Ecological Characteristics That Enhance Broussonetia papyrifera’s Invasion in a Semideciduous Forest in Ghana

Broussonetia papyrifera (L.) Vent. (Moraceae) was introduced to Ghana in 1969 and has since become second only to Chromolaena odorata as an invasive species in Ghanaian forests. This study determined its ecological traits that enhance its invasion of plant communities. Fruiting and viability patterns were studied through monthly monitoring of 985 trees (≥6？cm gbh) in one forest site. The effect of light on its seed germination was tested in light-proof boxes. Means of propagation were determined by tracking the origin of newly regenerated plants on a newly cleared plot of land that B. papyrifera had occupied. It fruited twice a year with one season (January–March) producing more fruits than the other (July-August). Fruiting occurred in trees as small as 9？cm？gbh but the percentage of individuals fruiting in each size class increased with tree size. There was a clear pattern of seed viability during the January–March fruiting period. The species did not appear to have a naturally high seed viability with germination always below 50% of each weekly collection. Seed germination was depressed in dark. These results suggest that the species may be competitive in disturbed forest sites and therefore its spread may be aided by forest degradation. 1. Introduction Of the important factors responsible for biodiversity loss in Ghanaian forests, species invasion is the least cited and investigated. This is despite the fact that the invasion of Chromolaena odorata for instance has been recorded in Ghana since 1972 [1] and is known to drive critical forest processes including fires [2]. Besides C. odorata another invasive species that has come up strongly is Broussonetia papyrifera, [3] a medium-size tree of the Moraceae family widely grown for paper production and native to Japan and Taiwan [4]. The species was introduced to Ghana by the Forestry Research Institute of Ghana (FoRIG) in 1969 to form part of an experimental programme to identify species for the local production of industrial cellulose [5]. It was planted in three forest reserves in the semideciduous forest zone on a trial basis, namely, Afram Headwaters, Bia-Tano, and Pra-Anum. From these three sites it has spread and invaded large canopy gaps and degraded farmlands in many parts of the forest zone. Its invasion has been most remarkable in the north west subtype of the moist semideciduous forest presumably due to its highly noticeable forest fragmentation. Viable populations of the species are found as far north as Dormaa Ahenkro near the Ghana-Cote d’Ivoire border. However, beyond the semideciduous