Appraisal of tree and fauna species is crucial; this ensures effective conservation of the forests and their resources. This study aims at an appraisal of tree and fauna species diversity in Osun-Osogbo Sacred Grove, Nigeria for record update, knowledge, and monitoring species status for conservation management. A total of 70 tree species belonging to 26 families were recorded. The tree species in the Fabaceae and Apocynaceae families were the most abundant. Tree species richness indices for the three zones were 2.16, 1.89, and 1.72, respectively. Most of the tree species encountered were in the IUCN categories of vulnerable (6.7%), least concerning (71.1%), and not evaluated (71.1%). The result revealed that the core zone was richer and more diverse than the buffer and the outer zones, with diversity indices of 3.06, 2.995, and 2.16, respectively. The fauna species diversity and richness index were 3.40 and 2.35, respectively. The least vulnerable fauna species were 86.4%, with 6.8% vulnerable. Class Aves has the highest percentage of 61.4%, with Gastropoda being the least-represented (2.3%). Mona monkeys were the most sighted fauna species in the area. Thus, there is an urgent need to increase the level of security around the sacred grove and to ensure sustainable management strategies are fully implemented in the study area.

Keywords: conservation, fauna species, sacred-grove, sustainable management, tree species

Sacred groves are forests that have been protected throughout the ages by traditional societies and norms.¹ They have served as valuable storehouses for biodiversity. Local communities derive different benefits through the preservation of sacred sites while practising their faiths and upholding their traditional customs.² As a result of sacred groves' significant contributions to the preservation of in-situ biodiversity, they are now recognized as biodiversity hotspots and serve as safe havens for threatened and endangered species by Myers. Sacred groves are currently significant remnants of climax vegetation and frequently support populations of rare and endangered plants.³

There is no recent documentation to show the effect of encroachment due to farming activities, illegal felling of trees for timber, harvest of plant materials for medicinal purposes and fuel, which are being carried out in the buffer and outer zones of the grove, on the biodiversity of the area. It is rumored that increased use pressures and encroachments at the grove's buffer and outer zones harmed the area. The extent of the damage these may have caused is yet to be ascertained. Be it trees or fauna, it is possible that species once thought to be present in the grove may have been decimated, be it trees or fauna. However, present conditions of individual tree and animal species are not documented. Similarly, the status of many species may have changed, and previously abundant species may be endangered, while those thought to be endangered might be on the verge of extinction due to limited information on the biodiversity of the area. This study aims to appraise the status of tree and fauna species diversity and distribution in Osogbo sacred grove due to anthropogenic encroachment on the study area, in order to provide updated documentation and knowledge on the distribution and abundance of species in the area for the purpose of conservation management.

Location of the study area

Osun Osogbo Sacred Grove (OOSG) is situated in Osogbo, the capital of Osun State in Nigeria. The study area is situated between longitudes 4:32:40 and 4:33:440 and latitudes 7:44:50 and 7:46:00. In Osogbo town, Osun State, Nigeria, the Sacred Grove is situated across the banks of the Osun River. It was established some 400 years ago, and it is Yorubaland's biggest remaining sacred grove.⁴ The grove is surrounded by a 47-hectare buffer zone and contains a 75-hectare forest area.⁵ OOSG was designated a UNESCO World Heritage Site in 2005.⁶

The National Commission for Museums and Monuments (NCMM), an agency of the Federal Government of Nigeria, is in charge of safeguarding cultural assets in Nigeria. In the instance of OOSG, armed guards are stationed there 24 hours a day.⁷ More than 400 plant species can be found in Osun OSG, which also serves as a refuge for animals including the endangered red-capped mangabey (Cercocebus sp.), putty-nosed monkey (Cercopithecus nictitans), and white-throated monkey (Cercopithecus erytrogaster).^8,9 The forest sanctuary is home to 40 shrines, two historic castles, and several sculptures and works of art dedicated to Osun and other gods.¹⁰ Around 27°C is the average annual temperature, while between 92 and 99 percent of the region is covered by relative humidity.¹¹ The average annual rainfall ranges from 1200 to 1450 mm. Within the grove, the microclimate is more humid than it is throughout most of southern Nigeria (Figure 1).¹²

