Agroforestry Tree Research Articles

Leaf-litter decomposition and nutrient release dynamics of some savanna agroforestry tree species: A model for soil improvement strategies

The application of leguminous agroforestry tree species using leafy biomass to improve soil fertility in the savanna alfisols is observed to be uncommon. Although, if applied, leguminous leafy biomass increases soil organic matter and improves its fertility potentials for crop productivity. This research investigated leaf-litter decomposition and nutrient release of some selected agroforestry tree species. Five species of agroforestry tree leafy biomass were selected (Faidherbia albida, Leucaena leucocephala, Gliricidia sepium, Senna siamea, Albizia lebbeck) and the effect of the biomass placement patterns of the litter bags in the soil was investigated; viz-a-viz surface placement (above-ground level) and embedded placement at 15cm depth (below-ground level) arranged as 5×2 factorial in Randomized Complete Block Design with four replicates. The data were analyzed using Analysis of Variance, while the means were separated using Duncan Multiple Range Test (p≤0.05). The soil results showed that the pH of the study area was near neutral (6.20) and loamy sand in nature. The leafy biomass of all the agroforestry tree species tested were noted to release nutrients two weeks after decomposition. However, it was observed that the species of leafy biomass and placement patterns had significant influence on both weight loss and nutrient release. The rate of leaf-litter decomposition and nutrient release (mineralization) were significantly higher in biomass embedded in soil at 15cm depth (below-ground level) than the surface placement (above-ground level). The nutrients released in the form of nitrogen, phosphorus, potassium, calcium, magnesium, sodium and organic carbon from leafy biomass embedded in the soil reached more than 50% in the 14 days of biomass decomposition. G. sepium leafy biomass among other species decomposed and released nutrients more rapidly, both at embedded and surface placements. It is therefore recommended that G. sepium leafy biomass be used as an alternative organic based fertilizer to improve soil fertility for increased crop production in savanna alfisols.

Vegetation Structure and Diversity in Northern Yobe, Nigeria

The study examined the diversity of vegetation (tree species and shrubs) for the preservation, utilization and conservation of tree species in Northern Yobe. A point centred quarter (PCQ) method was employed to study the vegetation structure in six randomly selected experimental sites across the three local government councils in Northern Yobe (Yunusari, Yusufari and Geidam). A total of 22 tree species and 7 shrubs belonging to 15 families were identified, with Fabaceae being the family with the highest number of tree species (5 members), and followed by Combretaceae, Mimosaceae, and Rhamnaceae each with 3 members. Aracaceae, Euphorbiaceae, Rhamnaceae, and Moraceae have 2 members each, while other identified families had a member of tree species. Specifically, Sodom apple was the dominant tree species based on Importance Value Indices (IVI) of 23.3, followed by Doum palm (22.0), then Guiera tree and Combretum species, each with IVI of 20.7, followed by Desert date (20.3), Thorn Acacia (19.9), and then Whistling thorn (19.3 as their IVI. The Diversity index was determined as 1, Simpson’s index of diversity was very low (-0.0082) and the species richness was 0.41. The low values indicate a less complex community, and the distribution pattern of the various parameters assesses was that of a typical Sahel-Savannah vegetation. Nevertheless, there was a large number of different tree species (29) recorded which implies many tree species are adaptable in the study area but only regenerated naturally without effort for intensive production. Therefore, the need of mass production of these trees in plantation and agroforestry for the conservation and utilization of the dominant (most adapted) tree species to halt environmental associated problems including desertification and erosion in the study area.

Bodhichitta (Ziziphus species), an agroforestry tree species planted in Timal Rural Municipality of Kavrepalanchok district, Nepal

This paper presents the findings of a case study carried out in three villages of Timal Rural Municipality of Kavrepalanchok district of Nepal to explore status of Bodhichitta (Ziziphus xiangchengensis), its cultivation practices, and the trade of its seeds. Methods followed in the whole study were household survey, key informants interview, focus group discussions and literature review.

Leaf and tree water-use efficiencies of Populus deltoides × P. nigra in mixed forest and agroforestry plantations.

