Secondary Invasions: Implications of Riparian Restoration for In‐Stream Invasion by an Aquatic Grass

Abstract

The complex nature of ecosystems with multiple invaders requires whole-system approaches to ecosystem management. Undesirable, unintended secondary effects may occur if interspecific interactions are ignored. Although degraded riparian zones urgently need effective restoration, broad-scale removal of introduced tree species (e.g., willows [Salix spp.]) and fencing of riparian zones to exclude livestock may facilitate spread of the invasive aquatic grass Glyceria maxima in southeastern Australia. We recorded occurrence of the grass at riparian sites with different amounts of woody vegetation, including willows, and monitored spread for 2 years in locations with and without livestock. Glyceria maxima occurred more frequently at sites with little or no woody riparian vegetation.Larger, older patches fenced from livestock spread fastest. Analyses of costs of controlling G. maxima with herbicide showed that it is more cost-effective to eradicate small patches than large patches if locations are known. However, the cost per m 2 reduction in patch size is cheaper for larger patches. We recommend that small, young patches should be eradicated as soon as detected and show that spread of large source patches can be controlled effectively with continued spraying over several years. If restoration of waterways is to succeed, riparian management strategies must recognize connectivity between riparian and freshwater habitats.

Impacts of an invasive willow (Salix × rubens) on riparian bird assemblages in south-eastern Australia

“…Riparian plant invasions can have large impacts, but removing them sometimes may have unintended harmful or unpredictable consequences (Fleishman et al . 2003; Loo et al . 2009).…”

Integrating Nonnative Species in Niche Models to Prioritize Native Fish Restoration Activity Locations along a Desert River Corridor

“…However, given the current constraints to complete ecosystem restoration (e.g., human water needs, nonnative fish and vegetation), provision of a more natural flow regime alone is unlikely to recover populations of native fish (Suding et al 2004;Propst et al 2008). Restoration activities aimed at improving habitat for native species may inadvertently increase suitability for nonnative species (e.g., Loo et al 2009;Korsu et al 2010), potentially increasing the negative effects of nonnative species. For example, our model predicts that the restoration of riffle habitat in reach 178 would to lead to a decrease in Flannelmouth Sucker abundance, a decrease likely resulting from a predicted increase in nonnative fish abundance following riffle enhancement.…”

Freshwater biodiversity conservation through source water protection: Quantifying the potential and addressing the challenges

“…(ii) impacts on native riparian plants, birds, and mammals from livestock exclusion (by fencing); and (iii) impacts on stream ecosystem condition from livestock exclusion. Studies generally confirm the value of excluding livestock from streams, reducing grazing intensity, and providing livestock with alternative water sources (Ellison, Skinner, & Hicks, 2009;Jansen & Robertson, 2001;Sievers et al, 2017); however, the degree and scope of benefits may be localized and overwhelmed by larger catchment land uses (Magierowski, Davies, Read, & Horrigan, 2012;Ranganath, Hession, & Wynn, 2009), and exclusion may also facilitate the establishment and spread of invasive plant species (Loo, Mac Nally, O'Dowd, & Lake, 2009). The effects of intensive grazing may also persist over many years after the removal of livestock, and recovery times for species will depend on a variety of factors (such as dispersal ability) (Homyack & Giuliano, 2002).…”