Figure 1 Map of Osun-Osogbo Sacred Grove.
Source: Adesoji et al.¹³

Data collection

Line transect sampling (random survey method) was adopted for the assessment of fauna diversity in the study area; while cluster and systematic sampling designs were adopted to assessed tree diversity at the three vegetation zones (riparian forest, dry high forest, and derived savanna) of the grove, which cut across the core zone, buffer zone and outer zone of the area. Three quadrants of 50 × 50 m were established at 100 m intervals in each of the vegetation zones of the sacred Grove. Nine quadrants were laid in total (i.e. three quadrants in each zone) and 100% enumeration of tree species ≥10cm was carried out at the outer zone of the area. All the species in the sample plots were identified. Direct observations of wildlife was done using a line transect sampling design (Random method) within the hours of 7am - 10:30am and 4:30pm - 6:30pm; information on wildlife species sighted by the workers was also collected.¹³

1. Tree species diversity

Tree species diversity index was calculated using Shannon - Wiener's diversity index as follows: 

$H^{\prime }=-{\displaystyle \sum _{t=1}^{s}Pi}ln(Pi)$  …………… (1)

Where: S, total number of species in the community; P_{i ,} proportion of S made up of the ith species; ln, natural logarithm.

2. Tree species richness

Tree species richness in the area was computed using Margalef’s index of species richness:¹⁴ 

$d=\frac{S}{\sqrt{N}}$  …………… (2) 

Where: S, number of species encountered; N, total number of individuals of all the tree species.

3. Tree species evenness

The species evenness was computed using Piolu's index modified by Magurran¹⁵ as:

$E^{\prime }=\frac{H^{\prime }}{lnS}$  …………… (3)

Where: H', Shannon-Wiener diversity index; S, number of species; E' is constrained between 0 and 1 (the lesser the variation between the species in the communities, the lower the value of E' and vice versa).

4. Fauna population estimation

Fauna population estimation was done using: 

$NH=\frac{nk+(1-)(nK-nK-1)}{\alpha }$  …………… (4) 

Where: NH, Estimated population, nk, highest value in observation, nk -1, next to highest value, α, confidence interval.

5. Population density

Fauna population density was determined using:

$\frac{NH}{A}$  …………… (5)

Where: A, area in km; NH, Estimated population

A total of 32 tree species, belonging to 19 families were encountered at the core zone of the sacred grove. Cola millenii was the most frequently occurring species in the area with diversity index of 0.307. The least occurring species were Alstonia boonei, Terminalia ivorensis, Zanthoxylum zamthoxyloides with diversity index of 0.025 each (Table 1). At the buffer zone of the sacred grove 27 tree species belonging to 17 families were encountered. Baphia nitidahas the most occurring frequency with diversity index of 0.2454. Alstonia boonei, Ceiba pentandra, Hevea brasiliensis and Terminalia ivorensis has the least frequency of occurrence in the area (Table 1). At the outer zone of the grove, 11 tree species were identified from 10 families; with Fabaceae having the highest occurrence of 11 tree stands in the area. This was followed by Arecaceae family which occurrence 6 while Piperaceae family was the least occurred family with a tree species (Peperomia pellucid) in the area (Table 1). 

A total of 26 families were identified at the osun osogbo sacred grove (core, buffer and outer) while most species sighted were belonging to family of Fabaceae (15.7%) and Apocynaceae (12.9%) and the least represented families were Acanthaceae, Connaraceae, Lamiaceae, Passifloraceae, Piperaceae, poaceae, Polygalaceae, Rubiaceae, Ulmaceae and Zygophyllaceaeas each had 1.4 % occurrence of tree stands (Table 2).