In a global context where water will become a scarce resource under temperate latitudes, managing tree plantations with species associations, i.e., forest mixture or agroforestry, could play a major role in optimizing the sustainable use of this resource. Conceptual frameworks in community ecology suggest that, in mixed plantations, environmental resources such as water may be more efficiently used for carbon acquisition and tree growth thanks to niche complementarity among species. To test the hypotheses behind these conceptual frameworks, we estimated water-use efficiency (WUE) for poplar trees grown in a monoculture, in association with alder trees (forest mixture) and in association with clover leys (agroforestry) in an experimental plantation located in northeastern France. Water-use efficiency was estimated (i) at leaf level through gas exchange measurements and analysis of carbon isotope composition, (ii) at wood level through carbon isotope composition and (iii) at tree level with sap flow sensors and growth increment data. We hypothesized that species interactions would increase WUE of poplars in mixtures due to a reduction in competition and/or facilitation effects due to the presence of the N2-fixing species in mixtures. Poplar trees in both mixture types showed higher WUE than those in the monoculture. The differences we found in WUE between the monoculture and the agroforestry treatment were associated to differences in stomatal conductance and light-saturated net CO2 assimilation rate (at the leaf level) and transpiration (at the tree level), while the differences between the monoculture and the forest mixture were more likely due to differences in stomatal conductance at the leaf level and both transpiration and biomass accumulation at the tree level. Moreover, the more WUE was integrated in time (instantaneous gas exchanges < leaf life span < seasonal wood core < whole tree), the more the differences among treatments were marked.

Direct seeding of six agroforestry tree species indigenous to the Sahel: the effect of fungicide and planting-hole depth on seed germination and seedling emergence capacity

Direct seeding of six agroforestry tree species indigenous to the Sahel: the effect of fungicide and planting-hole depth on seed germination and seedling emergence capacity

Combining air-layering and stem cutting techniques to optimize the production of quality planting materials for agroforestry tree species: a case study of Canarium schweinfurthii Engl. (Burseraceae)

ABSTRACT Using Canarium schweinfurthii as biological model, the present study evaluated the potential of combining air-layering and stem cutting techniques to optimize the production of agroforestry trees’ propagules. Three substrates and five concentrations of indole butyric acid (IBA) were tested for their effects on the rooting of air-layers. Stockplants were raised from air-layered propagules and used for stem cutting trial. Three levels of stockplant irradiance and five IBA concentrations were tested for their effects on the rooting of stem cuttings. Results showed that the combination of Sawdust substrate and 5 g/l IBA resulted in highest percentage of rooted layers (79.3 ± 7.6%) and highest number of roots per rooted layer (34.9 ± 0.7). Sawdust recorded the lowest layers’ mortality rate (6 ± 1.9%). Alive cuttings sprouted and rooted at 100%. The lowest mortality rates of cuttings (14 ± 4.8%) and the highest number of roots per rooted cutting (25.5 ± 0.1) were recorded with 10 g/l IBA × 50% ambient sunlight treatment combination. Using air-layered propagules for stockplant production could make it easy to achieve stockplant management practices like shading. Combining air-layering and stem cutting techniques enhanced the multiplication rate of propagules. This provides valuable insights for tree domestication practices worldwide.

Propagation of agroforestry tree species by airlayering: a case study of Canarium schweinfurthii Engl. in the Western Highlands of Cameroon

Objective: As a contribution to the domestication of Canarium schweinfurthii (Black olive tree), the present study examined its potential for clonal propagation by air-layering. Methodology and Results: Three substrates Topsoil, Sawdust and mixture of Sawdust and Topsoil in a 1:1 (v/v) ratio] and five concentrations (0, 1, 2.5, 5 and 10 g/l) of exogenously applied indole butyric acid (IBA) were tested for their effects on the rooting of air-layers. Results showed that the percentage of rooted layers and the mean number of roots per rooted layer were significantly (p ˂ 0.001) influenced by substrate and IBA concentration, whereas the layers’ mortality rate was influenced only by substrate (p ˂ 0.001). The highest percentage of rooted layers (78.57 ± 7.78%) was recorded with the combination of Sawdust substrate and 5 g/l IBA. The same treatment combination resulted in the highest mean number of roots per rooted layer (34.95 ± 0.76). The lowest mortality rate of layers (6 ± 1.94%) was recorded with Sawdust substrate. Conclusion and application of findings: C. schweinfurthii is amenable to vegetative propagation through air-layering technique. For prolific rooting of air-layers, Sawdust substrate and application of 5 g/l IBA are recommended. With the increasing demand for C. schweinfurthii fruits, these study findings would contribute to rapid and mass propagation of this multifunctional indigenous tree species which have suffered neglect in research. Selecting trees with desirable traits and propagating them asexually using simple and inexpensive method as described in this work would improve establishment of this plant whose fruits trade raises the living standard of many populations in Western and Central Africa. Keywords: Canarium schweinfurthii, Domestication, Non-timber forest products, Vegetative propagation, Western Highlands of Cameroon

