Marcel Houinato

Impact des feux de brousse sur la dynamique des communautés végétales dans la forêt de Bassila (Bénin)

Abstract The impact of bush fire on the dynamic of vegetation in Bassila forest was studied. The results show reforestation in the plot protected from bush fire and decrease of forest species in the plot affected by late fire. In the plot affected by early fire, most species present at the beginning of the study had a normal development. Late fire allowed apparition of new species of therophyte (36%) and decrease of phanerophyte species. Phanerophytes have the same values (45%) in the plots protected from bush fire and those affected by early fire.

Efficiency of inventory plot patterns in quantitative analysis of vegetation: a case study of tropical woodland and dense forest in Benin

The main issue in forest inventory is the reliability of data collected, which depends on the shape and size of inventoried plots. There is also a need for harmonisation of inventoried plot patterns in West Africa. This study focused on the impact of plot patterns on the quantitative analysis of two vegetation types of West Africa based on case studies from Benin. Twenty and fifteen plots of 1 ha each were demarcated in dense forest and woodland, respectively. Each 1 ha plot was divided into 100 quadrats of 100 m2 each and diameter at breast height (dbh) of trees was recorded in each quadrat. The required time to measuring trees diameter in each 1 ha plot was also recorded to compute the mean inventory effort. From the 100 quadrats in each 1 ha plot, 14 subplots of different shapes and sizes were considered by grouping together adjacent quadrats. The basal area of each subplot was computed and the relationship between estimation bias of the basal area and the size of subplots was modeled using Smiths Law (Smith 1938). The mean absolute error of the shape parameter c of Weibull distribution was computed for each of the subplot shape, size and direction. The direction and shape of subplots did not influence significantly (P > 0.05) the precision of the quantitative analysis of vegetation. However, square subplots were suitable in practice. On the contrary, plot size was significantly (P < 0.05) and inversely correlated to estimation efficiency. The optimal plot size for quantitative analysis of vegetation was 1 800 and 2 000 m2 with an inventory effort of 0.51 and 0.85 man-days per subplot in woodland and dense forest, respectively. It is concluded that use of standard sample sizes will help to harmonise a forestry database and to carry out comparisons at regional level.

A quantitative ethnobotanical approach toward biodiversity conservation of useful woody species in Wari-Maro forest reserve (Benin, West Africa)

Quantitative ethnobotany researches can contribute much to guide biodiversity conservation, especially in developing countries. Our study presents a step-by-step approach to identify priority species for local conservation of useful woody species. The presented approach includes (1) an investigation of the popularity and versatility of woody species in the local people, (2) an estimation of the ecological availability of useful tree species in the forest and (3) identification of local priority species for conservation. We focused the study on the Wari-Maro forest reserve in the Sudanian zone of Benin as an example to implement such approach and identify useful priority species for sustainable conservation and management strategies development. Ethnobotanical surveys were conducted with people in surrounding villages of the forest composed by different sociocultural groups. Floristic vegetation surveys were performed within the forest to assess the local ecological availability of used woody species. A principal component analysis was performed to analyze the versatility, the popularity and the ecological availability of species. Spearman’s correlation test was used to assess relation between variables. In total, 79 woody species were reported for seven main types of uses: technology, construction, medicinal, veterinary, food, forage and energy. Among them, 35 were most popular and versatile, and 3 were characterized as priorities for conservation especially regarding their less availability and more versatility. We discussed the used approach by the underlining importance of integrating wood uses or multiples uses in conservation priorities setting and conservation decision-making of useful woody tree species.

Practical aspects of grass forage seed production and quality with particular reference to planting row spacing and nitrogen fertilization in tropical regions: A review

