AMERICAN JOURNAL OF SCIENTIFIC AND INDUSTRIAL RESEARCH © 2011, Science Huβ, http://www.scihub.org/AJSIR ISSN: 2153-649X doi:10.5251/ajsir.2011.2.5.774.785

Distribution, regeneration and conservation status of Nuxia congesta R.

Br. ex Fresen. (Buddlejaceae) in Côte d’Ivoire Adou Yao C. Y.1,2,3 , N’Da D. H.1, Bakayoko A.2,4 , Kouassi K. E.1, N’Guessan K. E.1, Aké-

Assi L.3 1Laboratoire de Botanique, UFR Biosciences, Université de Cocody-Abidjan, 22 BP 582

Abidjan 22, Côte d’Ivoire (e-mail: adouyaocy@gmail.com) 2Centre Suisse de Recherches Scientifiques (C.S.R.S).

3Centre National de Floristique (C.N.F.) 4Laboratoire de Biologie végétale et Amélioration des Productions Agricoles, UFR Sciences

de la Nature, Université d’Abobo-Adjamé, Côte d’Ivoire ABSTRACT

In Côte d’Ivoire, Nuxia congesta (Buddlejaceae) was known only on some highest peaks of the country (Mounts Tonkpi and Boho) until 2006. Recent studies conducted from January to June 2007 and in 2008 identified two new locations in the region of Marahoué (department of Bouaflé), relatively far from the previously known ones and confirmed the disappearance of the species in Mounts Tonkpi and Boho. The distribution of this species was mapped and some ecological characteristics observed in those different locations were specified. The conservation status of the species was also assessed and discussed on the basis of the threats that its habitats were liable to, using the criteria of the IUCN Red List. The species can be characterized as rare in Côte d’Ivoire. Key words: Rare species, Conservation status, Nuxia congesta, Côte d’Ivoire

INTRODUCTION

The loss of the biodiversity is presently a crucial problem for conservationists and for ecologists. The biodiversity of Tropical African countries represents a very important part of the global biological diversity (Myers et al., 2000; Brooks et al., 2001). The knowledge of the biological diversity in tropical Africa began with the works of the first colonial administrators. It continued with the first botanists until present time. In Côte d’Ivoire, the botanical investigations began in 1882 with Chaper (Aké-Assi, 2001) in the regions of lagoons and continued on all the Ivorian territory. The collections allowed listing a big quantity of plant species constituting the Ivorian flora that is estimated at 3,853 species (Aké-Assi, 2001, 2002). If a significant number of the species of this flora is not threatened, a more reduced part undergoes pressures due to the human activities on the ecosystems that shelter them or directly on them. Other species are naturally rare or even threatened because living in fragile biotopes with fewer populations. In this last group of habitats, the edges of rivers, mangrove, the swamp forests and mountains appear as appropriate sites for choice (Adou Yao et al., 2010).

The evaluation of the state, of the trends of the biodiversity and the identification of the habitats subjected to particular threats constitute the two main objectives of the Convention on Biological Diversity (CDB, 2001). In this respect, three attributes of the biodiversity particularly draw the attention of the international community: the species’ richness, the richness of rare and endangered species, and the endemism (Caldecott et al., 1996). These rare and threatened species are indicator species for the functioning of the ecosystems, and can inform about an imminent degradation of the biodiversity elements (Golding, 2002). They are likely to replace those that are presently abundant in case of important change in the ecological conditions.

A red list of plant species is a fundamental tool for biodiversity conservation. Indeed, in front of the high cost of the preservation of the habitats which contain a biological diversity, these species have to benefit first and foremost from the efforts of conservation (Myers et al., 2000). For Côte d’Ivoire, there is a list of rare and threatened species drawn up by Aké-Assi (1998) and updated in 2001-2002. For western Africa, there is also a list of Hawthorne (1996) and Poorter et al. (2004) who listed the rare, threatened

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and endemic species of western African forests. The Red List of the IUCN lists on a precise criteria, the threats to the species. It thus allows to take measures and to establish conservation priorities (IUCN, 2001, 2003). The lists of fauna and flora are established for every State of the World. The IUCN list concerning the Ivorian flora published in 2009 contains 129 species among which the threat status of 120 at least have to be updated because of the lack of recent works.

