Agroforestry in buffer zones as a strategy for biodiversity conservation and resource management: A case study from Bouba Ndjidda National Park, Cameroon

doi:10.21203/rs.3.rs-4802358/v1

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Agroforestry in buffer zones as a strategy for biodiversity conservation and resource management: A case study from Bouba Ndjidda National Park, Cameroon

https://doi.org/10.21203/rs.3.rs-4802358/v1

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Protected areas in the Sudano-Sahelian zone face increasing threats from human activities. Implementing agroforestry systems (AFS) in buffer zones is recommended to mitigate these threats. We characterized AFS around Bouba Ndjidda National Park (BNNP), Cameroon, using ethnobotanical surveys and tree inventories in 50 m x 50 m quadrats. The study focused on AFS diversity, structure, woody plant diversity, and the uses of agroforestry trees and products by local communities to assess their contribution to conserving tree resources and proposing actions to reducing encroachment on the park's resources. Identified AFS included agroforestry parklands (98%), homegardens (83%), fallows (72%), and live fences (6%). Woody plant richness comprised 50 species from 42 genera and 23 families, with Fabaceae being the most dominant. Acacia polyacantha had the highest Importance Value Index at 88.65. Species richness was higher in fallows and agroforestry parklands. Live fences had the highest Shannon index and the lowest Simpson and Pielou's evenness indices. Tree density was higher in live fences (P < 0.05) than in other AFS. Farmers used woody plant species primarily for fuelwood (66.49%) and food (63.69%). Vitellaria paradoxa recorded the highest Use Value at 4.36, while Anacardium occidentale had the highest Cultural Importance Index at 1.00. Two endangered species, Khaya senegalensis and Vitellaria paradoxa, were found in the AFS. Enriching agroforestry systems with species that produce firewood and food while promoting the protection and cultivation of endangered species is crucial for biodiversity conservation and sustainable livelihoods.

Agroforestry systems

Biodiversity conservation

Bouba Njidda National Park

Ethnobotanical knowledge

Woody species diversity

The protection of resources in tropical national parks is continuously challenged by the encroachment of neighboring populations seeking firewood, arable land, and valuable commercial forest products used in cooking, traditional medicine, and carpentry. This conflict escalates as populations around national parks grow. Providing sustainable benefits to neighboring populations at various spatial and temporal scales is a key challenge (du Toit et al. 2004). Therefore, careful attention must be given to biodiversity conservation objectives and the sustainable livelihoods of local communities to truly achieve conservation goals in protected areas (McNeely and Scherr 2003; Bernard et al. 2016). Agroforestry, which integrates trees providing food, timber, and income to farmers (Leakey 2001, 2020), emerges as a promising approach to reduce farmers' encroachment on national parks (Murniati et al. 2001). This approach is most effective when implemented through participatory methods that meet local population needs and enhance adoption near protected areas.

Protected areas (PAs) in the Sudano-Sahelian zone face numerous threats, including livestock grazing, agriculture, excessive fuelwood cutting, and charcoal production (Tabopda 2009; Jiagho et al. 2016). To mitigate these threats, enhancing agroforestry systems (AFS) in peripheral areas of protected zones is recommended. AFS can provide goods and services that meet local needs (Nahayo and Uwineza 2012; Moreno et al. 2018). In semi-arid areas, trees in AFS offer shade, shelter, fuel, fodder, and various other benefits that support farmer livelihoods (Djossa et al. 2008; Gideon and Verinumbe 2013). Additionally, wild fruits complement daily diets, substitute exotic fruits, and provide income through local markets (Teklehaimanot 2004; Djossa et al. 2008). These benefits reduce reliance on PA resources, thereby alleviating pressure on biodiversity. According to McNeely and Schroth (2006), tree planting and management by rural communities contribute to biodiversity conservation by reducing pressure on protected areas, enhancing habitat for wild species, and improving landscape connectivity. Effective resource management in PAs requires comprehensive characterization of AFS in their vicinity. Furthermore, developing strategies to enhance biodiversity management and mitigate encroachment by adjacent communities reliant on park resources is essential. Identifying AFS around parks that exhibit high biodiversity indices and deliver multiple goods and services to the population is critical in achieving these goals.

