International Journal of
Biodiversity and Conservation

  • Abbreviation: Int. J. Biodivers. Conserv.
  • Language: English
  • ISSN: 2141-243X
  • DOI: 10.5897/IJBC
  • Start Year: 2009
  • Published Articles: 679

Full Length Research Paper

Woody species diversity of Vitellaria paradoxa C.F. Gaertn traditional agroforests under different land management regimes in Atacora district (Benin, West Africa)

Koutchoukalo Aleza
  • Koutchoukalo Aleza
  • School of Agriculture, University of Cape Coast, Ghana.
  • Google Scholar
Grace B. Villamor
  • Grace B. Villamor
  • Department of Ecology and Natural Resources Management, Center for Development Research (ZEF), University of Bonn, Germany.
  • Google Scholar
Kperkouma Wala
  • Kperkouma Wala
  • 3Laboratory of Botany and Plant Ecology, University of Lomé, Togo.
  • Google Scholar
Marra Dourma
  • Marra Dourma
  • 3Laboratory of Botany and Plant Ecology, University of Lomé, Togo.
  • Google Scholar
Wouyo Atakpama
  • Wouyo Atakpama
  • 3Laboratory of Botany and Plant Ecology, University of Lomé, Togo.
  • Google Scholar
Komlan Batawila
  • Komlan Batawila
  • 3Laboratory of Botany and Plant Ecology, University of Lomé, Togo.
  • Google Scholar
Koffi Akpagana
  • Koffi Akpagana
  • 3Laboratory of Botany and Plant Ecology, University of Lomé, Togo.
  • Google Scholar


  •  Received: 09 March 2015
  •  Accepted: 20 April 2015
  •  Published: 30 April 2015

 ABSTRACT

Agricultural production in northern Benin is characterized by smallholder traditional agroforestry systems, with on-farm remnant tree species. Among its numerous advantages, agroforestry is known for its valuable contribution to biodiversity conservation. This study quantifies the importance of Vitellaria paradoxa C.F. Gaertn agroforests in terms of woody species conservation in Atacora district in Benin. Forest inventories were performed within 50×50 m plots constructed on a net grid map of Atacora district. Diversity indices were computed for both adult and juvenile species in two land management regimes: fields and fallows. Overall 41 woody species were recorded; 28 in fields and 36 in fallows. Taking into account matured and juvenile individuals, the diversity of woody species increased: 86 species in total; 69 species in fields and 78 in fallows. The biodiversity of V. paradoxa’s agroforestry parklands increases from fields to fallows, and decreases from bulk species (considering mature and juvenile species) to adult ones. Leguminosae and Combretaceae were the most abundant families registered. From the Cover Value Index, V. paradoxa, Parkia biglobosa, Lannea microcarpa, Lannea acida and Diospiros mespiliformis were the most abundant species. Support for maintaining this kind of agricultural system is needed, as this exemplifies the synergy for providing, provisioning and supporting services and biodiversity conservation.
 
Key words: Agroforestry, conservation, ecosystem services, farmland, shea tree.
 
 
 

Abbreviation:      

 INTRODUCTION

Agroforestry, the integration of trees with annual crop cultivation, livestock production and other farm activities, is a series of land management approaches practiced by more than 1.2 billion people worldwide (Jamnadass et al.,
 
2013). According to some projections, the area of the world under agroforestry will increase substantially in the near future (Albrecht and Kandji, 2003). Therefore, agro-forestry that characterize agricultural areas, appears to be the future landscape in West Africa sub-region, where agricultural land covers more than double of the area covered by forests. The ratio between agricultural land and forests is expected to rise due to population growth inappropriate agricultural production mainly. In order to feed the burgeoning global population, agricultural production has to grow in the coming decades. This makes trees on agricultural land a promising tool to address climate change mitigation and adaptation (Verchot et al., 2007; Henry et al., 2012) while enhancing biodiversity and human populations’ livelihood.
 
The importance of agriculture in sub-Sahara African countries calls for new insights and consideration of agricultural activities not as a source of biodiversity loss but rather as a mean of its conservation considering the area covered by agroforestry. These strategies support the development of plans for ecoagriculture, a new type of agriculture that combines objectives of enhancing rural livelihoods, ensuring food security, and conserving biodiversity in the same landscape. ecoagriculture is advocated by many researchers to complement other conservation methods (McNeely and Scherr, 2003; McNeely and Schroth, 2006; Scherr and McNeely, 2002, 2012).
 
