Geerts and J. R. Mangachena
Department of Conservation and Marine Sciences, Cape Peninsula University of Technology, Cape Town, South Africa
When invasive alien trees are removed, ecosystems are usually left to “self-repair”. Little is known about the extent of recovery or whether plant and animal taxa respond similarly over time. In most cases, the absence of a historical condition makes it more difficult to measure restoration success and a flexible approach is usually followed using practical target communities. We explored these questions by sampling bird and plant assemblages after the removal of invasive trees, using a chronosequence (time-for-space substitution) approach. We used the Berg River as a case study, one of the most invaded riparian systems in the Cape Floristic Region of South Africa. Study sites – cleared of Eucalyptus camaldulensis in 2005, 2007, 2008 and 2014 – were sampled in 2014 and compared to invaded and near-pristine areas. In total 27 native plant species (four trees, six shrubs, seven forbs, four geophytes, and two vines) and 28 alien plant species (four trees, three shrubs, eleven herbs, and seven graminoids) from 50 genera and 31 families were recorded across all sites and years. Cleared sites had higher total plant species richness compared to invaded and near-pristine sites, but significantly lower canopy cover. 2049 birds from 52 species were recorded across all sites and years. A decade after clearing, bird species richness, abundance and composition partially recover as some species are still lacking and assemblages are not yet comparable to near-pristine sites. This is probably due to the lower abundance and diversity of native trees in cleared sites, which could be important as a habitat or food source for specialist birds in an agricultural landscape. We conclude that monitoring of cleared sites is vital to evaluate recovery and to determine the need for further management interventions.