A checklist of angiosperm diversity surrounding Awba Dam: an important reservoir in Ibadan, Nigeria

The present study undertakes an enumeration of the existing flora species around Awba dam, located within the University of Ibadan, Ibadan, Nigeria. Methods followed conventional practice as reported by previous authors of related studies. Findings showed that the study area is very rich in biodiversity. A total of 119 species in 47 families were recorded. The large number of species recorded, especially herbs which contribute 37% of the total enumeration suggest that the site may be further accessed for medicinal plant species which could possess beneficial health properties. Nonetheless, the presence of fauna and phytoplankton species also indicates their role in ecosystem balancing and thus sustaining human livelihood. With the continuous developmental activities, practical conservation approaches is ideal if the study area is to be saved from total loss of species.


Introduction
Assessment of biological diversity in a particular area has continued to be of interest to scientists around the world. Nigeria, with numerous flora and fauna species, has been faced with challenges to species conservation, gradually leading to total disappearance of these human sustainers (plants and animals). Several authors have documented the existing angiosperm species in some parts of the country (Soladoye et al., 2005;Soladoye et al., 2011;Ariwaodo et al., 2012;Ayodele et al., 2013), and with particular reference to their medicinal values (Gills, 1992;Adesina et al., 1995;Schmidt, 1996;Soladoye & Oni, 1996;Okoli et al., 2007;Odugbemi, 2008;Soladoye et al., 2012). Gbile et al. (1978) recorded 492 plant species in 112 families to be threatened, and in 1981 they compiled 480 rare plant species. Oguntala et al. (1996) reported 85 endangered tree species for Cross River State and its environs. As put by Valdecasas & Camacho (2003), the value of any biodiversity analysis and the adequacy of conservation measures depend on the quality of basic data. The data for biodiversity and conservation however, is mainly taxonomic. Much has been discussed about the phytoplankton and water quality of Awba reservoir (Akin-Oriola, 2003; Anago et al., 2013;Okeniyi et al., 2013;Tyokumbur & Okorie, 2013), but little is known about the rich angiosperm diversity which this important dam accommodates. With the recent threats resulting from the depletion of ozone layer, deforestation activities and rapid rate of urbanization, it has become imperative to constantly conduct biodiversity assessment of our forests and the entire ecosystems. This work thus takes into account, the existing flora species around Awba dam, located within the University of Ibadan, Ibadan, Nigeria. It also highlights the importance of some identified plant species and discourages further habitat destruction by the university community, to checkmate species extinction.

Study area
Awba dam reservoir is located at the south-western end of the University of Ibadan. It was constructed in 1964 by draining the Awba stream and impounding the water at a point where it flows through a natural valley. It lies on latitude 7°26'N and longitude 3°53'E, and at an altitude of 209 m above sea level (Fig 1). The ISSN: 2348ISSN: -1900 Horizon e-Publishing Group Reservoir has a surface area of 6 ha. According to Ugwumba (1990), the Reservoir is 8.3 m high, 110 m long with a crest of 12.2 m high. It has a maximum depth of 5.5 m and a maximum length of 700 m. It can hold about 230 million litres of water (Omotosho, 1981). The mean daily air temperature is 24.6°C. The reservoir is noticeable by two seasons: the wet and dry seasons. Rainy season occurs between April and October while the dry season is between November and March. The water level in the Reservoir is regulated at a spill-way through which excess water flows out so the level remains almost constant throughout the rainy season. However, during the dry season, the water level Reduces.

Species enumeration
The study was initiated in June, 2013 and completed in October, 2014. Field collection of plant species occurring at 50 meters distance on both sides of the dam was documented. The species were identified using the taxonomic keys provided in Hutchinson et al. (1954Hutchinson et al. ( -1972, Lowe & Stanfield (1974), Lowe (1989), Keay (1989) and comparison with previous collections deposited at Forest Herbarium, Ibadan (FHI) (Holmgren et al. 1990). Scientific names were checked and verified from the International Plant Name Index (IPNI) website (http://www.ipni.org). The species were thereafter carefully documented, along with their families, habits and local name(s) with which they are known within the study area.