The integration of trees and crops is an environmentally sound land management conducive to moisture, soil conservation, and thus to high productivity (Traoré, 2003; Tomlinson et al., 1995; Jonsson et al., 1999). Trees in agroforestry systems provide traditional medicines as well as basic food commodities, including a variety of gums, oils, proteins, fruits, and drinks to a large number of people (Atakpama et al., 2012; Avocèvou-Ayisso et al., 2012; Edwige et al., 2012). There is ample evidence of indigenous knowledge and practices involved in enhancing biodiversity at the landscape level (Gadgil et al., 1993). Some food-providing trees and palms, especially fruit-producing ones, have been managed by people in a transition from the wild to cultivation in farmland for millennia, resulting in complex agroforestry systems that contain many different foods (Torquebiau, 1985)
 
Shea tree, Vitellaria paradoxa C.F. Gaertn, a tree belonging to Sapotaceae’s family, is the most common species found in most of the traditional agroforestry parklands in West Africa (Breman and Kessler, 2011; Boffa, 2000; Aleza et al., 2015). In Atacora district in Benin, shea agroforests provide to rural households 36 to 46% of their income through the money gained from selling shea-based products (Gnanglé et al., 2009; Dah-Dovonon and Gnangle, 2006).
 
Previous studies in the region addressed the shea agroforests’ population structure, land management and productivity  (Djossa et al., 2008; Adissatou and Brice, 2009). Some showed its socio-economic and use values (Agbahungba et al., 2001; Assogbadjo et al., 2012) and its population adaptation along different ecological zones in Benin (Glèlè et al., 2011). Considering its wide distribution, agroforestry has the potential to enhance biodiversity conservation through in situ conservation. But the contribution of shea agroforests to the conservation of biodiversity at landscape level lacks scientific evidences.
 
For this reason, this study (i) examines the diversity of woody species in two land management regimes of Shea agroforests in Atacora district and (ii) compares the state of biodiversity conservation between adult woody species and the overall species taking into account juveniles and adults individuals. Addressing these objectives will show human impact on the agroforestry systems’ physiognomy and biodiversity conservation. It is expected that this study will help to improve adoption of agroforestry projects and provide insights for farmers’ management practices.
 
 
 


 MATERIALS AND METHODS

Study area
 
Benin is divided into 12 districts which are further subdivided into 77 communes. Atacora district, concerned by the current work, is the northwestern one and covers a surface area of 20 459 km2 over 112 622 km² of the country’s area. Four over nine of Atacora communes have been investigated in the current study. These four communes cover 12,117 km2 and are the following: Tanguieta, Materi, Cobly and Boukombé (Figure 1), all located in the Sudanian zone. Atacora district is one of the research sites of the WASCAL program (West African Science Service Center on Climate Change and Adapted Land Use) under which this study is enrolled. According to 2013 census, the district has a population of 769,337 inhabitants over 9,983,884 million of the total population (RPG4, 2013). A range of mountains extends along the northwest border and into the northeast Togo. Three major soil types can be found: tropical ferruginous soils, hydromorphic soils, and rough and undeveloped mineral soils. The climate in Atacora is characterized by two seasons: one rainy season from May to September, and one dry season for the rest of the year (Aregheore, 2009). The annual amount of rainfall varies between 900 and 1100 mm (Benin Republic, 1996). Variations in temperature increase when moving north through savannah towards the Sahel. A dry wind from the Sahara called Harmattan blows from December to March. On the social aspect, 70% of the population is rural with agricultural production the main activity. A wide variety of annual crops are grown: cotton, maize, sorghum, groundnut, cowpea, millet etc., associated with scattered multipurpose trees such as V. paradoxa and Parkia biglobosa Jacq. Dong (Aregheore, 2009; Vissoh et al., 2004).
 
 
Sampling design and data collection
 
Two land management regimes were examined in this study, namely fields and fallows. Fields are areas where annual crops are cultivated, whereas fallows are areas previously cultivated and left for a medium or long period to re-establish its vegetation structure and soil fertility. These are the most important land management regimes in Shea agroforests defined by scholars (Lovett and Haq, 2000; Boffa, 2000; Okiror et al., 2012; Akais Okia et al., 2005).
 