Crop Production and Carbon Sequestration Potential of Grewia oppositifolia-Based Traditional Agroforestry Systems in Indian Himalayan Region

Bhimal (Grewia oppositifolia) is the most important agroforestry tree species used for fodder, fuel and fiber in the Himalayan region. In the present study, G. oppositifolia-based traditional agroforestry systems were selected for the estimation of carbon stock and the production potential of barnyard millet (Echinochloa frumentacea) and finger millet (Eleusine coracana), with two elevational ranges, i.e., 1000–1400 and 1400–1800 m amsl, in Garhwal Himalaya, India. The results of the investigation showed a decline in the growth and yield attributes of both the millet crops under the G. oppositifolia-based agroforestry system at both elevations as compared to their respective control sites (sole crops). Among the elevations, the total number of tillers per plant (2.70 and 2.48), the number of active tillers per plant (2.18 and 2.25), panicle length (17.63 cm and 6.95 cm), 1000-seed weight (5.49 g and 4.33 g), grain yield (10.77 q ha−1 and 11.35 q ha−1), straw yield (37.43 q ha−1 and 30.15 q ha−1), biological yield (48.21 q ha−1 and 41.51 q ha−1) and the harvest index (22.53% and 27.78%) were recorded as higher in the lower elevation in both E. frumentacea and E. coracana, respectively, while plant population per m2 (18.64 and 25.26, respectively) was recorded as higher in the upper elevation. Plant height for E. frumentacea (180.40 cm) was also observed to be higher in the upper elevation, while for E. coracana (98.04 cm), it was recorded as higher in the lower elevation. Tree carbon stock was reported negatively with an increase in altitude. The maximum amount of sequestered carbon in the tree biomass for G. oppositifolia was 23.29 Mg ha−1 at the lower elevation and 18.09 Mg ha−1 at the upper elevation. Total carbon stock in the tree biomass was reported to be the highest (15.15 Mg ha−1) in the 10–20 cm diameter class, followed by 20–30 cm (6.99 Mg ha−1), &gt;30 cm (2.75 Mg ha−1) and the lowest (2.32 Mg ha−1) in the &lt;10 cm diameter class. The results show that the yield of E. frumentacea and E. coracana was not reduced so severely under the G. oppositifolia system; however, keeping in mind the other benefits of this multipurpose tree, i.e., carbon sequestration and socioecological relevance, farmers can get benefit from adopting these crops under G. oppositifolia-based agroforestry systems.

Selection of agroforestry tree-base participatory and ecological approach in Central Kalimantan, Indonesia

This study investigates the selection agroforestry tree species based on a participatory approach and an ecological approach in Humbang Raya village and Tumbang Mantuhe village. This study method was carried out using a participatory approach through Focus Group Discussion (FGD) activities and an ecological approach through the identification of tree species in open and closed forests. The results of the FGD selected tree species in Humbang Raya village as many as 17 tree species and in Tumbang Mantuhe village as many as five tree species. The results of the identification of tree species in Humbang Raya village in closed forest amounted to 34 tree species, while in open forest there were 10 tree species. In Tumbang Mantuhe village in closed forest there are 29 species of trees and open forest five species of trees. It was concluded that the selected tree species to be planted on agroforestry land in Humbang Raya village and Tumbang Mantuhe village each had 4 tree species.

