Abstract:
The Cape Floristic Region of South Africa is a global biodiversity hotspot threatened by
invasive alien plants (IAPs). We assessed the effect of plant invasions, and their subsequent
clearing, on riparian arthropod diversity. Foliage-active arthropod communities were
collected from two native and one invasive alien tree species. Alpha- and beta- diversity of
their associated arthropod communities were compared between near pristine, Acacia-invaded
and restored sites. Arthropod alpha-diversity at near pristine sites was higher than at restored
sites, and was lowest at invaded sites. This was true for most arthropod taxonomic groups
associated with all native tree species and suggests a general trend towards recovery in
arthropod alpha-diversity after IAP removal. Overall, arthropod species turnover among sites
was significantly influenced by plant invasions with communities at near pristine sites having
higher turnover than those at restored and invaded sites. This pattern was not evident at the
level of individual tree species. Although arthropod community composition was significantly influenced by plant invasions, only a few significant differences in arthropod community
composition could be detected between restored and near pristine sites for all tree species and
arthropod taxonomic groups. Assemblage composition on each tree species generally differed
between sites with similar degrees of plant invasion indicating a strong turnover of arthropod
communities across the landscape. Results further suggest that both arthropod alpha- and
beta- diversity can recover after IAP removal, given sufficient time, but catchment signatures
must be acknowledged when monitoring restoration recovery.