Results and Discussion
A total of 119 angiosperm species belonging to 47 families were recorded from the enumeration. These constitute trees, shrubs, herbs and climbers.  (Table 2). This is closely followed by Asteraceae (8 species; 6.7%), Moraceae and Papilionaceae with 7 species each (5.9%). However, a total of 4 families were represented with 5 species each, 3 families had 4 species each, 2 families had 3 species each, 10 families had 2 species each while the remaining 24 families were represented with one species each. The occurrence of these families with single species is a reflection of their role in ecosystem maintenance. Observations also showed that the Legumes generally contributed the largest number of species (Papilionaceae -7; Caesalpiniaceae -5; and Mimosaceae -4). Of these 16 legumes, 8 (50%) were trees while the remaining 8 comprises shrubs (3), herb (1) climber and creepers (2 each) as shown in Table 1. The presence of these taxa is noteworthy, and as nitrogen fixers, may be said to be responsible for the high fertility nature of the soil around the study area, which has continued to be reliable in the cultivation of several food crops especially vegetables and tubers.
Further results based on the life forms of these plant species also revealed that the study area is dominated by herbs, trees and a number of shrubs. The herbs constitute 44 species (37%) of the entire enumeration while the trees contribute 35 species (29%) and the shrubs, 20 species (17%). Nonetheless, climbers and creepers were also recorded, with 14 species (12%) and 6 species (5%) respectively (Fig 2). It is also interesting to note that of all the 47 plant families identified, the herbs are dominant, and are represented in 22 of these angiosperm families, followed by the trees in 18 families and the shrubs in 11 families. The climbers and creepers are also represented in 10 and 5 families respectively as shown in Fig 3. The avalanche of species, especially herbs, as recorded in this work is an indication that the study area is home to many plant species that could be screened for medicinal properties, thus reflecting the biodiversity richness of the study area and the University community at large. These plants have overtime been collected by the local people and used in the traditional treatment or management of ailments ISSN: 2348ISSN: -1900 Horizon e-Publishing Group and have also been reported by some authors of medicinal plants studies such as Gills (1992), Odugbemi (2008) and Soladoye et al. (2012) to mention but a few, while a number of them are also consumed as food in one way or the other. Some of these include: Blighia sapida, Carica papaya, Mangifera indica, Spondias mombin, Talinum triangulare, Vernonia amygdalina etc. Some of the plants identified in this work have also been earlier reported by Ayodele et al. (2013) to be occurring within the zoological garden of the University, where they occur ex-situ. This therefore justifies the importance of plant species in the maintenance of ecosystem and as a source of livelihood for man. Paramecium, Brachionus, Anuraeopsis, Diaphanosoma, Macrocyclops etc in the study area. All these in collaboration, ensures that the study area remains a functional ecological system. However, our rich biodiversity is fast disappearing owing to several human activities as earlier mentioned. The fact that some habitats have been disturbed, either in whole or in part, does not mean that we cannot reinstate them or minimize the adverse effects posed from the current developmental activities. This point was stressed by the Association of Conservation Biology workshop. They noted that it is important to understand that protecting biological diversity, as a practical matter, is independent of the pursuit of the Holy Grail of "pristine". Just because a system is not pristine does not mean that it has no value for conservation. The task of conservation is not to preserve some ideal pristine nature; rather, its task is to protect diversity as noted by Arne (1992). Edwin-Wosu and Edu (2013) also pointed out clearly that, for conserving biodiversity, it is fundamental to arrest the loss of natural plant resources by adopting proper conservation strategies and protection of natural regeneration of plant species.

Conclusion
This research reveals that the surrounding ecosystem of Awba dam and Nigeria's ecosystems in general, are important sources of food, raw material, medicine and items of trade for mankind. They hold a great potential to transform the nation's agricultural system and contribute to health care improvement. But on the contrary, our species are gradually disappearing. Findings from this work reiterate the fact that, practical conservation of the entire biodiversity especially the flora species existing within and outside the study area is very crucial if species extinction is to be averted, and ecosystem balancing is to be maintained. It may be proper to suggest a close monitoring of the study area to avoid indiscriminate habitat destruction by the inhabitants, visitors to the dam and the entire university community. Consequently, the University management has a great role to play if these goals are to be achieved.

Competing interests
The authors declare that they have no competing interests.

Authors' contributions
ECC and TAA initiated the research, and participated in its design and coordination. ECC identified the plant species while the two authors drafted the manuscript. ECC performed the statistical analysis. All authors read and approved the final manuscript.