Orchard Understory Species Diversity in Relation to Orchard Age and Soil Factors (in Ibadan, Southwestern Nigeria)

The relationship between species richness and environmental variables enhances valid conclusions on the effect of biodiversity on ecosystem processes. Extant literatures exist on the relationship between species richness, a measure of biodiversity and ecosystem functionality. Therefore, this study examined understory plant species diversity of Citrus orchards (Citrus sinensis) between the young (twenty years) and the old (forty years) in relation to soil parameters. Direct method of gradient analysis was used whereby sample plots were randomly located and marked at the study site and understory plant species per unit area recorded and categorized. A set of 30 quadrats and 39 quadrats were taken in the young and old orchards respectively. The collected data in the undergrowth were subjected to an ecological analysis. The data were analyzed using Simpson’s index, student T-test and canonical correspondence analysis (CCA). The result of the diversity index showed that the older orchards had greater species dominance than the younger ones. The t-test shows a significant difference between orchards (t = 0.03, P = 2.27). The placement of environmental variables in CCA showed that the first gradient (that is, the main explainable variation in floristic composition) was positively correlated with pH, total nitrogen and negatively with clay content.