The impact of Broussonetia papyrifera (L.) vent. on community characteristics in the forest and forest-savannah transition ecosystems of Ghana

Following its introduction in the late 1960s, Broussonetia papyrifera L. Vent. Moraceae (paper mulberry) has emerged as a major exotic invasive species in Ghana's forest ecosystems. This study was carried out to assess the effects of B. papyrifera invasion on community composition in forest and forest-savannah transition ecosystems. Comparative and removal experiments were conducted in paired B. papyrifera invaded versus uninvaded plots. In the comparative assessment, species composition was found to be similar in both invaded and uninvaded plots. However, relative per cent cover of resident species and guilds including Chromolaena odorata, indigenous broadleaves and indigenous grasses were significantly lower in invaded plots. Seven months after B. papyrifera was experimentally removed from invaded stands, cover by indigenous broadleaves increased by 35%, as against only 5% in control plots at the forest site. However, at the transition site, the increase in per cent cover of indigenous broadleaves (18%) was not significantly different from control (2.5%) plots. We conclude that B. papyrifera has the capacity to reduce the abundance of indigenous broadleaf species, although its removal is more likely to favour regeneration in a forest than a forest-savannah transition ecosystem. Resume Suite a son introduction a la fin des annees 1960, Broussonetia papyrifera L. Vent., une Moraceae (murier a papier), emerge comme une espece exotique envahissante majeure dans les ecosystemes forestiers du Ghana. Cette etude avait pour but d'evaluer les effets de l'invasion de B. papyrifera sur la composition des communautes dans les ecosystemes de forets et de transition foret-savane. Des experiences comparatives et par enlevement ont ete menees par paires dans des parcelles envahies par B. papyrifera et des parcelles non envahies. Dans les evaluations comparatives, on a trouve que la composition des especes etait semblable dans les parcelles envahies et non envahies. Cependant, le pourcentage relatif de la couverture des especes et des guildes residentes, y compris Chromolaena odorata, des mono- et des dicotyledones indigenes, etait significativement plus faible dans les parcelles envahies. Sept mois apres avoir experimentalement arrache B. papyrifera de peuplements envahis, la couverture de dicotyledones indigenes avait augmente de 35%, contre 5% seulement pour les parcelles de controle dans le site forestier. Cependant, sur le site de transition, l'augmentation du pourcentage de couverture des dicotyledones indigenes (18%) n'etait pas significativement differente de celle des parcelles de controles (2,5%). Nous en concluons que B. papyrifera est capable de reduire l'abondance d'especes de dicotyledones indigenes mais que son arrachage est plus susceptible de favoriser la regeneration dans une foret que dans un ecosysteme de transition foret-savane.