Wood-specific gravity and carbon proportion of multifunctional agroforestry trees in foothills of Nilgiris, Western Ghats, India

Wood-specific gravity and carbon proportion of multifunctional agroforestry trees in foothills of Nilgiris, Western Ghats, India

Determining the appropriate level of farmyard manure biochar application in saline soils for three selected farm tree species.

Salinity is a global problem, and almost more than 20% of the total cultivated area of the world is affected by salt stress. Phytoremediation is one of the most suitable practices to combat salinity and recently biochar has showed the tremendous potential to alleviate salt-affected soils and enhance vegetation. Trees improve the soil characteristics by facilitating the leaching of salts and releasing organic acids in soil. Moreover, in the presence of trees, higher transpiration rates and lower evaporation rates are also helpful in ameliorating salt affected soils. This study was designed to check the effect of different levels of biochar on the morph-physiological characteristics of three important agroforestry tree species: Eucalyptus camaldulensis, Vachellia nilotica, and Dalbergia sissoo, in saline soils. Farmyard manure biochar was applied at the rate of 3% (w/w), 6% (w/w), and 9% (w/w) to find appropriate levels of biochar for promoting the early-stage trees growth under saline conditions. Results of the current study revealed that maximum shoot length (104.77 cm), shoot dry weight (23.72 g), leaves dry weight (28.23 g), plant diameter (12.32 mm), root length (20.89 cm), root dry weight (18.90 g), photosynthetic rate (25.33 μ moles CO2 m-2s-1) and stomatal conductance (0.12 mol H2O m-2 s-1) were discovered in the plants of Eucalyptus camaldulensis at the rate of 6% (w/w). All tree species showed better results for growth and physiological characteristics when biochar was applied at the rate of 6% (w/w). In comparison, a decreasing trend in growth parameters was found in the excessive amount of biochar when the application rate was increased from 6% (w/w) to 9% (w/w) for all three species. So, applying an appropriate level of biochar is important for boosting plant growth in saline soils. Among different tree species, Vachellia nilotica and Eucalyptus camaldulensis both showed very promising results to remediate salt affected soils with Vachellia nilotica showing maximum potential to absorb sodium ions.

Restoration of degraded sodic soils through silvipastoral systems in the Indo‐Gangetic Plains

AbstractExcessive salts in degraded sodic soils aggravate the bio‐physicochemical properties of soils that need to be remediated and restored in a judicious way. The present study envisages smothering harmful effects of sodic soils and maintaining soil fertility through need‐based silvipastoral systems. We report on a three‐times replicated field experiment with 13 treatments comprised of three agroforestry tree species Acacia nilotica, Casuarina equisetifolia, and Eucalyptus tereticornis planted during 2005 on highly sodic soil of pH 10.6 and exchangeable sodium percentage (ESP) of 89 in the Indo‐Gangetic Plains. Fodder grass species viz. Chloris gayana, Panicum maximum, and Pennisetum purpureum were planted under each of the 10‐year‐old tree species. The maximum biomass production of understory grasses was recorded from A nilotica + C. gayana silvipastoral system while the highest nutritive value in terms of N. P, K, and crude protein content (%) was recorded in A. nilotica + P. purpureum. A strong correlation between photosynthetically active radiation (PAR) and understory grasses was observed. Significantly higher tree growth and biomass yield were recorded under silvipastoral systems over silvicultural system. A significant reduction in soil bulk density and increase in soil porosity, infiltration rate, and water holding capacity (WHC) were recorded in silvipastoral systems over silviculture and control due to reduced sodicity, addition of leaf litter, increase in microbial activities due to tree and grassroots, better plant growth, and fine root decay. Reduction in soil pH, exchangeable sodium percent (ESP), and increase in soil organic carbon were more pronounced under silvipastoral systems over the silviculture. The highest reduction in these parameters was recorded under the A. nilotica + C. gayana silvipastoral system. Similarly, soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP), and dehydrogenase activities were higher under silvipastoral systems over the silvicultural system The highest MBC was recorded in C. equisetifolia + C. gayana which was 302.8% higher than the control. However, highest MBN and dehydrogenase activities were recorded under A. nilotica + C. gayana silvipastoral system. Hence, on the basis of total biomass yield and improvement in soil bio‐physicochemical properties A. nilotica + C. gayana silvipastoral system could be a highly ameliorative and productive system for the restoration of degraded sodic soils.