Among plants which live in threatened covers such as the vegetation of mountain, there is Nuxia congesta (Buddlejaceae), an orophyte species, met for the first time in Mounts Tonkpi and Boho in the West of Côte d’Ivoire, in the region of Man. The

conservation status of this species, its distribution, and its structural parameters, as well as its companion species were analyzed in this study.

MATERIEL AND METHODS

Study area: The study took place in two densely populated administrative regions of Côte d’Ivoire: the regions of the ‘18 Montagnes’ and of the ‘Marahoué’ (Figure 1). The first region, as its name suggests, is the highest peak in Côte d'Ivoire. The elevations range from 500 to 1,000 m a.s.l.

Several mountains can be met in the ‘18 Montagnes’ such as Mount Tonkpi (1,189 m a.s.l) and Mount Boho (760 m a.s.l.) near the village of Zoanlé (Zonlé) about 24 km from the city of Man (Figure 2).

Fig 1: Map of population density and location of the administrative regions of the study sites.

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Fig 2: View of the landscape around Man from Mount Tonkpi (Photo Assi, 2009). It can be noticed the mountainous landscape and the city of Man (in background). The mean annual temperatures are about 27°C. The region belongs to the mountainous sector of the Guinean domain (Guillaumet and Adjanohoun, 1971), which is covered by mountain vegetation as defined by Yangambi (1956) (Guillaumet and Adjanohoun, 1971). The summit of Mount Tonkpi includes, in addition to communications facilities, an interesting agricultural station that hosts introduced species such as quinquina (Cinchona officinalis and C. succirubra), tea (Cameliea sinensis), pines (Pinus sylvestris, P. patula).. The vegetation of Mount Tonkpi is a transition to the semi-deciduous forest. Uapaca esculenta, Uapaca guineensis, Chidlowia sanguinea, Tarrietia utilis, and Chrysoplyllum perpulcrhum are the dominant species of this vegetation. The second study site is located in the administrative Department of Bouaflé, precisely at Kossou, in the Centre West of Côte d’Ivoire. This zone belongs to the mesophilic sector of the Guinean domain. Its vegetation corresponds to that of a mountain dry forest occupying hilltops (N’Da et al., 2008) where Zanthoxylum spp and Anthonotha crassifolia

dominate. Until 2006, Nuxia congesta was known only on Mounts Tonkpi and Boho. Thanks to an environmental impact study in the region of the ‘Marahoué’ in January 2007, the species was encountered randomly on the hills at 250 m and 600 m a.s.l. Data collection: Herbarium data: Materials of N. congesta from the two following Herbaria specimens were studied (Table 1): National Herbarium of Côte d’Ivoire (Herbarium Ivorensis, UCJ) located in the ‘Centre National de Floristique’ of the University of Cocody-Abidjan and the National Herbarium of France (Herbarium Musei Parisiensis, P) hosted by the National Museum of Natural History in Paris. This review helped to notice the sites where the species samples were recorded. To identify the occurrence zones in Africa and in World, on the basis of different works (Palmer and Pitman, 1972, Bouquet and Debray, 1974, Govaerts, 2006). Taxonomically, Nuxia congesta belongs to plant families of Buddlejaceae and Stilbaceae according to the classification adopted (Table 2).

Table 1: Summary of specimenas visa with information on places of deposit. Locality of harvest Collectors, n° de record, place of deposit Mount Tonkpi February 16th 1964 L. Aké-Assi 7361 UCJ Mount Tonkpi January 10th 1970 L. Aké-Assi 11006 UCJ Mount Tonkpi s.d. Leeuwenberg & Bouquet 3867 P Haut Sassandra, Mount Boho (760 m) near Zoanlé May 6th 1909 A. Chevalier 21494 P Mount Tonkpi December 1952 Miège & L. Aké-Assi 1986 P - 1932 Service Forestier Côte d’Ivoire1011 P

Herbarium Musei Parisiensis (P), Herbarium Ivoriensis (UCJ).

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Table 2: Taxonomic position of Nuxia congesta R.Br. ex Fresen according to the classification of Cronquist (1981) or APG 3 (2009).

