European Journal of Scientific Research ISSN 1450-216X Vol.23 No.4 (2008), pp.537-547 © EuroJournals Publishing, Inc. 2008 http://www.eurojournals.com/ejsr.htm
Preliminary Floristic Inventory and Diversity in Azagny National Park (Côte D'Ivoire)
Kouamé Djaha Laboratoire de botanique, UFR Biosciences, Université de Cocody-Abidjan (Côte d’Ivoire) 22 BP 582 Abidjan 22, Côte d’Ivoire E-mail: djahakouame@yahoo.fr Adou Yao Constant Yves Laboratoire de botanique, UFR Biosciences, Université de Cocody-Abidjan (Côte d’Ivoire) Centre National de Floristique (CNF), Université de Cocody-Abidjan (Côte d’Ivoire) E-mail: adouyaocy@gmail.com Kouassi Konan Edouard Laboratoire de botanique, UFR Biosciences Université de Cocody-Abidjan (Côte d’Ivoire) N’Guessan Kouakou Edouard Laboratoire de botanique, UFR Biosciences, Université de Cocody-Abidjan (Côte d’Ivoire) Centre National de Floristique (CNF), Université de Cocody-Abidjan (Côte d’Ivoire) Akoi Kouadio Wildlife Conservation Society (WCS) 01 BP 1240 Abidjan 01, Côte d’Ivoire Abstract A Botanical study based on plots and itinerant inventory has been conducted in Azagny National Park., located on the ivorian cost. The objective was to analyse the floristic diversity of the park. At the end of the study, 519 plant species were recorded. Among them, 57 are endemic of Upper Guinea and 24 are threatened and endangered, justifying the inclusion of the Park in the Guinean Forest of West African Hotspot. The woody species diversity in the Park computing by the Shannon index (H) was 3.78. The more diverse ecological area were the plateau (H = 3.49). The dominant species of the Park are Anthostema aubryanum, Berlinia confusa, Anthonotha macrophylla, Xylopia staudtii and Mytragyna ciliata. Keywords: Floristic diversity, endemic, threatened and endangered, Azagny, Côte d'Ivoire.
1. Introduction
Tropical forest that contains more of the half of the global specific diversity brings about increasing anthropogenic pressure which leads to fragmentation (Tchatat et al., 1999). These pressures provoke its progressive destruction with more than 10 % of lost of the forest per year (Puig, 2001). The
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degradation of the ecosystem has as consequences in the disappearance of certain relevant invaluable ecologic and economic species (Wilson, 1992). In Côte d’Ivoire, the high rate of regression of the woody covering can be explained essentially by the high intensity of forestry operation and farming (Myers, 1980; Barnes, 1990; Struhsaker, 1998). For this reason, few intact forest formations still existing in the rural area. In the area of the state, some fragments of forest are only found in reserved forest, forest withstand industrial plants. The real old forests are found in National Parks which take 1/3 of the total surface of protected zones (Poorter et al., 2004). National Parks and notably Azagny National Park (ANP) are then protected areas the best located for a study of biodiversity. It holds several vegetations (Bouichou, 1978). In the present state of knowledge, few studies on flora have been achieved in the Azagny National Park. The only botanic study implemented, is that of FGU-Kronberg (1979) which aimed at making a quick summary in order to help managers protecting and managing the forest and promote eco-tourism in the park as ecological entertainment field. To offset this insufficiency of floristic knowledge of the Park, it is essential to study the flora and the vegetation and follow the evolution of the biological diversity. The current study aims at contributing for the analysis of the floristic diversity of the ANP.
2. Materiel and Method of Study
2.1. Description of the study zone The Azagny National Park, located in the south of Côte d’Ivoire, between 5°14’ and 5°31’ of north latitude and 5°76’ and 5°01’ of west longitude, covers a superficies of 21850 ha. This Park is located in the “Région des lagunes”, in the ivorian littoral sector, about 125 km from Abidjan (Fig 1). It spreads all over the department of Grand-Lahou and Jacqueville and is a part of the phytogeographic region of “upper guinea” which goes from Togo to Senegal (White, 1983).
