Phytosociology, ecology, grazing value, productivity and carrying capacity of natural pasturelands at Nikki-Kalale in Northern Benin
SINSIN Brice (1993)
PhD, ULB, Belgium, 353 p
Phytosociology, ecology, productivity and grazing value of sudanian pasture lands were studied at Nikki-Kalalé in northern Benin. Factor analysis applied to the phytosociological relevés permitted to define ten new associations which were classified into five classes. Under the class: Hyparrhenietea Schmitz 1963 of the sudano-zambesian savanna communities, were placed the Loxodera ledermannii association that occurs in tree savannas, the Loudetia jlavida association that occurs on gravel-enriched soils, the Aspilia paludosa and Anadelphia afzeliana association that occurs on clay-enriched shallow and the Pennisetum unisetum association that occurs on well drained shallow. Under the class: Ctenio-Loudetietea togoensis of sudanian xerophytic communities were placed the Aristida kerstingii association and the Vernonia perrottetii association; all of those two associations were established on thin soils above cuirass. Under the class: Soncho-Bidentetea pilosi Hoff et al. 1983 of weed plant communities that occur in field and fallow lands were placed the Urochloa lata and Tephrosia pedicellata association that occurs on plateau fallow lands, the Desmodium hirtum association of shallow fallow lands and the Celosia trigyna association of weed plant communities. Under the class: Ruderali-Manihotetea emend. Hoff et Brisse 1983 of disturbed areas, was placed the Setaria longiseta and Sporobolus pyramidalis association that relies on cattle impacts. All of these phytosociological classes were subdivided in orders and alliances. Under the class: Hyparrhenietea were placed the order: Andropogonetalia gayani var. bisquamulati of West african savanna communities; this order was subdivided in two alliances, the alliance: Schizachyrio-Loxoderion ledermannii of savanna communities occurring on plateau and the alliance: Hyparrhenio-Andropogonion tectori of savanna shallow communities. Under the class: Ctenio-Loudetietea togoensis were placed the order: Loudetietalia togoensis of sudanian xerophytic communities; under this order was placed the alliance: Loudetion togoensis of communities occurring on thin soils above cuirass. Under the order: Ruderali-Euphorbietalia Schmitz 1971 (class: Ruderali-Manihotetea) was placed the alliance: Sido-Sennion obtusifoliae of nitrophilous communities occurring on well drained soils. Under the class: Soncho-Bidentetea pilosi was placed the order: Spermacocetalia stachydeae of sudanian communities occurring in fields and fallow lands; this order was subdivided into three alliances, the alliance: Spermacoco-Pennisetion polystachii of communities occurring on plateau fallow lands, the alliance: Andropogonion pseudaprici of communities on shallow fallow lands and the alliance: Kohaution grandijlorae of field communities. In the view point of biological types that composed the associations, therophytes were the dominant in field and fallow land associations. In the savanna associations, hemicryptophytes were less numerous than therophytes but they had the largest recovery values. In the view point of phytogeography, species which are largely distributed all over the tropics were dominant in field, fallow land and shallow associations, while typical sudanian species were much numerous in communities occurring on plateau in savannas. The associations of the alliance: Hyparrhenio-Andropogonion teetori had the highest grazing value but in generally speaking, the grazing values of all the associations were low and were less than 50. Soils and communities relationships analysis showed a good relation between soil factors and alliances; any good relationship was not obtained between soil factors and associations. Soil content of organic matter was well correlated to soil factors especially to textural and chemical components. The regressions established showed that soil organic matter content could permit to explain the fertility level of all the sites-sampled. Maximum phytomass of the associations was poorly correlated with soil factors. The highest maximum phytomass was obtained in the shallow communities. The lowest maximum phytomass was obtained in the Setaria longiseta and Sporobolus pyramidalis association when there is lacking in phytomass values of the alliance: Loudetion togoensis associations. The correlations between maximum phytomass and rainfall parameters were good. The curve of carrying capacities which correspond to periodical dry matter accumulation had the same trend for all the associations. Carrying capacity was very low in the dry season and very high in the rainy season. Chemical element stocks in phytomass depended on productivity and floristical composition of the associations. Most of the tree forages contained enough digestible protein and energy to much a TLU (Tropical Livestock Unit) needs. Grasses were deficient in protein especially at the end of the rainy season. The utilization of natural pastures by cattle herds was closely tied to the evolution of the carrying capacities of the associations. In the dry season, tree forages in savannas were essentially harvested and consumed; even though in the rainy season a great time was spent in fallow land pastures by the herds.
Key words: Phytosociology, ecology, pastoral value, phytomass, carrying capacity, pastureland, northern Benin