Biodiversity at all scales is intensely threatened by human actions, making it one of the most vital aspects of the worldwide environmental difficulty. Human activities have already resulted in all time losses of biodiversity through the extinction of many species and the loss of unique, natural communities. Ecologist forecast that unless there is significant difference in the way human affect ecosystems, there will be greater losses of biodiversity in the near future (Dawson et al., 2011).

In the past one decade, the complex problems surrounding biological diversity or biodiversity arise when it was recognized that there were many more species on earth that scientist had yet described, and that the rate of extinction of species far exceeds the rate of their preservation. The need to conserve them as a foundation for sustainable development becomes very important. As the global loss of biodiversity has been increased in not too distant past, awareness has improved of the potentially disastrous consequences of this trend for the earth’s ecological purpose and achievement of basic human development needs (Pereira et al., 2010).

The University of Agriculture, Abeokuta, having realized that, the conservation of the genetic variability of the native angiosperm community is very important, set aside 20 km² out of 97.3 km² land mass as a nature reserve.

Biodiversity can be protected in strict nature reserve, ecological reserves, etc. These are areas created for the conservation of natural values, usually the known habitat of endangered species, threatened ecosystem, or representative samples of widespread communities (Shotuyo, 2011, unpublished data).

The study area is contained in the 9,700 hectare land of the University of Agriculture, Abeokuta, situated north-eastern of Abeokuta, along Alabata road (Figure 1 and Figure 2). The site is located between latitude 7° and 7° 58′ and Longitude 3° 3′ and 3° 37′. Generally, the site gently undulating with mild slopes but punctuated in part by ridges, isolated residual hills, valleys and lowlands, all of which present a good landscape for aesthetics.
 

There is a general drop in elevation from the eastern to the western part towards Ogun river flood plain where the seasonal stream network within the sitew empties their content. Six soil series have been identified in the area. These are Egbeda series (Oxic paleudults), Asejire series (Typic psammaquent), Iregun series (Oxic ustropept), Balogun series (Psamentic hapludults), and Iwo series (Oxic paleudalts). The soil is mainly sandy to sandy loam with medium depth underlain by crystalline basement complex. The soils have low to moderate organic matter and essential nutrients (National Research Council (U.S.) and Board on Science and Technology for International Developmen, 1992).

1 Result
A hundred and eighteen (118) plant species (Table 1) being members of fifty-three families were found to constitute the major vegetation of the study site. The Gramineae contain the most number of species (nineteen) followed by Papilionaceae (nine) and Euphorbiaceae with eight species (Table 2). The predominance of the appearance of the species of Gramineae and particularly Papilionaceae could be attributed to the climatic condition, soil type and the seed dispersal mechanism of members of the family. Thirty-one shrub species (Table 3) were collected indicating the modification of the vegetation to a derived savannah ecosystem. Most of the plants encountered have simple leaves indicative of primitiveness as simple leaves were believed to have evolved earlier than compound leaves (Radford et al., 1974). Also the solitary inflorescences were observed in most cases. Dicotyledons accounts for more than 80 percent of the ecosystem (Figure 3). Tress like Blighia sapida, Cordia milllenii and Daniella olliverri etc., provides shades and comforts in quite many parts of the Nature Reserve.
 

2 Discussions
The loss of many plant species as a result of human activities is diminishing the world’s genetic resources and is endangering man’s heritage of biodiversity. Therefore, there is  no doubt to preserve genetic diversity including plant resources of known and unknown economic benefit which will ensure the availability of all potentials for sustainable use (Olowokudejo, 1987). The exploration of economic development and improvement of the life conditions must consider the resource restrictions and the situation of future generation must be considered in terms of carrying capacity of ecosystem. It demonstrates the importance of modern conservation. It is obvious that because they are precious global resource, biological diversity must be accorded, be indexed, used sustainably and preserved well. Three facts make it important for unprecedented urgency particularly in West Africa. Firstly, the environmental destruction is serious due to astronomical increase in human populations at a dangerous rate. Secondly, science is unraveling better uses for biological diversity in ways of alleviating both human troubles and environmental destruction. Thirdly, lots of the diversity are being irreversibly disappeared and may be extinction caused by the habitat destruction, which is widespread in Africa than elsewhere (Wilson, 1988). Dasman et al (1973) agreed that forest exploitation leads to the extinction of animals and plants whose genetic resources are of considerable value to present and future generations (Frankel, 1970). Forest depletion has resulted in the natural environment destabilization and genetic resources erosion throughout the southern part of Nigeria in order to meet the population sustenance and financial requirements of government i.e. the social, economic, demographic and political needs (Soladoye et al., 2005). Therefore, it is inevitable to exploit the forests. Opinions are divided however on vegetation depletion which is considered as a loss of natural heritage (Soladoye et al., 2005). Harvey and Hallet (1977) posits that it may not be profitable to preserve natural resources for descendants in any case because it is inadequate to state the future requirements, aspirations, lifestyles and needs of rural people now. Should we be waiting for the needs to be stated before we take action? Definitely not because all of these genetic resources would have disappeared before the needs are exactly stated (Soladoye et al., 2005). Hence, conservation is paramount to human welfare and has close relationship to human survival (Allen, 1980). Absence of conservation measures will result possibilities in an increasing number of endangered species and this will ultimately lead to elimination, which is the gradual but sure extinction of taxa (Allaby, 1998). The risk of eventual extinction is the most severe problem for many of the species that are already endangered if human beings do not pay attention to activities such as land development, logging and pollution. Gbile et al (1981a, 1981b) revealed that about four hundred and eighty plant species of the Nigerian flora have been described as endangered or rare, out of which many of these are being studied at the Forestry Research Institute of Nigeria, Ibadan. Apart from the gradual loss of biodiversity, the devastating environmental disasters in urban and rural areas of Nigeria indicate that these environments are under going on in the campus it is therefore a commendable deep scientific conclusion that the University deemed it fit to set aside a portion of its land mass as a nature reserve which will allow the vegetation to revert to climax status for posterity. This is the usual practice in most advanced parts of the world.

3 Materials and Methods
The study involved numerous visits to the site for samples collection. Specimens were collected through the vegetation of the nature reserve. Samples were dried, poisoned and mounted in line with conventional herbarium practice. Solvents employed in poisoning were ethylated spirit, cyanide gas, Paradichlorobenzene (PCDB), 2% mercurichloride, and naphthalene (Okoli et al., 1992). Identification of the specimens was done by comparison with herbarium specimens in the Department of Forestry and Wildlife, UNAAB Herbarium, the Forest Herbarium, Forestry Research Institute Ibadan (FRII) and the University of Ibadan Herbarium (UIH). Specimens were deposited at the Department of Forestry and Wildlife, UNAAB Herbarium.

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