Invasive species alter ecosystem structure, impact biodiversity, and have significant economic costs. In Oregon's Willamette Valley, invasive grasses Arrhenatherum elatius and Schedonorus arundinaceus alter the dynamics of the phenologically paired interaction between an endangered butterfly, Icaricia icarioides fenderi (Fender's blue), and its larval host plant, Lupinus oreganus (Kincaid's lupine). To test methods to restore this interaction, we established a 3-year experiment where a post-emergent grass-specific herbicide, fluazifop-p-butyl, was applied to Fender's blue habitat. Plant community data were recorded throughout the growing season at eight paired plots for 1 year prior to treatment and 3 years during treatment. We asked whether annual application of herbicide could reduce the height of invasive grasses to levels at or beneath the height of Kincaid's lupine racemes throughout the Fender's blue flight season. We hypothesized that native forb species, which are critical nectar sources for Fender's blue, would increase in cover and frequency following the release from competitive dominance of invasive grasses. Grass-specific herbicide reduced grass height during the flight season of Fender's blue, but with several costs. We found no change in nectar and a suppression of lupine growth in plots in response to experimental herbicide treatment. Each study site had multiple secondary invaders; the long-term impact of these new invaders is unknown. We suggest that herbicide application results in a net negative effect in the context of Fender's blue habitat restoration. That is, the costs to primary resources for Fender's blue and the influx of secondary invaders may be as problematic as the primary invasion by non-native grasses. Implications for Practice• Herbicide-assisted management tools for restoration should consider potential costs and benefits relative to desired restoration outcomes.• Grass-specific herbicide application reduces the height and "thickness" of the plant community, which is a clear benefit for access by pollinators.• Grass-specific herbicide application allows rapid expansion of invasive forbs.• Practitioners should carefully consider net potential benefits of grass-specific herbicide application with potential costs of invasive forb invasion when developing restoration plans.
Restoring habitat degraded by invasive species is often a primary focus of conservation strategies, yet few studies investigate the effects of invasive species control on multiple at-risk taxa. Selective herbicides are increasingly used because they can selectively reduce aggressive invasive plant species with the aim of minimizing effects on other taxa within the habitat. We conducted a four-year experiment to test how annual application of grass-specific herbicide affected the demography on Fender's blue butterfly (Icaricia icarioides fenderi) and Kincaid's lupine (Lupinus oreganus), two federally protected species which persist in highly degraded prairie remnants in western Oregon, USA. Effects of herbicide application were transitory for the butterfly; reduction of invasive grasses increased fecundity and led to higher annual population growth ( ) at one of two conservation areas in the first season. There were no detectable differences in in subsequent seasons-suggesting that treatments caused neither extensive harm nor extensive benefit to the butterfly population. For the lupine, there were no detectable differences in leaf and flower abundance between control and herbicide treatments. However, greater seed production in herbicide plots in the first and third seasons suggests that lupines in herbicide-treated plots have greater potential reproductive success. While treatments do not have a long-term benefit to annual population growth for the butterfly, increasing reproductive success of the threatened plant may justify integrating this strategy into restoration plans. Considering the impact of restoration practices on the demography of multiple at-risk taxa within a community is critical to effective recovery strategies. Key words: Fender's blue butterfly (Icaricia (=Plebejus) icarioides fenderi), full annual cycle, Kincaid's lupine (Lupinus oreganus), nontarget effects of herbicides, prairie restoration, vital rates Implications for Practice• Restoration plans which use herbicide-based management should consider the effects of treatments on the full annual cycle of focal species as well as effects on interacting trophic levels within the community. • Multi-year monitoring is essential; herbicide-based management may have initial desirable effects, but these effects may be temporary. • Full-life cycle monitoring integrates effects of restoration treatments over one or more generations to project net effects of restoration actions on focal species. • Multi-year and multi-site demographic response of at-risk species to restoration actions provides insight into the generality and utility of management actions, especially when actions cause both costs and benefits and vary across years.
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