Bouba Ndjidda National Park (BNNP or "the park") is part of the northern Cameroon protected area network and stands out as the richest and most biodiverse of the three national parks in this region (Omondi et al. 2008). It constitutes the Bouba Ndjidda Technical Operational Unit along with surrounding hunting zones. Over the past two decades, human population growth in this area has driven increased wood collection and agricultural expansion (Nature Information Tracks 2017). Given the diverse pressures on BNNP's vegetative cover and surrounding areas, understanding traditional tree-crop land-use systems, including plant diversity, structure, and products extracted by riverine populations, is crucial for developing activities that protect the park's genetic resources.

A study by Djiongo (2015) highlighted the potential of implementing AFS around PAs in northern Cameroon to mitigate conflicts between humans and wildlife, focusing primarily on local perceptions of AFS. This study aims to achieve four objectives: (i) identify and characterize agroforestry systems surrounding BNNP, (ii) assess biodiversity and carbon production in AFS near BNNP, (iii) analyze the contribution of surveyed AFS to biodiversity conservation, and (iv) identify tree species products and their utilization by neighboring communities to meet their needs.

Study area

The study was conducted in the periphery of BNNP (Fig. 1), east of the network of northern protected areas. Covering an area of approximately 220,000 hectares, the park extends between latitudes 08°21' and 09°00' North and longitudes 14°25' and 14°55' East (UNESCO 2018). The climate is characterized by a six-month rainy season (late April to mid-October) and a six-month dry season (mid-October to April). The Bouba Ndjidda area receives between 1,000 mm and 1,250 mm of rainfall per year (Weather Spark 2010). The average annual temperature is 28°C. Soils in the study area are generally a combination of leached tropical ferruginous and hydromorphic soils (Brabant 1972). Phytogeographically, vegetation in the study area is composed of species characteristic of the Sudanese zone, including wooded savannahs and dry open forests. The population on the outskirts of BNNP was estimated at 96,852 inhabitants in 2016 with a density of 16 inhabitants per km² (INS Cameroun 2019). Agriculture and livestock farming are the main activities extensively practiced in the area.

Data Collection

Identification and characterization of AFS around BNNP

Data was collected in villages around BNNP from August to October 2016. Semi-structured interviews with farmers or farmer-shepherds and field visits were conducted to identify agroforestry systems in the area. Since the villages were all socio-economically homogeneous (Djiongo 2015), their main criteria for choosing the right agroforestry practice were proximity to the park and accessibility. Out of the 28 villages adjacent to the park, 13 were sampled, resulting in a sampling rate of 46.42%. The interview respondents, all farmers or farmer-shepherds, were heads of households (male or female) or any other adult available to replace the head of the family in case of absence, who could make decisions concerning family and agricultural/pastoral work. Based on agricultural asset statistics obtained from the district delegations of the Ministry of Agriculture and Rural Development of Cameroon, approximately 30% of farmers in each village were included in the study (George and Christopher 2020). A total of 126 randomly selected farmers were interviewed.

The interview questionnaire was first tested with 10 farmers in Tam Village (peripheral to the park, but not among the selected villages) to improve it. The collected data were verified in focus group discussions held with an average of 15 farmers in each village. The farmers were interviewed primarily to obtain information on the types of crops grown, the tree species spared when clearing land for farming, the main system components of the cropping system, the number of strata in the cropping system, the main dominant species in each stratum, the types of associated crops grown, the spatial and temporal arrangements within the cropping system, and the animal species introduced into the farms. At the end of each interview, the farmers were shown pictures of their AFS taken during a reconnaissance survey in the study area to confirm their practices. Farm visits were then conducted with the farm owners to identify the observed woody species and corroborate the interview information with that collected on the farm.