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Figure 1: Localisation of Azagny National Park in the South of Côte d’Ivoire
The relief of Azagny National Park is a low land (meridional part) and composed of vast swamp areas (about 9000 ha) made of soft water which doesn’t show any sign of natural sinking. The northern part is made by a group of low plateaus. The altitudes in the park vary from 1 to 5 m. The park is ecologically specific because of its hydraulic system. In effect, it’s surrounding by ¾ by the river Bandama, canal of Azagny and Ebrié lagoon. Finally, the park is overflowed at 45 % all the year and at 62 % during the rainy seasons (Roth et al., 1979).
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The climate of the region, which is a sub-equatorial type comprise (Avenard et al., 1971; Laugenie, 1979) a great rainy season (end of April to half July) and one great dry season (from December to April) alternating with one small rainy season (from half September to the end of November) and one small dry season (half July-half September). The study area appears as a mosaic of formations very different from savannah to dense forests (Avenard et al., 1971; Bouichou, 1978). The fauna is characterised by the one of the Guinean domain (littoral sector). It’s also rich of species from lagoons, avifauna species of swamping eco-systems (Goliath heron, eagle fisher, etc.). This fauna is adapted to the swampy conditions of the area, which protect it. The habitat of the big fauna (elephant, buffaloes, hippopotamus), decreases with increasing area of industrial plantations of palms oil and rubber trees that find their refuge in the park. Some primates (cercocebus, cercopithecus, Van Beneden colobus), cephalophes, west african manatee, Bongo and harness guib are also found in the park. 2.2. Materiel In this study, biological material (plant species) and technical material (Global Positioning System: GPS, compass etc.) were used. 2.3. Field method Two methods were used: plot relevé and itinerant relevé. The plot method was usually use for forest inventories in tropical zone (Hall et Swaine, 1981; Mori et al., 1983; Spichiger et al., 1991; Cheek et Cable, 1997; Hawthorne, 1996; Adou Yao et al., 2007). It consists in recording species encountered in square, rectangle or circular area in order to record a maximum representative species of the inventory zone. For the current study, the park has been divided into 56 squares of 1 km by side. Each surface of 1 km2 is subdivided into hundred sub/squares of 100 m2 each one. In the accessible part of the park, 28 plots of 100 m2 according to their position on the topography have been chosen. The sampling is made by those 28 plots. The position (altitude/longitude) of each plot was recorded by a GPS. In each plot all vascular plant species (trees, shrubs, grass, and lianas) were recorded and identified on field. The non identified ones were collected for herbarium vouchers. Once in the Centre National de Floristique, the National Herbarium, they had been identified with the help of Prof. L. Aké-Assi. In each plot, a sub-plot of 25 m2 (Fig 2) was selected in which, some details data were recorded (DBH individuals numbers) for individuals with diameter equal or more than 5 cm at 1m 30 high.
Figure 2: Subdivision of the data collection plot
10 m
Quadrat
Quadrat
10 m
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Tchouto (2004) and Adou Yao (2005), have shown that forest diversity based only on trees individuals with DBH ≥ 10 cm do not reflect more than 50 p.c. of all the diversity of a given area. The DBH ≥ 5 cm has then been taken in the objective to take into account the maximum species and individuals. To get a more accurate estimation of species richness and composition, additional relevés were compiled thanks to itinerant prospection. These inventories focused on original spatially restricted habitats where no quadrat could be led. 2.4. Data analysis After establishing the list species found into the 28 plots, species relevés were preliminarily examined to identify and count endemics, referring to previously checklist established by Porter et al., 2004 for Upper Guinea endemic species. The endemism is an important criterion to characterize the state of conservation to a given area. The presence of numerous endemic species and endangered (particular status species) is broadly a sign of a great biodiversity and a good level of conservation (Adou Yao et Roussel, 2007). The list of threatened and endanger species was compiled according to the IUCN checklist of 2006. The diversity of the ANP flora was determined through the IVI and the Shannon and Weaver Index. Importance Value Index (IVI) was calculated for each species i as IVI = RDeni + RDomi + RFrqi (model 1) RDeni is relative density, RDomi is relative Dominance, and RFrqi is relative frequency of species i. It has been used in different tropical forest by different authors (Curtis and McIntosh 1950, Mori et al., 1983; Latour, 1994; Bakayoko, 1999 and Adou Yao et al., 2007) in order to appraise the preponderance of species. In order to appraise the floristic diversity, some woody species in the Azagny National Park, the Shannon and Weaver diversity index has been calculated. This index is usually used in ecological studies (Huston, 1995) as measure of heterogeneity and takes into account the regularity of species abundance (Peet, 1974). It’s calculated as the following formula: H = - Σ (Ni/N) x ln (Ni/N) (model 2) Ni is individuals number for species i and N is the total numbers of all species.
