Agroforestry Parklands Research Articles

Drought tolerant species dominate as rainfall and tree cover returns in the West African Sahel

After the severe droughts in the 1970s and 1980s, and subsequent debates about desertification, analyses of satellite images reveal that the West African Sahel has become greener again. In this paper we report a study on changes in tree cover and tree species composition in three village landscapes in northern Burkina Faso, based on a combination of methods: tree density change detection using aerial photos and satellite images, a tree species inventory including size class distribution analysis, and interviews with local farmers about woody vegetation changes. Our results show a decrease in tree cover in the 1970s followed by an increase since the mid-1980s, a pattern correlating with the temporal trends in rainfall as well as remotely sensed greening in the region. However, both the inventory and interview data shows that the species composition has changed substantially towards a higher dominance of drought-resistant and exotic species. This shift, occurring during a period of increasing annual precipitation, points to the complexity of current landscape changes and questions rain as the sole primary driver of the increase in tree cover. We propose that the observed changes in woody vegetation (densities, species composition and spatial distribution) are mediated by changes in land use, including intensification and promotion of drought tolerant and fast growing species. Our findings, which indicate a rather surprising trajectory of land cover change, highlight the importance of studies that integrate evidence of changes in tree density and species composition to complement our understanding of land use and vegetation change trajectories in the Sahel obtained from satellite images. We conclude that a better understanding of the social-ecological relations and emerging land use trajectories that produce new types of agroforestry parklands in the region is of crucial importance for designing suitable policies for climate change adaptation, biodiversity conservation and the sustainable delivery of ecosystem services that benefit local livelihoods in one of the world’s poorest regions.

Dynamics of soil carbon stock, total nitrogen, and associated soil properties since the conversion of Acacia woodland to managed pastureland, parkland agroforestry, and treeless cropland in the Jido Komolcha District, southern Ethiopia

ABSTRACTIn the arid, low biomass producing areas of Ethiopia, Acacia woodlands suffered a severe degradation due to exploitation for various uses, and conversion to grazing and cultivated lands. However, little is known on the impact of agricultural land uses on soil organic carbon (SOC), total nitrogen (TN) stocks, and other soil quality indicators. This study was planned to evaluate SOC and TN stock changes under parkland agroforestry (PAF), managed pastureland (MPL), and treeless cropland (TLCL) regimes by considering the remnant protected woodland (PWL) as a reference. We found that SOC and TN stocks were significantly higher in PWL and MPL areas. Conversion of Acacia woodlands to MPL, PAF, and TLCL resulted in the loss of SOC stock by 23, 50, and 56%, respectively. Higher SOC and TN stocks were found under PWL (144.3 Mg ha−1) and MPL (108.2 Mg ha−1). Significant changes in available phosphorous (P), exchangeable cations, and cation exchangeable capacity were observed following the woodland conversion to different land use types. Available P was the highest in MPL compared with the other land use regimes. Within the study area, the MPL land use type was the best land management option for protecting SOC and TN soil stocks.

Farmers’ perceptions of climate change impacts on ecosystem services delivery of parklands in southern Mali

Agroforestry parklands in the Sahel provide a number of ecosystem services that help farmers cope better with climate change effects and thus reducing their vulnerability. However, parklands are threatened due to the decline in densities of species that are sensitive to drought and that might compromise the delivery of the above mentioned ecosystem services to farmers. Therefore, data were collected by interviewing 400 smallholder farmers to elucidate farmers’ perceptions of climate change in southern Mali and potential consequences on the delivery of ecosystem services from the parklands. Descriptive statistics and multinomial logit model were used to analyse the data collected and identify the indictors as well as the determinants of farmers’ perception of climate change. The findings revealed increases in the frequency of strong wind, dust, drought, high temperatures and number of hot days as the main climate change-related indicators. Furthermore, an early cessation of the rainy season, frequent drought and wind were found to be the factors impeding a better delivery of the ecosystem services from the parklands. Early cessation of rains and frequent drought might affect the water availability which in turn affects the flowering and fruiting phases of the trees. The occurrence of strong wind causes the shedding of the flowers thus reducing the fruit production. Age, educational level, farm size and gender are key factors influencing farmer’s perception of climate change. The strategies adopted by these farmers to cope with climate shocks include use of improved drought-tolerant crop varieties, diversification of crops, off-farm activities and seasonal migration. Based on these findings, we therefore suggest the development of conducive environment that can help create agricultural related off-farm income earning activities that could protect active households from the impacts of climate change and variability.