Floristic survey

We set up 50 m × 50 m plots in thirty-seven plots following guidelines outlined in Froumsia et al. (2012) and Wala et al. (2005), except for homegardens, where 25 m x 25 m plots were set up. Land-use systems encountered in each sampled plot were inventoried. In the study area, agricultural parcels were divided into quarters of a hectare corresponding to the minimum area of a farmer's plot. Overall, thirty-seven sampling plots totalling 8.5 ha, from the volunteer farmers selected following the individual interviews were surveyed. In each sampling plot, we identified trees with a diameter at breast height (DBH) of at least 5 cm, based on their discriminating characteristics using Flora identification keys. We followed the Geerling (1985) and De Wolf and Van Damme (2010) nomenclature. Species not identified in the field were brought back to the Garoua Wildlife School herbarium for identification. We measured the diameter of each plant with a tape graduated to 5 m, 1.3 m above the ground and 0.30 m above any defects for tall trees that had some. The height of each plant was also measured using a clinometer and a decameter.

Tree uses

We evaluated the use of woody species through ethnobotanical surveys (Clinquart 2010), during semi-structured interviews and focus groups. These surveys focused on the tree species left in agroforestry plots when clearing land for farming, the reasons for their preservation, their main uses, the trees preferred to be left in the farms, whether or not the same resources were harvested in the park, and the reasons for harvesting tree products in the park. The aim was to identify the current uses of AFS woody plants around BNNP.

Data Analysis

For assessing AFS diversity, we analyzed woody flora using diversity indices (species richness, diversity indices) and structural parameters (density, frequency, dominance, diameter structure). To assess woody species diversity, we compiled a comprehensive floristic list of species identified within AFS. This list enabled a qualitative analysis categorizing species into genera and botanical families, following the Angiosperm Phylogeny Group (APG) III classification system (APG III 2009). Absolute abundance of species and families was determined based on total individual counts. Shannon-Weiner, Piélou, and Simpson indices were applied to floristic data (Froumsia et al. 2012; Jiagho et al. 2016) for assessing species diversity.

Statistical analysis included one-way analysis of variance (ANOVA) to evaluate differences in floristic diversity among AFS. In cases where normality and homoscedasticity assumptions were not met, the Kruskal-Wallis test was used as a non-parametric alternative. Post-hoc tests (Tukey’s Honesty Significant Difference or Wilcoxon) were employed for multiple comparisons depending on data distribution. Structural composition analysis involved comparing tree diameter classes and calculating parameters such as basal area, relative density, frequency, and dominance. Horizontal structure was assessed by categorizing trees into diameter classes ranging from < 10 cm to ≥ 60 cm. The Importance Value Index (IVI) (Cottam and Curtis 1956) and Family Index Value (FIV) were computed using combined floristic and structural data to assess species and family importance within the AFS context:

IVI = relative density + relative dominance + relative frequency

FIV = family relative diversity + relative density + relative dominance

To assess the contribution of AFS to biodiversity conservation, we categorized identified species according to IUCN Red List categories. Additionally, we analyzed the uses of woody species integrated into AFS, considering all species collectively and categorized by type of AFS. Ethnobotanical parameters proposed by Houehanou et al. (2016) were employed for analysis, including:

Use value (UV) modified from Phillips and Gentry (1993a,b) by Rossato et al. (1999), which evaluates the importance of a plant within a community.
Cultural Importance Index (CII) (Tardío and Pardo-de-Santayana 2008), used to assess the significance of a species within a specific use category.

Furthermore, tree species preferred by farmers for retention in their farms were ranked based on the frequency of mentions during interviews. Hence, species mentioned more frequently were considered more preferred by farmers.

Characteristics of AFS inventoried

We identified four agroforestry systems with agroforestry parklands being the most frequent in the sampled plots (Table 1). The dominant woody species varied with agroforestry system, except for Acacia polyancantha which was the most frequent woody species encountered in fallows and live fences (Table 2).

