerian village

Domestication of Irvingia gabonensis, a fruit tree grown in agroforestry systems in West and Central Africa, offers considerable scope for enhancing the nutritional and economic security of subsistence farmers in the region. Assessments of phenotypic variation in ten fruit, nut and kernel traits were made on twenty-four ripe fruits from 100 Irvingia gabonensis trees in Ugwuaji village in southeast Nigeria, a center of genetic diversity for this species. There were important differences between the young planted trees of this study and the older unplanted trees of a similar study in Cameroon. Significant and continuous tree-to-tree variation was found in fruit mass(69.0–419.8 g), flesh mass (59.5–388.8 g), nut mass (9.5–40.6 g), shell mass (4.9–30.9 g) and kernel mass (0.41–7.58 g); fruit length (49.2–89.3 mm) and width (46.2–100.5 mm) and flesh depth (12.9–31.4 mm), as well as considerable variation in flesh colour, skin colour, fruit taste and fibrosity. Some fruits were considerably bigger than those found in Cameroon. These quantitative results will help in the development of cultivars within participatory approaches to agroforestry tree domestication, and so promote poverty alleviation and sustainable agriculture. This revised version was published online in June 2006 with corrections to the Cover Date.     

Domestication of Dacryodes edulis: 1. Phenotypic variation of fruit traits from 100 trees in southeast Nigeria

A participatory approach to tree domestication is being pioneered by ICRAF and international partners in Cameroon and Nigeria. The domestication of Dacryodes edulis offers opportunities to improve the livelihoods of subsistence farmers and to diversify farming systems, such as cocoa farms. The trees produce marketable fruits as well as shade for cocoa and coffee. Twenty-four ripe fruits were collected from each of 100 D. edulis trees in Mgbuisi, southeast Nigeria by subsistence farmers. There was continuous and significant tree-to-tree variation in fruit mass (10.2±0.5–71.4±1.3 g), flesh mass (6.8±0.3– 62.2±1.2 g) and kernel mass (1.3±0.5–15.1±0.4 g). Mean fruit mass did not differ significantly between different land uses. Flesh mass:kernel mass ratio varied from 0.79 to 29.0. Two trees had fruits without kernels. There was also continuous and significant tree-to-tree variation in fruit length (39.0±0.6– 95.1±1.2 mm), fruit width (21.82±0.16–43.75±0.33 mm) and flesh thickness (1.82±0.1–6.39± 0.1 mm). Fruit length:width ratio varied from 1.35 to 3.18. Cooked fruits varied in taste with only 14% of trees getting the highest score. Similarly, fruits varied in oiliness with only 3% of trees getting the highest score. Thirteen skin colours were recorded, with the most common being dark blue (31%), greyish violet (29%) and deep blue (9%). Ninety-nine percent of the trees had been planted, with 57% in homegardens, 22% in crop fields, 17% in fallow land and 4% in cocoa. Tree height ranged from 4 to 22m, and DBH from 9.55 to 63.65 cm. Tree age ranged from 5 to 64 years. Farmers reported first fruiting from age 3 up to 22 years (average of 9.4 years). Most trees originated from seeds bought in markets (63%). Market prices of fruits from different trees, ranged from 2 to 12 fruits for 10 Naira (US0.07). These quantitative results will help in the identification of elite trees of D. edulis for cultivar development through clonal propagation.     

Domestication of Irvingia gabonensis: 2. The selection of multiple traits for potential cultivars from Cameroon and Nigeria.