Sustainable Agroforestry Crop Rotation System for the Tropics: A Theoretical Exposition

Population pressure is the key reason that has been reducing the duration of fallow in shifting cultivation. In many places, it has changed to bush fallow and subsequently is going towards the need to use available arable lands continuously. As a result, soil productivity is declining since long fallow is required for its regeneration after land is planted for a few years. An agroforestry tree crop/arable crop rotation system was proposed to mimic the natural fallow system and improve nutrient recycling through litter drops, which will improve soil organic matter. As soil organic matter improves the soil structure in addition to the ability of the soil to retain nutrients and water, the land becomes suitable for continuous crop production with appropriate fertilization regimes. The proposed tree crop/arable crop rotation will therefore result in continuous generation of income from harvestable produce in the rotation system year in year out. The paper, equally elucidated on other benefits of rotating tree crops with arable crops on the same land towards achieving maximum land productivity and obtaining benefits from the land without subjecting the land to the traditional fallowing system. This intervention will reduce abject poverty (SDG1), reduce acute hunger (SDG2), promote sustainable economic activities and growth, increase employment and decent work (SDG8) and promote sustainable industrialization and foster innovation (SDG9). The paper also identified the challenges associated with this type of rotation system and proffered suggestions on how to ameliorate such challenges.

Why Farmers Are Hesitant to Adopt What Appears Good on the Basis of Science: Understanding Farmers’ Perceptions of Biophysical Research

This study conducted a series of extension events that were followed by farmer interviews with 394 farmers who had participated in an initial household survey in 2018, involving four farmer categories: 1] those actively participating in the Trees for Food Security (T4FS) project from phase 1 (2014); 2] farmers neighbouring those actively participating in the T4FS project from phase 1; 3] farmers actively participating in the T4FS project from phase 2 (2017) and; 4] farmers living distant and unaware of the T4FS project. The study drew upon knowledge generated from biophysical experiments on tree water use, shade tree planting and management in smallholder coffee-bean agroforestry systems to assess farmers&amp;rsquo; perceptions and willingness to adopt practices emanating from the study following exposure to the research outputs. The main form of extension used was through display and viewing of posters and a translated power point presentation of the research outputs on impact of tree canopy pruning on tree and coffee plant water use and productivity of coffee and common beans. We present the key messages obtained by the participants from the extension activities conducted, their preferred crop and management combinations, perceptions towards the research outputs and willingness to adopt the practices recommended by the study. We contend that smallholder farmers are hesitant to adopt innovations due to an underlying culture of financial expectancy leading to &amp;lsquo;pseudo adoption&amp;rsquo;, underutilisation of existing social networks during research and extension, period of exposure to a technology, and limitations in measuring and predicting adoption. We align the four farmer categories to the Process of Agricultural Utilisation Framework (PAUF) criteria, leading to a better understanding of the impact of research and development projects and agroforestry tree planting and management adoption pathways among smallholder farmers. This would enable introduction of socially and biophysically appropriate agroforestry interventions into local realities.

Evaluation of soil physico-chemical properties as affected by canopies of scattered agroforestry trees on croplands

Agroforestry tree species play an important role in improving soil fertility. Though studies have confirmed that different species show different potentials to improve soil fertility, it is difficult to compare them as the studies were conducted in different areas. The potential for different tree species to improve soil fertility on croplands in northern Ethiopia is not known. The objectives of this paper are to determine the effects of presence or absence of agroforestry tree species on soil physico-chemical properties and the effect of distance from the tree trunk on the same soil physico-chemical properties. Sixty composite and undisturbed soil samples from beneath canopies and outside canopies and 90 composite and undisturbed soil samples from three different distances from tree trunks were collected. The results revealed that soil bulk density, soil moisture, soil organic carbon (SOC), total nitrogen (TN), available phosphorus (Av.P), exchangeable potassium (Exch.K) and soil organic carbon stock (SOCS) were significantly (p < 0.05) different between soils beneath canopies and outside canopies as well as at different distances from the tree trunk. Soils around these agroforestry tree species have increased SOC, TN, Av.P, Exch.K and SOCS by 11.9 to 91.5%, 22.2 to 125.0%, 31 to 71%, 32 to 151.6% and 15.2 to 90.9%, respectively, compared to soils outside tree canopies. Faidherbia albida (Delile) A.Chev. has the highest potential for soil fertility compared to Balanites aegyptiaca (L.) Delile, Cordia africana Lam., Ziziphus spina-christi (L.) Desf., Acacia sieberiana DC and Croton macrostachyus Hochst. ex Delile. This study could provide useful information for soil fertility management and farmers’ decision-making when selecting tree species. The findings of this study imply that scattered trees on croplands significantly improve soil fertility and reduce the need for external fertiliser inputs.

