Re-evaluation of a riparian restoration experiment in the Western Cape Province: Status 8 years down the line

Abstract

In 1998, a study was initiated to assess the relative effectiveness of three different sowing treatments for reducing soil erosion and restoring indigenous riparian vegetation cover after alien clearing in the Western Cape. The study concluded that introducing a mixture of seed to a riparian zone with a history of invasion can increase indigenous vegetation cover and species richness and has a stabilizing effect on eroded riverbanks. We report on a reassessment of the restoration plots after a period of 8 years (with no follow up control) and a summer fire in 2005. The re-assessment included a survey of all the burnt woody material within the different treatment plots to determine species presence (dead or resprouting) and abundance, as well as a survey of seedlings in a post-fire environment. Woody invasive plants (IAPs) dominated all plots, and had survived the burn with the majority re-sprouting, indicating the dire need for follow-up control to justify initial clearing and restoration cost. However the re-assessment revealed that indigenous vegetation cover was considerably higher in the plots that had received sowing treatments, while the control plots were dominated by Acacia mearnsii, the main invader of the tributary. Restoration of riparian areas after alien plant clearing has potential, but must be coupled with a long-term plan for follow up removal of post clearing IAP recruits.