Ten fruit and kernel traits were assessed in 24 fruits of each of 152Irvingia gabonensis trees in three distinct populations in west and central Africa [2 populations of non-planted trees in Cameroon: Nko'ovos II (21 trees) and Elig-Nkouma (31 trees) and 1 population of planted trees in Nigeria: Ugwuaji (100 trees)]. Strong relationships were found between fruit weight and other fruit traits (e.g. flesh weight[r ² = 0.99: P < 0.001],fruit length [r ² = 0.74–0.83:P < 0.001], fruit width[r ² = 0.77–0.88: P< 0.001]). In contrast, relationships between kernel weight and other kernel/nut traits (e.g. shell weight and nut weight) were found to be weak[r ² = 0.009–0.37, P =0.058–0.001], with the exception of nut weight at Nko'ovos II(r ² = 0.65, P < 0.001).Relations hips between fruit and kernel traits (fruit massv. kernel mass, fruit mass v. shell mass, flesh mass v. kernel mass, nut massv. fruit mass and flesh depth v.kernel mass) were found to be very weak. This indicates that domestication through the selection and vegetative propagation of multiple-trait superior phenotypes is unlikely to be able to combine good fruit characteristics and good kernel characteristics within cultivars. Consequently, domestication activities should independently focus on ideotypes representing: 'fresh fruit' traits, and 'kernel' traits, that combine high values of the different fruit and kernel characteristics respectively. Evidence from this study indicates that selection of the three trees closest to the fruit ideotype per village as the mother plants for vegetative propagation and cultivar development, should give village level gains of 1.3 – 2-fold in fruit mass, and up to 1.5-fold in taste. Similarly for the kernel ideotype, selection of the three trees with the best fit would give potential gains in kernel mass of 1.4 – 1.6-fold. This revised version was published online in June 2006 with corrections to the Cover Date.     

Domestication of Irvingia gabonensis: 1. Phenotypic variation in fruits and kernels in two populations from Cameroon

Twenty four fruits from each of 52 Irvingia gabonensis trees from two villages (Nko'ovos II and Elig Nkouma) of the humid lowland forest zone of Cameroon (West Africa) were assessed to determine the extent of variation in ten fruit, nut (endocarp), and kernel (cotyledon) characteristics. Highly significant differences were found in fruit length (Range = 46.2 to 77.3 mm), fruit width (45.1 to 72.5 mm), flesh (mesocarp) depth (11.2 to 21.8 mm), fruit mass (44.5 to 195.4 g), kernel mass (0.54 to 6.9 g) and shell mass (5.4 to 18.6 g). In each of these traits there was continuous variation. Differences were also observed in fruit taste and fibrosity. The most frequent skin and flesh color was yellow (Methuen Color Code 4A8). Mean fruit length, fruit width, fruit mass, shell mass and kernel mass differed significantly between villages, but did not differ between different landuses (homegardens, cocoa farms, crop fields or fallows). These results represent the first quantitative assessment of tree-to-tree variation in fruit traits for this species and are discussed with regard to the domestication potential of I. gabonensis.This revised version was published online in November 2005 with corrections to the Cover Date.     

Agroforestry potential of Dacryodes edulis in the oil palm-cassava belt of southeastern Nigeria

Between June 1993 and June 1994, 112 farmers in the oil palm (Elaeis guineensis)-cassava (Manihot esclentus) belt of southeastern Nigeria were interviewed to determine the status and agroforestry potential of Dacryodes edulis. Between 50% and 100% of respondents in different states within the belt owned D. edulis trees. On average, a farmer owned 9.3 trees, the largest number being 16, by farmers in Imo State. Twenty percent of farmers in the system rated D. edulis their best farm tree. It was present in all the farm niches: homegardens (51.4%), tree crop plots (20.7%) food crop plots (11.4%), secondary forest/fallow (14.2%) and virgin forest (2.5%). The tree is planted primarily for home consumption and sale to generate cash. At the current densities, on-farm D. edulis trees generally did not decrease yield of companion crops or trees. Except for ring weeding around the stem, D. edulis trees received little or no management attention. More than 50% of the trees produced 33 to 50 kg of fruit tree⁻¹ annually. This is valued at US $0.4 to 0.8 kg⁻¹. Farmers were willing to plant more D. edulis trees provided trees with traits such as less height for easy harvesting of fruits, larger fruit, more fruits, sweeter fruits and year round production of fruits were available. Possible agroforestry technologies into which D. edulis may fit include live fences, scattered trees in food crop fields, shade trees in tree crop plots and contour bund or hedgerow planting. Research is required to determine best tree accessions, canopy management strategies, optimum tree population and improved methods on post- harvest handling of fruits. This revised version was published online in June 2006 with corrections to the Cover Date.     

