Abstract
Invasive alien plants are a major global threat to biodiversity and ecosystem function, particularly in regions of high endemism. Effective control of these species often relies on herbicides, yet their impacts on non-target vegetation in biodiversity-rich ecosystems remain poorly understood. This study assessed the effectiveness of various herbicides in controlling invasive alien species and the potential impact of the herbicides on surrounding non-target fynbos (Mediterranean shrubland) vegetation. Three sites invaded by Pinus , Acacia , and Eucalyptus were selected, where seven treatments were implemented per site, namely two controls (Untreated and Manual clearing) and five herbicide treatments (Imazapyr, Glyphosate, Picloram, Triclopyr, and Metsulfuron-methyl). Vegetation assessments were conducted in ten quadrats per treatment plot over 259 days. Clearing invasive trees resulted in increased abundance of non-target vegetation functional groups, including grasses, broadleaves, and indigenous shrubs and trees. When cut-stumps were treated with herbicide, only eucalypts coppiced. Vegetation cover initially declined post-clearing but later recovered in treated plots, whereas the Untreated control saw continued suppression by invasives. Herbicide bioassays further indicated an absence of biologically active residues in the topsoil. The accumulative change in vegetation cover over time highlighted significant trends in treatments despite site variability. Metsulfuron-methyl, Triclopyr, Picloram, and Glyphosate were the most effective treatments for invasive suppression, vegetation recovery, and environmental sustainability. While Imazapyr showed high efficacy, its environmental impact made it less favorable. These findings enable responsible herbicide use in conservation-driven invasive species management.