Assessment of the diversity and abundance of tree species in Afe Babalola University, Ado- Ekiti, Ekiti State, Nigeria

In this study, an assessment of trees diversity and abundance in the Afe Babalola University Ado Ekiti, Ado Ekiti, Nigeria was carried out. Stratified sampling method was employed. The University was divided into four strata for adequate sampling (Stratum A, B, C, D). The results revealed a total of 816 individual trees of 21 tree species belonging to 16 families. The family Aracaceae has the highest number of species (3 (14%) species), The families of Caesalpiniaceae, Combretaceae, Verbenaceae had 2 species each, while other families (Anacardiaceae, Annonaceae, Apocynaceae, Araucariaceae, Caricaceae, Euphorbiaceae, Malvaceae, Meliaceae, Moraceae, Myrtaceae, Papilonaceae, Pinaceae families) had only one specie each respectively. The family Verbanaceae has the highest number of individual tree flora while Moraceae has the least with 1 tree stand in the study area. Gmelina arborea was the most frequently occurring tree species with a total of 472 (58%) individuals while Ficus benjamina was the least frequently occurring tree species with only 1 (0.12%) tree individual in the study area. This is suspected to be as a result of their poor establishment, thus special attention needs to be applied both to intensified efforts on planting as well as conserving the available species to avoid their extinction.


INTRODUCTION
The relevance of trees cannot be overemphasized. There are several uses of trees to man. Trees are determinants of a forest ecosystem as they considerably influence forest microclimate such as (available light, wetness, temperature). In Nigeria, (Raji and Babalola, 2018;Ihenyen et al., 2009;Keay, 1989) reported there are about 560 species of trees. Trees give oxygen, store carbon dioxide hence helps slow the rate of global warming, stabilize the soil and give life to the world's wildlife (Dwyer et al., 1992;Berman et al., 2012;Bratman et al., 2015;Lohr and Pearson-Mims, 2006;Mayer et al., 2009). They also provide man with materials for tools and shelter. They reduce wind speeds and cool the air as they lose moisture and reflect heat upwards from their leaves. It is estimated that trees can reduce the temperature in a city by up to 7ºC (Omoro et al., 2010). Trees also prevent flooding and soil erosion. Trees, apart from forming the major structural and functional basis of *Corresponding author. E-mail: mary.olanipekun@eksu.edu.ng.
Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License tropical rainforest also serve the functions of carbon sequestration, watersheds, provide shades and homes to many life forms and above all, act as purifier to the ecosystem Fuwape and Onyekwelu (2011) and (Singh, 2002). A university campus should be promoted as a model environment for sustainable development. Trees in academic institutions located in cities are part of forests resources and the trees can be used as its defining features. The presence of trees defines the landscape by their beauty and, in particular long-lived species, which can endure periodic reproductive features without direct negative demographic consequences (Suratman, 2012;Ashman et al., 2004). A higher number of tree species increases the number of ecologically niches as well as the number of associated species (Agbelade et al., 2016a;Adekunle et al., 2013;Kanowski et al., 2003;Wunderle, 1997).
Planting of trees are deliberately carried out in academic environment for reasons which including aesthetic and other environmental services (Olajuyigbe and Akwarandu 2019;Egunjobi, 1989;Babalola 2010;Martens et al. 2011).
However, trees have undergone different levels of disturbance due to unprecedented increase in human population which have led to cutting of trees for firewood collection, charcoal production, and infrastructural developments (Omoro et al., 2010).
To protect trees from declining, it is essential to examine the current status of species diversity, composition and abundance this will provide guidance for their management and valuable reference for assessment as well as improve knowledge in the identification of ecologically useful species. Therefore, the main objective of this study is to assess tree diversity and abundance in Afe Babalola University, Ado-Ekiti campus with the view to providing baseline information useful to development and conservation of the tree species in the study area. Thus, such information will be useful for tree managers seeking to maximize species diversity and the environmental benefits provided by trees.

MATERIALS AND METHODS
The study was conducted in the campus of Afe Babalola University, Ado-Ekiti, Ekiti State, Nigeria. Afe Babalola University is geographically located in Ado-Ekiti (Latitude 7º40'N and Longitude 5º18'E). Ado-Ekiti has two climatic seasons-a rainy season and a dry season, the rainy season lasts for about eight months and the dry season for about four months. The annual rainfall is about 1150mm.

Survey of trees species on campus
A stratified sampling technique was used in this study, the entire Afe Babalola University Campus was divided into four strata and each stratum was further sub divided into sub-strata. All the trees within each of the sub-stratum were counted and identified to species level with their scientific authentication, local and family names with the assistance of the curator in the Herbarium unit of the Department of Plant Science and Biotechnology as well as with the aids of tree identification guide books, including Tropical Tree Crops (Okpeke, 1987), Trees of Nigeria (Keay, 1989), Flora of West Tropical Africa (Hutchinson and Dalziel, 1968) and Useful Plant of West Tropical Africa (Burkill, 1985(Burkill, , 1995(Burkill, , 1997(Burkill, , 1994(Burkill, , 2000. Voucher specimens of the identified trees species were equally prepared and deposited at the herbarium unit. The names of the trees were recorded for all the strata and sub-strata and its number of occurrence were determined. Frequency of occurrence, relative frequency, Shannon-Weiner index, and Simpson diversity index and species evenness was calculated for each stratum, sub-strata and for the entire sampled area.

