An inventory of woody and herbaceous invasive alien plants in Thohoyandou Botanical Garden, Limpopo Province, South Africa

Abstract

Species migration out of their local range into new zones by people has brought about the rise of biological invasions. Exotic or non-native species need to conquer various boundaries to establish, naturalize, produce localized self-supporting populations, and in the end spread naturally before they are considered as invasive. These invasive alien species are currently perceived as key drivers of human’s instigated global change as they have negative impacts on biodiversity, ecosystem services and human prosperity which makes the investigations on invasive species imperative to direct approach plan and management important. This study was motivated by the need to control invasive alien plants in protected areas and this inventory of invasive alien plants (IAP) marks the first step in creating baseline data for managing invasive alien plants in the garden. Protected areas are threatened by the impacts of invasive alien plants that invade them and Thohoyandou Botanical Garden is no exception. Invasive alien plants are the second greatest threat to biodiversity worldwide and estimates suggest that invasive alien species cost the country over R 6.5 billion per year. The study aimed to document the woody and herbaceous invasive alien plant species in Thohoyandou Botanical Garden in the Vhembe District. Three belts of 100 m x 500 m were constructed and within them quadrats of 10 m x 10 m were randomly constructed. All the invasive alien plant species were identified and grouped as per their growth forms. Their impacts on the adjacent native species were investigated and their health status identified using a sliding scale of 1 – 5, where 5 is healthy and 1 is unhealthy. All the data were stored in Microsoft Excel and later analyzed using One-way analysis of variance(ANOVA) was also used to compare mean frequency count and mean height between invasive and native species. Data was analysed through the Microsoft Excel programme. This study has shown that invasive species have the potential to reduce native species at a rate of 2.92 species per every 40 invasive species, on average. Thus, for every 40 invasive species that are found in any chosen area within Thohoyandou Botanical Garden, an average of 3 native species will be lost as a result. These results have a very strong implication in that they can guide management and control strategies aimed at ensuring that the impact of invasive species on the growth and survival of native is kept to minimal levels.