Table 1

Agroforestry systems practiced by riverine populations around the Bouba Ndjida National Parc, Cameroon
Land-use system	Classification based on the nature of components	Number of strata	Main woody species encountered	Other woody species encountered	Main crops grown	Other crops grown	Animals found	Frequency
Agroforestry parklands	Agrisilvicultural system	3 (one woody stratum about 20 m high at maturity, one woody stratum about 10 m high at maturity, one herbaceous stratum)	Burkea africana	Daniellia oliveri Prosopis africana Terminalia laxiflora	Zea mays Gossypium sp. Arachis hypogaea	Sorghum bicolor Panicum miliaceum Vigna unguiculata		98%
Homegardens (Trees-crops-animals mix around homesteads)	Agrosilvopastoral system	3 (one woody stratum about 20 m high at maturity, one woody stratum about 10 m high at maturity, one herbaceous stratum)	Commiphora kerstingii	Mangifera indica Acacia polyacantha Cassia siamea	Abelmoschus esculentus Zea mays	Cucumis melo Ipomoea batatas	Gallus gallus domesticus Capra hircus Ovis aries	83%
Fallows	Silvopastoral systems		Acacia polyacantha	Ficus glumosa Combretum glutinosum Piliogstigma thonningii			Bos taurus Capra hircus Ovis aries	72%
Live fences -	Agrisilvicultural system	2 (One woody stratum about 20 m high at maturity and one herbaceous stratum)	Acacia polyacantha	Anogeissus leiocarpus Cassia siamea Sterculia setigera	Gossypium spp.	Vigna unguiculata Arachis hypogaea		6%

Table 2

The five dominant tree families in terms of Family Index Value (FIV), number of species and Importance Value Index (IVI) in the four AFS
Dominant families and species	Agroforestry parklands	Fallows	Homegardens	Live fences
Dominant family in terms of (FIV)	Fabaceae (126,85) Combretaceae (64,20) Anarcardiaceae (28,33) Moraceae (19,28) Myrtaceae (11,87)	Fabaceae (123,48) Combretaceae (58,60) Moraceae (52,21) Loganiaceae (11,60) Bombacaceae ( 9,39)	Fabaceae (116,23) Burseraceae (85,72) Anarcardiaceae (20,92) Sapotaceae (19,24) Rutaceae (18,65)	Fabaceae (268,27) Burseraceae (13,33) Anarcardiaceae (8,31) Sapotaceae (6,29) Rutaceae (2,41)
Dominant family in terms of specie number	Fabaceae (8) Combretaceae (5) Anarcardiaceae (2) Meliaceae (2) Moraceae (2)	Fabaceae (8) Combretaceae (7) Moraceae (3) Rubiaceae (2) Anarcardiaceae (1)	Fabaceae (2) Anarcardiaceae (1) Burseraceae (1) Euphorbiaceae (1) Rhamnaceae (1)	Fabaceae (3) Loganiaceae (1) Moraceae (1) Rhamnaceae (1) Sterculiaceae (1)
Dominant species in terms of IVI	Burkea africana (45,3) Daniella oliveri (39,68) Prosopis africana (28,65) Terminalia laxiflora (24,79) Anogeissus leiocarpus (15,58)	Acacia polyancatha (61,77) Ficus glumosa (39,86) Combretum glutinosum (24,06) Piliostigma thonningii (18,13) Burkea africana (16,43)	Commiphora kerstingii (85,72) Acacia polyacantha (65) Cassia siamea (51,23) Manguifera indica (20,92) Vitellaria paradoxa (19,24)	Acacia polyancatha (218,8) Cassia siamea (44,81) Sterculia setigera (13,33) Ficus sycomorus (8,31) Anogeissus leiocarpus (6,3)

AFS woody floristic composition, diversity and structure

AFS woody species richness and diversity

The inventory identified 420 trees belonging to 50 species, 42 genera, and 23 families. Species richness was higher in fallows (32 species) and agroforestry parklands (31 species) compared to homegardens (9 species) and live fences (8 species; Table 3). The Shannon index was significantly higher in fallows than in live fences, and the live fences also had significantly lower Simpson index and Pielou's evenness index compared to the other three agroforestry systems studied (Table 3).