3. Results
3.1 Floristic composition This inventory (a surface listing combined to an itinerant listing) constitutes the first one implemented in the Azagny National Park. In total, 519 plant species have been listed in the ANP. Among them, 364 (70.13 %) are from plots (28 plots, about 2800 m2) and 155 (29.87 %) of listed itinerant relevés. The 519 species are belonged to 100 families and 351 genera. The five richest families, representing a rate of 25.6 % of species, are the Rubiaceae (7.3 %), Apocynaceae (5.2 %), Euphorbiaceae (5 %), Caesalpiniaceae (4.2 %) and Fabaceae (3.9 %). The other 95 families represent a rate of 74.4 % of species. 3.2. Endemic species of Upper Guinea and rarity in the ANP The comparison of obtained lists with those of Poorter et al. (2004) showed that 57 species are Upper Guinea endemic species (Table 1). They represent 11 % of the total number recorded in this study.
Preliminary Floristic Inventory and Diversity in Azagny National Park (Côte d'Ivoire)
Table 1:
N° 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57
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Upper Guinea endemic species recorded in the ANP during the present study.
Species recorded Adenia dinklagei Aframomum excapum Albertisia cordifolia Anthocleista nobilis Anthonotha vignei Argocoffeopsis afzelii Baissea zygodioides Chrysophyllum azaguieanum Coelocaryon oxycarpum Cola caricifolia Connarus thonningii Copaifera salikunda Crossostemma laurifolium Dialium aubrevillei Dichapetallum fiicaule Dichapetalum toxicarium Diospyros heudelotii Drypetes aylmeri Ehretia trachyphylla Euadenia eminens Eugenia calophylloides Ficus ottoniifolia Globimetula cupulata Gymnestemon zaizou Heritiera utilis Hugonia ruffipilis Hunteria simii Hypolytrum poecilolepis Iodes liberica Ixora laxiflora Keetia rubens Landolphia membranacea Leptoderris miegei Macaranga beillei Maranthes aubrevillei Maschalocephalus dinklagei Milicia regia Millettia takou Mussaenda grandiflora Myrianthus libericus Neostenantera hamata Nephthytis afzelii Neuropeltis prevosteoides Penianthus patulinervis Placodiscus attenuatus Placodiscus bancoensis Platysepalum hirsutum Polycephalium capitatum Ptychopetalum anceps Pycnanthus dinklagei Raphia palma-pinus Sherbournia calycina Syrrhonema hexastamineum Tabernaemontana africana Tetracera potatoria Uvariodendron occidentale Xylopia villosa Families Passifloraceae Zingiberaceae Menispermaceae Loganiaceae Caesalpiniaceae Rubiaceae Apocynaceae Sapotaceae Myristicaceae Sterculiaceae Connaraceae Caesalpiniaceae Passifloraceae Caesalpiniaceae Dichapetalaceae Dichapetalaceae Ebenaceae Euphorbiaceae Boraginaceae Capparaceae Myrtaceae Moraceae Loranthaceae Simaroubaceae Sterculiaceae Linaceae Apocynaceae Cyperaceae Icacinaceae Rubiaceae Rubiaceae Apocynaceae Fabaceae Euphorbiaceae Chrysobalanaceae Rapateaceae Moraceae Fabaceae Rubiaceae Cecropiaceae Annonaceae Araceae Convolvulaceae Menispermaceae Sapindaceae Sapindaceae Fabaceae Icacinaceae Olacaceae Myristicaceae Arecaceae Rubiaceae Menispermaceae Apocynaceae Dilleniaceae Annonaceae Annonaceae
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For the threatened and endangered species, 24 have been recorded in the ANP (table 2), according to the UICN (2006) list. Among them, 3 species are really in danger (Chrysophyllum azaguieanum, Placodiscus attenuatus and Tieghemella heckelii), 2 endangered species but with a minor concern (Irvingia gabonensis and Milicia excelsa) and 19 others are a category of vulnerable species.
Table 2:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Threatened and endanger species listed in the ANP according to IUCN (2006).
