Forest-savanna Transition Zone Research Articles

Fodder production responses to pruning height and fodder quality of some trees and shrubs in a forest-savanna transition zone in southwestern Nigeria

Seasonal fodder production responses of five shrubs (Centrosema arenarium, Desmodium strigillosum, Desmodium velutinum, Phyllodium pulchellum, and Tadehagi triquetrum)and five trees (Albizia gummifera, Berlinia grandiflora, Albizia niopoides, Bauhinia monandra, and Inga edulis) to pruning heights ranging from 15 to 75 cm were evaluated during the main-wet, minor-wet, and dry seasons of 1993 and 1994 in the forest-savanna transition zone of West Africa. Fodder from the main-wet season was analysed for nitrogen (N) and phosphorus (P), and dry matter degradation characteristics after 6, 12, 24, 48, 72 and 96 h of incubation in rumen-fistulated N'Dama steers. In the minor-wet season, fodder production of all species increased in response to increasing pruning height with the exception of P. pulchellum and A. gummifera. Highest fodder production was attained at a pruning height of 45 cm for the Desmodium species, 50 cm for P. pulchellum, and 75 cm for the rest of the species. Concentrations of N and P varied significantly among the species; for N the ranges were 28.7–38.8 g kg−1 (shrubs) and 25.3–44.5 g kg−1 (trees), while for P the ranges were 3.26–7.04 g mg−1 (shrubs) and 3.58–6.76 g mg−1 (trees). Dry matter degradation characteristics differed significantly among shrubs and trees; ranges for shrubs were: soluble fraction (a), 128–185; degradable fraction (b), 664–703; potential degradability (PD), 793–857, as g kg−1; rate of degradation (c), 0.0241–0.0308 as % h−1 while for trees ranges were: (a), 139–160; (b), 651–826; (PD), 824–970, as g kg−1; (c), 0.0143–0.0227 as % h−1. Based on fodder production and quality, C. arenarium, D. strigillosum, D. velutinum, B. monandra, I. edulis, and A. niopoides were the most promising species for the development of animal agroforestry technologies in the west African forest-savanna transition zone and similar environments in the tropics.

Investigating the optimum planting date for sorghum in the forest–savanna transition zone of Nigeria

Ten planting dates were selected at weekly intervals for the purpose of determining the optimum planting date for two late maturing sorghum (Sorghum bicolor) cultivars in the 1995 and 1996 cropping seasons. Both the floral characteristics and the ultimate grain yield were affected by variation in planting date. The highest grain yield for each cultivar (977 and 958 kg ha−1 for Janare and Farin Dawa respectively in 1995, and 975 and 955 kg ha−1 respectively in 1996) resulted from planting delayed for exactly 51 days after the onset of the rains. Consequently, 10–12 June appeared to be the optimum planting dates for sorghum in the area. A comparison of the result with previous work done in the same ecological unit revealed that delaying planting until 10–12 June increased grain yield by about 25–27 kg ha−1. The effects of the characteristics of the onset of the rains on the optimum planting date have been discussed and the implication of the study for traditional agricultural practice in Nigeria has also been noted.

Evaluation of the effects of some agroforestry practices on selected properties of soils in a sub-humid zone of Ghana

The study investigated the effects of three 5-year-old cropping systems comprising Leucaena hedgerows with cowpea (Vigna unguiculata), maize (Zea mays L.), and groundnut (Arachis hypogaea) on the accumulation of soil organic carbon, bulk density, porosity, and aggregate stability; and compared these with soils under a Leucaena woodlot of similar age in a forest-savanna transition zone of Ghana. The woodlot soils had the highest accumulation of organic carbon and total porosity. The aggregate stability in this system was more than twice the values for the alley cropping systems. Furthermore, the aggregate stability correlated well with the soil organic matter (r = 0.77**), suggesting that it can be well estimated from organic matter content. Among the three alley cropping systems, the accumulation of organic carbon was in the order cowpea> maize > groundnut, but the aggregate stability did not show any consistent pattern with organic matter content in these systems. The results indicated that despite the periodic addition of organic matter from pruned Leucaena hedgerows to the soil, the alley system did not improve the aggregate stability as much as the woodlot system. Ghana Jnl agric Sci. Vol.32(2) 1999: 153-158

