Floristic diversity of classified forest and partial faunal reserve of Comoé-Léraba , southwest Burkina Faso

The classified forest and partial faunal reserve of Comoé-Léraba belongs to the South Sudanian phytogeographical sector of Burkina Faso and is located in the most humid area of the country. This study aims to present a detailed list of the Comoé-Léraba reserve’s flora for a better knowledge and conservation. Floristic inventories have permitted to record 540 plant species belonging to 342 genera and 91 families, thus representing 26.12% of Burkina Faso’s phytodiversity (2067 species). Fabaceae and Poaceae with 89 and 51 species respectively, were the dominant families. The vegetation is characterized by the dominance of both phanerophytes (45.51%) and therophytes (32.73%). The importance of Guineo– Con golian species proves that the Comoé-Léraba flora belongs to the Sudano–Guinean transition sector. Comoé-Léraba also accounts the highest number of exclusive species followed by the reserve of Sahel in the country. Exclusive species bring out its value in flora conservation.


INTRODUCTION
An updated checklist of the vascular plants of Burkina Faso with 2067 species was recently published (Thiombiano et al. 2012), with most of these species documented from protected areas.Nevertheless, published lists of phytodiversity in protected areas are scarce.There are 81 protected areas in the country (Thiombiano and Kampmann 2010), but local floras have been published for only three of them: Bangr-Weoogo urban park (Gnoumou et al. 2008), the partial faunal reserve of Pama (Mbaygone et al. 2008) and Arly National Park (Ouédraogo et al. 2011).
Among Burkina Faso's protected areas, the Comoé-Léraba reserve is unique due to its geographical position and flora.The reserve is located in the most humid zone of the country.The vegetation is dominated by woodland and islands of tropical dry forest, with some patches of dense non-riparian forests (Neumann and Müller 1999;Gnoumou 2011b), which are very rare habitats in Burkina Faso.The annual rainfall may reach 1000 mm and the rainy days per year exceed 90 days.Hence, a floristic inventory can be expected to include many exclusive species in comparison to the other parts of the country.With the ultimate objective toassess floristic diversity for better conservation and management of the Comoé-Léraba reserve, this paper aims to provide a detailed floristic list.

Study site
The classified forest and partial faunal reserve of Comoé-Léraba is located in the southwest part of Burkina Faso (Figure 1) between the latitudes 10°02′ and 09°31′ N and the longitudes 004°55′ and 004°13′ W. It was established from two existing classified forests (Diéfoula and Logoniégué) in 2001 and covers 125,000 ha.The Comoé-Léraba reserve belongs to Category IV of IUCN protected areas (IUCN 2004) and is a Ramsar site since 2009 (http://www.ramsar.org;Ramsar 2014) mainly due to the two permanent rivers (Comoé and Léraba) that cross the reserve.The reserve is managed by the local association "AGEREF" (Comoé-Léraba classified forest and partial faunal reserve's inter-village association of natural resource management).Hunting and ecotourism are permitted under a forester agreement in a specific period of each year during the dry season.Land use pressure is high in the cultivation zone surrounding the reserve.Indeed, the conservation of this protected area is sustained by the integrated management based on local participation (through the AGEREF).After 13 years, positive results (e.g., reconstitution of fallow land) have been obtained, according to the survey of vegetation structure in the protected area (Gnoumou et al. 2011b).

Data analysis
The family concept follows Thiombiano et al. (2012), therefore Fabaceae and Malvaceae have been considered in a wider sense (with Caesalpinoideae and Mimosoideae as subfamilies of Fabaceae and Bombacoideae, Grewioideae, Sterculioideae as subfamilies of Malvaceae), which is now generally accepted (e.g., APG III, 2009) but may differ from previous analyses from West Africa.Life forms follow Raunkiaer (1934) and have been assembled from literature (Mbayngone et al. 2008;Ouédraogo et al. 2011;Thiombiano et al. 2012).The chorological types refer to the phytochoria of White (1983), widely used in West African studies (Sinsin 2001;Mbayngone et al. 2008), and distributional information from the Global Biodiversity Information Facility (http://www.gbif.org/species).To determine floristic similarity with other protected areas, Sørensen indices were calculated using the Community Analysis Package (CAP 2002).