Species Albizia ferruginea Anopyxis klaineana Anthonotha vignei Chrysophyllum azaguieanum Copaifera salikounda Entandrophragma candollei Entandrophragma cylindricum Entandrophragma utile Guarea cedrata Gymnostemon zaizou Heritiera utilis Irvingia gabonensis Lophira alata Milicia excelsa Milicia regia Nauclea diderrichii Neostenanthera hamata Nesogordonia papaverifera Placodiscus attenuatus Rhodognaphalon breviscupe Terminalia ivorensis Tieghemella heckelii Turraeanthus africanus Warneckea memecyloides Families Mimosaceae Rhizophoraceae Caesalpiniaceae Sapotaceae Caesalpiniaceae Meliaceae Meliaceae Meliaceae Meliaceae Simaroubaceae Sterculiaceae Irvingiaceae Olacaceae Moraceae Moraceae Rubiaceae Annonaceae Sterculiaceae Sapindaceae Bombacaceae Combretaceae Sapotaceae Meliaceae Melastomataceae Threatened (UICN, 2006) VU A1cd VU A1cd VU A1c, B1+2c EN B1+2c VU A1d VU A1cd VU A1cd VU A1cd VU A1c VU B1+2c VU A1cd LR/nt VU A1cd LR/nt VU A1cd VU A1cd VU A1c, B1+2c VU A1cd EN A1c, B1+2c VU A1cd VU A1cd EN A1cd VU A1cd VU A1c, B1+2c
3.3. The importance value index of the species recorded in the ANP The IVI of the forest vary between 4.49 and 48.23 (table 3). Anthostema aubryanum (48.23) and Berlinia confusa (43.48) have the highest IVI values.
Table 3: Importance Value Index (IVI) of the species in the ANP
Relative frequency 0.29 0.22 0.52 0.15 0.29 1.84 1.84 0.74 Relative density 47.45 41.67 36.91 33.33 21.1 19.54 18.13 9.49 Relative dominance 0.49 1.59 0.19 0.29 7.21 0.23 0.96 0.39 IVI 48.23 43.48 37.62 33.77 28.60 21.61 20.93 10.62
Species Anthostema aubryanum Berlinia confusa Anthonota macrophylla Xylopia staudtii Mytragyna ciliata Tabernaemontana crassa Strombosia pustulata Other species
3.4. Index (H) of diversity The Shannon index of woody plant is 3.78 for the whole study area (table 4). In relation to topography, the diversity index for the plateau (H= 3.49) is higher than that of shallows (3.23) and slopes (2.9).
Preliminary Floristic Inventory and Diversity in Azagny National Park (Côte d'Ivoire)
Table 4: Diversity Index (H) of the inventoried areas in the ANP
H 3.49 2.90 3.23 3.78
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Sector Plateau Slope Shallows Azagny National Park
4. Discussion
4.1. Qualitative diversity of Azagny National Park The ivorian flora inventoried by Aké Assi (2001-2002) comprises 3853 species. This flora concerns whole country (322 462 Km2) and its ecosystems with a density of 1.19 species per Km2. For a space of 218.5 Km2, this study has listed 519 species (13.47 % of national floristic richness) for a density of 2.38 species per Km2. This value is the double of the national density. With a small superficies and a great floristic density, the Azagny National Park appears as a rich Park. This forest known as “Rubiaceae-Apocynaceae-Euphorbiaceae” present the same characteristics as the most of ivoirians forests as Monogaga classified forest, the south of the Taï National Park and Bossematié classified forest (Adou Yao, 2005; Adou Yao et al., 2005; Kouassi, 2007). These authors have presented these forests as dominated by Rubiaceae, Euphorbiaceae, Apocynaceae and Caesalpiniaceae families. In the whole study area, the plateaus were the sites where the greatest number of species was recorded (92). This great diversity of species in this area can be explained by the fact that it is located between cocoa plantation and a non disturbed forest. In the opposite, the poorest plot in species (21) is found in shallows. This poverty is due to the fact that it is located in a very swamp zone where Raphia palma-pinus (Arecaceae) is the dominated species. The permanent presence of water would have influenced on the species richness of these zones. Currently, the floristic list of the park is appraised to 604 species according to two combined inventories: the one of FGU-Kronberg (1979) and the current study. The forest species-richness can be higher if we take into account the fact that the whole forest has not been inventoried yet. In effect, it’s very difficult to do it because of the permanent overflowed, swampy areas hardly accessible. In a recent study, Wieringa and Poorter (2004) have listed 2800 plant species for all the “upper Guinean” phytogeographical region. Among them, 616 (22 %) are said to be endemic to this region. The “upper Guinea” is the forest block that goes from Togo up to Senegal (White, 1983). After comparison, 57 species of this list, either 9.25 % are found in the achieved listing by the team. The presence of such species in our list justifies the connection of the study area to the region of the Guinean Forest of West African Hotspot. Their presence in the Park is also justified by the fact that ANP belongs to “Côte d’Ivoire group”, one of the five great forest refuges of Africa (Mayr et O’hara, 1986). The floristic composition, the endemism and the threatened and endangered species of UICN categories shows that the ANP is qualitatively much diversified. 