The poor seed yield from some pasture grasses may result from a number of causes, such as the choice of site production, low soil fertility, inappropriate sowing rate, inadequate crop management practices particularly plant density, fertilizer input, poor seed recovery, etc. Compared with sowings of general plant use, seed crops warrant more care and expense during the establishment phase. Seedbeds should be prepared more thoroughly and the seed sown more precisely using adequate seeding rates. The effect of row spacing on the one hand and nitrogen level application on the other hand, have variable effect on grass seed production and there are a conflicting report in some cases depending on species, management practices and environmental conditions, and therefore a case-by-case study for each species and environment is important. In general, seed growers had better to sown seed in row than broadcasting and row spacing of 50-80 cm can be recommended for seed production depending on grass species or cultivars. The selection of optimal production areas depends on soil fertility, the photoperiod and temperature which can interact with rainfall and humidity of the site. The optimum sowing depths was 0-30 mm with some species and cultivars emerging from greater depths than others. With some exceptions, larger seeds were generally able to germinate successfully from greater depths. It was reported that seeds of Brachiaria brizantha and Panicum maximum established better when covered by 20-50 mm. Generally, applying fertilizer nitrogen to seed crops has implications for yield component dynamics such as tiller increasing, number of fertile tillers, floret per spikelet, and seed per head and ultimately increases seed yield and quality. Amounts of nitrogen fertilizer required will depend on species, soil type and rainfall. More often, 100-250 kg of nitrogen per ha and crop and rate more than 300 kg N/ha caused reduction in seed yield by severe plant lodging. For optimum time for nitrogen application, it can be recommended to growers to apply nitrogen in the period from vegetative to spikelet initiation. Keywords : Planting density, sowing, fertilization, seed yield, quality, tropical areas.

The Effect of Seasonal Variations, Covariations with Minerals and Forage Value on Itchgrass’ Foliar Silicification from Sudanian Benin

Silica (SiO 2) in forage grasses has been found in reducing cell-wall digestibility. This study investigates whether: (i) the seasonal variability affects the silica and minerals accumulation and forage values of leaves of R. cochinchinensis and (ii) silica concentration is correlated with minerals and fodder value. In an itchgrass population selected in the W Biosphere Reserve, leaves were collected on 90 marked plants from May to October 2003 and 2004, at 15 days intervals except May, June and October. Some 300 g of fresh blades from the 3 rd most recently expanded leaves were oven dried and analyzed for dry mass, SiO 2, ash, N, Na, Ca, P, K, and Mg. Digestible Nitrogen Matter (DNM) and Fodder Energetic Value (FEV) were calculated using the Demarquilly formula. Apart from SiO 2, ash and forage value, data were log-transformed to restore homoscedasticity before statistical analyses. SiO 2 ranges from 5.69 % to 9.95 %, i.e. varying 1.4 fold between May and October, reaching 1.75 fold at mid-September. SiO 2 is positively related to Ca but negatively to K, P, N, DNM and FEV. The negative correlations suggest that SiO 2 concentration in R. cochinchinensis could be reduced with a significant increase in energy and accumulation of important nutrients such as N, P and K. Therefore, leaf silicification and nutritive value relationship should be conclusive in the case of itchgrass.

Assainissement de l’environnement par la valorisation des ressources non conventionnelles en alimentation de porcs en croissance

La presente etude s’est interessee a la comparaison des performances zootechniques et economiques des porcs nourris avec des aliments commerciaux et des aliments non conventionnels. Au total, 90 porcelets metis (race locale X Large white) âges de 60 a 90 jours dont 45 mâles castres et 45 femelles, ont ete repartis en 15 lots de 6 animaux, a raison de 3 loges de 6 porcelets par traitement alimentaire. Chaque lot a ete nourri a volonte avec un aliment commercial et quatre aliments contenant differents taux de Azolla, Moringa, son de riz, visceres de poulet Cobb 500 et de poisson Oreochromis niloticus . Une difference significative (P < 0,05) a ete notee entre les gains moyens quotidiens (GMQ). Apres 90 jours d’experimentation, les GMQ etaient de 197g/j pour les porcs du lot a aliment commercial et de 63 a 101g/j pour ceux soumis aux aliments a base de ressources non conventionnelles. Il ressort des calculs economiques que le cout alimentaire (Ca) par kg de gain de poids (GP) etait plus faible pour l’aliment non conventionnel (716 FCFA/kg GP) par rapport a l’aliment commercial (830 FCFA/kg GP). Il est donc possible d’utiliser ces ressources non conventionnelles pour nourrir de facon efficiente des porcs dans un systeme integre d’exploitations familiales tout en rendant l’environnement sain.