First assessment of naturalised Rubus ellipticus Sm. populations in South Africa - A potential invasion risk?

Abstract

The first naturalised Rubus ellipticus populations are described from KwaZulu-Natal, South Africa. Surveys were undertaken at five sites in Hillcrest, during which site specific distribution data were collected. Plant density estimates were calculated by dividing the number of plants per polygon area at each site. Basic physiological data such as plant height and number of stems were recorded at three of these sites (n=399).We recorded 422 plants in total, and site-specific plant densities were below 30%. Only 6 % of the population sampled had flowers, and the shortest flowering individual measured 0.9m. The tallest individual recorded was 3.5m. Distribution data from the largest population (n=329) were mapped, and results showed that some seedlings occurred more than 10m away from the nearest adult, which could be attributed to dispersal of the seeds by birds, indicating a minimal level of spread. The initial weed risk assessment score of 21 indicates a high potential invasion risk to South Africa, and the bioclimatic modelling map highlighted 2% of the country as being highly suitable climatically for the species. Our study indicates that R. ellipticus can be considered at an early stage of invasion in South Africa (C3 classification), and we support its current legal categorisation as a category 1a plant invader and eradication-target species. We propose that implementation of an eradication programme would entail removal of all existing populations, monitoring and evaluation of clearing efforts, rapid response to new populations detected, and targeted awareness campaigns and surveys in high risk areas identified in the bioclimatic modelling map.