Bois et forêts des tropiques

 

Volume 333 – 3e trimestre – septembre 2017 – p. 5-16

ISSN: L-0006-579X

 

 

 

 

 

 

 

Inventory and multicriteria approach to identify priority commercial timber species for conservation in Benin

 

Jean Didier Tèwogbade Akpona1, Achille Ephrem Assogbadjo1, 2, Adandé Belarmain Fandohan1, 2, 3, Romain Glèlè Kakaï1

 Auteur correspondant / Corresponding author:

Jean Didier Tèwogbade Akpona

 

Doi: 10.19182/bft2017.333.a31461

Licence Creative Commons :

Attribution - Pas de Modification 4.0 International.

Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0)

Citer l’article / Cite the article

Tèwogbade Akpona J. D., Assogbadjo A. E., Fandohan A. B., Glèlè Kakaï R., 2017. Inventory and multicriteria approach to identify priority commercial timber species for conservation in Benin. Bois et Forêts des Tropiques, 333: 5-16. doi: http://dx.doi.org/10.19182/bft2017.333.a31461

 

 

 

Photo 1.

Wood of Pterocarpus erinaceus logged in Pendjari Biosphere Reserve.

Photo J. D. T. Akpona

 

 

Introduction

In several regions of the tropics, timber species are harvested at rates that are far beyond their rhythm of regeneration. These species are preferred by people as the first interest is timber for building material, lumber, etc. and can have other uses for people. It was showcased that, in all International Tropical Timber Organization (ITTO) member countries, only 3.5% of permanent forest estates are sustainably managed (ITTO, 2007). In most developing countries, untrained and unsupervised tree fellers and skidder drivers are used for legal and illegal logging and they often work without planned paths of log extraction, and without financial incentives to reduce the negative environmental impacts of their activities (ITTO, 2007). According to Putz (1991), even at low harvesting intensities (e.g., < 5 trees extracted per hectare), forests lose much of their sylviculture value due to soil damage and damage to future crop trees, coupled with the increased livelihood of invasion by lianas and alien species.

Benin is a moderately forested country with vegetation dominated by savanna mosaics whereby degradation of forests is still a major concern. According to FAO (2011), the forest cover is estimated at 4,511,000 ha, which represents 40% of the country total area. Yet, recent investigations show that Benin loses 50,000 hectares of natural forest in average yearly (FAO, 2011). Illegal tree felling, land clearing for agriculture, bushfires, charcoal production and overgrazing are often referred to as the main drivers of forest degradation and destruction in Benin. This has resulted in decline of the populations of many economically important indigenous timber species (Dimobe et al., 2014). Developing sylvicultural packages to guide reforestation and/or forest enrichment is necessary to ensure conservation and sustainability use of these species. In Benin, several species are used for timber and few studies have been focused on the commercial timber species and identifying priority species for conservation. People have developed specific choice criteria for choosing timber species so that when one species becomes rare, they move to another one more abundant. This process negatively impacts biodiversity conservation. Since all species cannot be focused on at once, prioritization is necessary to select the most important species that need urgent conservation effort. This prioritization informs a wide array of conservation decisions and can help for decision-making.

Establishing priorities for conservation is an obvious and key step to designing a realistic and efficient conservation strategy. According to Magos Brehm et al. (2010), species prioritization is particularly important when the focus is the conservation of socio-economically important species and prioritization for conservation can be undertaken at different levels (species, ecosystem, etc.). It allows conservation managers to know which species are not priorities and which have information gaps to be filled (Idohou et al., 2013). Different methods of prioritization based on range, habitat specificity and local abundance have been described (Rabinowitz et al., 1986). There has been considerable debate over which criteria should be considered when prioritizing species for conservation (see Maxted et al., 1997). Magos Brehm et al. (2010) proposed various criteria and different prioritization schemes. Their methodology has recently been used to set priorities for crop wild relatives in Benin (Idohou et al., 2013) as well as medicinal tree species (Yaoitcha et al., 2015). Developing an innovative prioritization scheme and making use of the available data so as to identify priority TS for conservation in order to establish a national timber conservation strategy is the main goal of this study. Two questions were asked: What is the diversity of commercial timber species in Benin? And, which species need urgent priority conservation at national scale? It stands as a useful case study that establishes a national list of logged timber species in Benin and highlights priority species for conservation.