Data analysis
The data collected during the tree survey were analyzed and calculated using different indices such as Shannon and Wiener, Simpson diversity and species evenness. Statistical analysis was carried out using Statistical Package for the Social Sciences (SPSS 20.0).

RESULTS AND DISCUSSION
This study described the taxonomy, diversity, and environmental relevance of tree flora in Afe Babalola University, Ado-Ekiti, Ekiti State. Diverse tree species were identified and collected at this higher institution of learning. Field observation revealed a total of 816 tree flora spread across 21 tree species belonging to 16 families in this study area (Table 1). The results obtained revealed that the abundance and diversity of trees in the academic area of this University were high. This may be attributed to provision of an aesthetic environment and beautification of the landscape for students, staff and other inhabitants of the University. The study revealed that the family Arecaceae has the highest number of 3 (14 %) species (Table 1). These results corroborate the assertion of Ogwu et al. (2016) on the abundance and diversity of trees in University of Benin. This family mainly occur in tropical and subtropical regions, with most genus and species found in Asia, Indonesia, and the Americas.
Also, the predominance of this family may be as a result of its great economic importance. The poor establishment of some trees under the families (Moraceae, Papilonaceae), could be attributed to anthropogenic activities that both endangered, unsettled and negatively target these families. This was supported by the reports of Wardle et al. (2004), who recorded that anthropogenic activities affected the establishment of certain families of trees and placed them at more risk of extinction if not properly and intentionally conserved. Other members of the family in the campus include Cocos nucifera, Acrocomia aculeata, Phoenix dactylifera and Mauritia flexuosa.
The Arecaceae family was closely followed by the Verbenaceae and Combretaceae families. These were well known for their economic and medicinal purposes as
Similarly, the results of relative frequency, relative diversity and relative abundance of the tree species surveyed in strata A, B, C and D were observed in the Tables 5 to 9 respectively. G. arborea has the highest relative frequency in all the four strata with 60.75 in strata A, 36.67 in strata B, 38.10 in strata C, and 60.18 in strata D. This is followed by E. camaldulensis, in strata A with 8.35 relative frequencies, T. grandis in strata B with 10.67 relative frequencies, A. cunninghamii in strata C with 15.24 relative frequencies, and C. nucifera in strata D with relative frequency of 8.85. It was also observed that G. arborea has the highest relative density in all the four strata, with 72.16 in strata A, 37.00 in strata B, 37.25 in strata C, and 59.41 in strata D. It was followed by E. camaldulensis in strata A with a relative density of 8.24, T. grandis in strata B with 11.00 relative density, A. cunninghamii in strata C with 14.71 relative density and C. nucifera in strata D with 9.00 relative density. Similarly, G. arborea has the highest relative abundance in all the four strata, with a relative abundance 0.72, 0.37, 0.37, 0.59 in strata A, B, C and D respectively, followed by E. camaldulensis with relative abundance of 0.08 in strata A, Tectona grandis with relative abundance of 0.11 in strata B, A. cunninghamii with relative abundance of 0.15 in strata C while C. nucifera with relative abundance of 0.09 in strata D.
Most of the trees planted in ABUAD were exotic breed, information from the respondents revealed that the residents of the campus could not ascertain the reason for this, however, the planting of exotic breeds forms a trend as reported by Alfred et al. (2014) who found that exotic species flourished and grew more rapidly from the period of emergence to the maturity of the plants. G. arborea is an economic plant that was used to construct various furniture works. Also, G. arborea tree was used to carve out a lion throne, the last surviving of the eight royal thrones of myañmar, now in the national museum of Yangon Ma (Thanegi, 2017). Amazingly, a few tree species such as C. papaya, F. benjamina and a few others however had a total count of less than five stands in the whole of the study area, the reason for this is suspected to be their poor establishment, thus special attention needs to be applied both to intensified Table 4. Frequency of occurrence of the identified tree species in ABUAD campus.

Rank
Tree species Number of Individual (%)
Azadirachta indica 2.34 11. efforts on planting as well as conserving the available species to avoid extinction of the species. The study also revealed the poor establishment of some trees under the families (Moraceae, Papilonaceae), this could also be attributed to anthropogenic activities that unsettle and negatively targets these families, this school of thought agrees with Wardle et al. (2004) who also recorded that anthropogenic activities affected the establishment of certain families of trees and placed them at more risk of extinction if not properly and intentionally conserved.

Conclusion
This study found out that most of the trees planted in the University campus were exotic breed. The distribution of trees in the study area could be based on specific needs of the University system as well as its relevance to the resident living on campus (such as noise attenuation, landscaping and beautification, cooling). The relevance of trees is very important as it encourages all the beneficiaries of services of the trees to become involved in preservation and conservation of trees. However, special attention must be paid to trees that are not easily established such as F. benjamina and others to prevent their extinction. The study also revealed the poor establishment of some trees such as F. benjamina, and D. latifolia under the families (Moracaceae and Papilonaceae respectively) this could be attributed to anthropogenic activities that unsettle and negatively targets these families, this is in accordance with the work of Wardle et al. (2004) who reported that anthropogenic activities affected the establishment of certain families of trees and placed them at more risk of extinction if not properly and intentionally managed and conserved. Therefore, the tree compositions on Afe Babalola University Campus could be described as relatively available and well diverse. However, there is need to  properly and adequately handle and conserve the trees so as to ensure its continuous availability as the need arises.

CONFLICTS OF INTERESTS
The authors have not declared any conflicts of interests.