The invasive alien Hypericum canariense in South Africa: Management, cost, and eradication feasibility

Abstract

The shrub Hypericum canariense L. (Hypericaceae) is an emerging invader in several parts of the world. In this study we determined the current invasive distribution in South Africa, assessed soil seedbanks, determined size at reproduction, and evaluated the current management protocols. We further assessed the feasibility of eradication and provide recommendations for control. In South Africa H. canariense is considered a rare ornamental and naturalised populations have escaped cultivation at ten localities in the Southwestern Cape and one in the Eastern Cape. In total, 9 populations are in disturbed areas – mostly along roadsides and informal dumping sites – but three populations are within protected areas. Once established, H. canariense forms large persistent seed banks with between 20 and 2040 seeds/m2. It resprouts after cutting, with about half the plants resprouting if no herbicide or 3% Garlon (Ismapyr) is applied. If 2% Hatchet (Triclopyr) is applied, resprouting still occurs, but resprouting is significantly lower. Annual follow-up clearing is required to control resprouting and seedlings and should continue for an estimated 10 years until the seedbank is exhausted. We estimate that initial clearing of the naturalised populations of H. canariense would take 20 person days and from thereon 4.5 person days per year for the following 10 years to eradicate this species from South Africa. The initial cost of clearing all populations in South Africa will amount to ZAR2400, with a total cost for eradication estimated at ZAR25000. We recommend management efforts to eradicate this species and list it as 1a on the National Environmental Management: Biodiversity act (NEM:BA, Act 10 of 2004).