 

 

Photo 2.

Ceiba pentandra trees in Sacred Forest of Bonou.

Photo J. D. T. Akpona

 

Materials and methods

Study area

The study was carried out in the Republic of Benin, located between 6° N and 12°50’ N and 1° E and 3°40’ E in West Africa (Adomou, 2005). The study system encompasses three centres of plants endemism subdivided into ten phytogeographical districts: the Sudanian (Atacora Chain, Mekrou-Pendjari and Borgou-North districts), the Sudano-Guinean (South-Borgou, Bassila and Zou districts), the Guineo-Congolian (Coastal, Plateau, Pobè and Oueme Valley districts) (Adomou, 2005). The National ora is estimated at 2,807 species of plants divided into 1,129 genera and 185 families (Akoègninou et al., 2006). The ratio of timber species among the total number of species in the country is 8‰. Vegetation in the Guineo-Congolian centre is dominated by undifferentiated savanna mosaics, semi-deciduous forests and swamp forests. Isoberlinia-dominated woodlands and Acacia and Combretum-dominated savannas are the major vegetation types in the Soudano-Guinean and the Sudanian centre, respectively (White, 1983). Rainfall is bimodal in the Guineo-Congolian region but tends to be unimodal in the Sudano-Guinean and Sudanian region.

Generally, mean monthly temperatures oscillate between 26 and 30 °C over the country with peaks of 35 °C to 40 °C in the dry season upmost north (Adomou, 2005). Since 1960, forest exploitation has targeted several indigenous timber species of high economic (More than 64.600m3 for a period of 5 years) and socio-cultural value: Milicia excelsa (Welw.) C.C. Berg, Triplochiton scleroxylon K. Schum., Khaya senegalensis (Desv.) A. Juss., Afzelia africana Sm. and Pterocarpus erinaceus Poir. While these species are faced with local extirpation, no silviculture package (tree establishment, growth, health and quality of forests to meet diverse needs and values) has been so far developed to promote their conservation and integration into national reforestation plan (Gogan, 2010).

Inventory of marketable timber species in Benin

The starting point for preparing a national timber conservation strategy is the inventory of logged species. First of all, a literature review was done in order to investigate the existing knowledge on species used as timber using especially the book “Flore du Bénin” (de Souza, 2008). Secondly, semi-structured interviews and focus group discussions were conducted among different stakeholders (sawyers, joiners, loggers, timber traders and wood industrials) involved in the timber sector over the three biogeographical zones of Benin.

The data collection phase took place between June and October 2013. Before starting the survey, prior informed consent was obtained from local leaders in the target zones. Detailed information of the study and its importance were provided to the leaders. An exploratory survey was conducted in two districts randomly chosen in each phytochorological zone: Tanguieta, Natitingou in the Sudanian zone; Bassila, Dassa in the Sudano-Guinean zone and Aplahoué, Zogbodomey in the Guineo-Congolian zone. In each zone, 140 informants were asked if they are involved in the timber sector. The proportion (p) of positive answers was used to compute the numbers (n) of the individuals to be surveyed following Dagnelie (1998):

Where n is the sample size considered in the phytodistrict, p is the proportion of stakeholders or interviewees that were involved in logging. The interviewees were asked if they are involved in logging.

§  U is the value of the Normal random variable at probability value of 1 – α/2.

For a probability value of 0.975 (or α = 0.05), U1 – α/2 1.96;

§  d is the margin of error of the estimation of any parameter to be computed from the survey and a value of 5% was considered.

At the end, in order to have only one sample size, one proportion was considered by putting together the answers from each phytochorological zone. By computing with the formula above, the number of informants randomly considered for all the phytodistricts was 650.

In each biogeographical zone, the informants were asked to list all timber species used as well as their specific usage types apart for timber. Data were collected using semi-structured interviews. Interviews were conducted orally with, sometimes, the assistance of a local translator. Different demographic parameters (gender, age, education, ethnicity, etc.) were collected before the listing of timber species.