Characterization of Faidherbia albida (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.

Susceptibility of soil to wind erosion in arid area of the Central Rift Valley of Ethiopia

In Central Rift Valley (CRV) of Ethiopia, renewable land resources are under pressure. Acacia woodland clearance, frequent cultivation, crop residue removal and mono-cropping are among the major land mis-management practices in the area. This has largely been affecting the soil quality. The current study is aimed at assessing the impact of Acacia woodland conversion, and the subsequent mis-managements on selected soil physical properties, and their relation to the prevailing wind erosion in the area. For this study, four land use/land cover types, namely protected woodland (PWL), managed pastureland (MPL), parkland agroforestry (PAF) and treeless cropland (TLCL) were considered. Higher (P 0.25 mm) fraction of soil was found under PWL and MPL while higher fraction of micro-aggregates (0.053–0.25 mm) of soil was found under PAF and TLCL. Soil under PAF and TLCL had higher (P < 0.001) proportion of aggregates of < 1 mm, implying potential susceptibility of the soil to wind erosion. Higher soil bulk density (BD) was found in the most top layer (0–15 cm) of TLCL and PAF, and this could be attributed to the trampling effect by animals freely released to these land use types. In the study area, conversion of native woodland to PAF and TLCL and the subsequent mismanagements negatively affected some soil physical properties, thereby enhancing severity of soil erosion by wind. In contrast, although not commonly practiced by smallholder farmers, soil under MPL is more stable and less susceptible to wind erosion.

English

Agricultural production in northern Benin is characterized by smallholder traditional agroforestry systems, with on-farm remnant tree species. Among its numerous advantages, agroforestry is known for its valuable contribution to biodiversity conservation. This study quantifies the importance of Vitellaria paradoxa C.F. Gaertn agroforests in terms of woody species conservation in Atacora district in Benin. Forest inventories were performed within 50×50 m plots constructed on a net grid map of Atacora district. Diversity indices were computed for both adult and juvenile species in two land management regimes: fields and fallows. Overall 41 woody species were recorded; 28 in fields and 36 in fallows. Taking into account matured and juvenile individuals, the diversity of woody species increased: 86 species in total; 69 species in fields and 78 in fallows. The biodiversity of V. paradoxa’s agroforestry parklands increases from fields to fallows, and decreases from bulk species (considering mature and juvenile species) to adult ones. Leguminosae and Combretaceae were the most abundant families registered. From the Cover Value Index, V. paradoxa, Parkia biglobosa, Lannea microcarpa, Lannea acida and Diospiros mespiliformis were the most abundant species. Support for maintaining this kind of agricultural system is needed, as this exemplifies the synergy for providing, provisioning and supporting services and biodiversity conservation. Key words: Agroforestry, conservation, ecosystem services, farmland, shea tree.

Separating autotrophic respiration due to roots from soil heterotrophic respiration in an agroforestry parkland system in Saponé, Burkina Faso

Soil respiration is the largest component of ecosystem respiration but little is known about it and its components in parkland systems. We therefore conducted an experiment to estimate the amount of CO 2 respired and to partition it into soil, tree root and crop root contributions in parkland systems in Burkina Faso. Three factors effects were estimated: pruning, species and presence of tree canopy. Pruning showed no significant effect on soil respiration. The soil respiration was significantly higher under Parkia biglobosa (1.54 g CO 2 m -2 h -1 against 0.93 in the open area) than under Vitellaria paradoxa (0.98 g CO 2 m -2 h -1 against 0.52 in the open area). The autotrophic respiration associated with the P. biglobosa system due to sorghum roots was 0.37 g CO 2 m -2 h -1 and due to tree roots was 0.61. For the V. paradoxa system, the figures were 0.13 g CO 2 m -2 h -1 for sorghum roots and 0.46 for tree roots. We observed higher CO 2 emissions from under trees crowns than in open areas owing to higher tree-root respiratory activities, and higher water and organic matter contents. However, further studies are needed to discover if these low values of soil CO 2 fluxes from parklands translate into higher amounts of carbon fixed than emitted taking into consideration the seasonal variations. Keywords : Carbon balance, CO2 flux, carbon-sink, carbon-source.

