Active restoration in South African fynbos – A long-term perspective from the Agulhas Plain

Abstract

In 2019 we re-surveyed a site on the Agulhas Plain, South Africa, which had been part of a restoration project conducted in 2008. The site was invaded by invasive trees, mainly Australian Acacia species. In the original restoration program, the site had been burned and various treatments (i.e. sowing of competitive, fast-growing native species) were conducted to determine the effectiveness of different restoration strategies. The sowing of native species to assist the recovery process is defined as an active restoration method, whereas passive restoration only removes stressors for the ecosystem (e.g. removal of the invader) and leaves it to recover by itself. For this study, we conducted a vegetation survey at the previously restored sites and compared them with a nearby reference site where no intervention had taken place and which is characterised by near-pristine native fynbos vegetation. Secondly, we compared the new data from 2019 with older data from 2010. However, a decade after the initial restoration effort, both active and passively treated plots had not achieved the same condition (species richness, diversity, evenness) as the reference site. The results also show that active restoration is most likely unnecessary in fynbos restoration projects where there are nearby patches with native vegetation or the existing native seed bank is of sufficient size. It seems that it is more important to prevent the reinvasion of invasive alien plants so that the vegetation can recover over time without further disruption.

Keywords:

• Biological invasions
• Invasive alien species
• Monitoring
• Restoration ecology
• Tree invasions

Acknowledgements

Thanks to the Grootbos Foundation and Flower Valley Conservation Trust, including all their members, for providing vital information and for helping in other ways with this project. DMR acknowledges support from the DSI-NRF Centre of Excellence for Invasion Biology and the Millennium Trust.