The sampling method used is a cluster sampling. First, squares sized 10 x 10 km were chosen on a net grid map of Atacora’s district. Within each selected square, one to ten plots sized 50 x 50 m (2500 m2) were established according to the availability of shea stands and the accessibility of the considered area. Plots size was justified by the fact that they were successfully used in the same region during previous parklands studies (Wala et al., 2005; Byakagaba et al., 2011; Padakale et al., 2015). Overall, data were collected from 213 plots: 50 in Boukombé, 39 in Cobly, 47 in Materi and 76 in Tanguieta (Figure 1). The first plot was located randomly whilst the following ones were established at least at 100 m away from the first one. In each plot, all woody species were recorded and dendrometric parameters (circumference and total height) measured for adult trees species with diameter at breast height (DBH) ≥10 cm while those with DBH <10 cm were considered as juveniles. Species names were further conformed to those set by Brunel et al. (1984) and Akoègninou et al. (2006). Moreover, geographical coordinates of each plot were registered for cartography purposes.
 
Data analysis
 
Data collected were processed using Minitab 16, and ArcGIS 10. The first software was used for diversity indices calculation, the second one for statistical analysis where Fisher test was used to verify hypothesis in the difference of variables. The third one was used for mapping.
 
Alpha diversity indices of all species
 
All species encountered in this study were categorised into their respective families and genera according to those set by (Brunel et al., 1984; Akoègninou et al., 2006). Alpha diversity indices were computed for bulk species (both adult and juveniles). Each land management regime was characterized by alpha diversity indices: species richness (S), Shannon-Wiener diversity index (H) and Pielou evenness index (E) (Brower and Zar, 1984). The Pielou’s evenness measures the similarity of the abundance of the different woody species sampled. Its value varies between 0 and 1. The value tends to 0 when one or few species had high abundance than others and 1 in the situation where all species had equal abundance (Magurran, 2004).
 
The species richness S is the total number of species recorded in a given land management regime. Shannon diversity index (H) was expressed as:
 
 
Where Ni is the number of species i, N the total number of individuals sampled in a considered land management regime and S the total number of species encountered.
 
Whereas, Pielou evenness index (E) is computed as follows:
 
 
Diversity indices of adult woody species
 
In addition to alpha diversity indices, woody species diversity indices were computed for adult woody species and also for the two distinguished land management regimes. Target indices are the cover value index (CVI), which was defined by Förster (Bailey and Dell, 1973) and used by de Olivera-Filho et al. (1989), the importance value index (IVI), (Curtis and McIntosh, 1950; Cottam and Curtis, 1956; Pereki et al., 2013) and the Sorenson-Dice coefficient (β) to compare the similarity of fields and fallows biodiversity.
 
CVI is used to evaluate the importance of the species within each of the land management regime. It gives equal weights to the species density through the number of individuals and equal size through the total basal area of the individual. CVI is expressed as:
 
CVI = RDe + RDo                                                                                  (3)
 
where, RDe, the relative density is computed as follows:
 
RDe = (number of individuals of species i / total number of individuals) × 100
 
RDo, the relative basal area is obtained by using the following formula:
 
RDo = (total basal area for species i / total basal area of all species) × 100
 
 
g, the basal area is computed as follows:
 
 
Where, dis the DBH of species i                                              
 
The importance value index (IVI) is calculated as a sum of relative frequency, relative density and relative basal area of each species. The following formula was used:
 
IVI = CVI + RF                                                                 (6)
 
where RF, the relative frequency is calculated as follows:
 
RF = (frequency of species i / sum frequencies of all species) × 100                                                                                 (6)
 
Sorenson-dice coefficient is expressed as follows:
 
 
where, C is the number of species common to the two land management regimes, A is the number of species recorded in fields and B is the number of species registered in fallows.
 
 
 


 RESULTS

Alpha diversity of woody species in fields and fallows
 
Overall, 1622 adult trees were measured over a total of 53.25 ha of land. Within this area, 86 woody species were recorded: 69 in fields and 78 in fallows (Table 1). The two land management regimes have many species in common. This is shown by Sorenson-Dice coefficient values: 0.72 for adult species and 0.79 for both juveniles and adult. Fisher test showed a significant difference in species richness between fields and fallows (p = 0.000). An average of 8±4 and 11±6 species per plot was counted for fields and fallows, respectively.
 