Tree tenure and its implications for sustainable land management: The case of Parkia biglobosa in the Northern Region of Ghana

Parkia biglobosa is a multipurpose species found in Savannah agroforestry parklands of West Africa. The species is important as it prevents against land degradation while providing food and other products. This study focuses on how land and tree tenure arrangements affect tree populations in three traditional areas in the Northern Region of Ghana (Dagomba, Gonja and Mamprusi) and the implications that these arrangements have for sustainable land management. Focus group discussions and key informant interviews were held in the three communities to provide information on the tenural arrangements of Parkia biglobosa. A tree census was conducted to estimate the densities of Parkia biglobosa in crop and fallow fields. The study shows that differences in tenure systems in the three traditional areas have implications for Parkia biglobosa populations and also for sustainable land management. It is concluded that traditional tenure systems along with regulation protect the trees from destruction as observed in the Dagomba and Gonja areas compared to the open access system identified in Kperiga in the Mamprusi area.

Tree crown mapping in managed woodlands (parklands) of semi-arid West Africa using WorldView-2 imagery and geographic object based image analysis.

Detailed information on tree cover structure is critical for research and monitoring programs targeting African woodlands, including agroforestry parklands. High spatial resolution satellite imagery represents a potentially effective alternative to field-based surveys, but requires the development of accurate methods to automate information extraction. This study presents a method for tree crown mapping based on Geographic Object Based Image Analysis (GEOBIA) that use spectral and geometric information to detect and delineate individual tree crowns and crown clusters. The method was implemented on a WorldView-2 image acquired over the parklands of Saponé, Burkina Faso, and rigorously evaluated against field reference data. The overall detection rate was 85.4% for individual tree crowns and crown clusters, with lower accuracies in areas with high tree density and dense understory vegetation. The overall delineation error (expressed as the difference between area of delineated object and crown area measured in the field) was 45.6% for individual tree crowns and 61.5% for crown clusters. Delineation accuracies were higher for medium (35–100 m2) and large (≥100 m2) trees compared to small (<35 m2) trees. The results indicate potential of GEOBIA and WorldView-2 imagery for tree crown mapping in parkland landscapes and similar woodland areas.

Shea (Vitellaria paradoxa) tree and soil parent material effects on soil properties and intercropped sorghum grain-Zn in southern Mali, West Africa

Agroforestry parklands are an important agricultural practice in southern Mali where trees such as the Shea (Vitellaria paradoxa C.F. Gaertn) improve soil fertility and crop growth. However, it is not known whether Shea trees can ameliorate Zn-deficient soils or improve Zn uptake from soils of high-Zn, mafic origin. A total of 22 Shea trees preserved in traditional parklands with sorghum (Sorghum bicolor L. Moench) were selected from two soil parent material (PM) types (mafic and non-mafic). Sorghum grain and soil samples were taken along a transect from the bole to 12 m beyond the canopy and analyzed for soil and grain parameters including diethylenetriaminepentaacetic acid (DTPA)-extractable soil-Zn and grain-Zn concentration. Zn-deficient soils were observed with most occurring at non-mafic PM. Mean DTPA-extractable Zn concentrations ranged from 0.55-2.98 μg g−1 in mafic soils and 0.34-1.02 μg g−1 in non-mafic soils. PM influenced soil available-Zn, but not grain-Zn concentration. Both soil available-Zn and grain-Zn concentrations decreased away from trees with grain-Zn concentration not consistently decreasing across all soils. These results suggest that Shea trees grown in soils derived from mafic PM can improve soil-Zn availability, but that other growth factors are more important in determining grain-Zn content.

Rootstock Propagation Methods Affect the Growth and Productivity of Three Improved Cultivars of Ber in Mali, West Africa

The adaptation of three improved cultivars of ber (Ziziphus mauritiana) from India to farming conditions in the Sudanian zone of the Sahel region was tested in Mali. The three cultivars used as scions were Seb, Umran, and Sotubata. The use of coppices of local ber resulted in a significantly better growth and higher fruit production on all the grafts of the three cultivars when compared with nursery seedling rootstocks. The cultivars also performed significantly better in the South Sudanian zone than in the more-arid North Sudanian zone. The highest fruit yield of 38 kg per tree was achieved on coppices in the South Sudanian zone. It was concluded that the high success of this experiment offers a great opportunity for adoption of the three improved cultivars of ber using coppice shoots as rootstock to optimize their use in parkland agroforestry systems in the South Sudanian zone of the Sahel region of West Africa.