Setting priorities for timber species conservation

The process of establishing priorities among a set of species is a first step in any conservation strategy (Maxted and Kell, 2009ab). The criteria used for the prioritization were adapted from those proposed by Magos Brehm et al. (2010) and used by Idohou et al. (2013). Ten criteria were used and described in the current study (table I).

 

Table I.

Criteria used for establishment of priority timber species for conservation with their different levels or modalities.

 

Prioritization approach

Four different methods of combining the above mentioned ten criteria (figure 1) were adapted from Magos Brehm et al. (2010) and Idohou et al. (2013): point scoring procedure (PSP), point scoring procedure with weighting (PSPW), compound ranking system (CRS) and binomial ranking system (BRS).

In the PSP, the priority value of each reported species was computed as follows:

Score1 = ∑ (native status + economic importance + ethnobotanical value + knowledge of technical routes + conservation status + global distribution + plasticity + legislation + international threat status + national threat status)

The above formula was combined with specific weight (Magos Brehm et al., 2010) for each criterion to get the PSPW approach:

Score2 = ∑ {0.15 (native status) + 0.075 (economic importance) + 0.05 (ethnobotanical value) + 0.075 (knowledge of technical routes) + 0.1 (conseration status) + 0.15 (global distribution) + 0.1 (plasticity) + 0.1 (legislation) + 0.1 (international threatened status) + 0.1 (national threatened status)}

For the CRS approach, the rank varied between 1 to n (number of the criterion).

The total ranking is obtained by summing individual ranks of each criterion (see Magos Brehm et al., 2010).

represent the coefficient of the rank (R) and β represent the index of the rank.

From this ranking perceptive, we could not derive priorities species. So, we got scores from those ranks as follows:

Score3 = (1*β 1) + (2*β 2) + … + (n*β n)

Considering the score rank by each species, priorities were given to decreasing value of the score.

For the BRS method, binomial approach was used with value 1 if the criterion is verified and 0 otherwise. The score is obtained as follows:

 Score4 = ∑ (native status + economic importance + ethnobotanical value + knowledge of technical routes + conservation status + global distribution + plasticity + legislation + international threat status + national threat status)

Using the abovementioned different approaches, the top 15 selected species were the same across the four prioritization methods with the same ranking (PSP, PSPW, CRS and BRS). To identify the most important timber species for conservation in Benin, the new score was affected to each species in each method used by order of appearing of each species in each of the methods.

 

 

Figure 1.

Methodology used for establishing conservation priorities for timber species in Benin, Adapted from Magos Brehm et al. (2010).

 

Results

Socio-demographic characteristics of interviewees

The interviewees were mostly men (96.43%). A categorization of surveyed people according to age, educational level and seniority showed that all interviewees are mostly adults (81.43%); and their level of education range from primary (10.38%) to secondary school (69.29%). There were two main groups in terms of seniority in the timber sector, namely: those who have been involved for less than ten years (46.43%), and those who have been involved over ten years (14.29%). A total of 18 socio-cultural groups were represented with the top three being Fon (28.57%),

Nago (13.57%) and Bariba (12.15%). Surveyed people were mainly from five specialties (profession): sawyers, joiners, wood industry, logger, timber traders (figure 2).

Figure 2.

Percentage of respondents involved in the activity.

 

Priority timber species for active conservation

Twenty four species belonging to nine families were recorded. The three most represented families are the Fabaceae (25%) with six species: A. africana, Daniellia oliveri (Rolfe) Hutch. & Dalz., Isoberlinia doka Craib & Stapf, Isoberlinia tomentosa (Harms) Craib & Stapf., Prosopis africana Guill. et Perr., P. erinaceus; Malvaceae (20.83%), five species: Bombax costatum Pellegr. & Vuillet., Ceiba pentandra (L.) Gaertn., Cola cordifolia (Cav.) R. Br., Cola gigantean A. Chev., T. scleroxylon and Meliaceae (16.67%), four species: Azadirachta indica A. Juss., Khaya grandifoliola C. DC., K. senegalensis, Pseudocedrala kotschyi (Schweinf.) Harms (figure 3). These species were used for other purposes including firewood, art and sculpture, food and medicine (table II).