The 69 woody species in fields belonged to 57 genera and 30 families. Among the dominant species recorded are V. paradoxa (found 115 times within 115 plots), Combretum collinum Fresen. (55), Parkia biglobosa (53), Stereospermum kunthianum Cham. (47) and Annona senegalensis Pers. ssp. oulotrieha Le Thomas (45). The most represented families are Leguminosae (12 species), Combretaceae and Rubiaceae (7 species), Moraceae (6 species) and Anacardiaceae (4 species). The alpha diversity estimated by Shannon is 1.56 and Pielou evenness index is 0.85 (Table 1).
 
In fallow areas, a total of 78 species belonging to 65 genera, and 32 families were recorded. Among the dominant species recorded are V. paradoxa (found 97 time within 97 plots), C. collinum Fresen. (59), S. kunthianum Cham. (49), A. senegalensis Pers. ssp. oulotrieha Le Thomas (48), and Acacia polyacantha Willd. ssp. campylacantha (Hochst.ex A.Rich.) (44). The most well represented families were Leguminosae (15 species), Combretaceae (8 species), Anacardiaceae (7 species), Rubiaceae (6 species) and Meliaceae (4 species). The Shannon diversity index is estimated to 1.63 and Pielou eveness index to 0.86 (Table 1).
 
Though fallows appear to be more diversified, Fischer test showed that land management regime does not influence species richness (p = 0.112). However, Fisher test showed significant differences between adult species diversity and bulk ones in fields (p = 0.00) and fallows (p = 0.00) (Appendix 1b).
 
Diversity of adult woody species
 
Overall, V. paradoxa agroforests registered 41 woody species. Among 69 species found in fields, 28 were adults belonging to 24 genera, and 14 families. Table 2 shows adults woody species vegetation indices. According to the importance value index (Table 2), the
 
 
 
five most abundant species are V. paradoxa (184.27%), P. biglobosa (51.51%), L. acida (8.33 %), Diospiros mespiliformis Hochst. Ex A. De. (6.86%) and L. microcarpa (5.37%). In terms of families’ representation, Meliaceae, Anacardiaceae, Combretaceae and Leguminosae are the most represented families. In fields, the Shannon diversity index is 0.46 and the Pielou eveness index is 0.32. The complete list of woody species registered in Atacora and their frequency is found in appendix 1a.
 
 
On the other hand, fallow areas registered a total of 36 adult species representing about 22% more species than that of fields. These species belonged to 31 genera and 17 families. The IVI showed that, the five most abundant species found in fallows were: V. paradoxa (184.75%), P. biglobosa (35.58%), L. acida (14.6%), L. microcarpa (6.86%) and D. oliveri (5.35%) (Table 2). The most represented families in fallows are Leguminosae (8 species), Anacardiaceae (7 species) and Combretaceae (5 species). The Shannon diversity index is 0.59 and Pielou evenness index is 0.39.
 
 
 


 DISCUSSION

Adult woody species richness was estimated to be 41 tree species in Atacora. Comparable to our findings is report by Augusseau et al. (2006) and Ouinsavi and Sokpon (2008) who recorded respectively, 50 tree species in agroforestry parklands of the sub-humid part of Burkina Faso, and 45 species in Milicia excelsa (Welw.) C.C.Berg agroforesty parklands in Benin. On the other hand, our findings are higher than Fifanou et al. (2011) findings with 21 species in Pendjari Biosphere Reserve in Benin. Wala et al. (2005) recorded 25 species in Doufelgou’s parklands in northern Togo and Folega et al. (2011) found 29 species under fallow in protected areas of Northern Togo. Cline-Cole et al. (1988) also found less species (22) in Kano’s farmed parklands in northern Nigeria with almost the same agroecological zone. The differences in species richness could be explained by factors such as sampling design, sampling effort or both. In eastern and central Africa, Kindt et al. (2005) found 127 tree species in western Kenya’s farms. The difference in woody species diversity between our study and that of Kindt et al. (2005) could be due to the study area’s ecoregion, which in Kenyan case belongs to the Victoria Basin forest-savanna mosaic ecoregion (Kindt et al., 2005). Indeed, the later is known for its high species diversity and endemism which results from the mixture of habitat types. Wala et al. (2009) reported that woody species diversity in parkland varied according to the latitudinal gradient in Togo. Moreover, conservation of woody species in agricultural areas is directed by the use and knowledge of local communities and the traditional management practices (Ræbild et al., 2011).
 