Taxonomic position of Nuxia congesta according to of CRONQUIST (1981)

Taxonomic position of Nuxia congesta according to the classification APG3 (2009)

Règne : Plantae Règne : Plantae Sous-règne : Tracheobionta Sous-règne : Tracheobionta Division : Magnoliophyta Division : Magnoliophyta Classe : Magnoliopsida Classe : Magnoliopsida Sous-classe : Asteridae Sous-classe : Asteridae Ordre : Scrophulariales Ordre : Lamiales Famille : Buddlejaceae Famille : Stilbaceae Genre : Nuxia Genre : Nuxia

Espèce : Nuxia congesta Espèce : Nuxia congesta

Field data: The identified localities of occurrence of Nuxia congesta and some other localities presenting similar elevations and vegetation were visited twice in the region of the ‘18 montagnes’ and its surroundings during 2006 and 2009. The visited sites of the ‘18 montagnes’ were named S1 on mount Tonkpi and S2 on mount Boho. In the region of the ‘Marahoué’, eight (8) field visits were conducted during 2007 and 2009, one visit every quarter. The surveys in this region were performed using a compass (for the direction) and GPS (for the record of geographical coordinates).The sites were named S3, S4, and S5. The purpose of the surveys was to see if the sites still hosted N. congesta. Based on the results of these surveys, the sites of the Marahoué area were chosen for botanical inventories to describe habitats and threats to the species, to determine the number of the individuals remaining, to map the distribution of the species and to identify the species that live in its immediate vicinity. Two inventory techniques were used: the itinerant inventory (Kouamé, 1998; Adou Yao et al., 2007) was used to test in the sites if Nuxia congesta was still present. After noticing the occurrence of the plant, the number of individuals was counted, and 10 individuals were chosen randomly. Around those 10 individuals, circular plots (diameter of 10 m) were placed to record all the species present, and to count the seedlings and saplings of N. congesta. In the 10 plots, the threats that can affect the species and its habitat were noted to discuss the conservation status of the species. Data Analysis: The collected data help to map the distribution of Nuxia congesta on the Ivorian territory

and on the sites of the region of the ‘Marahoué’. The mapping was performed using the software Excel and Arcview 3.2.

The works of Keay and Hepper (1954, 1972), White (1983), and Aké-Assi (2001, 2002) were used to supplement the localities of occurrence in Côte d’Ivoire. Plant species richness and diversity in the 10 circular plots were estimated using the software Estimate S 8.10. Structural parameters of all individuals of N. congesta on the sites S3, S4, and S5 (densities, basal areas, tree stems distribution on diameter classes) were computed. The density and basal area of three species (one in the higher stratum: Cola millenii, one in the medium: Baphia bancoensis, and one in the lower stratum: Lecaniodiscus cupanioides), among the most frequent around N. congesta stems, were calculated. Similarly, a histogram showing the variation of altitudes in Africa for 92 records of the species mentioned in the literature (Govaerts, 2006, GBIF Data Portal, 2010) was drawn to identify preferential elevations. The criteria of IUCN (2001, 2003) concerning rare and threatened species were used to assess the conservation status of Nuxia congesta on the Ivorian territory. Given the quality of the collected data, the criterion ''b'' which means the number of the national localities of occurrence was taken into account. The abundance of the species on different sites was also considered as well as the pressures of human activities on it (gold mining, farming and wood harvesting for diverse purposes). RESULTS

Description of the species: Nuxia congesta is a tree or shrub, 2–20 m high with fluted trunk (Figure 3)

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without buttresses up to 60 cm in diameter. It has a pale grey-brown to dark brown shedding bark and hairy branchlets. It is usually found in clumps of stems from a strain that outcrops above the ground or fully buried. The leaves are hairy, dark green, slightly leathery, variable in shape and size, and are usually found in whorls of 3. On the younger specimens, the leaves are distinctly toothed and the twigs are reddish while on the mature trees, the leaf margins are usually whole and rolled under it. The leaf blades are narrowly elliptic and up to 14 cm long, 2-4 cm wide, tapering gradually to an acuminate

peak. The petioles measure 0.5 to 2 cm in length. The inflorescences are terminal or axillaries cymes, pubescent when young and glabrous when they are mature. The flowers are small, about 5 mm long, tubular and creamy white, often tinged with mauve or purple, especially in bud. The calyx is 4 mm in length, almost cylindrical, densely pubescent outside and hairy inside, with lobes well demarcated and erected. The corolla is white to yellow with glabrous lobes rounded above, and a glabrous ovary. The flowering time observed during this study goes from January to June.

