Assessment of Tree Species Diversity and Abundance in Yelwa Campus, Atbu Bauchi, Nigeria

Assessment of Tree Species Diversity and Abundance in Yelwa Campus, Atbu Bauchi, Nigeria

Umar Ali¹, *Shamsudden Abdullahi², Simbarashe Mudavanhu³

¹Department of Biological Sciences, Abubakar Tafawa Balewa University, Nigeria

^2,3School of Ecology and Environment Studies, Nalanda University Bihar, India

DOI: https://doi.org/10.51584/IJRIAS.2025.10030029

 Received: 26 February 2025; Accepted: 04 March 2025; Published: 05 April 2025

ABSTRACT

This study examines the diversity and abundance of tree species in Yelwa campus of Abubakar Tafawa Balewa University, Bauchi, Nigeria. The campus was divided into 3 sites namely Site A, B and C where 3 plots of 100m x 100m were randomly laid in each site, making a total of nine sampling plots. Tree species were identified and direct counting method was performed in each plot. The Girth at Breast Height (GBH) of all the trees within each plot was measured and recorded. A total number of 35 different tree species from all the study sites were recorded; meanwhile, a total number of 904 individuals were sampled. Site ‘B’ had the highest species diversity (77.14%), followed by site ‘A’ (68.57%) and lastly site ‘C’ has minimum species diversity (54.29%). Senna siamea is the most dominant species, making up 21.58% of the total tree population, followed by Khaya senegalensis (10.40%), Terminalia ivorensis (8.41%), Gmelina arborea (6.20%), and Anogeisus leiocarpa (5.09%) respectively. Fifteen (15) tree families we found and Fabaceae family recorded the greatest number of individuals thus, the most abundant family. The study ultimately documented the baseline tree diversity and abundance of Yelwa University campus; therefore, one would recommend collaborative effort in conservation of trees species especially those that are least abundant like Acacia sp, Adonsonia digitata, Borassus aethiopum, Ficus sp, Vitex doniana, Phoenix dactylifera and Hyphaene thebaica.

Keywords: Abundance, Diversity, Distribution, Girth at Breast Height (GBH)

INTRODUCTION

Over the years the world has faced increased pressure on natural resources especially trees, that have undergone different levels of disturbance due to unapparelled rise in human population which have led to cutting of trees for firewood collection, charcoal production and infrastructural developments (Benneh et al. 1996; Omoro et al., 2010). This has consequences on tree species composition, diversity and abundance. Universities are regarded as champions, role models and advocates in fueling sustainable development which support coexistence between humans and biodiversity. In light of the conservation of trees to save them from declining, it is important to study the existing status of tree species diversity and abundance to provide baseline reference for assessment and guidance for their management (Suratman, 2012).

Many universities worldwide have green spaces (GS) as an integral part of their campuses because of significant benefits for ecological function and urban communities. Benefits from GS ranges from air purification, pollination and erosion control (Susilowati et al., 2021). In the wake of environmental crisis, with specific mention to global warming, a good quality urban forest is becoming paramount important as vegetation is key in mitigating the pangs of climate change and improvement of the quality of life (Morgenroth et al., 2016). Built up ecosystems or urbanized ecosystems tend to exclude a big proportion if not all-natural vegetation and as a result urbanization processes often cause vegetation loss and extinctions (Lessi et al 2017).

A study on diversity and spatial distribution of trees in the Federal University of São Carlos campus by Lepczyk et al (2017), revealed a satisfactory species diversity (H^’= 3.89). Furthermore, the study reveals low dominance of tree species with a same species individuals’ aggregation, which all species with the highest abundance have an aggregated spatial distribution. Exotic species in this University were more than the native species, which a problematic situation in case of invasion by non-native species. An extensive floristic survey on tree diversity and their abundance in District Science Centre, Tirunelveli, Tamil Nadu, India was also done by Priya et al., (2020), and reported 80 tree species in the campus. Among 80 species confined in 34 families and 68 genera, Polyalthia longofolia was the most dominant and frequent species. During the study several anthropogenic activities like cutting of branches, plastic bags and plastic bottle thrown around the vegetated areas exploited the tree population in the campus. These studies done elsewhere and the revelations from their findings ignited the need for the present study which acted as a pioneer research on tree composition diversity and abundance in university campuses in Abubakar Tafawa Balewa University Bauchi, Bauchi State, Nigeria.

A recent study was done to ascertain the composition, diversity, distributional pattern, and present management of woody species in the Dire Dawa University (DDU) complex in Ethiopia (Tadesse, 2023). From the 34 plots in the University Compound that were specifically chosen, several species were identified using a straight forward inventory procedure. The study identified 41 distinct species of woody plants from 24 distinct families with Fabaceae, Bignoniaceae, Malvaceae and Moraceae having more species. Overall, the findings of this study showed that the University had a significant amount of genetic diversity. It is against this background that the current study was initiated so as to understand the existing situation on the composition, diversity and abundance of woody vegetation at Yelwa University campus.