Shannon diversity index and Pielou eveness index recorded in fields are similar to that of fallows. This can be explained by the interconnectivity existing between the two land management regimes. Species that are conserved in fields are selected among those that grow in natural areas. The selected species are conserved and managed until the depletion of soil fertility and shifting from field to fallow.
 
Leguminosae and Combretaceae were the most important families registered in Atacora district. Previous studies found similar results in northern Togo’s agroforestry systems (Wala et al., 2005, 2009; Folega et al., 2011; Kebezikato et al., 2015). The current study site and the above ones are located in Sudanian tropical climate, which vegetation is dominated by families men-tioned earlier. Indeed, Combretaceae and Leguminosae are part of the most dominant families in the Sudanian tropical zones (Aubreville, 1950). In addition, Leguminosae trees are known for their importance in agroforestry and silvo-pastoral systems, which function primarily in restoring and maintaining soil fertility through their ability to establish in nitrogen-deficient soils and the benefits of the nitrogen fixed to associated crops (Dommergues, 1987; Danso et al., 1992; Sprent, 1999).
 
Abundance of V. paradoxa, P. biglobosa, L. microcarpa, L. acida and D. mespiliformis is the result of farmers willingness to conserve trees in agricultural areas. Many researchers mentioned the above species as the most dominant one in agroforestry systems of the Sudanian zone (Wala et al., 2005; Folega et al., 2011; Aleza et al., 2015). Species listed in annex 1 are conserved in fields and fallows by local farming communities. Their presence and abundance confirm their importance for local communities (Agbahungba et al., 2001; Dah-Dovonon and Gnanglé, 2006; Gnanglé et al., 2009; Assogbadjo et al., 2012).
 
The woody species diversity associated with shea agroforestry parklands increases from fields to fallows, and decreases from bulk species to adult ones. This aspect reflects the selective character of conservation when it comes to species associate with crops. Many tree species grow naturally in lands allocated to agriculture, but not all of them reach the adult stage within the study area. Only those that are important for farmers and pastoralists are conserved and managed until their adult stage. Undesirable and unwanted species are removed during agricultural activities such as tillage, weeding, pruning, etc.
 
On-farm trees are integrally part of agricultural systems in Atacora as well as in other places in West Africa for their multiple uses. Nowadays, in addition to the uses and importance of trees in farmlands, they play a major role in the context of climate change. Indeed, some researchers have proposed agroforestry as a potential strategy for helping subsistence farmers reduce their vulnerability to climate change (Challinor et al., 2007; Verchot et al. 2007). Agroforestry among the land uses analyzed in the land-use, land-use change and forestry report of the IPCC (Intergovernmental Panel on Climate Change) offered the highest potential for carbon sequestration in non-Annex I countries (they are countries that have ratified or acceded to the UNFCCC but are not included in Annex I which means they are not required to reduce their greenhouse gas emissions)
 
Agricultural land use affects large parts of terrestrial area, so its contribution to biodiversity is critical for successful conservation projects. Lands used for agricul-tural activities are estimated to 28.31% of Benin surface area and are expected to rise in the future (FAO, 2010). There is possibility to simultaneously conserve biodiversity while reducing farmers’ vulnerability to climate change. Agroforestry has such a high potential because there is a large area that is susceptible for land use change (Verchot et al., 2007). Traditional agroforestry systems, practiced by the majority of farmers in Atacora, are known to be more supportive of biodiversity than mono-cropping (Schroth, 2004), even though they are not substitute for natural habitat.
 
 
 


 CONCLUSION

Through in situ conservation, V. paradoxa, agroforests has the potential to contribute to biodiversity conservation in agricultural areas. A total of 41 adult woody species were recorded in V. paradoxa’s agroforest, whereas according to land management regimes, 28 species are found in fields and 36 species in fallows. The composition of woody species in Atacora parklands reflects the needs of local communities and their implication in people’s livelihood. The results shown in this study suggest the possibility to conserve part of the biodiversity while nourishing the population and reducing its vulnerability to climate change. There is a need to support and maintain this kind of agricultural system, as this exemplifies the synergy for providing, provisioning and supporting services and biodiversity conservation. Moreover, a good understanding of how agroforestry parklands are managed could give insight into sustainable development.


 CONFLICT OF INTEREST

The authors did not declare any conflict of interests.



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 APPENDIX

 




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