BOIS ET FORÊTS DES TROPIQUES, 2007, N° 294 (4) PEUPLEMENTS FORESTIERS 5 SAVANE SOUDANAISE Woody species composition, structure and diversity of vegetation patches of a Sudanian savanna in Burkina Faso Patrice Savadogo1 Mulualem Tigabu1 Louis Sawadogo2 Per Christer Odén1 1 Swedish University of Agricultural Sciences Faculty of Forest Sciences Department of Forest Genetics and Plant Physiology In order to develop conservation guidelines, information on the state of Tropical Silviculture Sudanian forests is urgently needed. Inventories conducted in four types of forest–dense and Seed Laboratory woodland, open woodland, gallery forests and fallow land–have shown in particular that the SE- 901 83 Umeå Fabaceae and Combretaceae families are the most abundant. Young individuals are Sweden predominant, and there are numerous rare species. Species with high conservation importance should be reintroduced in order to maintain a viable population. 2 Centre National de Recherche Scientifique et Technologique Institut de l’Environnement et de Recherche Agricole Département Production Forestière BP 10 Koudougou Burkina Faso Photo 1. Dense woodland. Photo D. Tiveau. BOIS ET FORÊTS DES TROPIQUES, 2007, N° 294 (4) 6 FOREST STANDS SUDANIAN SAVANNA Patrice Savadogo, Mulualem Tigabu, Louis Sawadogo, Per Christer Odén RÉSUMÉ ABSTRACT RESUMEN COMPOSITION, STRUCTURE ET WOODY SPECIES COMPOSITION, COMPOSICIÓN, ESTRUCTURA Y DIVERSITÉ DES ESPÈCES LIGNEUSES STRUCTURE AND DIVERSITY OF DIVERSIDAD DE LAS ESPECIES EN SAVANE SOUDANAISE AU VEGETATION PATCHES OF A SUDANIAN LEÑOSAS DE LA SABANA SUDANESA BURKINA FASO SAVANNA IN BURKINA FASO EN BURKINA FASO La variabilité climatique croissante et The woodlands of the Sudanian region La creciente variabilidad climática y el les impacts des activités humaines are heavily degraded due to increasing impacto antrópico provocan una fuerte entraînent une forte dégradation des climatic variability and anthropogenic degradación de los bosques de la forêts de la région soudanienne. Afin de impacts, and only relatively small región sudanesa. Para desarrollar orien- développer des orientations de conser- patches are left within the savanna taciones de conservación, es urgente vation, il est urgent de disposer d’infor- area. In order to develop conservation contar con informaciones sobre el mations sur l’état actuel de ce type de guidelines, information on the current estado actual de este tipo de vegeta- végétation. Nous présentons ici la com- status of this vegetation type is urgently ción. Presentamos aquí la composi- position, la structure et la diversité des needed. We describe the species com- ción, estructura y diversidad de las espèces ligneuses sur des parcelles de position, structure and diversity of especies leñosas en cuatro tipos de quatre types : forêt dense, forêt claire, woody species in four patches of vege- parcela: bosque espeso, bosque forêt-galerie et jachère abandonnée. tation: dense woodland, open wood- abierto, bosque de galería y barbecho Toutes les espèces ligneuses ont été land, gallery forest and abandoned fal- abandonado. Todas las especies leño- systématiquement identifiées et mesu- low. All woody species were systemati- sas fueron sistemáticamente identifica- rées sur un échantillon de quinze par- cally identified and measured in fifteen das y medidas en una muestra de celles de 0,25 ha. Les densités, domi- 0.25-ha sample plots. Density, domi- quince parcelas de 0,25 ha. Se calcula- nances, fréquences et valeurs d’impor- nance, frequency, and species and fam- ron densidades, dominancias, frecuen- tance générique ont été calculées pour ily importance values were computed to cias y valores de importancia de género caractériser la composition spécifique. characterize the species composition. A para caracterizar la composición espe- Plusieurs paramètres ont été calculés variety of diversity measures were cal- cífica. Se calcularon varias medidas pour déterminer l’hétérogénéité de culated to examine the heterogeneity of para determinar la heterogeneidad de chaque parcelle. Au total, 89 espèces each patch. A total of 89 species repre- cada parcela. Se registraron un total de représentatives de 29 familles et 66 senting 29 families and 66 genera were 89 especies representativas de 29 genres ont été enregistrées, avec un found; of which 67, 60, 35 and 23 familias y 66 géneros, con un número nombre décroissant en forêt dense et species were recorded in the dense decreciente en bosque espeso y claire, en forêt-galerie et en jachère. Les woodland, open woodland, fallow, and abierto, en bosque de galería y en los familles les plus abondantes sont les gallery forest, respectively. Fabaceae barbechos. Las familias más abundan- fabacées et les combrétacées. La den- and Combretaceae were the most abun- tes