Impacts and Best Management Practices for Erect Veldtgrass (Ehrharta erecta)

Abstract

Erect veldtgrass (Ehrharta erecta Lam.) is an invasive grass actively spreading in California that is capable of invading multiple habitats. Our objective is to contribute to a better understanding of the ecology, impacts, and potential for control of E. erecta in order to guide management practices. In a mixed-evergreen forest in Santa Cruz County, we measured impacts of E. erecta on native plant species richness and abundance in an observational comparison across 11 sites. Strikingly, we measured nearly four times greater total vegetation cover in plots invaded by E. erecta. However, native plants were not significantly less abundant in invaded plots than in reference plots, and native cover was not significantly predicted by E. erecta cover within invaded plots. We did, however, find evidence of change in community composition in response to E. erecta abundance. Our findings demonstrate that native species can persist in the presence of E. erecta, although the long-term impacts on populations of the perennial plants that dominate this forest understory are still unknown.We also compared the effectiveness of mechanical (hand pulling with volunteers) and chemical (glyphosate) management methods. Twenty-two months following management treatments, we found substantial reductions in E. erecta using both mechanical and herbicide treatments, but herbicide application also produced greater reductions in native species cover and species richness. Transplanting native yerba buena [Clinopodium douglasii (Benth.) Kuntze] into management plots following treatment did not slow regrowth of E. erecta. It did, however, increase total native plant percent cover in herbicide and pull treatments, although largely by increasing C. douglasii cover. Effective management is possible using either manual or chemical removal methods; the optimal method may depend on the availability of manual labor and the sensitivity of the habitat to non-target effects on native plants.

Evaluating the efficacy of removal treatments on wavyleaf basketgrass (Oplismenus undulatifolius)

“…The least effective treatments were fluazifop plus fenoxaprop (0.21 kg ai ha −1 fluazifop þ 0.06 kg ai ha −1 fenoxaprop), imazapic (both 0.09 and 0.18 kg ai ha −1 ), quizalofop (0.05 kg ai ha −1 ), and sulfometuron methyl (0.11 kg ai ha −1 ). This variation in treatment effectiveness corroborates the findings from others for similar invasive grass species (Enloe et al 2018;Flory 2010;Ray et al 2018), further highlighting the need to test several treatments before widespread removal.…”

“…Despite the potential for invasive plant control and native community restoration, several factors can lead to unsuccessful outcomes. Invasive removal strategies that are not thoroughly tested can prove ineffective (Abella 2014;Ray et al 2018;Tu 2000). Control strategies can even exacerbate the invasion if the invader has high compensatory growth at low densities, leading to higher reproductive output (Ruiz-Navarro et al 2013).…”

“…Treatment methods themselves can also cause direct negative effects on native species, highlighting an important component of management decisions. Chemical removal methods have been shown to drive down native species richness and cover immediately after control, and this decline may last several years (Harmoney et al 2007;Louda et al 2005;Ray et al 2018;Rinella et al 2009;Skurski et al 2013). We know little regarding what factors drive the high variability in native plant responses, yet many studies continue to quantify management effectiveness without investigating the native response (Abella 2014;Kettenring and Adams 2011).…”

“…Several reviews on the topic have found that a majority of studies are occurring over a year or less or are simply not documenting the effects of treatment timing (Abella 2014;Kettenring and Adams 2011;Stricker et al 2015). There is strong evidence, however, that many control strategies require extensive follow-up (Aulakh et al 2014;Beerling 1990) and that their effectiveness can vary significantly over time (Flory 2010;Ray et al 2018). Given these temporal effects, management efforts may need to be reprioritized over time to target the most problematic species (Flory and D'Antonio 2015).…”

Controlling invasive plant species in ecological restoration: A global review

“…Hand‐pulling methods were more common in smaller restoration projects, since labour costs are prohibitive at larger scales (Ganem et al., 2020; Ray, Sherman, Godinho, Hanson, & Parker, 2018). Cutting was more frequent in tropical biomes where invasive shrubs and trees were more common (Hooper, Condit, & Legendre, 2002; Zamith & Scarano, 2006).…”