Invasiveness of Calliandra calothyrsus in Ruhande Arboretum in Rwanda

Many plant species are known to be invasive, with power to subdue others plant species within their proximity. The objective of this study was to assess the invasiveness of Calliandra calothyrsus, one of the popular agroforestry shrubs at the Ruhande Arboretum in Rwanda. Using Geographical Positioning System (GPS), we marked the plots where C. calothyrsus was planted. For each of the C. calothyrsus plots, coordinates were recorded once at its centre. Linear transects were established perpendicular to C. calothyrsus plots in the four cardinal directions to where the plots extended to the neighboring plots. It was observed that although total area originally planted with C. calothyrsus was 2.75ha the area invaded totaled to 1.4ha. The dispersal distance in invading other species was greatest in the square plots, followed by the perpendicular lines, and the least is single line planting. The invasion rate in neighboring plots planted with other tree species varied depending on species, being the highest in Eucalyptus spp. and the least in Araucaria cunninghamii. These results shows that the rate of invasion of C. calothyrsus biodiversity of Ruhande Arboretum is threatened by the invasion of C. calothyrsus as it increases is exponentially, thus threatening biodiversity at Ruhande Arboretum. The species should be managed cautiously and future, if necessary, should be far from more susceptible species like Eucalyptus. Key words: Araucaria cunninghamii, Calliandra calothyrsus, Rwanda