son las fabáceas y combretáceas. La sité des tiges de diamètre (dhp) supé- dant families. The density of stems densidad de tallos de un diámetro N a 5 rieur ou égal à 5 cm et la surface terrière N 5 cm dbh and the basal area were cm y el área basimétrica son más altas sont les plus élevées en forêt-galerie. La higher in the gallery forest than in the en los bosques de galería. La curva de courbe de répartition par classe de other patches. The size class distribu- distribución por clase de dimensión dimension est en forme de J inversé, tions of the vegetation produced a tiene una forma de J invertida, lo que indiquant une prédominance d’indivi- reverse J-shaped curve, indicating that indica un predominio de individuos dus jeunes. Les indices de diversité the forest is dominated by young indi- jóvenes. Los índices de diversidad montrent une diversité plus élevée en viduals. Diversity indices showed that muestran una diversidad más alta en forêt dense et une similitude générale- dense woodland was the most diverse, bosque espeso y una similitud general- ment faible entre parcelles. La distribu- and similarity between patches was mente baja entre parcelas. La distribu- tion de l’abondance spécifique pour generally low. The species abundance ción de la abundancia específica en chaque parcelle est logarithmique, patterns for each patch displayed the cada parcela es logarítmica, indicador attestant d’un grand nombre d’espèces log series distribution, indicating large de un gran número de especies raras. rares. Les espèces de grande impor- numbers of rare species. We identified Las especies de gran importancia para tance pour la conservation doivent être species with high conservation impor- la conservación deben reintroducirse réintroduites, afin de maintenir une tance that should be reintroduced to para mantener una población con un population de taille viable. maintain a viable population size. tamaño viable. Mots clés : biodiversité, conserva- Keywords: biodiversity, conserva- Palabras clave: biodiversidad, con- tion, forêt sèche, espèce menacée, tion, dry forest, threatened species, servación, bosque seco, especie en zone boisée. woodland. peligro, zona forestal. BOIS ET FORÊTS DES TROPIQUES, 2007, N° 294293 (4)(3) PEUPLEMENTS FORESTIERS 7 SAVANE SOUDANAISE Introduction African dry forests and wood- savanna that determine vegetation biodiversity conservation (Bellefon- lands vegetation types are character- patterns (Scholes, Walker, 1993; taine et al., 2000). The Tiogo forest, ized by more or less continuous tree Menaut et al., 1995). Local species where the present study was con- cover (70%), prolonged drought lasting richness and diversity of savanna ducted, is one of these State forest more than three months per year, and ecosystems are generally maintained reserves in Burkina Faso. It was delim- by their occurrence within the savanna by dynamic interaction between local ited by the French colonial administra- biome (Menaut etal., 1995). They colonization processes from species tion in 1940, and covers 30 000 ha. cover approximately 13 million km2, pools at larger spatial scales and Phytogeographically, it is situated in 43% of the total area of the continent, local extinction due to competitive the Sudanian regional centre of and are divided into two distinct exclusion processes, which in turn endemism in the transition from the regions, in the northern hemisphere are influenced by disturbances. northern to the southern Sudanian (Sudanian region) and the southern Degradation of savanna wood- zone (White, 1983; Fontes, Guinko, hemisphere (Zambezian region). The lands due to agricultural expansion, 1995). The Tiogo forest is not strictly Sudanian region lies between 6° and overgrazing, fire and wood cutting is a protected against human impacts and 13° N and covers an area of 5.25 mil- serious environmental concern in is being utilized both legally and ille- lion km2 (Menaut et al., 1995). The dry Burkina Faso, as in many tropical gally by local people living around the forests and woodlands of the Sudanian countries (Fries, Heermans, 1992). reserve. The impact of such exploita- region are tending to disappear due to Natural forests in the country currently tion on biological diversity in Tiogo increasingly severe climate conditions cover approximately 7 million ha and forest is not well documented. and anthropogenic impacts, leaving forest plantations cover 67 000 ha, This study is contributing to an only relatively small patches within the representing 26% of the country’s on-going study aiming to develop savanna area (Menaut et al., 1995). land area (274 200 km2). The remain- models for sustainable management Vegetation patterns, dynamic ing woodlands and dry forests are pre- of savanna woodlands in Burkina processes