Figure 3.

Number of commercial timber species per family in Benin.

 

The top 10 species were those who reached the highest score (table III). For the PSP and PSPW methods, the five top prioritized species were: K. senegalensis, K. grandifoliola, P. kotschyi (Meliaceae), A. Africana (Fabaceae) and M. excelsa (Moraceae). For the CRS method, the top species were K. senegalensis, K. grandifoliola, A. africana, P. erinaceus and M. excelsa. Finally, for the BRS method, the top species were A. africana, K. senegalensis, K. grandifoliola, M. excelsa and P. erinaceus. Two species appeared at the top, whatever the method used: K. senegalensis and K. grandifoliola. From this ranking results, K. senegalensis could be considered the most important species for active conservation in Benin.

 

Table II.

Family diversity and derived products of timber species.

          

Table III.

List of the top 10 priority timber species for active conservation and silviculture in Benin, obtaining by combining four different priority methods.

 

Table IV.

Ethnobotanical uses, national distribution and threats of the most prioritized timber species.

In order of importance, the top ten species are listed in the table IV with their uses, national distribution and threats. Different uses were recorded for the top 10 timbers species. These uses were mostly timber, medicinal, food, charcoal and firewood. At national level, the “Décret n° 96-271 du 2 juillet 1996” (law 93.009 related to forest regime in Republic of Benin) has targeted 7 species as protected. Some priority species are under this law. The top 10 timber species are distributed along the 10 phytodistricts. The most widely distributed species (figure 4) are A. africana and P. erinaceus (6 phytodistricts); K. senegalensis (5 phytodisctrits); M. excelsa, A. leiocarpa and I. doka (4 phytodistricts); K. grandifoliola, I. tomentosa and P. kotschyi (3 phytodistricts) and A. toxicaria (2 phytodistricts). According to the threat assessment, five species are endangered (K. senegalensis, K. grandifoliola, A. africana, M. excelsa and P. erinaceus) and using IUCN red list (international), three species are vulnerable (K. senegalensis, K. grandifoliola, A. africana), one near threatened (M. excelsa) and one of least concern (I. doka).

 

Figure 4.

Map of the Republic of Benin showing the phytogeographical districts and the occurrence of the most prioritized timber species.

 

 

Photo 3.

Woody species used in charcoal production.

Photo J. D. T. Akpona.

 

 

Discussion

This study aimed at establishing the first national TS inventory using multicriteria approach and setting priority for conservation in Benin. Our procedure for developing effective biodiversity conservation priorities of timber species in Benin was adapted from Magos Bhrem et al. (2010) and based on the availability of data information of local perceptions (UNEP, 1995). As many West African countries shared in a given degree the same timber species, we believe that it can be used or adapted to assist in species’ prioritization and can also help in regional conservation of socio-economically important plant species. An active conservation of woody species is required, particularly timber species diversity, by establishing priority within species (Maxted et al., 2006). But effective strategies for biodiversity conservation (Maxted et al., 2006) has been developed using different methods. Our approach differs methodologically, from those used by Lawrence et al. (2005), Maraseni (2008), Vodouhe et al. (2009) and N’Danikou et al. (2011) who identified the most important Non-Timber Forest Products in Cameroun, Nepal, and Benin, respectively using community independent scoring in species value and conservation criteria. All these methodologies differ from the one used in this study and recently used by Idohou et al. (2013) because their findings were not based on the combination of criteria and in different methods. They argue on the importance of the use of the scoring method for studies of this type (N’Danikou et al., 2011). Brehm et al. (2010) argue that prioritization of species should be a dynamic process and multicriteria approach should be more relevant and criteria can change depending to the species or group of species considered (Idohou et al., 2013).