Assessing the value of agroforestry and food security among households in Isingiro District, South-western Uganda

ABSTRACT Agroforestry trees have been used to enhance food production through a combination of soil nutrient management. The study aimed at assessing the value of agroforestry and food security among households practicing agroforestry in the Isingiro District. The study employed a cross-sectional survey design using household interviews and randomly sampling 284 households to obtain current qualitative and quantitative data. The study used multiple regressions to predict the value of selected dependent variables. The results indicated that households (49%) in Kabaare Parish, Kigyendwa (33%), and Kikokwa (18%) were food secure. Out of these, households that practiced agroforestry and were food secure accounted for 21% while 79% were insecure. The values of agroforestry and food security include economic, environmental, and social value. The major reasons for practicing agroforestry include an increase in food level and improvement of income. Few households in Kabaare (41%), Kigyendwa (22%), and Kikokwa (37%) had knowledge of agroforestry systems and their values. The variable with a positive but insignificant effect on the value of agroforestry and food production was land acreage, while the land size and monthly income had a negative and insignificant effect. The value of agroforestry and food security in the study area is still low. Therefore, there is a need for understanding households’ psychological and behavioral factors that hinder them from adopting agroforestry practices. It is vital that the government invests in capacity building of household farmers in agroforestry and food production, and reviews land policy to support households to strengthen their income base.

Insights into the Cocoa and Forests Initiative: Smallholder Engagement with Certification Programs and Agroforestry

The Cocoa and Forests Initiative (CFI) in Côte d’Ivoire aims to address forest loss associated with cocoa cultivation by reducing deforestation and encouraging agroforestry. This study explores the relationship between certification programs, which operate primarily through cooperatives, and agroforestry to better understand the environment in which smallholder cocoa farmers operate. This study employs qualitative interviews and quantitative survey data to investigate farmer perceptions of certification programs and agroforestry initiatives and the impact of certification on participation in such initiatives. Farmers widely practiced low levels of agroforestry, about which they held generally positive views, and while certified farmers did not have more agroforestry trees, they were more knowledgeable about the benefits to cocoa production than non-certified farmers. Furthermore, many certified farmers conflated certification with cooperative membership. Understanding the role of preexisting institutions like certification and cooperatives is essential for the successful implementation of the CFI in a smallholder context.

Effect of mineralized nitrogen through decomposition of plant residues on the uptake of maize (Zea mays L.) in sudan savannah ecological zone of Nigeria

A field experiment was designed to determine the effect of mineralized nitrogen (N) through the decomposition of leafy biomass of agroforestry tree species as residues to underscore its uptake by maize under Sudan savannah conditions. The experiment was laid out as 3 x 4 x 2 factorial in a split-split plot design with three replicates for two cropping seasons. The factors considered include: control, biomass species (Albizia lebbeck and Parkia biglobosa) as main plots, four levels of nitrogen fertilizer (0, 40, 80, 120 kg N ha-1) as sub-plots, and two maize varieties (DMR-ESR-7 and 2009 EVAT) as sub-sub plots. Data were analysed using Analysis of Variance (ANOVA). Chemical composition of A. lebbeck biomass had higher average contents of N (32.4 g kg-1) and C (186.4 g kg-1) and lower average C: N ratio (57.5) than P. biglobosa and this affected their decomposition rates, hence, A. lebbeck decomposed faster than P. biglobosa. 56 % of N in the litter bags were released within the first 2 weeks of biomass incorporation and progressively increased up to 10 weeks after planting (WAP). Total N uptake by maize was lowest (2.8 kg N ha-1) in P. biglobosa and was highest (8.6 kg N ha-1) in A. lebbeck amended plots. It is then concluded that total N uptake by maize crop increased rapidly between 4-6 WAP, and the impact was obvious in plots amended with A. lebbeck biomass than in P. biglobosa plots during the two cropping seasons.

