The threat of an indigenous medicinal plant encroacher: Artemisia afra in Klipriviersberg Nature Reserve, Johannesburg, South Africa

Abstract

AbstractArtemisia afra was identified as an encroaching shrub in the Klipriviersberg Nature Reserve (KNR). Ecological factors that influence the encroachment of A. afra and its population structure were unknown, making it difficult to monitor and control the spread of the plant. This study assessed the density and size‐class distributions (SCD) of A. afra across the main habitats in the KNR (streamside, plains and ridges, with ridges divided into crest, mid‐slope and bottom slope), as well as the relationship between A. afra density and certain ecological factors. Results showed that there was a significant difference (p < 0.05) between plant density on the different habitats with the ridge and bottom slope having by far the highest density (>900 plants/ha). Canopy volume was considered the best measure for the SCD of A. afra. Overall, the population structure of A. afra displayed an inverse J‐shaped curve, indicating that despite clearing efforts and the drought of 2015–2016, it is effectively a recruiting population. Over 71% of the A. afra population were flowering, suggesting relatively rapid attainment of reproductive maturity, and high seed production. Hence, the high levels of encroachment are likely to continue. Further research on controlling A. afra with the integrated use of more intense winter fires, herbicides and the feasibility of sustainable harvesting of this medicinal plant should be undertaken. We also need a much better understanding of the regeneration ecology of A. afra in order to better control it.