Plant Communities, Forest Site Identification and Classification In
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BOIS ET FORÊTS DES TROPIQUES, 2006, N° 288 (2) 25 GROUPEMENTS VÉGÉTAUX / LE POINT SUR… Plant communities, forest site identification Jean Cossi Ganglo1 Bruno de Foucault2 and classification in Toffo 1 University of Benin, Faculty reserve, South-Benin of Agronomy Department of Environmental Management BP 1493 Calavi Republic of Benin 2 Department of Botany Faculty of Pharmaceutical and Biological Sciences BP 83, 59006 Lille Cedex France Nine plant communities in Toffo forest reserve (southern Benin) were identified by using a phytosociological approach. Within each non-pioneer plant community, site conditions and productivity levels were remarkably homogenous. The relationships between plant communities, ecological factors and plantation productivity were used to identify and map five forest sites, for which management specifications are indicated. Chromolaera odorata plant community Photo J. C. Ganglo. 26 BOIS ET FORÊTS DES TROPIQUES, 2006, N° 288 (2) FOCUS / PLANT COMMUNITIES Jean Cossi Ganglo, Bruno de Foucault RÉSUMÉ ABSTRACT RESUMEN GROUPEMENTS VÉGÉTAUX, PLANT COMMUNITIES, FOREST SITE AGRUPACIONES VEGETALES, IDENTIFICATION ET CLASSEMENT IDENTIFICATION AND CLASSIFICATION IDENTIFICACIÓN Y CLASIFICACIÓN DES STATIONS FORESTIÈRES DANS IN TOFFO RESERVE, SOUTHERN BENIN DE LAS ESTACIONES EN LA RESERVA LA RÉSERVE DE TOFFO, SUD-BÉNIN DE TOFFO, SUR DE BENÍN. Des études phytosociologiques ont Phytosociological surveys were car- Se efectuaron estudios fitosociológi- été faites, entre novembre 2001 et ried out from November 2001 to cos, entre noviembre de 2001 y marzo mars 2004, dans la forêt de Toffo March 2004 in Toffo forest reserve de 2004, en el bosque de Toffo (6° 51’ - 6° 53’ latitude nord et 2° 05’ (latitude N 6° 51’ - 6° 53’ to longitude (6° 51’ - 6° 53’ N y 2° 05’ - 2° 10’ E), - 2° 10’ longitude est), au Sud-Bénin E 2° 05’ - 2° 10’) in southern Benin en el Benín meridional (África occi- (Afrique de l’Ouest), en vue d’identi- (West Africa), in order to identify and dental) para identificar y clasificar las fier et de classer les stations fores- classify forest sites. The method used estaciones. El estudio de la vegeta- tières. L’étude de la végétation a été for the vegetation survey was based ción se hizo siguiendo el enfoque de faite selon l’approche de la phytoso- on the synusial approach to phytoso- la fitosociología sinusial. El estudio ciologie synusiale. Celle des sols a été ciology. The soil survey was made by de suelos se realizó analizando dos réalisée en analysant deux profils analysing two soil profiles per plant perfiles edáficos en cada agrupación pédologiques au sein de chaque grou- community. Topographical parame- vegetal identificada. Se anotaron los pement végétal identifié. Les para- ters such as slopes, positions and parámetros topográficos como pen- mètres topographiques tels que les exposure were noted. Two soil sam- dientes, posiciones topográficas y pentes, les positions topographiques ples from each soil profile were taken exposición. Se tomaron dos muestras et l’exposition ont été notés. Par profil for laboratory analysis. Dendrometric de suelo por perfil edáfico, en los pédologique, deux échantillons de sol parameters (height and diameter at horizontes superficiales, para su aná- ont été prélevés dans les horizons de breast height) were measured in at lisis en laboratorio. Los parámetros surface pour analyse de laboratoire. least four sample plots of 300 m2 dendrométricos (diámetro a 1,3 m del Les paramètres dendrométriques (dia- (15 m x 20 m) within each plant com- suelo y altura) se midieron en al mètre à 1,3 m du sol et hauteur) ont munity. The study has enabled us to menos cuatro parcelas de 300 m2 été mesurés dans au moins quatre identify and describe nine plant com- (15 m x 20 m), en cada agrupación placettes de 300 m2 (15 m x 20 m), au munities. In the non pioneer plant vegetal. Los estudios permitieron sein de chaque groupement végétal. communities, site conditions and for- identificar y describir nueve agrupa- Les études ont permis d’identifier et est productivity were remarkably ciones vegetales. En cada agrupación de décrire neuf groupements végé- homogenous. An analysis of planta- no pionera, observamos una notable taux. Au sein de chaque groupement tion productivity according to plant homogeneidad, tanto de los factores non pionnier, nous avons noté une communities has identified three lev- ecológicos como de la productividad homogénéité remarquable, aussi bien els of productivity that differ signifi- de las plantaciones. El estudio de la des facteurs écologiques que de la cantly at the 5% probability level. The productividad de las plantaciones en productivité des plantations. L’étude correlations between plant communi- función de las agrupaciones vegeta- de la productivité des plantations en ties, ecological factors and plantation les permitió caracterizar tres niveles fonction des groupements végétaux a productivity have enabled us to iden- de productividad, significativamente