Unassisted invasions: understanding and responding to Australia’s high-impact environmental grass weeds

Abstract

Abstract. Alien grass species have been intentionally introduced into Australia since European settlement over 200 years ago, with many subsequently becoming weeds of natural environments. We have identified the subset of these weeds that have invaded and become dominant in environmentally important areas in the absence of modern anthropogenic disturbance, calling them 'high-impact species'. We also examined why these high-impact species were successful, and what that might mean for management. Seventeen high-impact species were identified through literature review and expert advice; all had arrived by 1945, and all except one were imported intentionally, 16 of the 17 were perennial and four of the 17 were aquatic. They had become dominant in diverse habitats and climates, although some environments still remain largely uninvaded despite apparently ample opportunities. Why these species succeeded remains largely untested, but evidence suggests a combination of ecological novelty (both intended at time of introduction and unanticipated), propagule pressure (through high reproductive rate and dominance in nearby anthropogenically-disturbed habitats) and an ability to respond to, and even alter, natural disturbance regimes (especially fire and inundation). Serious knowledge gaps remain for these species, but indications are that resources could be better focused on understanding and managing this limited group of high-impact species. They require new management approaches, especially to counteract the advantages of ecological novelty, reduce propagule pressure and better direct the large-scale disturbance regimes that continue to shape plant communities across Australia.

Lag times and invasion dynamics of established and emerging weeds: insights from herbarium records of Queensland, Australia

“…A similarity of long lag phases in trees and grasses, despite differences in life form and generation time is thus perplexing (see also Sutherland 2004). It is plausible that because members of both groups were intensely introduced simultaneously in late 19th and early twentieth centuries (Cook and Dias 2006;van Klinken and Friedel 2018), the subset of introduced grass species that evolved with time to become high impact invaders (e.g. grader grass [Themeda quadrivalvis], hymenachne [Hymenachne amplexicaulis] and Aleman grass [Echinochloa polystachia]) have followed similar high spread trajectories as that of the trees-seemingly encouraged by ecological novelty (unprecedented human-mediated changes at different ecological levels), high propagule pressure and ability to respond to and even alter natural disturbances of fire and inundation (van Klinken and Friedel 2018).…”

Ranking buffel: Comparative risk and mitigation costs of key environmental and socio‐cultural threats in central Australia

“…Non‐native grasses in general threaten the integrity of vast areas of Australia (Firn et al., 2015; van Klinken & Friedel, 2018), yet their control and the recognition of their impact represents a chronic policy failure (Downey et al., 2010; Godfree et al., 2017). Unlike other key threats that have largely realized their potential ranges and impacts, buffel continues to rapidly spread beyond the 68% of the continent previously considered suitable for its establishment (Lawson, Bryant, & Franks, 2004) as evidenced by its invasion of new habitats and climates (Hobbs, Naby, & Schutz, 2015; Tschirner, Gibbs, & Heap, 2016).…”

“…Whereas other serious weeds of central Australia, like Tamarix aphylla and Parkinsonia aculeata, are outcompeted by established natural vegetation or are largely restricted to agricultural or disturbed areas with enhanced water or nutrient availability (Grice & Martin, 2006), buffel is an aggressive invader of many Australian arid and semi‐arid zone habitats (Fensham, Wang, & Kilgour, 2015; Firn et al., 2015; van Klinken & Friedel, 2018). Buffel directly suppresses (Abella, Chiquoine, & Backer, 2012; Eilts & Huxman, 2013) and threatens the persistence of many native plants (Clarke et al, 2005; Edwards, Schlesinger, Ooi, French, & Gooden, 2019; Eyre, Wang, Venz, Chilcott, & Whish, 2009; Fairfax & Fensham, 2000; Friedel et al., 2006) including threatened species (Griffin, 1993; Jackson, 2005).…”

Germination biology, distribution and control of the invasive species Eragrostis curvula [Schard. Nees] (African Lovegrass): A global synthesis of current and future management challenges

“…Following these assessments, it was not included in the top 32 but was still deemed to be a significant threat to Australian biodiversity (Navie and Adkins, 2007). A recent study by Van Klinken and Friedel (2017) found that E. curvula within Australia is a high impact species but only in the localised communities where it is found, not nation- (Csurhes et al, 2016;Sharp, 2011). For Queensland and Northern Territory, it is not prohibited but there is a general biosecurity duty to remove and eliminate the species where practical to minimise any potential spread (Csurhes et al, 2016).…”

“…Following these assessments, it was not included in the top 32 but was still deemed to be a significant threat to Australian biodiversity (Navie and Adkins, 2007). A recent study by Van Klinken and Friedel (2017) found that E. curvula within Australia is a high impact species but only in the localised communities where it is found, not nationally. The management of the species is mandated by the relevant state or territory government within Australia.…”