The dispersal and spread of invasive alien Myrtillocactus geometrizans in the southern Karoo, South Africa

The invasion of Cactaceae into semi-arid and arid ecosystems in South Africa is of conservation concern, particularly those species that produce juicy fruit that attract avian frugivores. Bird-dispersed Bilberry Cactus (Myrtillocactus geometrizans) is invading natural areas around the village of Prince Albert and appears to have originated from a cactus collection that was established about 40 years ago, and from there has spread locally over an area of about 1 km(2). We surveyed the invaded area, recording a GPS point and size data for each of 156 Bilberry Cactus plants. The height-class distributions of Bilberry Cactus plants recorded in our survey suggest that recruitment is episodic rather than continuous or annual, with clearly defined invasion, or survival events. As this cactus species matures slowly and recruits episodically, the rate of the invasion has been slow. However, the presence of suitable pollination and dispersal mutualists and indigenous shrubs that serve as protective host plants suggest that the populations will continue to grow and spread unless controlled. Moreover the large size of mature Bilberry Cactus plants is likely to have a negative effect on the small endemic succulents that share the same host plants. (C) 2018 SAAB. Published by Elsevier B.V. All rights reserved.