Assessing success in attempts to eradicate an emerging invader plant: Tephrocactus articulatus (Pfeiff.) Backeb in arid areas of South Africa

Abstract

Tephrocactus articulatus (Pfeiff.) Backeb (family: Cactaceae) is an emerging invader plant that is native to Argentina and was introduced as an ornamental plant in South Africa. The South African national regulations and legislation for controlling biological invasions dictate that emerging alien species must be eradicated. We evaluated the effectiveness of foliar spray in clearing the populations of T. articulatus, and determined the management challenges in 16 representative sites. We also applied bioclimatic models to forecast how T. articulatus invasion might respond to climate change. The exposure to climate change forecasts for T. articulatus was quantified using the Intergovernmental Panel on Climate Change - IPCC (2014) two representative concentration pathways – RCP scenarios (4.5 and 8.5) for the 2061–2080 period. Overall, the foliar spray method significantly suppressed T. articulatus populations in all sites (i.e., 75–99%) except in four sites that did not display the population suppression threshold of X ≥ 75%. The clearing success (i.e., % of dead plants), was significantly and negatively correlated to the size of the site (ha) wherein the bigger sites had relatively low success. Climate suitability projections under the RCP4.5 and RCP8.5 scenarios for T. articulatus produced excellent data fits (i.e., training AUC = 0.939 and test AUC = 0.914). Noteworthy, both future scenarios model projections have shown an expansion of suitable habitat for T. articulatus: 49.9% and 60.4% respectively, of the current estimated total spatial coverage of 219102 km2, and with possible expansion into neighbouring countries, Namibia and Botswana. The significant variation in the projections was contributed by precipitation in the wettest (47.5%) and warmest quarters (48.9%). Our results advance the importance of predictive models in planning optimisation in the management of emerging alien plant species in South Africa: if the ongoing eradication of T. articulatus in the core invasion areas fails, and climate change prevails, a switch from foliar spray to biological control method will be essential.