Oyerinde et al (2018), conducted an assessment of avenue tree diversity at Federal University of Technology (FUT) and Adekunle Ajasin University (AAU) in Ondo State, Nigeria. They conducted a total enumeration of all avenue trees in the two campus and the noted a rich tree species diversity of 513 tree species with 24 different species from 14 families in FUT and 22 species with 274 tree species from 13 families in AAU. They also noted that the dominant family was Caesalpiniaceae followed by Mimosaceae and Verbenaceae in the two campuses. Their study is one of the few studies done in Nigerian universities and they only focused on trees along avenues neglecting those that a not on avenues. Therefore, the current study was the first at Yelwa campus, Abubakar Tafawa Balewa University and it focused on the whole University campus’ tree species composition, diversity and abundance. Nevertheless, the main aim of the study is to assess the tree species diversity and abundance in Yelwa Campus.

METHODOLOGY

Study area

This study was conducted at Abubakar Tafawa Balewa University Bauchi, Yelwa campus, located at latitude 100 17I North, longitude 80 49I East, at the altitude of 690.2 M above sea level in the northern guinea savannah ecological zone of Nigeria (Zaharaddeen et al., 2010). The soil type is highly weathered and fragile with low activity clays. The climate is characterized by a rainy season that starts in April and ends in October, with the amount of rainfall of about 1300 mm per annum (Hassan, 2010), with the lowest mean monthly relative humidity of about 29%. The month of April is the hottest month of the year with mean minimum and maximum temperatures of 13.7°C and 30.11°C respectively (Bose et al., 2014). The vegetation type is open woodland, dominated with tall grasses ranging between 1 and 3 m high in open areas and trees are up to 15 m high usually with short boles, small leaves, and isolated crowns. The vegetation is subjected to wildfire almost annually in the dry seasons; it is therefore dominated by fire-resistant species, (Obioha, 2009).

Fig 1. Map of Africa Showing the location of Nigeria. Source: World Atlas.

Fig 2. Map of Nigeria Showing the location of Bauchi State (study area). Source: Administrative map of Nigeria.

Materials

In this Study, Various materials were applied to realize perfect collection and analysis of data. Measuring tape was used for determining the diameter at breast height (DBH) of trees and ranging pole for accurate measurements. Both a plant identification guide and a mobile application meant for plant identification enabled the identification of different plant species. The data concerning tree species, their frequency and others were recorded on a record sheet using a pencil and an eraser. Also, data entry and analysis were undertaken using a computer system.

Research design

The study area was divided into three sites (site A, site B and site C). Site A starts from the school main gate to the new geology building, using the campus bank road as the boundary, it includes the whole Faculty of Science. Site B starts from the campus bank road to the end of the School Library building, it includes the whole Faculty of engineering and engineering technology. Site C starts from the end of the School Library building to the end of the campus premises, it includes the whole Faculty of environmental technology. In each site, three sample plots of equal size were laid measuring (100 x 100m) as representative of each study site, making a total of nine sampling plots. In a case where identification was not possible in the field, a photograph was taken and the tree species were later identified by a professional Botanist.

Data collection

Direct count method was employed during data collection at the selected sites. Trees of the same species at the site were written only once on a data sheet at a site, their number or distribution from the site was distinguished in the occurrence column on a data sheet. The number of occurrences of individual species was then summed up in the frequency column. The procedure was applied to all species. After species were identified they were recorded in a data sheet. Origin of trees (indigenous or exotic) was also taken note of. Diameter at breast height (DBH) of all the trees was measured above 1.3m from the ground levels. In cases where tree trunk buttresses, the DBH was taken from the point just above the buttress, and in the case of a tree that bole branches at a breast height or below, the diameter was measured separately for all the branches and averaged as one DBH. In a case where more than one tree of the same species is found in a site, their DBH was measured all and averaged as one to avoid biases.

