Restoration of riparian systems through clearing of invasive plant species improves functional diversity of Odonate assemblages

Abstract

Riparian systems are threatened globally, but contribute disproportionately to biodiversity and ecosystem function. Restoration to reverse their loss is costly, and requires careful monitoring and evaluation. Odonates are amongst the most reliable arthropod bio-indicators for monitoring riparian ecosystems. Despite functional diversity (FD) reflecting ecosystem pattern and processes better than taxonomic diversity, Odonate FD has yet to be used in evaluating riparian conservation and restoration outcomes. We surveyed 45 sites across six river-systems in northeastern South Africa, to compare Odonate FD and standardised effect size of Odonate FD (sesFD) in riparian systems that had been invaded by alien plants, cleared of alien invasives, and sites that had never been invaded (15 sites each). Although species richness did not differ between treatments, Odonate sesFD was lower in invaded sites than those that had been cleared of alien riparian vegetation and those that had never been invaded. Clearance of 40% of alien riparian vegetation was associated with sesFD greater than that of invaded sites by almost two standard deviations. Representation of traits varied between treatments but was similar between cleared and natural sites, suggesting that invasion by alien plants directly impacts food webs, and that clearance can restore ecosystem processes and ecological services. This study confirms that Odonate FD can respond to restoration efforts. Secondary impacts of restoration to complete suites of functional groups can be anticipated to enhance ecological services and impact food webs at a range of scales.