Four hundred and sixty six individual trees were identified with 70 species, 44 genera and 26 families. Tree species diversity index of the study area had an estimated index of 3.88, dominance of 0.027, species richness of 3.24 and evenly distributed index of 0.69. Trees identified at the buffer, Core and Outer zones were 220, 205 and 41 respectively; tree species were recorded at the Core zone (32), 27 (Buffer zone) and 11 at Outer zone. Tree species diversity index of 3.06 was recorded at the Core zone; this was followed by Buffer zone (3.00) while the Outer zone had 2.16 diversity indexes. The species richness index of 2.16 was recorded at the Core zone, followed by Buffer zone which had 1.89 and Outer zone had an evenly distributed species richness of 1.72 in the study area (Table 3). Tree species composition and status of the study area were assessed and the result of the finding is presented on Table 4. Based on this finding, the grove was composed of 46 tree species; 8 tree species had a status of “Least concern” on IUCN list, 3 species had a status of “Near threatened”, 32 species had a status of “Not evaluated” and 3 species had a status of “Vulnerable” on the IUCN list.

Most families sighted within the study area were categorized using the IUCN list (version 2018); “not evaluated” had 71.1%, followed by “least concern” had 17.8%, “vulnerable tree species had 6.7% while “near threatened” had 4.4% of the tree species identified in the area. The result on diversity index of fauna species sighted at Osun-Osogbo sacred grove is presented on Table 5. Based on the result from the finding, Cercopithecus mona had a relative frequency of 17.76%, followed by Gastropoda spp had 6.55%, Sciuridae spp had 5.65% of relative frequency, Chiroptera spp had 4.17% of relative frequency; while fauna species sighted with the least relative frequency (less than 1) include: Cuculus gularis, Centrochelys sulcata, Lonchura bicolor, Atherurus africanus, Falco tinnunculus, Erythrocebus patas, Dendrohyrax dorsalis, Ploceus cucullatus and Milvus migrans. 

A total of 43 fauna species was sighted at the sacred grove. Mona monkey was the most frequently occurring species in the area with diversity index of 0.303; while the least occurring species was Western Bluebill with diversity index of 0.0173 (Table 5). Figure 2 of this result shows status of fauna species in the IUCN categories list of 2018. Based on the result of this finding, fauna species that had a status of “least concern” on IUCN list were mostly sighted, this had a86.36% of all the sighted fauna species in the area, while the status of “not evaluated” and “vulnerable” fauna species had a 6.82% each. The fauna species family of Aves was recorded with the highest (61.36%) fauna species sighted, followed by the family of Mammalia which had 31.82%of the fauna species sighted in the area, followed by reptiles which had 4.55% of the sighted fauna species while Gastropoda family had 2.27% of the sighted fauna species in the area based on the result of this finding (Table 6).

Figure 2 Percentage of fauna species in each of the IUCN categories.

A total of 336 individual fauna were identified belonging to 43 species, 41genera and 4 families. Fauna species diversity index of the study area had an estimated index of 3.40, dominance of 0.05, species richness of 2.40 and evenly distributed index of 0.68. The fauna population estimate and density in the area is presented in Table 7. The result of this finding showed that, core zone of the area was the most populated area with 0.39 population estimate and 0.06 population density per hectare, followed by buffer zone which had 0.26 estimate and population density of 0.005; while the out zone was d least populated area with 0.21 and 0.003 density population per hectare (Table 6).

A total of 466 individual trees were identified from 70 tree species belonging to 44 genera and 26 families. The tree species diversity index of the study area had an estimated index of 3.88, dominance of 0.027, species richness of 3.24, and an evenly distributed index of 0.69. A total of 43 fauna species belonging to 4 classes were sighted in the study area, which corresponds to what Scheiner reported in 2003.¹⁶ The most numerous tree species belonged to the groups Fabaceae and Apocynaceae; Pausas and Austin¹⁷ reported a similar situation regarding species richness in respect to the environment. According to Austin et al.,¹⁸ edaphic conditions are very important for the establishment and richness of species in an ecosystem. The Fabacea family was listed by Iheyen et al.,¹⁹ as being the most prevalent family in the Ehor forest reserve in Edo State. This family's dominance may be due to their effective seed distribution system and regeneration potential. Most members of the Fabaceae and Apocynaceae families are wind disseminated, which would explain why they are so common.

