Floristic indicators of tropical landuse systems: Evidence from mining areas in Southwestern Nigeria

Abstract

Most forests in the tropics have not only been reduced in size but have also experienced forest degradation. The delicate balance of the components of the forest ecosystem has been altered largely by the landuse systems which have resulted in the disappearance of some species and the introduction of new ones. In order to understand the influence of human disturbance caused by artisanal mining on plant biodiversity and the physical environment, this study assessed changes in vegetation characteristics using plant functional groups, such as invasive, pioneer and understory species. The study was conducted at two sites in two Southwestern states of Nigeria, Itagunmodi in Atakumosa West Local Government Area of Osun State and Olode in Oluyole Local Government Area of Oyo State. Complete enumerations of woody, non-woody and herbaceous plant species were carried out in 20 m by 20 m plots selected using stratified random sampling as representative of landuse classes: freshly mined (<6 months), abandoned mine (>6 months) and a control plot (secondary forest). The results showed that the control plot in Itagunmodi had undergone degradation as indicated by the presence of Alchornea laxiflora, Geophilia obvallata, Musa sapientum,Elaeis guineensis and Keetia hispida. However, if left undisturbed, it has the potential of regeneration back to its original state because of its woody tree species composition and lianas (Triclisia gilletii). In addition the forest soils in the mines had been exposed to direct insolation for a long period, and the soil structure and texture have been affected, consequently altering the viability of the seed bank. Poaceae and Papilionoideae were the most common in the freshly mined plots while invasive species were the most common in abandoned mined plots. In conclusion, the floristic composition in the mining sites has been altered and there was no clear evidence that regrowth would bring restoration of the lost ecosystem services.