Agroforestry Practices among Male and Female Farmers in South–South, Nigeria

Perceptions of the benefits of agroforestry practices (AFPs) and the level of utilization of these practices by male and female participants were examined in the agroforestry programs of the Akwa Ibom and Cross River State Governments of the South–South region of Nigeria. Responses were derived from 250 randomly selected respondents. Overall, respondents perceived the major benefit of agroforestry practices as enhancement of environmental conservation. Female respondents however perceived increased income as the major benefit of agroforestry practices. A composite perception index revealed that women farmers were more favourably disposed than male respondents to the utilization of agroforestry practices. The farmers were favourably disposed to the utilization of only five of the 16 identified AFPs in the study area, including ‘leaving of isolated woody trees on farmlands’, ‘utilizing woody trees as windbreaks’ and to ‘demarcate farm boundaries’, ‘planting of woody trees in combination with fruit trees’, and ‘planting of woody trees in combination with vegetable crops’. Male and female responses were generally similar although a major difference was observed with regard to ‘planting of trees for fuel wood’. The composite index, however, revealed a general low level of utilization of AFPs, although female farmers were relatively more disposed to the utilization of AFPs. The key policy implication of the study is the necessity to embark on sustained education and environmental awareness campaign, with a focus on presenting AFPs as livelihood sustaining and risk mitigation activities, against its present misperception as simply a government strategy to increase the stock of woody trees in the environment. This policy should endeavour to target landless women farmers who have been found to be more interested in the adoption of AFPs into their farming system.     

Quantitative descriptors of variation in the fruits and seeds of Irvingia gabonensis

Methods were developed to quantify variation in the fruit, nut and kernel traits using the fruits from four trees of Irvingia gabonensis, an indigenous fruit tree of west and central Africa. The measurement of 18 characteristics of 16–32 fruits per tree identified significant variation in fruit, nut and kernel size and weight, and flesh depth. Differences were also identified in shell weight and brittleness, fruit taste, fibrosity and flesh colour. Relationships between fruit size and weight with nut and kernel size and weight were found to be very weak, indicating that it is not possible to accurately predict the traits of the commercially-important kernel from fruit traits. Seven key qualitative traits are recommended for future assessments of the levels of genetic variation in fruits and kernels. These traits describe ideotypes for fresh fruit and kernel production.This revised version was published online in November 2005 with corrections to the Cover Date.     

Population status and gender imbalance of the marula tree, Sclerocarya birrea subsp. caffra in northern Namibia

The population status of many wild fruit trees that support rural people in Africa remains poorly understood despite its importance for their management. Here, we establish a baseline for size class distribution and gender ratios for marula (Sclerocarya birrea subsp. caffra), a widespread but sparsely distributed species of wooded farmland, that has both traditional importance to rural communities and an emerging commercial potential. A population of marula trees around two neighbouring villages in northern Namibia was surveyed in August 2001. The stem diameter at 1.3 m height (dbh) of all individuals ge1 cm dbh in 40 fields, totalling 286 ha in area, was measured and their gender was recorded as female, male or unknown. Over 400 trees were enumerated, the largest >100 cm dbh. Despite the low threshold (1 cm dbh) for inclusion, relatively few trees (around 40%) were ¡20 cm dbh, suggesting the population may not be self-sustaining. The area was nevertheless well-stocked, with ca 1 tree ha^?1 ge20 cm dbh – an unusually high density for Sclerocarya. Tree gender becomes evident when individuals reach about 15 cm dbh. In one village, the sex ratio of larger trees (40–80 cm dbh) was significantly skewed in favour of females. This was attributed to selective elimination of individuals that have failed to fruit and was much less pronounced in the second village. The sparse distribution and gender imbalance of trees have implications in relation to management requirements for ensuring adequate pollen flow.     

Human impact on population structure and fruit production of the socio-economically important tree Lannea microcarpa in Burkina Faso

Non-timber forest products (NTFPs) are of high socio-economic value for rural people in West Africa. Main factors determining the status of the populations of socio-economically important tree species providing those NTFPs are human activities. This study assesses the impact of human population density, land use, and NTFP-harvesting (pruning and debarking) on population structure and fruit production of the socio-economically important tree Lannea microcarpa that is normally conserved by farmers on fields. We compared L. microcarpa stands of protected sites with those of their surrounding communal sites in two differently populated areas in Burkina Faso. Our results reveal an opposed land use impact on the population structure of L. microcarpa in the two areas. In the highly populated area, the species population was more stable in the protected site than in the communal site, while the opposite was observed for the less populated area. Trees of the communal sites bore more fruits than trees of the protected sites. Debarking and pruning had a negative impact on fruit production of the species. We conclude that low intensity of human impact is beneficial for the species and that indirect human impact facilitates fruit production of L. microcarpa. In contrast, in the densely populated area, human impact has reached an intensity that negatively affects the populations of L. microcarpa. While the extent of protecting L. microcarpa on fields still seems to be enough to guarantee the persistence of this important species in the less populated area, it is no longer sufficient in the densely populated area.     