caractérisé trois niveaux de producti- tify and map five forest sites for which diferentes en el umbral de probabili- vité, significativement différents au we indicate management specifica- dad del 5 %. Las correlaciones entre seuil de probabilité de 5 %. Les corré- tions. agrupaciones vegetales, factores eco- lations entre les groupements végé- lógicos y productividad de las planta- taux, les facteurs écologiques et la Keywords: phytosociology, forest ciones permitieron identificar y carto- productivité des plantations a permis site, plant community, Toffo forest grafiar cinco estaciones y aportar d’identifier et de cartographier cinq reserve, Benin. recomendaciones de ordenación. stations forestières pour lesquelles des recommandations d’aménage- Palabras clave: fitosociología, esta- ment ont été faites. ción, agrupación vegetal, reserva forestal de Toffo, Benín. Mots-clés : phytosociologie, station forestière, groupement végétal, réserve forestière de Toffo, Bénin. BOIS ET FORÊTS DES TROPIQUES, 2006, N° 288 (2) 27 GROUPEMENTS VÉGÉTAUX / LE POINT SUR… Introduction Area under study Benin’s natural forest resources results of forest research. Research Our investigation area was Toffo are not extensive, covering about results from many authors (Steen, forest reserve (6° 51’ - 6° 53’N; 2.65 million hectares according to the Coupé, 1997; Ganglo, 1999 and 2° 05’-2° 10’E) (figure 1). This forest 2001 FAO forest inventory. These lim- 2005; Yessoufou, 2002; Klinka et area has a subequatorial climate, ited forest resources are vulnerable to al., 2003; Aoudji, 2003; Noumon, with a long rainy season from March degradation from seasonal fires, 2003) show that plant communities to July and a short rainy season from intensive grazing and extensive agri- are reliable tools for forest site classi- September to October. There is a long culture. Benin is currently losing fication. This article describes the dry season from November to some 70 000 ha of forests per year main results obtained in the identifi- February and a short dry season in due to degradation (Fao, 2001). In cation and classification of forest August (figure 2). From 1961 to 2003, the early 1940s, some reforestation sites in the Toffo forest reserve. Based mean annual rainfall of the study was carried out by the government, on a study of natural undergrowth in area was 1 030 mm, mean daily tem- and the country now has about teak plantations in Toffo forest, plant perature was 27.5° C and relative 112 000 ha of plantations (Fao, communities were identified, descri- humidity varied from 52% to 95%. 2001). Sustainable management of bed and their relationships with site Two major soil types are found these limited forest resources is factors (soils, topography, geomor- in the study area: essential if the country is to continue phology) and plantation productivity ▪ Ferrallitic soils of the Continental to meet demand for forest products. were used to identify and classify dif- Terminal geological period are found Any sustainable management of for- ferent forest sites. in the southern parts of the forest. In est resources must be based on the the upper horizons of these soils, Mallotus oppositifolius and Reissantia plant community. Photo J. C. Ganglo. 28 BOIS ET FORÊTS DES TROPIQUES, 2006, N° 288 (2) FOCUS / PLANT COMMUNITIES Figure 1. Toffo forest reserve. sand is dominant (81-95%). The soil may harbour some relic natural forest Material pH varies from 6.7 to 7.7 and organic species, of which Ceiba pentandra matter content from 0.5% to 8%. The and Antiaris toxicaria are the most and methods C/N ratio is 10-13%. Cationic common. The black cotton soils exchange capacity varies from 3 to favour liana communities of Paullinia Phytosociological study 20 meq/100g of soil and the rate of pinnata and Combretum hispidu, of spontaneous vegetation saturation ranges from 33% to 100%. where the relic natural forest species ▪ Black cotton soils (“vertisols”) are Milicia excelsa and Diospyros To carry out the phytosociologi- found in the northern part of the for- mespiliformis are commonly found. cal study, we used a 1/10000 forest est. Clay is dominant in these profiles In the river zones, the vegetation map for plant community mapping (59-68%). The organic matter content varies with the occurrence of water. and orientation in the field. A Global is higher (3-28%) than in the ferral- We frequently recorded Nymphaea Positioning System (GPS) was used litic soils. The C/N ratio is also high maculata in stagnant water and to record relevant points and plant (12-18%). The pH is 6 - 7 whereas the Leersia hexandra, Alternanthera ses- community contours; a SUUNTO com- cationic exchange capacity varies silis, Mitragyna inermis, Berlinia pass was used for field orientation. from 19-28 meq/100g of soil with a grandiflora and others on muddy and In the study of the spontaneous saturation rate of 80% to 100%. swampy soils surrounding water vegetation, we used the synusial The above two soil types are points. approach to phytosociology devel- separated by the muddy, swampy The Toffo forest reserve currently oped by Gillet et al.