The Future of Food: Domestication and Commercialization of Indigenous Food Crops in Africa over the Third Decade (2012–2021)

This paper follows the transition from ethnobotany to a deeper scientific understanding of the food and medicinal properties of African agroforestry tree products as inputs into the start of domestication activities. It progresses on to the integration of these indigenous trees as new crops within diversified farming systems for multiple social, economic and environmental benefits. From its advent in the 1990s, the domestication of indigenous food and non-food tree species has become a global programme with a strong African focus. This review of progress in the third decade is restricted to progress in Africa, where multi-disciplinary research on over 59 species has been reported in 759 research papers in 318 science publications by scientists from over 833 research teams in 70 countries around the world (532 in Africa). The review spans 23 research topics presenting the recent research literature for tree species of high priority across the continent, as well as that in each of the four main ecological regions: the humid zone of West and Central Africa; the Sahel and North Africa; the East African highlands and drylands; and the woody savannas of Southern Africa. The main areas of growth have been the nutritional/medicinal value of non-timber forest products; the evaluation of the state of natural resources and their importance to local people; and the characterization of useful traits. However, the testing of putative cultivars; the implementation of participatory principles; the protection of traditional knowledge and intellectual property rights; and the selection of elite trees and ideotypes remain under-researched. To the probable detriment of the upscaling and impact in tropical agriculture, there has been, at the international level, a move away from decentralized, community-based tree domestication towards a laboratory-based, centralized approach. However, the rapid uptake of research by university departments and national agricultural research centres in Africa indicates a recognition of the importance of the indigenous crops for both the livelihoods of rural communities and the revitalization and enhanced outputs from agriculture in Africa, especially in West Africa. Thus, on a continental scale, there has been an uptake of research with policy relevance for the integration of indigenous trees in agroecosystems and their importance for the attainment of the UN Sustainable Development Goals. To progress this in the fourth decade, there will need to be a dedicated Centre in Africa to test and develop cultivars of indigenous crops. Finally, this review underpins a holistic approach to mitigating climate change, as well as other big global issues such as hunger, poverty and loss of wildlife habitat by reaping the benefits, or ‘profits’, from investment in the five forms of Capital, described as ‘land maxing’. However, policy and decision makers are not yet recognizing the potential for holistic and transformational adoption of these new indigenous food crop opportunities for African agriculture. Is ‘political will’ the missing sixth capital for sustainable development?

Support trees in vanilla agroforests of Madagascar: diversity, composition and origin

Trees in agroforestry systems provide multiple ecological and economic functions. Smallholder vanilla agroforests include shade trees common across agroforestry systems, and small-statured support trees carrying the vanilla vine. Support trees have received little scientific attention so far. The objectives of our study were to assess the diversity, composition and geographic origin of support trees in vanilla agroforestry systems of north-eastern Madagascar. The region is a global biodiversity hotspot, has been undergoing a rapid land-use change and produces a large share of the globally traded vanilla spice. The studied vanilla agroforests differed in land-use history: established either directly inside forest (forest-derived) or on land previously used for slash-and-burn agriculture (fallow-derived). Among the support trees, we found 122 species of which 25% were endemic to Madagascar. The species richness per plot was four times higher in forest-derived than in fallow-derived vanilla agroforests. The species distribution was particularly uneven in fallow-derived vanilla agroforests with one species (Jatropha curcas) comprising 52% of all individuals. In forest-derived vanilla agroforests, 44% of all trees were native or endemic to Madagascar, whereas in fallow-derived vanilla agroforests only 11% were native or endemic. We conclude that there is a considerable diversity among support trees in Malagasy vanilla agroforestry. The support tree diversity is strongly affected by land-use history. Fallow-derived vanilla agroforests currently have a comparatively low species richness, yet they can play an important role in land rehabilitation, and more emphasis on growing native and endemic tree species would contribute to aligning production with conservation goals.