Interactions between Widely Spaced Young Poplars (Populus spp.) and Introduced Pasture Mixtures

Silvopastoral systems involving poplars are widespread in rural landscapes in a number of regions of New Zealand. The effect of widely spaced trees of Populus nigra × P. maximowiczii, aged 8–11 years, on the growth and botanical composition of understorey pasture mixes was determined over 3 years at a southern North Island hill country site. Pasture mixes comprised existing pasture, and two introduced test swards comprising new grass (Agrostis capillaris, Dactylis glomerata, Lolium perenne) and legume (Lotus uliginosus, Trifolium repens) cultivars. Pasture accumulation beneath trees (6.6 t DM ha⁻¹ year⁻¹) was 23% less than open (unshaded, no trees) pasture (8.6 t DM ha⁻¹ year⁻¹) and differences in accumulation occurred between tree aspects (North and South sides of trees) when trees were foliated. In early spring, North plots produced 11–14% more herbage than South plots whereas in late summer, South plots produced up to 44% more herbage than North plots. Yield of both test swards (6.4 and 8.0 t DM ha⁻¹ year⁻¹) was not significantly different from that of the existing sward (7.4 t DM ha⁻¹ year⁻¹) but productivity varied between swards in spring and summer. One test sward included Lotus uliginosus cv. Grasslands Maku, and the sward produced 30% more DM than the other swards in mid-summer. Dactylis glomerata cv. Grasslands Wana comprised 37% of the DM of swards in which it was sown and was the most successful cultivar, followed by Grasslands Maku. Both cultivars are recommended for silvopastoral systems where pasture is lightly grazed.     

Production and phenology of the fruit shrub Eugenia stipitata in agroforestry systems in Costa Rica

Arazá (Eugenia stipitata), a fruit shrub originating from Western Amazonia, was evaluated growing in association with timber shade trees (Acacia mangium or Cordia alliodora) or with plantain (Musa sp.) as a potential commercial species for the tropical moist lowlands of Talamanca, Costa Rica. Height and crown width of the four-year-old shrubs varied between 2.7–2.8 m and 2.9–3.1 m, respectively. Flowering was positively correlated with initial fruit formation 1 month later and initial fruit formation with fully developed fruits a subsequent month after that. Three to four-year-old plants produced 20.0, 20.0, and 24.5 t ha⁻¹ yr⁻¹ (fresh fruits) in associations with A. mangium, C. alliodora and plantain, respectively, with higher production in rainy months. Fruit production in later years under C. alliodora (six to eight-year-old shrubs) was 26.5 t ha⁻¹ yr⁻¹. Where markets exist for E. stipitata fruit, the association can be recommended for tropical humid lowlands of Central America.     

Fruit- and seed-germination characteristics of Strychnos cocculoides an indigenous fruit tree from natural populations in Zambia

Domestication and improvement of traditionally used wild indigenous fruit trees hold great promise in agroforestry development. Strychnos cocculoides is a wild indigenous fruit tree that was ranked third by farmers and is one of the priority species chosen for domestication in southern Africa. This study was conducted with the objective of determining the variability in fruit, seed and germination characteristics of four populations of Strychnos cocculoides collected from Zambia. Results showed significant differences (P < 0.05) between and within provenances in fruit, pericarp and pulp weights. Fruits from Kalulushi provenance were heaviest (296 g) whereas the lightest were Petauke provenance fruits (158 g). The pulp content of heavy and light fruits were 52.8% and 47.6% respectively. There was no significant difference (P > 0.05) in the number of seeds per fruit within and between the provenances. In contrast, the seed weight was significantly different (P < 0.05) within and between provenances. The heaviest seeds were found in the heaviest fruits — Kalulushi while the lightest were found in Serenje provenance. Fruit weight was positively correlated with pulp weight (P < 0.001, r = 0.70), pericarp weight (P < 0.001, r = 0.54) and seed weight (P < 0.001, r = 0.76). The provenances differed significantly (P < 0.05) in cumulative germination percentage, ranging from 56 (Kalulushi) to 83 (Kasama).This revised version was published online in November 2005 with corrections to the Cover Date.     

