Blair Cowie1,2, Nic Venter1, Ed Witkowski1 and Marcus Byrne1,2
1School of Animal, Plant & Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa
2DST-NRF Centre of Excellence for Invasion Biology, School of Animal, Plant & Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa
The invasive shrub Parthenium hysterophorus L. (Asteraceae) is one of South Africa’s most significant invasive plants as it poses a severe threat to national food security, native biodiversity and human health. The rapid reinvasion of P. hysterophorus in grazing, pastural and crop lands after clearing efforts remains a constant problem in managing the weed. However, native grasses may be useful as competitive and restorative species. To investigate the restoration potential of native grasses, trial patches were established in a nature reserve during the spring of 2016. 30 trial patches, each 10 m2 in size, were used and consisted of 10 sown patches with native grass seed (1g/m2), 10 non-sown patches with all P. hysterophorus cleared, and 10 non-sown and uncleared patches. Patches sown with grass seed showed significant increases in basal grass cover and grass species richness thus reducing the overall density of P. hysterophorus by more than 50%. Additionally, plots sown with native grass seeds presented significantly higher biomass as well as smaller P. hysterophorus plants when compared to those without seeds. Unsown patches which were not cleared also showcased lower P. hysterophorus densities than those which were unsown but cleared, highlighting the detriment of disturbance. This research suggests that the active restoration of P. hysterophorus invaded landscapes is feasible provided that good land management practices are employed subsequent to clearing efforts, with particular attention paid to the avoidance of overgrazing and similar disturbances.