Demographic costs and benefits of herbicide‐based restoration to enhance habitat for an endangered butterfly and a threatened plant

Abstract

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.

Why are some plant species missing from restorations? A diagnostic tool for temperate grassland ecosystems

“…While the herbicide did reduce grass height, and improve access by pollinators, as well as increase seed production in the lupine, it also had unintended impacts on the lupine, including suppression of its growth, and introduction of several secondary invaders (particularly forbs) that arrived after the grass was reduced. The authors conclude that grass-specific herbicide is not the ideal tool to use in the restoration of L. oreganus/Icaricia icarioides fenderi habitat due to the secondary impacts (Bennion et al, 2020;Schultz and Ferguson, 2020). Herbicide has an important role in restoration, but it is important to consider the costs, benefits, and possible spillover impacts when deciding on an herbicide plan.…”