Fig 3: View of two fluted trunks of Nuxia congesta R.Br. ex Fresen (Buddlejaceae) on the S3 site. (Photo: Adou Yao, 2008). Distribution of Nuxia congesta within Africa according to the literature: Several synonyms of Nuxia congesta can be found in the literature among which Nuxia sambesina Gilg and Nuxia viscosa Gibbs. It is a pioneer species that grows in the light of the high lands, and on hilltops. On the sites of this study, it was encountered on upper slopes and hilltops. Nuxia congesta is also common on rocky ridges.

In the World, the species can be met in Africa and in the Arabian Peninsula. In Africa, it was recorded in more than 20 countries: the Centre, East, and South of the Continent. The species was said to be native from Botswana, Ethiopia, Kenya, South Africa, Sudan, Swaziland, Tanzania, Uganda, Zimbabwe, in Eastern Africa. In West Africa, it was collected in Côte d'Ivoire, Ghana, Guinea, Nigeria, and Sierra Leone. In Central Africa, it is reported in Cameroon, Angola and DRC.

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Distribution of the species on the Ivorian territory: In Côte d'Ivoire, Nuxia congesta was reported in natural stations on Mount Tonkpi (7.45 ° N, -7.65 ° W: S1) at1,189 m a.s.l., Mount Boho (7.57 ° N, -7.7 W: S2) around the village Zoonlé (or Zoanlé) at 760 m a.s.l. (Figure 4). The field surveys reported the presence of the species on the hills, in the site of the ‘sub-prefecture of Kossou.’ The first stations of occurrence were made of two hills in the area of the mine of Cluff Gold near the village Angovia (S3) in the ‘Sub-prefecture of Kossou’ (Administrative

Department of Bouaflé). Two other populations of the species were located on two hills in the south of villages named N'Da Koffi Yébouékro (S4) and Bokasso (S5), in the same ‘Sub-prefecture of Kossou’ (Figure 5). The three sites of Kossou were all hills whose altitudes were between 247 m and 484 m a.s.l. In Côte d’Ivoire, no individual was recorded in plains and lowlands; it lived only on hills and mountains.

Fig 4: Location of the N. congesta in the region of “18 Montagnes” according to herbarium specimens consulted.

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Fig 5: Map of village Angovia showing the sites of occurrences (S3, S4, and S5) of Nuxia congesta R.Br. ex Fresen (Buddlejaceae) in the “Sub-Prefecture” of Kossou. Vegetation of occurrence sites and companion species: The sites of occurrence are covered by a dry dense forest of mountain as noted by N’DA & al (2008) but, it is more fragmented here. The higher stratum (about 20 m) is made of species such as Nuxia congesta, Zanthoxylum xanthoxyloides, and Cola millenii. The medium stratum consists of Baphia bancoensis and Anthonotha macrophylla. The lower stratum includes Olax subscorpiodea, Lecaniodiscus cupanioides and herbs such as Olyra latifolia, and young individuals of the species mentioned above. Griffonia simplicifolia is the most abundant liana met in these vegetations. On the floor, there is a large amount of dry matter composed of dead leaves, branches, and many termite mounds. The inventory in the 10 circular plots allowed recording 47 species on an area of 785.4 m2. It allowed identifying, in addition to the above

characteristic species, some frequent and abundant species around N. congesta such as Monodora tenuifolia, Dialium guineense, Ochtocosmus africanus, Pouteria alnifolia, and Holarrhena floribunda. Structural parameters Stem density of Nuxia congesta: Tree stem densities of Nuxia congesta in the three sites (S3, S4, and S5) varied from 2.4 (S5) to 12.2 individuals (S3) (table 3). The distribution of the individuals was mentioned on a map (Figure 6) for site S3 and presented a gregarious tendency. The species can subsist alone (cases of Ni3, Ni23, and Ni38) but, usually, it was found in clumps of stems on the same underground strain (or plateau). Ni22 was the denser clump with eight (8) individuals in the same strain.

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Table 3: Summary of the taxon densities in the three sites of occurrence in the “sub-prefecture” of Kossou (region of Marahoué).