Determinants and constraints of integrating natural acacias into mechanised rain-fed agricultural schemes Sennar State, Sudan

Agroforestry practices in Sudan take on various forms across the country, depending on the arrangement, distribution and integration of trees with agricultural crops and/or livestock. The study aimed to describe and analyse the arrangement of acacia trees with crops on parklands in El Dali and El Mazmum areas in Sennar State, Sudan. Specifically, an attempt was made to identify the determinants of integration of natural acacia trees with crops in mechanised rain-fed agricultural schemes forming agroforestry parklands. Another specific aim was to determine farmers’ perceptions about the constraints of adopting such agroforestry practices were also determined. Data was collected using a social survey method, in which 50 % of the total numbers of villages was randomly selected after classification into small, medium and large villages. Moreover, 5 % of the heads of households in the selected villages were interviewed face to face. The number of respondents was 281. Logistic regression model results indicated that the number of household members, the administrative unit, the incentive received from agricultural union and the land size were the main determinants for integrating acacia trees with agricultural crops in mechanised rain-fed agricultural schemes forming the agroforestry parklands. Constraints related to the prevalence of agroforestry practices included the absence of extension services and planting materials, unfavourable tree tenure, the destruction of trees/crops by animals, and the practice of renting land for sole crop cultivation. Several suggestions are given increased adoption of sustainable agroforestry for more production farming. As a priority land tenure and tree tenure issues must be clarified.

The effect of trees on preferential flow and soil infiltrability in an agroforestry parkland in semiarid Burkina Faso.

Water scarcity constrains the livelihoods of millions of people in tropical drylands. Tree planting in these environments is generally discouraged due to the large water consumption by trees, but this view may neglect their potential positive impacts on water availability. The effect of trees on soil hydraulic properties linked to groundwater recharge is poorly understood. In this study, we performed 18 rainfall simulations and tracer experiments in an agroforestry parkland in Burkina Faso to investigate the effect of trees and associated termite mounds on soil infiltrability and preferential flow. The sampling points were distributed in transects each consisting of three positions: (i) under a single tree, (ii) in the middle of an open area, and (iii) under a tree associated with a termite mound. The degree of preferential flow was quantified through parameters based on the dye infiltration patterns, which were analyzed using image analysis of photographs. Our results show that the degree of preferential flow was highest under trees associated with termite mounds, intermediate under single trees, and minimal in the open areas. Tree density also had an influence on the degree of preferential flow, with small open areas having more preferential flow than large ones. Soil infiltrability was higher under single trees than in the open areas or under trees associated with a termite mound. The findings from this study demonstrate that trees have a positive impact on soil hydraulic properties influencing groundwater recharge, and thus such effects must be considered when evaluating the impact of trees on water resources in drylands.Key PointsTrees in dryland landscapes increase soil infiltrability and preferential flow Termite mounds in association with trees further enhance preferential flow

Competition and facilitation-related factors impacts on crop performance in an agro-forestry parkland system in Burkina Faso

Parkia biglobosa and Vitellaria paradoxa are known to improve soil fertility and redistribute water under their crowns in parkland systems. A field experiment was conducted to separate above and belowground interactions between these species and associated Sorghum bicolor using root trenching and crown pruning during three cropping seasons. Trenching increased soil water availability because Sorghum plants displayed higher leaf water potential (-0.73 ± 0.11 MPa) in the trenched plots than control plots (-1.32 ± 0.14 MPa). There were no significant differences in grain (315 ± 80 kg ha-1 versus 217 ± 48 kg ha-1) and straw biomass (1639 ± 295 kg ha-1 versus 1307 ± 278 kg ha-1) yields between trenched and control plots. Crown pruning increased sorghum grain yield in the trenched plots in 2008 and 2009 under P. biglobosa while the opposite happened under V. paradoxa. Better performance of Sorghum in the trenched plots under unpruned V. paradoxa trees than pruned trees could be an indication that light was less limiting under this species as previously thought but also that crown removal induced soil water evaporation and decreased soil water content under this species. An implication of this is that recommendations for including trees in cropland, or for management of existing trees within cropland, must be context and species specific. Key words: Crown pruning, plant water potential, tree-crop interactions, root trenching.

