EFFECTS OF SHORT ROTATION NATURAL FALLOW ON DIVERSITY OF PLANT SPECIES AND POPULATION OF SOIL MICROBES IN APONMU, ONDO STATE, NIGERIA

Abstract

Oke DO. 2012. Effects of short rotation natural fallow on diversity of plant species and population of soil microbes in Aponmu, Ondo State, Nigeria. Bush fallowing is a common farming system in the humid zone of West and Central Africa. However, population pressures have resulted in shortened fallow periods with consequent effects on soil nutrients and biodiversity. To assess the effect of the shortened fallow period on plant species diversity, data were collected in a primary forest (forest reserve) and an adjoining 5-year-old bush fallow in Aponmu, Ondo State, Nigeria. Four plots of 25 × 25 m each were sampled from the forest reserve and one each from four abandoned fallow lands around the forest reserve. All trees with diameter at breast height greater than or equal to 5 cm were identified. A total of 0.25 ha of bush fallow and 0.25 ha of primary forest were surveyed. Ground vegetation was assessed from a subsample of 5 × 5 m in each of the sampled area. In the 0.25 ha of bush fallow surveyed, 64 individual trees were encountered (256 trees ha^-1) representing 34.2% of the tree density found in 0.25 ha of primary forest, which contained 187 individual trees (748 trees ha^-1). A higher value of Shannon’s index (2.95) for the primary forest is an indication that it contains more variety of tree species per unit area than the bush fallow (2.37). There were slight differences in bacterial and fungal populations from the two ecosystems. This study indicated a lower number and variety of tree species under short rotation fallow. This may imply gradual loss of many of the benefits associated with trees.