Interactions between Widely Spaced Young Poplars (Populus spp.) and the Understorey Environment

Silvopastoral systems involving poplars are common to rural landscapes in many parts of New Zealand. The effect of widely spaced trees of Populus nigra × P. maximowiczii, aged 8–11 years, on the surrounding micro-environment in a tree-pasture system was determined over 3 years at a southern North Island hill country site. Relative to open (unshaded, no trees) pasture, understorey pasture received 33% less radiation while radiation on the north side of trees (North) was similar to that on the south side of trees (South). Around one tree, soil temperature averaged 14.9°C annually on the North and 13.8°C on the South. Soil water content was highest in spring and winter (0.35–11;0.39 m³ m⁻³) and lowest in summer and autumn (0.21–11;0.26 m³ m⁻³), and differences occurred between plots in open pasture and those beneath trees in all seasons except spring. Soil water content of tree aspects differed slightly (<10%) in summer (South > North) and autumn (North > South), but not in spring and winter, when contents were similar. Soil pH was 0.2 units higher beneath trees than in open pasture in one of 2 years. Concentrations of Ca, K, Mg, P, and S were similar in tree and open environments. The study results complement those collected for mature trees, and will be useful in developing tree-pasture models.     

Baobab (Adansonia digitata L.) fruit production in communal and conservation land-use types in Southern Africa

Baobab fruit are harvested and used throughout Africa as an important source of food and are sold to generate income. Commercial use is increasing rapidly as derivatives of the fruit such as baobab seed oil and fruit pulp are being exported to Europe and North America. The cash derived from the sale of fruit support thousands of rural people. This study examines baobab fruit yields in an area being harvested for commercial use. It represents baobab populations and harvesting scenarios typically found in Southern Africa and is the first study in Africa to combine demographic and production data in determining baobab fruit yields.Fruit production was examined across five land-use types (nature reserves, rocky outcrops, plains, fields and villages) and over three consecutive years. Factors assessed included differences in life-stage, tree size, land-use type, inter-annual variation and quantifiable fruit predation.Results showed that adult trees produced 8 times more fruit than sub-adult trees. Fruit production fluctuated between size-classes and exhibited weak linear and logarithmic trends between fruit production and dbh and crown volume, respectively. There was high variation between trees with 41% of adult trees consistently producing <5 fruit per year, which we classed as ‘poor-producers’. Different land uses showed no significant differences in fruit production per tree, but where baboons were present, in nature reserves and rocky outcrops, predation of immature fruit resulted in up to 85% fruit loss. Villages and fields had the highest tree density and yielded the most fruit/ha. Inter-annual variation was significant with a two and a half fold difference between the highest and lowest year.The results of this study are important for economic planning and management and are key to determining sustainable harvesting levels of baobab fruit in Southern Africa.     

Early growth performance and water use of planted West African provenances of Vitellaria paradoxa C.F. Gaertn (karité) in Gonsé, Burkina Faso

A participatory selection trial of five provenances from Burkina Faso (3), Mali (1) and Senegal (1) was established in Burkina Faso in 1997 with the aim of addressing issues of the long juvenile phase and the large variability in annual fruit yields of Vitellaria paradoxa C.F. Gaertn in West Africa. The objectives of the present study were to evaluate survival rate and the growth performance of the five provenances, characterize the wetting profile under which the trees of these provenances are growing and quantify the variation in their seasonal transpiration. The design was a randomized complete block design (RCBD) with single tree as the experimental unit which was replicated 70 times. The results showed a mean survival rate of 50% for all provenances. Passoré (Burkina Faso), Djonon-Karaba (Mali) and Botou-Fada (Burkina Faso) provenances showed the highest height and collar diameter whereas the provenance of Gonsé (Burkina Faso) performed poorly. Djonon-Karaba provenance displayed the highest water use (2.70 l day⁻¹ tree⁻¹ in 2004 and 2.85 l day⁻¹ tree⁻¹ in 2005). Soil water content under Passoré provenance was the lowest (9.38%) whereas its content under Gonsé provenance (11%) was the highest with no clear pattern according to the distance from tree trunk. Samecouta and Djonon-Karaba provenances showed the highest transpiration values per sapwood unit area in 2004 (0.079 l cm⁻² day⁻¹) and in 2005 (0.069 l m⁻² day⁻¹), respectively. Based on growth performance and water use, it can be recommended at this early stage the selection of Djonon-Karaba and Passoré provenances as the most suitable for semi-arid regions of West Africa. However, there is a need for further data to model the long term effects of these provenances on soil water balance and their fruit production before reliable recommendations can be made to farmers.     