Longterm alley cropping with four hedgerow species on an Alfisol in southwestern Nigeria – effect on crop performance, soil chemical properties and nematode population

A longterm alley cropping trial was undertaken on an eroded Oxic paleustalf in the forest-savanna transition zone of southwestern Nigeria from 1981–1993. Two nitrogen fixing hedgerow species (Gliricidia sepium and Leucaena leucocephala) and two non legume hedgerow species (Alchornea cordifolia and Dactyladenia barteri) were used in the trial compared to a control (with no hedgerow) treatment. Plots were sequentially cropped with maize (main season) followed by cowpea (minor season). With 4 m interhedgerow spacing and pruning at 0.75 m height, the mean annual pruning biomass yields were observed in the following order: Leucaena (7.1 t ha-1 ) > Gliricidia (4.9 t ha-1 ) > Alchornea (3.7 t ha-1) > Dactyladenia (3.0 t ha-1 ). Alley cropping with the four woody species greatly enhanced the total plot (woody species + crop) biomass yield/ha as follows; Leucaena (21.8 t ha-1) > Gliricidia (17.7 t ha-1) > Alchornea (11.7 t ha-1) > Dactyladenia (9.5 t ha-1). Total biomass yield of crops in control plot was 5.3 t ha-1. Higher biomass yields with alley cropping also increased nutrient yield and cycling. Gliricidia and Leucaena showed higher nutrient yields than Alchornea and Dactyladenia. Alley cropping with Gliricidia and Leucaena could sustain maize yield at moderate level (>2 t ha-1), which would require a N-rate of 45 kg N ha-1 with sole cropping. Application of N in Gliricidia and Leucaena alley cropping still improved maize yield. Higher nitrogen rates are required for alley cropping with Alchornea and Dactyladenia hedgerows. A low rate of phosphorus application is needed for sustaining crop yields with all treatments. Occasional tillage is recommended to increase maize yield. Alley cropping and tillage showed little effect on cowpea seed yield. Surface soil properties declined with time with continuous cultivation. Alley cropping with woody species maintained higher soil organic carbon, phosphorus and potassium levels. Plots alley cropped with Gliricidia and Leucaena showed lower pH and extractable calcium level. Leucaena alley cropped plot also showed lower magnesium level. The decline in soil pH and extractable cations may be due to increased cation leaching with application of high rates of Gliricidia and Leucaena prunings. Alley cropping with the four woody species showed no effect on population of parasitic nematodes.

Incidence and severity of African cassava mosaic disease (ACMD) and cassava bacterial blight (CBB) on some local and exotic cassava varieties in different ecological zones of Ghana

Seven exotic varieties of cassava, namely TMS 30001, TMS 91934, TMS 4(2)1425, TMS 30555, TMS 50395, TMS 63397, and TMS 30572 developed in IITA, Ibadan, Nigeria, and three local varieties, namely 'Ankra', 'Bosomensia' and 'Katawia' were evaluated for African cassava mosaic disease (ACMD) and cassava bacterial blight (CBB) resistance in five ecological zones of Ghana. The trials were conducted in experimental fields of Crops Research Institute at Fumesua (Forest zone) in 1988, 1989, 1990; Aiyinase (High Rain Forest zone), Pokuase and Ohawu (Coastal Savanna zone), and Ejura (Forest-Savanna Transition zone) in 1989 and 1990; Techiman (Forest-Savanna Transition zone); and Nyankpala and Damongo (Guinea Savanna zone) in 1990. ACMD and CBB damage at 3 and 6 months after planting were scored on a 1-5 scale based on the severity of the diseases. The exotic varieties were significantly more tolerant to ACMD across the 3 years at Fumesua as well as in 1989 and 1990 across all locations. For CBB in 1990, the exotic varieties were significantly more tolerant than the local varieties in the Coastal Savanna zone where CBB incidence and severity was relatively high. Ghana Jnl agric. Sci. Vol.31(1) 1998: 35-43