Table 3

Summary of diversity indices in agroforestry systems around Bouba Ndjidda National Park
Index	Agroforestry parklands	Fallows	Homegardens	Live fences
Number of observations	124	93	23	180
Number of families	16	16	8	6
Number of genera	27	25	9	8
Specific Richness	31	32	9	8
Shannon Index	0,94 ± 0,14 ab	1,15 ± 0,18 b	0,5 ± 0,2 ab	0,16 ± 0,19 a
Simpson Index	0,61 ± 0,04 a	0,64 ± 0,05 a	0,53 ± 0,07 a	0,13 ± 0.01 b
Piélou Equitability	0,88 ± 0,03 a	0,90 ± 0,04 a	0,90 ± 0,07 a	0,24 ± 0,12 b
Mean values with different letters indicate significant differences at P < 0.05

Structural characteristics of AFS around BNNP

Tree density, in terms of the number of stems per hectare, was significantly higher in live fences than in the other three studied agroforestry systems (Table 4). In contrast, tree diameter was larger in agroforestry parklands than in the other surveyed agroforestry systems (Table 4). Trees were taller in agroforestry parklands and live fences than in the other studied agroforestry systems, whereas tree basal areas were thicker in live fences (Table 4). The largest basal areas among the 50 species identified were recorded in Acacia polyacantha, Daniellia oliveri, and Ficus glumosa, with values of 7.52 m²/ha, 3.72 m²/ha, and 3.04 m²/ha, respectively.

Table 4

Dendrometric characteristics of agroforestry systems around Bouba Ndjidda National Park
Parameters	Agroforestry parklands	Fallows	Homegardens	Live fences
Tree density (number of stems/ha)	29 ± 1 a	37 ± 2 a	31 ± 1 a	180 ± 8 b
Mean diameter (cm)	28,90 ± 1,46 a	23,60 ± 1,69 b	17,56 ± 3,41 b	21,91 ± 1,21 b
Mean height (m)	10,45 ± 0,44 b	7,23 ± 0,51 a	5,08 ± 1,03 a	9,72 ± 0,37 b
Mean basal area (m²/ha)	0,75 ± 0,15 ab	0,72 ± 0,20 ab	0,15 ± 0,26 a	1,8 ± 0,31 b

Ecological importance and IUCN Species Conservation Status

Acacia polyacantha was the dominant species, with an Importance Value Index (IVI) of 88.65. Co-dominant species included Daniellia oliveri, Burkea africana, Cassia siamea, and Prosopis africana (Fig. 2). These five species constituted the primary woody floristic components of agroforestry systems around BNNP, representing more than 65% of all species by IVI. Regarding the IUCN conservation status, about 90% of the species found in agroforestry systems were not evaluated. Vitellaria paradoxa, found in homegardens and agroforestry parklands, and Khaya senegalensis, found only in agroforestry parklands, were classified as vulnerable species. In contrast, Detarium microcarpum and Isoberlinia doka were classified under the least concern category.

AFS horizontal structure

The diameter structure of the surveyed trees (Fig. 3) showed the dominance of trees in three intermediate classes: [10–20], [20–30], and [30–40], which is characteristic of uneven-aged stands. These classes represented 67.74%, 68.55%, 97.78%, and 47.83% of all woody plants inventoried in fallows, agroforestry parklands, live fences, and homegardens, respectively. The species with the largest diameters in the agroforestry systems were Daniellia oliveri and Ficus glumosa, with mean diameters of 119 cm and 102 cm, respectively.

AFS tree products and AFS products harvested by neighboring communities

The Cultural Importance Index (CII) and Use Value (UV) were calculated for all species, with those having UV > 2 recorded in Table 5. Overall, the CII varied across species according to different use categories. Vitellaria paradoxa had the highest UV, followed by Acacia polyacantha (Table 5). Acacia polyacantha ranked highest for fuelwood supply and soil fertilization, while Mangifera indica, Anacardium occidentale, and Vitellaria paradoxa ranked highest for food supply (Table 5).

