Invasive potential of Melaleuca parvistaminea in South Africa and the need to assess invasive potential of dry-seeded Myrtaceae
Llewellyn Jacobs1,2,3, Dave Richardson2, John Wilson2,3
1 Scientific Services, CapeNature, Private Bag X5014, Stellenbosch, 7599
2Centre of Excellence for Invasion Biology, Department of Botany and Zoology, University of Stellenbosch, Private Bag X1, Matieland, 7602
3Invasive Species Programme, South African National Biodiversity Institute, Private Bag X7, Claremont, 7735
Melaleuca parvistaminea Byrnes (Rough-barked Honey myrtle) was first brought to SANBI's ISP attention in 2009. Here we describe the survey and management of the population (the first record of an invasion for this species in the world). As yet not all areas have been searched exhaustively. We have found over 13 000 plants spread over 372 ha (condensed canopy area of ~0.73 ha) at 3 sites between Tulbagh and Wolseley, in the Western Cape. Population structure indicates considerable spread by seed with at least 63% of plants being seedling or juvenile. Clearing and fire trigger seed release causing prolific recruitment (up to ~18 000 seedlings/m2) after winter rain. No evidence for a soil stored seed bank was found. Risk assessment shows significant invasive potential, while bioclimatic niche modelling indicates high suitability in the southern Cape region. Plants however only reproduce at 5 years or older, allowing for sustained clearing efforts before juveniles can set seed.
Initially, this serotinous reseeder was identified as Melaleuca ericifolia Sm. (Swamp paperbark), a sister taxon, but examination of morphology and reproductive characters led to revised identification, highlighting the need for taxonomic work on new detections.
Given the potential for the species to dominate wetland habitats, we propose that this species should be listed as a target for compulsory control (i.e. eradication). We estimate eradication would currently cost ~R1.6 million.
There are several other invasive melaleucas in South Africa, and we briefly discuss current management and research efforts on each. Building on this work, we propose an MSc- project looking at a detailed assessment of dry-seeded Myrtaceae—assessing the factors that determine success at each stage of invasion at a global scale; evaluating which species are present in South Africa and which pathways these are associated with; and exploring the mechanisms underlying invasiveness in the ornamental genera Melaleuca and Callistemon.