Stations ni nb of tufts Surface Stem Densities Density of tufts Mean DBH (ha)

S3 116 40 9.5 12.2 4.2 17.5* S4 9 3 2 4.5 1.5 7.7** S5 6 2 2.7 2.4 0.7 23.4*

ni: number of stems ; nb tufts: number of tufts; * & ** mean DBH statistically different. The density of the main associated species varying between 203 and 1413 individuals/ha greatly

exceeded that of N. congesta (Table 4). However, their mean DBH was less.

Table 4: Comparison of densities, mean DBH and basal areas of Nuxia congesta and three companion species on the site S3.

Species Surface (ha) Number of individuals

Density (stems/ha) Mean DBH (cm) Basal area (m2/ha)

Nuxia congesta 9.5 116 12.2 17.5a 3.7 Cola millenii 0.079 16 203.7 9.6b 2.3 Baphia bancoensis 0.079 111 1413.3 4.6c 3.2 Lecaniodiscus cupanioides 0.079 36 458.4 4.5c 1.1

a, b, c denote means that are statistically different.

Fig 6: Distribution map of the 40 tufts of N. congesta recorded on the site S3 within the exploitation perimeter of Cluff Gold. Diameter classes and basal areas: The largest diameter of S3 was 45.2 cm; those of S4 and S5 were respectively 20.7 cm and 36.9 cm. The smaller diameters were 1.6 cm for S4, 3.5 for S3, and 4.8 for S5. The mean diameters of the three occurrence sites are summarized in table 3. The mean diameter varied from 7.7 cm (S4) to 23.4 cm (S5). The stems recorded in S4 were more numerous than those in S5 but the mean diameter in S5 was three times higher.

The distribution of stems in diameter classes showed the absence of trees with very large diameters. Even mature and flourished, the diameters of trees did not exceed 60 cm. The histogram presented a bell shape centered on the class [10-20 [, showing that trees with small and large diameters are fewer than the medium trees (Figure 7).

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The total basal area of N. congesta stems on the three sites is 4.07 m2. Per site the basal area of S3 is 3.7 m2, far more important than S4 (0.06 m2) and S5

(0.3 m2). The trees on S5 are larger than those on S4.

Fig 7: Cumulative diameter classes distribution of Nuxia congesta on the site of the “sub-prefecture” of Kossou. Human population and threats to the species: The region of the ‘18 montagnes’ is populated by 1,334,387 inhabitants in an area of 16,600 km2 (with population density of 80.4 inhabitants/km2) (OFFICE NATIONAL DE L’IDENTIFICATION, 2010). That of the ‘Marahoué’ covers an area of 8,500 km2 and hosted 791,689 inhabitants with a density of 93.1 inhabitants/km2 (Figure 1). Those population densities were higher than the national mean density (63.8 inhabitants/km2). The first threat to the species was the high population around the sites of occurrence and farming activities within the remaining forest patches which were not exploited until recently. The second threat to the species was its phenology. During two years of monitoring on sites S3, S4, and S5, only a vegetative state (young and old leaves) and flowering (flower buds or flowers) of the plant was met. During the period of study

(January 2007 - December 2008), no fruits or seeds was observed. Similarly, during the surveys, it was sought in vain for seedlings. Another great threat to the population of the species was the mine of Cluff Gold. Station S3 on which most of the individuals were found was located on the perimeter bordering the mine gold around the village Angovia. DISCUSSION Most consulted samples showed that the occurrence of Nuxia congesta ranges from 152 to over 2,800 m a.s.l. However, although it could be found at elevations below 200 m (the case of Ghana: 152 m), the histogram of the number of samples based on the minimum altitudes of records (Figure 8) indicated that 65% were observed between 1,500 and 2,500 m a.s.l.: the preferential sites of occurrence of Nuxia congesta in Africa were therefore highlands.