 There were 24 timber species currently used in Benin. Much attention has historically been given to plant conservation (Codjia et al., 2003; Vodouhê et al., 2010; N’Danikou et al., 2011; Idohou et al., 2013; Yaoitcha et al., 2015; Sèwadé et al., 2016) and priority plant species have previously been suggested for conservation plans. These studies were related to crop wild relatives, wild edible plants and useful medicinal tree species.

Overall, 10 timber tree species were highlighted as priority for conservation in Benin. Among these species, K. senegalensis, K. grandifoliola, A. africana, M. excelsa, P. erinaceus appear as the top 5 priority species as available financial resources were not enough to conserve all species at once. Among the top 10 priorities species, 7 were protected under Benin Law 93.009 related to forest regime in Republic of Benin. This shows the importance of these species for conservation since 1993. Recent works from Yaoitcha et al. (2015) covering a single forest reserve, reported A. africana, K. senegalensis, M. excelsa, P. erinaceus, to be rare as perceived by local population around Wari-Maro forest reserve (Central Benin). Some other related works also revealed that prioritized species such as K. senegalensis, P. erinaceus and M. excelsa are threatened by overexploitation (Ouinsavi et al., 2005; Gaoué et al., 2007; Glèlè Kakaï et al., 2008; Bonou et al., 2009; Houehanou et al., 2013); which support their importance as priority species for active conservation. Three species (K. senegalensis, A. africana and P. erinaceus) identified as priority for conservation were reported to be threatened in both open access and protected areas of Pendjari Biosphere Reserve of Benin (Houehanou et al., 2013). Besides it being a good lumber species, M. excelsa is also believed to possess some diabolic powers, thus making it severely overexploited in Benin (Ouinsavi et al., 2005). To date, a detailed threat assessment using IUCN Red List Criteria has only been assessed for a few species (table IV), yet most species facing human harvesting pressure were often exposed to decline (Idohou et al., 2013). According to the IUCN Red List, P. erinaceus has not yet been evaluated but was evaluated in for Benin Red List (Adomou et al., 2011) as endangered, along with A. africana, K. senegalensis, M. excelsa. The last three species were identified as vulnerable on the international IUCN Red List. P. kotschyi used also as medicinal and animal feed plant, appears in the top 10 important timber species and was listed as a socio-economically important species that needs close attention regarding its current exploitation trends (Yaoitcha et al., 2015; Sèwadé et al., 2016).

Active conservation of TS in Benin should be a priority as the country occupies an important part in the “Dahomey Gap” (Akoègninou et al., 2006) who is a Savannah corridor separating the African rainforest into the western Guinea zone and the Central African Congo zone and where Biodiversity occur. Assuming the ora of Benin shares many species with that of other neighbouring countries covered by dense forests, then they may be facing the same problems because of the presence of similar timber species. The implications of this must be the implementation of trans-boundary strategies of conservation.

Many studies have previously been conducted on some of the identified priority species in Africa such as P. erinaceus (Ouédraogo et al., 2006; Nacoulma et al., 2011; Segla et al., 2016), A. africana and K. senegalensis (Gaoué et al., 2007; Traoré et al., 2011; Delvaux et al., 2009). All these studies have assessed population variations across ecological regions, the impact on population structure under different land use systems, viability of these species and proposed conservation strategies for their sustainable management and finally targeted sensitization of populations around habitats where the species occur to ensure conservation of these highly valued species. More attention should now be given to developing silviculture packages for priority species.

Conclusion

This study highlights timber species diversity in Benin and yield substantial information on priority species for conservation and silviculture. A total of 24 timber species were inventoried and most of them are used for medicine, food and charcoal. Ten species were selected as priority active conservation of these species requires allocating more effort for developing silviculture packages and policy need to be developed to conserve the remains populations.

 

 

Photo 4.

Khaya senegalensis tree in urban area in Benin.

Photo J. D. T. Akpona

 

Acknowledgments

Funding for this project was provided by Rufford Foundation through grant N° 14635-1 provided to the first author. We are very grateful to the members of the Laboratoire de Biomathématiques et d’Estimations Forestières (University of Abomey-Calavi).

 

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Bois et forêts des tropiques - Revue scientifique du Cirad

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