18 October 2024 | By Dr Luke Potgieter and Prof Dave Richardson
In a recent study, Dr Luke Potgieter (C·I·B postdoctoral research fellow), Michele ter Huurne (former C·I·B MSc student) and C·I·B Professor David Richardson used data from the popular community science platform, iNaturalist to assess the distribution and invasion ecology of Melaleuca species across South Africa.
Invasive species pose a significant threat to ecosystems worldwide, and non-native trees and shrubs are among the most damaging of invaders. Community science initiatives, where the community contributes biodiversity observations, are proving to be game changers for detecting and managing these biological invasions. Platforms like iNaturalist allow community members to report sightings of and organism, and these data can be vital for shaping strategies to control invasive species.
Melaleuca L. (bottlebrushes, paperbarks and tea trees in the family Myrtaceae is a genus, native to Australia, that includes several commonly planted garden and street trees in South Africa. Melaleuca species have been present in South Africa for about 150 years and have been widely cultivated for over 50 years. However, in recent years, they have started to spread beyond gardens into natural areas, raising concerns about their impact on local ecosystems.
By September 2023, there were over 3,200 records of 26 Melaleuca species in the country, with around 2,800 confirmed as reliable after filtering. Melaleucas were found in all provinces across the country, with some growing wild, indicating naturalisation — a key step toward becoming invasive. An “Invasiveness Index” (the ratio of the number of wild-growing records to the total number of records) was developed to show which species are already invasive or have substantial invasion debt.
The study found that 32% of the records were of wild-growing (naturalised) Melaleuca species, with the City of Cape Town being a hotspot for the occurrence of wild-growing melaleucas . This is particularly worrying as invasive melaleucas can significantly disrupt local ecosystems, potentially requiring costly control measures. Importantly, iNaturalist data provided new insights on five Melaleuca species that were not previously known to be invasive in South Africa. The data could also be used to select a series of “sentinel sites” (e.g., Table Mountain National Park) for detecting new sites of naturalisation or invasion. These findings highlight the value of community science in identifying and tracking invasive species early, before they cause widespread harm. The study emphasizes the value of these data in informing management practices and in helping to prevent or mitigate the impacts of invasive species on local biodiversity.
Read the paper
For more information, contact Luke Potgieter at lukepotgieter2@gmail.com