Statistical analysis

Trees diameter at breast height (DBH) was taken by measuring the Girth at Breast Height (GBH) of  particular tree, and divide by π (3.142). as described by (Husch et al., 2003) Mathematically as shown below:

DBH = Girth at Breast Hight/3.142

Basal area was calculated (Avery et al., 2015) by multiplying DBH² with 0.005454. Mathematically:

Basal area (BA) = 0.005454 X DBH²

Relative frequency was calculated by dividing the individual frequency by the total number of frequencies, mathematically as shown below:

Relative frequency (RF) = Individual frequency/Sum of all frequency

Relative density was calculated by dividing the number of individual species by the total number of species, mathematically as shown below:

Relative density (RD)  =   Number of individual species   X 100/Total number of individuals

Relative abundance was calculated by dividing the relative density of a species by 100, mathematically as shown below:

Relative abundance (Pi) = Relative density of a species/100

Margalef species richness index (d) was also used as a simple measure to determine species richness, according to Margalef (1958)

d = (S-1)/lnN

Where S = Total number of species, N = Total number of individuals in the site, and ln = natural logarithm

According to Shannon and Wiener (1949). Shannon diversity index was also used in analyzing the data in measuring the diversity. Shannon Wiener’s diversity index is mathematically represented as:

        S

H = ∑ – (P_i * ln P_i)

         i=1

Where H = the Shannon Wiener’s diversity index.

P_i = Fraction of the entire population made up of species i.

S = Numbers of species encountered.

∑ = Sum from species 1 to species S

Important value index (IVI) will then be calculated by summing relative frequency, relative density, and relative abundance to measure how dominant a species is in a given area (Wiryani et al., 2018). Represented as

IVI = (RD) + (Pi) + (RF)

RESULTS

A total number of 904 trees were recorded belonging to 35 different species (Table 1). These species belong to Fabaceae, Malvaceae, Combretaceae, Meliaceae, Arecaceae, Rosaceae  Rutaceae, Ebenaceae, Myrtaceae Euphorbiaceae, Moraceae, Lamiaceae, Anacardiaceae Sapotaceae, Verbenaceae families. The most abundant trees belong to three families; Fabaceae, Anacardiaceae, and Combretaceae. Fabaceae family has the highest number of individuals with ten (10) species and Malvaceae is the least with only one species (Table 1).

Table 1: List of tree species in the study area with their species code, common name and family name

KEY: The species code was formed from the combination of two first letters of generic and species name

Site-Based Species Diversity Results

Site ‘B’ has the highest species diversity, followed by site ‘A’ and lastly site ‘C’ has minimum species diversity (Table 3). Senna siamea has the highest occurrence in site ‘A’ with 130 individuals’ trees, followed by Azadirachta indica with 103 individuals, and Khaya senegalensis with 58 individuals (Table 3). In site ‘B’ Khaya senegalensis and Dalbergia latifolia recorded the highest occurrence with 32 individuals followed by Azadirachta indica with 28 trees. For Site ‘C’ Terminalia ivorensis has the maximum number of occurrences with 55 individuals, followed by Senna siamea with 45 individuals and lastly Parkia biglobosa with 8 trees as shown in Table 2.

Table 2: Total count of species within the study area

Site Based Shanon-Wierner’s Diversity Index

The results from Shanon-Wierner’s index diversity revealed that, site “B” has highest index value (H¹= 2.654435) followed by site “A” index value (H¹= 2.539791) and lastly is site “C” (H¹= 2.03297) as shown in the figure below:

Figure 1: Diversity index across the study sites

Shanon-Wiener’s Diversity Results

Results from Shanon-Wiener’s diversity shows highest abundance of Fabaceae family (H¹ = 0.36544) and the least family is Malvaceae (H¹ = 0.0345).  The rest of the results are as follows (Table 3).

Table 3: Families relative density, relative abundance and Shannon-wiener’s diversity

Keys: RD = Relative density, Pi = Relative abundance and H = Shannon diversity

Origin of the Tree Species

Trees’ species varies in origin, some are indigenous while some are exotic (foreign) as shown in Table 4. The proportion of indigenous trees to exotic within the campus is almost the same, while the origin of few species was yet to be identified (unknown), as can be seen in Table 4.

Table 4: Origin of tree species found in the study area

Species Abundance

In general, the study area (Yelwa campus), Senna siamea is dominant species with highest important value index (IVI), followed by Anogeisus leiocarpa Khaya senegalensis, Terminalia ivorense, and Gmelina arborea respectively (Table 5).

Table 5: Species with frequency, relative frequency, relative density, relative abundance and important value index

KEY: FREQ = Frequency, RF= Relative frequency, RD= Relative density, Pi= Relative abundance and IVI= Important value index.

