Biological Invasions

, Volume 15, Issue 12, pp 2691–2706 | Cite as

Consumers and establishment limitations contribute more than competitive interactions in sustaining dominance of the exotic herb garlic mustard in a Wisconsin, USA forest

  • Mathew E. DornbushEmail author
  • Philip G. Hahn
Original Paper


The understory is a diverse component of temperate forest ecosystems, contributing significantly to forest ecosystem services. Despite their importance, many native understories face stresses from current and past land use, habitat fragmentation, invasive species, and overabundant herbivores. We established a four block, three factor experiment to evaluate the relative contribution of native plant establishment, competitive effects from the invasive herb garlic mustard (Alliaria petiolata), and herbivory from white-tailed deer (Odocoileus virginianus) to better understand the mechanisms promoting low native plant richness and cover and understory dominance by the biennial exotic herb garlic mustard in a NE Wisconsin, USA forest. Four years of garlic mustard removal failed to increase native plant richness or cover in non-restored plots. However, deer access and the introduction of native plants (restoration treatment) both significantly enhanced native plant cover and richness, with restored species cover in fenced plots approximately 216 % that of open-access plots, and the majority of these species flowered at significantly higher proportions inside of fenced areas. In contrast, deer access did not significantly alter the cover, or seed production of garlic mustard. We also found no significant effect of garlic mustard presence on the cover or flowering of restored native species. We conclude that multiple factors, including limited natural establishment by native species and selective herbivory drove low native, high exotic dominance at our site, suggesting that a shift in focus from invasive plant removal to combined native plant restoration and herbivore control is needed to maximize the recovery of this degraded forest understory.


Alliaria petiolata Invasive species control Lowland deciduous forest Propagule limitation Restoration ecology Selective browsing 



We thank the Bay Beach Wildlife Sanctuary, Green Bay, WI, for supporting the establishment of our project, and for the logistical support provided throughout its duration. This project was funded through grants from the Invasive Species Fund of Brown Co., WI and a Research Enhancement Grant from the University of Wisconsin-Green Bay to M.E.D. P.G.H. was supported by the Barbara Hauxhurst Cofrin Graduate Research Fellowship in Environmental Science and Policy. M. Draney, J. Heraly, J. Martinez, A. von Haden, L. Caelwaerts, R. Wactl, and S. Kolb provided invaluable field assistance. We thank several anonymous reviewers for their beneficial comments on previous versions of this manuscript.


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Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  1. 1.Department of Natural and Applied SciencesUniversity of Wisconsin-Green BayGreen BayUSA
  2. 2.Environmental Science and Policy Graduate ProgramUniversity of Wisconsin-Green BayGreen BayUSA
  3. 3.Department of ZoologyUniversity of Wisconsin-MadisonMadisonUSA

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