Table 5

Cultural Importance Index (CII) and Use Value (UV) of some species around Bouba Ndjidda National Park
Species	Cultural Importance Index (CII) by Use Category									Use Value (UV)	Agroforestry systems
Species	Fu	Fo	Sh	Fe	Fd	He	Ti	Ph	Ot	Use Value (UV)	Agroforestry systems
Vitellaria paradoxa	0,56	0,97	0,56	0,42	0,91	0,00	0,04	0,64	0,26	4,36	HG ; AP
Acacia polyacantha	0,96	0,00	0,20	0,94	0,76	0,37	0,23	0,13	0,26	3,85	HG; F; AP; LF
Burkea africana	0,58	0,09	0,45	0,42	0,43	0,02	0,33	0,64	0,26	3,23	F; AF
Anacardium occidentale	0,46	0,98	0,13	0,42	0,42	0,02	0,13	0,45	0,18	3,21	AP
Anogeissus leiocarpus	0,81	0,60	0,33	0,42	0,29	0,10	0,04	0,37	0,12	3,08	LF; F; AP
Mangifera indica	0,38	1,00	0,33	0,06	0,43	0,02	0,00	0,40	0,36	2,98	HG; AP
Combretum glutinosum	0,38	0,09	0,33	0,42	0,43	0,02	0,13	0,64	0,26	2,70	F; AP
Ficus sycomorus	0,60	0,48	0,17	0,30	0,70	0,02	0,13	0,13	0,06	2,60	F
Eucalyptus camaldulensis	0,44	0,00	0,07	0,00	0,00	0,18	0,94	0,36	0,17	2,17	F; AP
Pilliostigma thonningii	0,97	0,01	0,50	0,06	0,21	0,03	0,03	0,14	0,12	2,07	LF; F; AP
Fu: Fuelwood; Fo: Food; Sh: Shade; Fe: Fertilization; Fd: Fodder; He: Hegdes; Ti: Timber; Ph: Pharmacopeia; Ot: Others; HG: Homegardens; F: Fallows; AP: Agroforestry parklands; LF: Live fences

Examining the relationship between agroforestry system (AFS) use categories and types (Fig. 4) revealed that in fallows, woody plants were primarily harvested for fuelwood (78.48%) and food (52.69%). In agroforestry parklands and homegardens, shade provision for both livestock and humans was a priority, with 91.94% and 78.26% of citations, respectively. However, within live fences, respondents mainly valued wood production, plot boundary delineation, and crop protection against livestock. The majority of species identified in AFS contributed to fuelwood supply. Additionally, there were similar trend curves between use categories and the number of species contributing to each category, indicating a proportional relationship between the variables (Fig. 4).

The characterization of riparian traditional agroforestry systems adjacent to a park is essential for developing programs aimed at reducing the encroachment of nearby populations into the park. Analysis of floristic diversity showed that the Fabaceae family dominated all agroforestry systems, both in terms of importance value index and specific uses. The specific dominance of Fabaceae found in the AFS that were surveyed in our study can be explained by the family's taxonomically diverse species with multiple uses. This reflects the importance of this large family for the well-being of populations, but it could also be due to the classification used in this study. The APG III classification includes the former families of Mimosaceae, Caesalpiniaceae, and Fabaceae itself under Fabaceae. The same result was observed by Charahabil et al. (2018) and Nature Information Tracks (2017). The dominance of Fabaceae can also be explained by their forage use, with zoochorous pods spread by herbivores typically introduced into fields after harvesting. Our results differ from those obtained by Charahabil et al. (2013) in the Sudano-Sahelian zone in Senegal, who reported that the Combretaceae family was the most important. This difference could be due to low anthropogenic pressure on this family’s species in Charahabil et al.’s study area, leading to greater natural regeneration capacity. According to these authors, poor climatic conditions favor the expansion of Combretaceae, a family apparently more adapted to aridity, whereas BNNP is located in a semi-arid zone.