Crop production under different rainfall and management conditions in agroforestry parkland systems in Burkina Faso: observations and simulation with WaNuLCAS model

Traditional agroforestry parkland systems in Burkina Faso are under threat due to human pressure and climate variability and change, requiring a better understanding for planning of adaptation. Field experiments were conducted in three climatic zones to assess Sorghum bicolor (L.) Moench (Sorghum) biomass, grain yield and harvest index in parklands under different rainfall pattern and compared to simulations of sorghum biomass and grain yield with the Water, Nutrient and Light Capture in Agroforestry Systems (WaNuLCAS) model for calibration and parametrisation. For planning adaptation, the model was then used to evaluate the effects of different management options under current and future climates on sorghum biomass and grain yield. Management options studied included tree densities, tree leaf pruning, mulching and changes in tree root patterns affecting hydraulic redistribution. The results revealed that sorghum biomass and grain yield was more negatively affected by Parkia biglobosa (Jacq.) Benth. (nere) compared to Vitellaria paradoxa C. F Gaertn (karite) and Adansonia digitata L. (baobab), the three main tree species of the agroforestry parkland system. Sorghum biomass and grain yield in different influence zones (sub-canopy, outside edge of canopy, open field) was affected by the amount of precipitation but also by tree canopy density, the latter depending itself on the ecological zone. The harvest index (grain as part of total biomass) was highest under the tree canopy and in the zone furthest from the tree, an effect that according to the model reflects relative absence of stress factors in the later part of the growing season. While simulating the effects of different management options under current and future climates still requires further empirical corroboration and model improvement, the options of tree canopy pruning to reduce shading while maintaining tree root functions probably is key to parkland adaptation to a changing climate.

Prospects for an integrated control of Loranthaceae species parasitizing &lt;em&gt;Vitellaria paradoxa&lt;/em&gt; C. F. Gaertn in Burkina Faso

This study investigated the potential components of an integrated management of Loranthaceae species (mistletoes) which constitute a major constraint to the survival and fruit production of many trees such as Vitellaria paradoxa in West Africa. Three types of pruning, five doses of each of two herbicides and host resistance were evaluated in mistletoe-infested parklands. Natural enemies were surveyed with a view to biological control. Pruning of the host branch along with the parasite’s haustorium (endophytic system) led to the total elimination of the parasite. When the endophytic system was spared, the time of pruning and species of parasite significantly influenced the number of sprout stalks per tuff. Their interaction was also significant. Death of at least 80% of treated Loranthaceae tufts was recorded for doses of 15 g l -1 of glyphosate and 20 g l -1 of 2,4-D. The artificial infestation of stands with parasite seeds revealed the likely existence of genetic resistance to mistletoe in V. paradoxa . The agroforestry parkland survey showed that birds, chiefly Pogoniulus chrysonocus , and insects are potential natural enemies of Loranthaceae. Results showed that Loranthaceae control could be achieved with techniques already used to successfully manage weeds. However, there is need to improve control components and their integration to successfully manage mistletoes in Burkina Faso. Keywords : Vitellaria paradoxa , Loranthaceae, mechanical, herbicides, host resistance, bio-control

Carbon sequestration potential of parkland agroforestry in the Sahel

Abstract Establishing parkland agroforestry on currently treeless cropland in the West African Sahel may help mitigate climate change. To evaluate its potential, we used climatically suitable ranges for parklands for 19 climate scenarios, derived by ecological niche modeling, for estimating potential carbon stocks in parkland and treeless cropland. A biocarbon business model was used to evaluate profitability of hypothetical Terrestrial Carbon Projects (TCPs), across a range of farm sizes, farm numbers, carbon prices and benefit sharing mechanisms. Using climate analogues, we explored potential climate change trajectories for selected locations. If mature parklands covered their maximum range, carbon stocks in Sahelian productive land would be about 1,284 Tg, compared to 725 Tg in a treeless scenario. Due to slow increase rates of total system carbon by 0.4 Mg C ha−1 a−1, most TCPs at carbon prices that seem realistic today were not feasible, or required the participation of large numbers of farmers. For small farms, few TCP scenarios were feasible, and low Net Present Values for farmers made it unlikely that carbon payments would motivate many to participate in TCPs, unless additional benefits were provided. Climate analogue locations indicated an uncertain climate trajectory for the Sahel, but most scenarios projected increasing aridity and reduced suitability for parklands. The potentially severe impacts of climate change on Sahelian ecosystems and the uncertain profitability of TCPs make the Sahel highly risky for carbon investments. Given the likelihood of degrading environmental conditions, the search for appropriate adaptation strategies should take precedence over promoting mitigation activities.