Soil organic carbon and aggregation under poplar based agroforestry system in relation to tree age and soil type

The poplar based agroforestry system improves aggregation of soil through huge amounts of organic matter in the form of leaf biomass. The extent of improvement may be affected by the age of the poplar trees and the soil type. The surface and subsurface soil samples from agroforestry and adjoining non-agroforestry sites with different years of poplar plantation (1, 3 and 6 years) and varying soil textures (loamy sand and sandy clay) were analyzed for soil organic carbon, its sequestration and aggregate size distribution. The average soil organic carbon increased from 0.36 in sole crop to 0.66% in agroforestry soils. The increase was higher in loamy sand than sandy clay. The soil organic carbon increased with increase in tree age. The soils under agroforestry had 2.9–4.8 Mg ha⁻¹ higher soil organic carbon than in sole crop. The poplar trees could sequester higher soil organic carbon in 0–30 cm profile during the first year of their plantation (6.07 Mg ha⁻¹ year⁻¹) than the subsequent years (1.95–2.63 Mg ha⁻¹ year⁻¹). The sandy clay could sequester higher carbon (2.85 Mg ha⁻¹ year⁻¹) than in loamy sand (2.32 Mg ha⁻¹ year⁻¹). The mean weight diameter (MWD) of soil aggregates increased by 3.2, 7.3 and 13.3 times in soils with 1, 3 and 6 years plantation, respectively from that in sole crop. The increase in MWD with agroforestry was higher in loamy sand than sandy clay soil. The water stable aggregates (WSA >0.25 mm) increased by 14.4, 32.6 and 56.9 times in soils with 1, 3 and 6 years plantation, respectively, from that in sole crop. The WSA >0.25 mm were 6.02 times higher in loamy sand and 2.2 times in sandy clay than in sole crop soils.     

The importance of an indigenous tree to southern African communities with specific relevance to its domestication and commercialization:a case of the marula tree

Local communities in southern Africa derive many benefits from marula [Sclerocarya birrea(A.Rich.) Hochst.subsp.caffra(Sond.) Kokwaro].These include the contribution of this species towards health,nutrition,food security and conservation by sharing local skills and knowledge related to it.Marula fruits can be eaten fresh,squeezed to make juice,brewed in traditional beer or used to make jam and jelly.The kernels are also edible and can be pressed to extract oil for cooking and cosmetics,i.e.,for skin and hai...     

Harvesting and postharvest handling practices and characteristics of Uapaca kirkiana (Muell. Arg.) fruits: a survey of roadside markets in Malawi

Uapaca kirkiana (Muell. Arg.), a highly valued indigenous fruit species, is being domesticated to increase its utilization in southern Africa. Vendors, who were also the fruit gatherers, that were selling U. kirkiana fruits at roadside markets in Dedza, Malawi, were interviewed on four occasions during the marketing season (October 2003–January 2004) and fruit samples were concurrently sampled from each vendor. Information was obtained on when and how the fruits had been harvested and handled. Timing of fruit harvest was based on experience, aided by indicators such as occurrence of first heavy rains, natural abscission, size and color changes. Harvesting by knocking down unripe fruits from trees was practiced throughout the␣season, but naturally abscised fruits were also gathered in December and January. Fruits harvested when mature but unripe required incubation in soil, plain and woven plastic bags or clay-pots. The incubation method changed and the duration of incubation decreased between October (3–4 days) and January (≤2 days). Fruit samples were evaluated for damage, color and soluble solids concentration (SSC). Fruit SSC and color lightness/brightness (L*) increased from 10.1 to 16.4% (P<0.01) and from 45.7 to 50.5 units, (P<0.01), respectively. Higher SSC values were generally associated (R ²=0.68, P<0.001) with increasing pulp color intensity. Cracking, at 48%, constituted the most common form of damage in sampled fruits. On average, fruits were saleable for only 3–4 days, this being attributed to inherent fruit characteristics combined with immaturity at harvest, and damage during harvesting and storage in hot dry conditions. Lack of appropriate harvesting and handling techniques were associated with fruit darkening, drying, rotting and other postharvest problems.