Tree species Diversity in the Department of Forest Resources Management, University of Ibadan, Nigeria

Abstract

Trees, which are important for the sustenance of life and the health of our planet, are disappearing at an alarming rate. Consequently, the need for actions to develop effective strategies to conserve them is receiving considerable attention worldwide. Forest genetic resources are fast becoming depleted in most natural forests due to the pressures of deforestation, urbanization, poor management and a regeneration programme that is virtually nonexistent. In Nigeria, the impacts of climate change will further aggravate the plight of many indigenous and exotic tree species as climatic variability may limit the ability of forest trees to quickly adapt to the changing climate. The huge presence of various indigenous and exotic tree species on the University of Ibadan campus and the fact that some of these trees are no longer found in most natural forests underscores the potentials of the campus as an important live gene bank. There is little or no information on the taxonomy, diversity and growth characteristics of many of the trees on campus. This information is very important for their conservation and sustainable management. There is therefore, an urgent need for their identification, conservation and management.
An inventory of trees (>10cm diameter at breast height (dbh)) growing within the premises (~1.2ha) of the Department of Forest Resources Management (DFRM), University of Ibadan, Nigeria, was conducted as a case study of the species quality (richness and diversity) and quantity (volume) found on the University campus. The trees were identified to species level and the total height, merchantable height, canopy cover, diameters at the base, breast height and top of each tree was measured and volume calculated. The health status of trees was visually assessed based on the presence or absence of disease symptoms and pest attack. Data were analysed using descriptive statistics. A total of 27 species from 15 families were identified with Eucalyptus torrelliana F.V. Muell. and Gmelina arborea Roxb. representing 19% and 18%, respectively. A mixture of 14 indigenous and 13 exotic tree species was found within the study area including some threatened indigenous species such as Milicia excelsa (Welw) C. Berg. and Khaya grandifolia Thompson. The mean total height, merchantable height, volume and dbh were 15.57 ± 0.73m, 9.11 ± 0.57m, 6.68 ± 1.10m3 and 44.58 ± 3.58cm, respectively. Eleven percent of the trees were in a ‘very good’ state of health (i.e. no signs or symptoms of pest and disease attacks) while 4% were in a ‘bad state’ (major leaf defoliation, leaf galls, growth of epiphytes and stem rot). It was also observed that only 16% of the trees had straight boles while others had crooked and epicormic branches. The study indicated high species variability within a small area of 1.2ha. There is a need for policy intervention to aid the identification, documentation and conservation of forest genetic resources in the University.

Keywords: Species diversity, University of Ibadan campus, Climatic variability, Tree health