DISCUSSION
The flora of Comoé-Léraba reserve represents 26.12% of the vascular plants of Burkina Faso (Thiombiano et al. 2012).The five most important families are similar to those of Pama reserve (Mbayngone et al. 2008).The family composition is also close to the flora of Arly National Park, but we found more species of Combretaceae.
Family diversity is higher (91 families) in the Comoé-Léraba reserve compared to Arly National Park (83) and the Partial faunal reserve of Pama (73).Fabaceae and Poaceae are the most dominant families in the protected areas in the North and South Sudanian sector (Schmidt et al. 2005;Schmidt et al. 2010) with typical savanna vegetation.With increasing water availability, gallery forests and dense dry forests become more important landscape elements.This explains the high availability of Rubiaceae members in Comoé-Léraba and Pendjari located in the more humid areas (Sambaré et al. 2010;N'Da et al. 2008, Bakayoko et al. 2004;Ake Assi, 2002).
The life form pattern found in Comoé-Léraba reserve, with a dominance of phanerophytes and therophytes, is in accordance with other studies from the North Sudanian (Ouédraogo et al. 2011) and South Sudanian phytogeographical sectors (Assédé et al. 2012).The dominance of phanerophytes in this study is due to the presence of different forest types.These results are similar to South Sudanian Zone (Thiombiano et al. 2012).
The chorological spectrum of the flora is characterized by a high proportion of Sudanian species (25.19%).However, the number of Guineo-Congolian species is also very important in the reserve (20.93%).These elements are found in each vegetation type of the reserve as opposed to Arly National Park where they are mainly confined to the gallery forests (Ouédraogo et al. 2011).This study confirms the phytogeographic placement of Comoé-Léraba in the Sudano-Guinean transition zone as shown by the presence of open forest of Isoberlinia (Adjanohoun et al. 1989) and the presence of Monotes and Uapaca.Within the chorological spectrum a high proportion of widespread species has been documented (Pluriregional African, Paleotropical, Pantropical, Sudano-Zambezian a ndAfrotropical).Chromolaena odorata, a neophyte from the Americas, has been identified.In West Africa, C. odorata shows the limit between denser rain forest and Guinean savanna (Akbundu and Agyakwa 1989).In other areas of the world, it is considered as an aggressive invader (US Forest Service 2014).
The comparison of protected areas of Burkina Faso and Benin includes four neighbouring areas.W-Burkina Faso (Nacoulma et al. 2011), Arly (Ouédraogo et al. 2011), Pama (Mbayngone et al. 2008) are geographically grouped together with the biosphere reserve of Pendjari in Benin in the so-called WAPO complex (W-Arly-Pendjari-Oti).Two other protected areas have been considered: Bangr-Weoogo urban park (Gnoumou et al. 2008), in the central part of the country, and the classified forest of Kou (Guinko and Thiombiano 2005), in southwest Burkina Faso.The last one is the country's largest protected area located in its northernmost corner -the Sahel reserve (Schmidt et al. 2008).
The highest floristic similarity was found between W-Burkina Faso and Arly national parks (Table 1) and also these protected areas are also similar to Pama and Pendjari in species composition.
Moreover, W-Burkina Faso, situated in the North Sudanian sector has a flora most similar to the Comoé-Léraba reserve.This is probably due to the similarity of more ecosystems, such as (1) groves on termite's mounds, (2) woodland savannah on flood plains, in high, middle and lower glacis, (3) gallery forest on river beds, (4) forest in middle glacis and high glacis, which is quite opposite to Kou reserve which is geographically closer to Comoé-Léraba.The W-Burkina Faso has high  species richness with few exclusive species in comparison to the other protected areas.However, low dissimilarity exists between Comoé-Léraba reserve and the other transboundary protected areas further east.The environmental differences and larger distance to the other reserves make the Bangr-Weoogo urban park and the Sahel reserve the most distinctive in species composition.Comoé-Léraba accounts the highest number of exclusive species followed by the reserve of Sahel in the country (Table 2).Exclusive species bring out their value in flora conservation.

Figure 1 .Figure 2 .
Figure 1.Map of the classified forest and partial faunal reserve of Comoé-Léraba and its surroundings, Burkina Faso.

Table 1 .
Comparison of the protected areas: Sørensen index

Table 2 .
Comparison of the protected areas: common species, exlusive species and species richness.