Abstract:
Alien invasive plants (AIPs) are major drivers of biodiversity loss, and roads often act
as effective corridors for their spread. This study analysed long-term changes in AIPs
along the Bakwena N4 Toll Route, South Africa, using annual audit data collected
between 2011 and 2024. Biodiversity indices and statistical analyses were used to
assess rates of change, identify persistent invasion hotspots, and predict future trends.
The study further compared invasion dynamics between the open, grass-dominated
Marikana Thornveld and the denser woody Savanna vegetation types along the route,
examined patterns across urban, peri-urban, and rural land-use zones, and evaluated
the influence of vegetation quality and soil type on AIP presence. Results showed clear
contrasts between land-use zones and vegetation structures. Urban areas displayed
fluctuating but broadly stable AIP counts, with no significant long-term decline,
suggesting continued reinvasion linked to disturbance. Peri-urban areas remained
persistent hotspots, supporting high diversity and richness despite management
interventions. Rural areas showed significant reductions in AIP densities, although
diversity trends were more variable, indicating ongoing species turnover. Plots within
the more open Marikana Thornveld differed from those in the other, generally more
wooded or structurally complex vegetation types, indicating that vegetation structure
may influence invasion patterns along the route. Degraded vegetation quality was
strongly associated with invasion hotspots, while soil type showed limited explanatory
power. Similarity and dissimilarity indices revealed high turnover in urban
assemblages, relative stability in peri-urban environments, and gradual compositional
shifts in rural areas. The findings indicate that management has reduced AIP densities
in rural sections of the route, but has been less effective in urban and peri-urban areas.
Persistent reinvasion in disturbed areas highlights the need for targeted, adaptive
management. Sustained monitoring, restoration, and context-specific interventions will
be important for maintaining ecological integrity along the Bakwena N4 Toll Route.
