Secondary invasion: The need for a proper river restoration management plan

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Sheunesu Ruwanza

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Effective ecological restoration following alien plant removal requires detailed monitoring to determine the success achieved through different interventions. However, unintended secondary invasion by alien plants may occur, thus affecting the native species recovery trajectory. Between 2011 and 2017, vegetation recovery was monitored on riparian sites along the Berg River in the Western Cape, South Africa, that were cleared of Eucalyptus camaldulensis in 2010 using two clearing methods (fell-and-stackburn and fell-and-remove) and two restoration approaches: passive and active. In 2011, significant increase in vegetation cover (P < 0.001) and diversity (P < 0.05) of secondary invaders, mostly alien grasses and herbs was recorded in both passive and active restoration sites. Although native vegetation cover and diversity increased six years later, the increase in the cover of woody invasive alien plants was observed. Only four of the nine native species that were planted to fast-track restoration were still present, but the abundance of these native species was significantly (P < 0.001) lower in 2017 than in 2011. The study concludes that although native vegetation recovery following E. camaldulensis removal is following a positive recovery trajectory, the reinvasion by secondary invaders has the potential to slow down and halt the recovery process. Management interventions that prioritizes removal of secondary invaders are required. Such interventions may include removal of reinvading invasive alien plants during follow-up monitoring, seeding fast growing native species that can out compete secondary invaders, and soil nutrient manipulation soon after clearing to reduce growth of secondary invaders.

Resource Type:
Audio/Video, Conference Presentation, SER2019

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Society for Ecological Restoration