The differences observed in our study between fallows, homegardens, and agroforestry parklands in terms of diversity could be explained by the level of human intervention in each AFS and the farming practices used. The high woody diversity in fallows could be attributed to the absence of human intervention, promoting the natural regeneration of certain species and the preservation of trees. Also, after harvesting crops in agroforestry parklands, the system is left to fallow, which explains the little difference in diversity between fallows and agroforestry parklands in our study. Overall, the species richness of AFS in our study (50 species) was low compared with that inside the BNNP (97 species; Nature Information Tracks, 2017), confirming the assumption that traditional agroforestry systems are less diversified than natural forests (Oke and Jamala 2013). The Shannon index values obtained in fallows, homegardens, and agroforestry parklands were higher than those reported by Jiagho et al. (2016) in the eastern periphery of Waza National Park. These values were under 3.5, indicating that the floristic community is at risk (Kent and Coker 1992). However, Kent and Coker’s (1992) result applies to tropical rainforest areas, whereas plant diversity is generally low in semi-arid areas like that of the BNNP due to climatic and soil conditions.

The densities obtained in agroforestry parklands, fallows, and homegardens were higher than those found in the tree parks in Far North Cameroon (Karr et al. 2001) and lower than those reported by Wala et al. (2005) in Northern Togo and by Saré and Sinsin (2009) around the W complex in Benin. The results of our study indicate that tree density was higher in live fences, highlighting the role of trees in the system. Live fences serve as barriers to prevent animals from entering farmlands, while agroforestry parklands allow more space for farming. The high diversity observed in live fences can explain the low tree stem diameter compared to the other surveyed AFS due to competition between trees for soil nutrients and light. As agroforestry is based on the assumption that trees must acquire resources that crops would not otherwise acquire, the choice of tree species to be included in an AFS system should depend on tree architecture, including the rooting system.

Importance of AFS in conserving plant diversity in park peripheries

Agroforestry systems, with their rich flora, constitute a pool of biodiversity that deserves special attention for in-situ conservation of indigenous woody species (Ouinsavi and Sokpon 2008). All woody species found in the AFS around BNNP are multipurpose, with use categories varying from one system to another, confirming the findings of Lovett and Haq (2000), who claimed that plant diversity in AFS is mainly dominated by tree species useful to local communities. Most woody species found in the AFS in our study are used for fuelwood production and food, corroborating the findings of Nahayo and Uwineza (2012) around the Volcanoes National Park in Rwanda. This slightly differs from the findings of Fifanou et al. (2011), which showed that, around the Pendjari Biosphere Reserve, the contribution of tree species to household food and health were the two main reasons supporting their integration into AFS.

The results of our study indicate that several products expected from a tree species determine its preference for introduction in AFS by farmers. Therefore, a multi-criteria approach must be used for participatory identification of tree species to be introduced on farms. The period of harvesting the desired agroforestry product is also critical for tree selection. For example, V. paradoxa and A. occidentale yield fruits during the dry season, explaining their high Cultural Index for food use category among the surveyed species in BNNP our study. Also, enhancing biodiversity and preference for Vitellaria paradoxa, cashew tree and exotic fruit species such as M. indica can be explained by the fact these species provide farmers with marketable and edible fruits during dry season. Fuelwood provision for household is essential for the day-to-day living in savanna areas in the rural tropics, reason why A. polyacantha has high Importance Value Index. The farmers expect the species to provide them with marketable products that will generate additional income, especially during the dry season when they face food shortages. This explains their preference for shea butter (Vitellaria paradoxa), cashew nuts (Anacardium occidentale) and exotic fruit species, most of which they plant themselves. These fruit species with a high Cultural Index for food use category are not among the most frequent species in BNNP, whereas Anogeissus leiocarpus, Combretum glutinosum and Terminalia laxiflora with high cultural indices for fuelwood, pharmacopoeia and forage, respectively are common in the park (Nature Information Tracks, 2017). These results suggest that these species should be intensively promoted within the AFS to protect park resources. Farmers are convinced that trees contribute to soil improvement, especially Acacia sp, but they reduce their densities to allow higher crop production. Through the Water - Soil - Tree (WST) project, the Cotton Development Company has raised awareness regarding the ability of certain legumes to fix atmospheric nitrogen (N₂) with rhizobial associations and convert it into the form that plants can directly assimilate (NH₃) in the soil. By doing so, most farmers were able to plant and conserve Acacia polyancatha plants offered by the project not only for soil fertilization and crop protection purposes (fences), but also for gum arabic production. This explains why A. polyancatha is the multipurpose species found in all AFS. Hence, the intensification of agroforestry practices could contribute to the conservation of protected area biodiversity through farmers adopting a sedentary lifestyle. Gum arabic from Acacia is not marketed in the area. However, children make juice and chewable sweets after mixing gum arabic with Balanites aegyptiaca fruits in the study area. Like gum arabic, there is no organized production, processing or marketing chain for cashew and shea products. However, these non-timber forest products offer many opportunities for local, national and international economic development. Thus, the status of this vulnerable species could be raised through the densification of shea tree parklands.

