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Parthenium hysterophorus L. (Asteraceae) is a noxious, annual invasive herb prevalent in more than 50 countries worldwide. In South Africa, the weed is a highly damaging invasive species, particularly in savanna regions, threatening food security, native biodiversity, livelihoods and human health. Given the multitude of threats posed by P. hysterophorus, this study aimed to determine the influence of the invasion of P. hysterophorus and its associated seedbank dynamics at a small spatial scale. To assess this, two neighbouring savanna reserves, with differing stocking densities (i.e. over- and understocked), were selected and assessed seasonally over a four-year period. Overstocking exacerbated the invasion of P. hysterophorus, with greater densities, larger plants and increased seed production, at a plot level. This enhanced invasion was also reflected in changes to the site's above-ground plant community, with significantly lower species richness, evenness, and diversity. Parthenium hysterophorus comprised more than 80% of the overstocked reserve's seedbank, and was responsible for continued declines in the richness, evenness and diversity of species below-ground. Whereas P. hysterophorus at the understocked reserve, occupied a smaller proportion of the seedbank (∼70%), with richness, evenness and diversity all showing signs of recovery over the four-year period. Overall, this research highlighted the impacts of P. hysterophorus in South Africa, as well as the potential role grazing management has in limiting or facilitating P. hysterophorus invasions and their impacts within savannas. |
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