4.2. Quantitative diversity of Azagny National Park Anthostema aubryanum, Berlinia confusa, Anthonota macrophylla, Xylopia staudtii and Mytragyna ciliata are predominantes species with great IVI (28.6 to 48.23). Anthostema aubryanum has the highest IVI, his relative frequency and relative dominance are very weak (inferior to 1). This species is represented by a great number of individuals in 4 plotss. It can then be considered as gregarious species. Tabernaemontana crassa and Strombosia pustulata with respective IVI of 21.61 and 20.93 less high than those of previous species appears in 25 out of the 28 inventoried plots. These two species, abundant in the entire park, can be considered as faithful species.
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The Shannon and Weaver index for the whole study zone is 3.78. In the south of the Taï where Adou yao et al. (2005) worked with a DBH ≥ 10 cm, the index was 3.76. Therefore the forest of Taï National Park is considered as the richest of Côte d’Ivoire (Aké Assi, 2001, 2002; Poorter et al., 2004). This great diversity of the ANP is certainly imputable to the use of a DBH ≥ 5 cm for this study. This confirms the apprehension of Tchouto (2004) and Adou Yao (2005); who states that the diversity produced by the only individuals of DBH ≥ 10 cm doesn’t reflect all the diversity of a given area. Other works on the vegetation having used the same DBH have not been found to appreciate the specific diversity of the zone. This result is considerable as first of this kind in the Azagny National Park. The comparison of the floristic diversity of the three topographical sites show that plateau zones are the more diversified than the two others (shallows and slopes) zones.The plateaus were the preference areas for cultivations. After the abandonment by the peasants, these zones started the reconstitution of their vegetation. This forest reconstitution implying the reappearance of many plant species could explain the great floristic diversity of the zones of plateaus in the ANP. The shallows were also used for the market-gardening activities and rice growing. With the abandonment of these activities, the reconstitution of the vegetation of the swampy zones could translate their high floristic diversity. The slopes, sight the streaming of water, did not constitute favourable zones for cultivation. They thus kept a certain structure of their vegetation, which in spite of the abandonment of the zone would not have varied much floristically what explains a diversity of the flora weaker than the zones of plates and shallows.
5. Conclusion
At the end of this first inventory in the Azagny National Park, 519 species have been listed. One of the particularities of the present study is the use of a DBH ≥ 5 cm. The objective of this choice is to work t on a maximum of individual of species. Several endemic species of upper Guinea have been found, justifying the relationship between the park and this region of great value of biological diversity. Compared with the list of the UICN (2006), 24 endangered species have been listed, what reinforces the idea of the inclusion of that study zone in the Guinean Forest of West African Hotspot. The predominant species of the ANP are Anthostema aubryanum, Berlinia confusa, Anthonotha macrophylla, Xylopia staudtii and Mytragyna ciliata. The floristic diversity of the forest calculated with the Shannon and weaver index is important.
Acknowledgment
We are grateful to the OIPR (Office Ivoirien des Parcs et Réserves) for permission to carry out research in Azagny National Park This work was supported by the Centre National de Floristique (CNF) and WCS (Wildlife Conservation Society). We thank Prof. Aké-Assi Laurent for helping in identification of plant vouchers and samples. We thank also Mr Assi Yapo Jean for his help on field and laboratory. We’re grateful to the forester agents who work in the ANP. Finally, we thank all the field assistants who were very useful.
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