Responses of non‐native earthworms to experimental eradication of garlic mustard and implications for native vegetation

K A Stinson,K Martinez,E Coates‐Connor,S D Frey,M Anthony,M R Jackson

doi:10.1002/ecs2.2353

Abstract

AbstractRecent studies in invasion biology suggest that positive feedback among two or more introduced organisms facilitate establishment within a new range and drive changes in native plant communities. Here, we experimentally tested for relationships between native plants and two non‐native organisms invading forest habitats in North America: garlic mustard (Alliaria petiolata, Brassicaceae) and earthworms. In two forested sites, we compared understory vegetation and earthworm biomass in plots where garlic mustard was removed for three years, plots without garlic mustard invasion, and plots invaded by garlic mustard that was not removed. Earthworm biomass was highest in the plots with garlic mustard, and long‐term eradication of garlic mustard reduced earthworm biomass to levels similar to those observed in the uninvaded control plots. Invasion treatment, and the interactions between earthworm biomass and treatment, explained most of the variation in plant community composition and diversity—suggesting that earthworms alone do not necessarily drive forest understory floristic patterns. In contrast to broader geographic patterns indicating earthworms as the main driver of vegetation change in the presence of non‐native plants, we show that garlic mustard solely, or in conjunction with earthworm biomass, drives changes in native plant composition and diversity at the scale of individual forests. From a local management perspective, our data suggest that garlic mustard eradication can directly assist in the conservation of native plant communities and simultaneously reduce earthworm biomass.

Highlights

It is widely accepted that the introduction of non-native species into new habitats has profound ecological implications for biodiversity and ecosystem function, but the mechanisms that determine the success or failure of a given species beyond its home range remain elusive (Levine et al 2003, Facon et al 2006)
A compelling case that earthworms engineer forest soils in a manner that facilitates plant invasions has been made in recent meta-analyses and correlative studies; earthworm biomass is broadly associated with increases in non-native plant species and declines in the presence of native plant species across a range of forest types and invaders (Nuzzo et al 2009, Craven et al 2016)
There was no effect of garlic mustard removal on soil moisture, soil C, or inorganic N, but soil pH was slightly higher in invaded plots than in eradicated and control plots (Table 1)

Summary

Introduction

It is widely accepted that the introduction of non-native species into new habitats has profound ecological implications for biodiversity and ecosystem function, but the mechanisms that determine the success or failure of a given species beyond its home range remain elusive (Levine et al 2003, Facon et al 2006). The invasion meltdown hypothesis (Simberloff and Von Holle 1999) and the notion of ecosystem engineers (Frelich et al 2006, Eisenhauer et al 2009) predict that invasive organisms create conditions under which others can successfully invade in a new range. A compelling case that earthworms engineer forest soils in a manner that facilitates plant invasions has been made in recent meta-analyses and correlative studies; earthworm biomass is broadly associated with increases in non-native plant species and declines in the presence of native plant species across a range of forest types and invaders (Nuzzo et al 2009, Craven et al 2016). Experiments investigating responses of earthworms to the removal of invasive plants, and their respective associations with native plant communities, are limited to a small number of studies, mainly with invasive shrubs (Madritch and Lindroth 2009, Lobe et al 2014, Roth et al 2015)

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Results

Conclusion