The class of aves made up 61.36 percent of the fauna in the area. When the diversity of tree species in the Afi Mountain wildlife sanctuary was evaluated, Edet et al.,²⁰ reported less disturbance than what this study found. This is a result of the rapid tree cutting for construction projects in the grove's outer zone, which is extending into the buffer zone, as well as the hunting for food and profit by poachers. It is impossible to overstate the importance of biodiversity as a source of renewable resources for rural and urban populations, which makes biodiversity protection important. Before any significant conservation efforts can begin, surveys of both flora and fauna species that are an essential component of the animal and forest ecology in wildlife-based protected areas are required.² The biodiversity indices for tree species in the area's core zone are consistent with Daniel et al.,^2,20 observations, whereas those for the area's outer and buffer zones are lower.

There may be a significant number of species under threat since human activity has an impact on how new species are produced. Since there aren't enough rangers to police the entire grove, they only focus on the central region. Similar cases involving plant communities on anthropogenic disturbed locations in the Chukotka Peninsula have been documented by Marshal and Swaine.²¹ This study suggests that there were a variety of tree and animal species in the area, some of which are threatened by anthropogenic activity. To maintain ecosystem productivity and biodiversity, sustainable management practises are needed.²² Due to competition for nutrients, restricted light from canopy trees, and destruction of undergrowth during illegal logging on the forest floor, several families with low species representation did not develop well. Furthermore, it could be due to the majority of players (such as governments and non-governmental organizations) paying little to no attention to the successful conservation of local biodiversity. A similar incident was recorded by Egbe et al.,²³ in the Cameroonian Korup national park's degraded and naturally regenerating forest.

The Fauna species diversity index of 3.40, species richness of 2.40, and species evenness of 0.68 indices were derived from the study area. The values obtained indicate high values, which confirm that the study area (Core zone) is of rich tree and fauna species diversity. This observation agrees with the earlier reports of Joshi and Joshi,²⁴ who reported a rich and varied biodiversity in various ecosystems of Syabru village, in Langtan National Park, Nepal. Due to high anthropogenic activity and encroachment, the buffer zone and outer zone of the grove had a low diversity index, species richness, and evenness for trees and fauna species. This result is in line with the report of Yager et al.,²⁵ on Makurdi Zoological Garden, Benue, Nigeria.

The area's relatively high population of vertebrate species is typically made up of taxa from West Africa.²⁶ The fact that people in the nearby towns do not eat primates as meat may be related to the high prevalence of Mona monkeys and other primates in the area. Mbaya and Malgui²⁷ made a comparable observation in the Sambisa game reserve. A significant incidence of poaching for traditional medicine and meat is suggested by the relatively low status of various mammals and reptiles in the forest. According to the IUCN classification, the majority of tree and animal species were of least concern, and only a small number of them were threatened species. Estimates were made of the density and number of the fauna. Due to their home ranges and potential for reproduction, some animal species are more tolerant of hunting pressure than others.²⁸ Some animal species are also influenced by vegetation patterns that give them a good perspective of their surroundings and allow them to move quickly and deftly through the underbrush.

Based on the results of this finding, there is continuous forest exploitation in the study area. Most of the tree species and fauna encountered in the area are of least concern, and very few species are threatened globally. This could be due to use-pressure and anthropogenic activities such as tree felling in the buffer and outer zone of the area, obtaining tree parts for herbs in the core zone of the area, farming and grazing in the buffer and outer zone of the area, resulting in a rapid decrease in the number of tree species in the area. Fabaceae and Apocynaceae were the families encountered with dominant tree species in the area. All stakeholders should give more attention and managerial resources to the conservation of the sacred grove. There is an urgent need to block all the known routes used by poachers and loggers in the study.

None.

The authors declared that, there is no any conflict of interest exists.

None.

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