Structural root form and fine root distribution of some woody species evaluated for agroforestry systems

Fine root distribution and structural root characteristics of four-years-old multipurpose woody species with potential for use in agroforestry systems were investigated on an Alfisol in the forest savanna transition zone of south-western Nigeria. Rooting patterns of woody species studied differed considerably. Lonchocarpus sericeus had the lowest percentage (21%) of total fine roots confined to the upper (0 to 30 cm) soil layer, compared to 84% with Tetrapleura tetraptera. Despite the superior tap root system of Enterolobium cyclocarpum and the fine root form of Nauchlea latifolia however, their extensive distribution and very large lateral woody root volume density may pose a major problem for seedbed preparation and tillage operations in simultaneous agroforestry systems. Lonchocarpus sericeus appears to have the most desirable structural and fine root architecture among the species studied for simultaneous agroforestry systems. The total root density below the underlying distal soil layers was linearly related to the sum of square of tap root diameter and the corresponding soil depths.

Local Resource Management in the Forest-Savanna Transition Zone: The Case of Wenchi District, Ghana

Summary In Ghana's forest‐savanna transition zone, recent ecological debates counterpose the dominant view that human activities cause progressive savannisation of forests, with competing views that the forest‐savanna boundary is relatively stable, and even that people can assist the formation of forest in savanna. Applying the environmental entitlements approach to people‐vegetation interactions in the Wenchi area of Brong Ahafo region, this article shows that ecological outcomes vary for different parts of the landscape, depending on the particular practices of socially‐differentiated land users. The cases of farming by local landowners, farming by immigrants from the north, and charcoal production illustrate how such practices are shaped by diverse local and state‐level institutions, especially land and tree tenure arrangements, with implications for current attempts to develop collaborative forms of forest management in Ghana.

AN INVESTIGATION OF THE AGROCLIMATIC POTENTIAL OF THE FOREST–SAVANNA TRANSITION ZONE OF NIGERIA FOR THE CULTIVATION OF SORGHUM

The agroclimatic potential of the forest–savanna transition zone of Nigeria for the cultivation of sorghum (Sorghum bicolor) was investigated. Five phenological stages of the crop formed the basic unit of time for the investigation. Selected agroclimatological thermal and moisture indices were measured daily and processed into ten-day (decadal) averages for the 1993 and 1994 cropping seasons. The thermal indices, temperature and photoperiods were optimal for sorghum growth but, on the basis of the distribution of rainfall and actual water availability in relation to the crop's water consumption, the moisture indices were above optimum. However by relating effective water availability to the indices of moisture adequacy for the growth of the crop, it was found that the agroclimatological moisture indices were optimum during the moisture sensitive stages. A comparison of the vegetative growth and grain yield of sorghum in the study area and elsewhere in the savanna region confirmed the agroclimatic potential of the forest–savanna transition zone for sorghum production.

Nitrogen use efficiency and N-competition betweenLeucaena hedgerows and maize in an alley cropping system

A two-year field experiment was undertaken on an Alfisol in the forest-savanna transition zone of southwestern Nigeria, to study the effect of alley cropping, root barrier, application of N fertilizer andLeucaena leucocephala (Lam.) de Wit. prunings, on N utilization by maize andLeucaena hedgerows. The trial was conducted using a split-plot design with three replications. Mainplot treatments were alley cropping withLeucaena leucocephala planted at 4m interhedgerow spacing and control (no hedgerows). Four subplot treatments were with and without addition of hedgerow prunings, and with and without presence of root barriers. There were no significant effects of presence ofLeucaena hedgerows and root barriers on maize grain yield.Leucaena hedgerows recovered about 7% of the 30 kgN/ha applied as (15NH4)2SO4 to maize during one year. Application of hedgerow prunings increased maize yield by 82% and N-uptake in the grain by 50% over the treatment without prunings. Recoveries of15N-labelled prunings and fertilizer N by maize plants were about 10 and 16% respectively. Prunings addition increased15N-fertilizer recovery in main season maize and the residual value during the minor season by about 36% over the treatment without prunings. Pruning N-use efficiency was higher for plants grown adjacent to the hedgerows than in the middle of alleys during main season and the reverse was observed during the minor season. Absence of a root barrier increased N-use from prunings. Large amounts of applied N in the system were unaccounted for. Results of the trial showed, that without root barrier there was no measurable below-ground N competition betweenLeucaena hedgerows and maize.