PHOTOSYNTHESIS AND BIOMASS PRODUCTION BY MILLET (PENNISETUM GLAUCUM) AND TARO (COLOCASIA ESCULENTA) GROWN UNDER BAOBAB (ADANSONIA DIGITATA)AND NÉRÉ (PARKIA BIGLOBOSA) IN AN AGROFORESTRY PARKLAND SYSTEM OF BURKINA FASO (WEST AFRICA)

SUMMARYPhotosynthesis and biomass production by millet (Pennisetum glaucum) and taro (Colocasia esculenta) grown under baobab (Adansonia digitata) and néré (Parkia biglobosa) was studied at Nobéré (Burkina Faso) with the aim of optimising parkland systems productivity. Millet yielded the highest biomass under Baobab and the lowest biomass was recorded in the zone close to the tree trunk of néré. In contrast, the biomass of taro was higher in heavy shaded zones under néré and the zone close to baobab's trunk. The two crops showed an increasing trend of photosynthesis rate (PN) from tree trunk to the open area. However, the increase in thePNof taro from tree trunk to the open field was lower compared to that of millet. By increasing its leaf area index (LAI) under shade, taro displayed higher biomass production under tree compared to the open area while an opposite trend was observed in millet. The high millet biomass production under baobab could be explained by light availability and the reduction of temperature under shade compared to the open field. The adaptation of taro to shade by increasing its LAI and thus avoiding drastic reduction inPNunder shade resulted in better biomass production under heavy shade. Therefore, it was concluded that by replacing millet with taro under dense tree crowns the productivity of agroforestry parkland systems could be increased.

Separating competition-related factors limiting crop performance in an agroforestry parkland system in Burkina Faso

To address tree–soil–crop interactions in the Sahel, we examined the growth-limiting factors (water, light and mineral nutrients) of Sorghum bicolor growing under trees in agroforestry parklands of Burkina Faso. Growth and yields of sorghum were measured after (1) pruning crowns of Vitellaria paradoxa and Parkia biglobosa trees, and (2) applying mineral fertilizers (nitrogen and/or phosphorus) and supplemental irrigation during normal wet cropping seasons in 2007 and 2008. Irrigation treatments led to non-significant 29% and 23% gains in grain and dry matter yields (from control values of 455 and 1,140 kg ha−1), respectively. The fertilizer showed variable but in general significant increases in grain and straw yields and more consistently in the height of sorghum plants. The crown pruning increased the values of these variables much more strongly, by 520% and 348% (from control, no-pruning values of 282 and 612 kg ha−1), respectively. The growth and production of S. bicolor were also >56% higher under V. paradoxa than under P. biglobosa. The same trends were observed in both cropping seasons, although rainfall was much heavier in 2008 than in 2007, and the mean sorghum grain yield was approximately twice as high in 2008. The results clearly indicate that competition for light limits sorghum growth more than competition for other resources in the studied system, suggesting that parkland management should aim at either increasing light availability (by reducing tree density or pruning) or growing shade-tolerant crops under the trees. However, use of a poorly soluble phosphorus source during the first year, modest amount of water applied through the supplemental irrigation (48 mm) and the wetness of the rainy season in 2008 (which led to abandonment of the irrigation treatments and floods in the experimental plots) may have masked possible effects of the applied fertilizers and irrigation. Therefore, more prolonged analyses of the effects of fertilizers and deficit irrigation are required before robust recommendations can be made to farmers.

Chiefs and Trees: Tenures and Incentives in the Management and Use of Two Multipurpose Tree Species in Agroforestry Parklands in Northern Ghana

Amid growing concerns about the perceived population decline of shea (Vitellaria paradoxa) and locust bean (Parkia biglobosa) trees in the agroforestry parklands, this article explores the impacts of differing tree tenure regimes on their management and use. Using a case study of two communities in Northern Region, Ghana, the study shows that the differing institutional arrangements governing the ownership, access, and use of these two species have led to different sets of incentive structures that have contrasting effects on the management of these species. Shea, in general, seemed to fare much better than locust bean under the current customary regulations. The research finds that in the absence of proper incentives, old and dying locust bean trees might not be replaced by young ones, thereby further jeopardizing its population, and along with it a variety of benefits it accrues to these rural communities.