Species Richness

The results of the study show that, in terms of species richness index, Senna siamea has the highest number accounting 28.48692 (d-index) followed by Anogeisus leiocarpa having d-index of 19.23601. The rest of the results on species richness are shown on table (6) below:

Table 6: Species richness index, species diversity with Diameter at breast height and Basal Area

KEY: d-index = Margalef species richness, H-index = Shannon-Weiner’s diversity index, DBH = Diameter at breast height and BA = Basal Area

DISCUSSION

The current study revealed that Fabaceae family was dominant in Abubakara Tafawa Balewa University Yelwa Campus. Based on the study on Diversity and Distribution of Nigerian Legumes (Fabaceae) by Abubakar et al., (2021), the Northern region of Nigeria is dominated with Fabaceae (43%) more than any other region. The university under study lies in the northern region of Nigeria hence the abundance of Fabaceae family. Similarly, the findings of our research concurred with the findings of Yilangai et al., (2023), Diversity, abundance, and conservation status of woody species in a West African dry forest, which reveals that the Fabaceae family was among the dominant families in the area, highlighting its prevalence in the region’s flora (and unsurprisingly, ATBU is situated in the same region). These findings also aligned with the study conducted by Ogunyebi et al. (2018), in University of Lagos; Assessment of tree species diversity, in which the result revealed that; the family Fabaceae had the highest frequency (14 species) representing 20.59% of total species enumerated in all the plots followed by Moraceae which consists of 7 species (10.29%).

The findings of the current study were consistent with findings of Bukar et al., (2021), which stated that Azadirachta indica and Eucalyptus camaldulensis are the most abundant species, with Faidherbia albida (a member of the Fabaceae family) having the highest basal area in University of Maiduguri Campus. This indicates a notable presence of Fabaceae species, though not necessarily dominant. Furthermore, the findings of this study were consistent to those of Bello et al., (2021), which identifies 552 taxa within the Fabaceae family in Nigeria, encompassing 540 species across 155 genera and six subfamilies. Notably, 36 of these taxa are new records for the country, highlighting previously undocumented species.

It was shown that in site “A”, Senna siamea was the predominant species than any other species. It is important to note that the site is a residential building and the plant has ornamental value, medicinal uses and some environmental benefits (Ogunkunle & Ladejobi, 2006; Bello et al., 2021). This could be the reason for the abundance of this tree species in this site as residents of this place could be keeping it to accrue the benefits that the tree offers. Research conducted by Ogunniran et al., (2024), reveals that Senna siamea leaves possess significant nutritional and phytochemical properties, including antioxidant and antimicrobial activities. These attributes enhance its utility in local communities, further promoting its cultivation.

Meanwhile, Site “B” Khaya senegalensis and Dalbergia latifolia dominated. These two species are considerably sensitive to climatic and soil conditions of a place, therefore their abundance in this area might be due to a favourable local climate and soil conditions of the area (da Silva et al., 2023). Terminalia ivorensi dominated site “C” a species that usually act as one of the pioneer tree species in disturbed areas (Whole Earth Education, 2020). Given this background the abundance this species might be a result of its colonizing capabilities of disturbed or open areas, where no trees are growing or where trees have been removed, such as Yelwa campus.

The proportion of indigenous trees to exotic within the campus is almost the same, while the origin of few species was yet to be identified (one unknown). This scenario might require attention because according to research conducted by Escobedo et al., (2011); Guerrero-Leiva et al., (2016) and in Santiago, the ecosystem services provided by native tree species with evergreen foliage are multiple, temporarily persistent, and highly demanded. Therefore, the abundance of exotic species in Yelwa campus ATBU might destabilise the proportion of ecosystem services offered by indigenous species despite the provision of ecological services that might be offered by exotic species. In Addition, there is invasive potentiality by the exotic species in case they become invasive, spreading rapidly and causing significant ecological and economic damage. The dominance of exotic species can lead to a decline in native biodiversity, affecting the ecological integrity and cultural heritage of the area, (Guerrero-Leiva et al., 2016).

CONCLUSION AND RECOMMENDATION

The diversity and abundance of tree species in Abubakar Tafawa Balewa University, Yelwa campus have been documented. The area is blessed with vegetation resources that either directly or indirectly give contribution or support life of people. The study has shined little light on many tree species within the study area and this increased understanding of tree diversity within the campus. This study provides a reference baseline for monitoring changes in diversity and abundance of tree species which is of vital importance to the ecology of green spaces of Abubakar Tafawa Balewa University.

These diverse flora species provide invaluable environmental and economic services and thus, are of great importance. Conservative measures should be put in place to checkmate their disappearance as well as promote the cultivation of more trees. Trees species that have medicinal value (such as Senna spp) should be put into intensive research to explore their potentials. Awareness and orientation should be given towards sustainable uses of trees as well as the negative effects of unlawful felling of trees to enable us to appreciate the plants in the University campus.

Government and non-governmental organizations should come together in collaboration with the university campus to mount a program on the sustenance and conservation of both the exotic and indigenous trees like Acacia sp, Adonsonia digitata, Borassus aethiopum, Ficus sp, Vitex doniana, Phoenix dactylifera, Hyphaene thebaica, etc. that are on the verge of extinction in the study area. Duplication of similar studies in different parts of Nigeria is highly recommended to understand green spaces in institutions of high learning, so as the transfer of managerial knowledge among Nigerian institutions in order to achieve sustainable development that consider conservation of trees.

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