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Fig 8: Cumulative occurrences distribution of Nuxia congesta based on minimum elevations classes in Africa (data from GBIF Data Portal). In Côte d'Ivoire, before this study, the species was found at the lowest altitude of 760 m a.s.l. on Mount Boho. By observing Nuxia congesta at the elevations between 247 and 484 m a.s.l., it could be said now that the occurrence of the species varies between 247 and 1,100 m in the country. In addition, five sites were known to harbor this species: Mounts Tonkpi, Boho, and the three hills of the ‘Sub-prefecture’ of Kossou. Two of them were no longer likely to host this plant. Indeed, because of human activities (farming on upper slopes and on summits of mountains and hills), the surveys in these two latter stations failed in observing the taxon. In the site S3, the species occupied the upper slopes and the summit of a large hill within a perimeter of gold mining. It was therefore likely to disappear when the mine reaches this part that contained the largest population. N. congesta occurred only in the dry dense forests of the mountains, but with the intense pressures on them, it remained only some fragments that were used as places for hunting activities. Many sockets were collected in those fragments.

There was a relationship between the temperament of species and the distribution of their stems in diameter classes (Geldenhuys, 1992; Sokpon and Biaou, 2002; Adou Yao et al., 2007). A distribution presenting Gaussian or bell shape is generally regarded as characterizing light demanding species.

This probably explains why N. congesta was subservient to the habitats of hills and mountains where light is received more easily. Information on population structure of a tree species indicates the history of the past disturbance to that species and the environment and hence, used to forecast the future trend of the population of that particular species (Tamrat Bekele, 1994; Demel Teketay, 1997).

The absence of seedlings was probably due to a high mortality at this age of growth. The Gaussian shape could also explain the absence of seedlings and saplings under and near mature trees. But as Hawthorne (1995) pointed out, an attention should be paid because several other factors may have intervened.

The lack of fruits, seeds and seedlings around mature trees created a serious threat of extinction to the species. Indeed, during the mine activities, all the hills where the species were more found will be destroyed, so that the survival of the current population was seriously threatened. Farmers cultivate local rice named ‘Yowèrè rice’ on the high slopes and even the tops of some hills. Nuxia congesta living only on such areas will disappear if no action is undertaken.

In addition to deforestation, fires that were used for farming contributed to threaten a species whose

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population was already sparse nationally. Nuxia congesta was not the sole threatened species by mining and agriculture activities. Fourteen (14) other species were listed on the IUCN Redlist and recorded by N'Guessan et al. (2007) on the same site, were also threatened. There were 11 species in the category "vulnerable" and three of "LR". Yowèrè people living in this locality used only the stems of N. congesta for construction. Several other species are used for house building so that the disappearance did not worry almost anyone. The non-use of the studied plant in some other domains such as medicine, food, crafts, exposed the taxon to a disappearance if no one takes precautions to cultivate it elsewhere (eg village). Indeed, when people use the species, they develop strategies and practices to safeguard them. This was, for instance, the case of Abbey people who preserved a few individuals of Monanthotaxis capea in the region of Agboville (Adou Yao et al., 2010). The lack of knowledge and knowhow of the local people about the species could be a source of threat. It can therefore be said that Nuxia congesta is endangered in Côte d'Ivoire due to its very small population and human activities on it.

Conclusion: At the end of this study, we can say that Nuxia congesta R. Br. ex Fresen. (Buddlejaceae) is reported in five sites among which only three (3) located in the ‘Sub-préfecture’ of Kossou in the Centre-West of Côte d’Ivoire still host the species. Although it grows preferentially around 1,500 m a.s.l., it could be found at lower elevations (152 – 240 m a.s.l.) in West African forests (Ghana and Côte d’Ivoire) and in South Africa (152 m a.s.l.). Among the threats to this species that was already rare in the Ivorian vegetations, the higher population density in the regions of occurrence, the slash, and the burn farming activities on upper slopes and summits of the mountains seemed very crucial especially when people use bushfire techniques. The intrinsic characteristics of N. congesta (lack of fruits and seeds, and seedlings) also contributed to threaten its survival. The mining activities on the largest site of occurrence are currently the greatest threat to this species that deserves the status of endangered (EN) species on the IUCN Red List for the Ivorian flora. Protection activities are to be undertaken to preserve its natural habitat.

ACKNOWLEDGEMENTS

We would like to show our sincere gratitude to the managers of Cluff Gold who permitted us to conduct surveys in their area and who also helped fund part of this study. We also thank the technicians and the

field guides for their valuable assistance. Our thankfulness goes to anonymous people whose critics and comments were helpful for this work.

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