The multiple uses of AF woody products contribute to reducing pressure on woody resources within BNNP, as they allow populations to obtain product supplies previously harvested from the park. The regeneration of species classified as vulnerable in AFS also contributes to their conservation in more secure and better managed agricultural systems. This result was also observed by Nahayo and Uwineza (2012) around the Volcanoes National Park in Rwanda. AFS actually provide the opportunity to manage trees and animals in the same area and can contribute to solving a major issue regarding protected areas in the Sudano-Sahelian zone: the need for land security for local populations, but also for access to fodder during lean periods.

Despite the ability of AFS around BNNP to provide many products and uses, their performance is far from optimal. Many species are under-represented due to lack of knowledge about their regeneration and management in agricultural systems. To be productive, profitable and sustainable, AFS around protected areas should be ecologically and economically intensified through the domestication of species socially valued by populations. Greater involvement by local communities in the management of protected areas (Aymoz et al. 2013), raising their awareness and training them in tree domestication, and intensification practices in AFS would be major assets for the conservation of these protected areas.

This study showed that out of the four agroforestry systems observed around BNNP, fallows and dispersed trees on croplands were more diversified than home gardens and live fences and that the Fabaceae and Combretaceae families were the most dominant because of their multiple uses. The potential of AFS for the conservation of vulnerable and endangered species is seen as a significant contribution to the conservation of natural resources in protected areas. The multi-functional role of AFS argues in favour of enhancing strategies to promotion their use around Sudano-Sahelian protected areas. AFS can be considered as an approach likely to improve farmers' livelihood, reduce poverty, create an enabling environment for many woody species, alleviate pressure on resources by reducing conflict between protected area managers and local populations, and contribute to the sustainable management of protected areas.

Author Contribution

E.J.D.B. collected data, contributed to data analysis and drafted the initial manuscript. A.A.R. wrote the final manuscript. M.L.A.T., L.Z., A.D. and D.K. designed and supervised the work. I.G.M.D. contributed to data analysis and drafting of the initial manuscript.

Acknowledgments

We thank the Queen Elizabeth Scholars program for funding this research and, in particular, the local populations around Bouba Ndjidda National Park for their hospitality. We also acknowledge the Natural Sciences and Engineering Research Council of Canada (NSERC) for the discovery grants awarded to André Desrochers and Damase Khasa.

The authors declare no competing interest.

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Agroforestry in buffer zones as a strategy for biodiversity conservation and resource management: A case study from Bouba Ndjidda National Park, Cameroon

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Abstract

Figures

Introduction

Materials and Methods

Identification and characterization of AFS around BNNP

Floristic survey

Tree uses

Data Analysis

IVI = relative density + relative dominance + relative frequency

FIV = family relative diversity + relative density + relative dominance

Results

AFS woody species richness and diversity

Structural characteristics of AFS around BNNP

Ecological importance and IUCN Species Conservation Status

Discussion

Conclusion

Declarations

Author Contribution

Acknowledgments

References

Additional Declarations

Status:

Version 1