Using iNaturalist to determine invasiveness of Melaleuca species in South Africa
Woody invasive alien plant species can have a wide range of negative impacts from displacement of plant species to negative impacts on water resources and degradation of agricultural land. The genus Melaleuca comprises of a number of fast growing tree species that are invasive in different regions/areas of the world. For example M. quinquenervia, which is native to Australia, has been widely introduced into tropical regions of the world where it can become invasive with negative impacts. Melaleuca species are relatively recent additions into South Africa where they have been planted in gardens and along roadsides since at least the 1980s. Reports of invasions are now being recorded, for example for Melaleuca rugulosa, and M. hypericifolia. Data was collected for all Melaleuca species reported in iNaturalist. In 2023, in total there were 3 221 records from across the country. Following filtering of uncertain records, a total of 2 815 records were left comprising of 26 species in total. Before this study, for 5 of the species, there was no information on their invasive potential in South Africa. For each of the 26 species, an Invasiveness Index was calculated for each municipality. The Invasiveness Index was used to determine which areas have the highest risk of invasion. Cape Town had the highest number of records. 56 % of the records in the city of Cape Town were recorded as casual (cultivated) and 43 % were naturalised. The species with the highest invasion potential were M. rugulosa, M. armillaris, M. hypericifolia, M. styphelioides, and M. quadrifida. These species can be the focus of management efforts to mitigate any spread into natural areas.
Sources
Potgieter LJ, ter Huurne MB, Richardson DM (2024) Community science can inform invasive species management: Melaleuca (Myrtaceae) in South Africa. Ecological Solutions and Evidence 5, https://doi.org/10.1002/2688-8319.12391