Reading Forest History Backwards:The Interaction of Policy and Local Land Use in Guinea's Forest-Savanna Mosaic, 1893-1993

Abstract Sophisticated local agricultural and forest management techniques have underlain the creation and maintenance of the main landscape features in Kissidougou Prefecture of Guinea's forest-savanna transition zone. Social anthropological, oral historical, archival and aerial photographic evidence shows how over long periods, peri-village forest islands have been created from savannas, productive rice swamps from inland valleys, and productive upland soil and vegetation conditions from unimproved herbaceous savanna. From 1893, colonial policy was based on reading the region's environmental history backwards, assuming forest islands to be relics of a once-extensive dense humid forest cover which local agriculture and fire-setting had destroyed. Archival evidence shows how the deductions of botanists, agronomists and foresters, coupled with the assumptions of administrators and other visitors, mutually reinforced each other to create and sustain a vision of degradation so pervasive that it still underlies modern environmental policy. The paper examines how colonial and post-colonial policies conceived within this vision have interacted with local land use. Given varying administrative capabilities, it considers the extent to which changes in local practices have been conditioned by policy as opposed to other social, economic, political or ecological changes, and the extent to which environmental changes have fortuitously coincided with policy objectives.

Natural Resource Management: the Reproduction and Use of Environmental Misinformation in Guinea's Forest-Savanna Transition Zone

Summary An erroneous analysis of environmental change has informed environmental policy in part of Guinea for a century. Using this case study, the relationship between the production of information about environmental problems and external institutions which address them, is examined. To see how certain analyses of change have gained credence and validity, while others ‐ including local people's own ‐ have been excluded from investigation, the relative dominance of particular disciplines, of methods and data sets within them, and of deductive theories guiding data interpretation, are considered. Such dominance depends on the sociopolitical and financial structures within which environmental policy institutions have evolved and operate. Resume La gestion naturelle des resources: la replacation et le deploiement de fausses informations sur l'environnement dans la zone de transition foret‐savane en Guinee Depuis un siecle deja, c'est sur une analyse erronnee des changements environnementaux que se fonde la politique environnementale dans une certaine partie de la Guinee. Dans la presente etude de cas, les auteurs offrent un examen du rapport entre la production de l'information concernant les problemes environnementaux et les institutions externes qui s'y adressent. Pour voir dans quelle maniere certaines analyses du changement sont devenues plus vraisemblables et donc plus acceptables alors que d'autres ‐ y compris celles des autochtones ‐ auraient ete marginalisees de l'etude, les auteurs reflechissent a la dominance relative des diverses disciplines, des methodes et des series de donnees au sein de celles‐ci, et des theories deductrices qui gerent l'interpretation des donnees brutes. Cette dominance dependrait des structures socio‐politiques et financieres au sein desquelles se sont evoluees les institutions responsables de la politique environnementale, et au sein desquelles elles operent toujours. Resumen El manejo de recursos naturales: reproduccion y uso de la desinformacion ambiental en la zona de transicion bosque/sabana de Nueva Guinea Las pautas de accion ambientales en partes de Nueva Guinea han recibido informacion basada en el analisis erroneo de cambios ambientales por un espacio de un siglo. Usando este caso, se examina en el articulo la relacion entre la produccion de informacion sobre los problemas ambientales y las instituciones externas que se aplican a resolverlos. Se considera la forma en que ciertos analisis de cambio han ganado credibilidad y validez, mientras que otros ‐ incluyendo algunos de grupos locales ‐ han sido excluidos de la investigacion, del relativo predominio de algunas disciplinas en particular, de metodos y datos contenidos en ellas, y de teorias deductivas que guian la interpretacion de datos. Este predominio depende de las estructuras sociopoliticas y financieras dentro de las cuales las institutuciones ambientales han evolucionado y operado.