Project Team Leader: Dr. Paul P. Bosu
Background
Broussonetia papyrifera (paper mulberry, PM) is a non-native invasive woody plant which was deliberately introduced into Ghana in the late 1960’s in an attempt to utilize it for industrial scale production of pulp and paper. After a lag period of about 25 years B. papyrifera emerged as a serious woody invasive species in the landscape of Ghana. Current estimates put distribution at between 50,000 - 60,000 km2 of the closed forest region. It seriously threatens the regeneration of native species and succession processes in degraded forest areas wherever is found. It is also a weed of significant proportion in farms, tree and cash crop plantations throughout the forest regions of Ghana. The species is also gradually becoming established as a dominant vegetation in the transition forest zone.
The transition zone is a unique ecosystem in Ghana and forms a corridor between the deciduous forest regions of the south and the savannah woodland ecosystems of the north. Additionally, a small stand of B. papyrifera was recently discovered along the bank of the Red Volta near Bolgatanga in the Guinea Savannah zone. This stand is believed to have survived from previous abortive attempts to introduce the species in the north.
The objective of the study was to assess the effect of B. papyrifera invasion on community characteristics in the forest transition ecosystem. The study was carried out in and around the Afram Headwaters Forest Reserve (AHFR) from March 2008 to April 2009. This location was chosen because of the high density of PM stands in and around the reserve. The studies included comparative and removal experiments. In each plot, the relative percent cover of PM, Chromolaena odorata, grasses and shrub or herbaceous species was estimated to the nearest 5 percent. At the transition site, removal of PM resulted in a doubling of cover by the vegetation guilds, with C. odorata becoming the dominant vegetation in the absence of PM. However, in the forest site PM removal increased the regeneration of indigenous herbaceous species at the expense of C. odorata or grasses. Furthermore, relatively more indigenous species were lost than recruited in the removal plots at the transition site compared to the forest site.
The results suggest that control of paper mulberry in invaded forest stands may be justified to promote natural regeneration in the forest zone. On the other hand, the presence of PM may actually lead to increased regeneration in the transition forest zone and this observation supports previous observations. This study was executed under a British Ecological Society Overseas Bursary Fellowship (OBF1428/1798).