Secondary invaders in riparian habitats can remain up to 10 years after invasive alien Eucalyptus tree clearing

Abstract

After the clearing of invasive alien plants, non-target alien species often move in. This is known as secondary invasion and these alien species can suppress native plant species’ recovery. This is a global problem that has only recently received attention in South Africa. But whether secondary invaders in riparian areas have similar effects than those in more terrestrial areas is largely unknown globally and in South Africa. Therefore, here we ask which species and growth forms are associated with secondary invasion in riparian areas in the Fynbos biome, and secondly whether secondary invader species richness changes over time post clearing. We found 13 secondary invader species in a riparian area after clearing of alien invasive Eucalyptus trees. In the first year after clearing, there were only annuals, but thereafter it was a mix of annuals and perennials (shrubs, herbs, and graminoids). Secondary invader richness did not significantly differ with time after clearing, persisting even up to 10 years. In this riparian area, secondary invader species richness was much lower than that for non-riparian Fynbos areas. From this preliminary study we highlight the need for more research in understanding how secondary invaders influence restoration efforts and native species recovery in riparian systems.