Effects of road and woodland type on the invasibility of woodlands invaded by Lantana camara in southern Africa

Abstract

The susceptibility of a plant community to invasion is influenced by multiple factors including the characteristics of the invading species and the invaded environment but how road presence and woodland type affect invasibility in woodlands invaded by Lantana camara (hereafter, lantana) in southern Africa is not well known. We identified roads adjacent to miombo, Vachellia (hereafter, vachellia) and mixed woodlands. Parallel to each road, we laid two transects (200 × 30 m) and replicated them twice, one adjacent to the road and another in the interior. In each transect, we laid 5 plots (30 × 20 m), making a total of 60 plots (3 woodland types x 2 transects x 2 replicates x 5 plots). Our sampling plan yielded six woodland clusters: roadside vachellia, interior vachellia, roadside miombo, interior miombo, roadside mixed and interior mixed. Road presence increased invasibility in all clusters but was more pronounced in less diverse miombo and vachellia than in more diverse mixed woodland. Interior mixed woodland was 1.4 and 1.8 times more diverse than interior miombo and interior vachellia woodlands, respectively; whereas roadside mixed woodland was twice more diverse than roadside miombo and roadside vachellia. Invasibility in the interior mixed woodland was 19% and 24% lower than in the interior miombo and interior vachellia, respectively; whereas in the roadside mixed woodland, it was 19% and 21% lower than in roadside miombo and roadside vachellia, respectively. We found a negative diversity-invasibility relationship in all clusters. Vachellia woodlands had significantly higher soil C, N, P and K concentrations than miombo but were equally susceptible to lantana invasion. Collectively, our findings suggest that high diversity rather than low soil nutrient status might be more important in hindering plant invasion. We emphasize the importance of conserving native diversity in roadside habitats to reduce the success of invading plant species.