Comparison of the Effect of Early and Late Removal of Second-Year Garlic Mustard (Alliaria petiolata) on First-Year Plants and Deciduous Forest Spring and Summer Dominant Herbaceous Groundlayer Species in Central Illinois, USA

Abstract

Garlic mustard, a biennial Eurasian species, has extensively invaded eastern North American deciduous forests. We studied effects of 3 years (2005)(2006)(2007) of annual removal of second-year garlic mustard plants on first-year plants and native spring herbaceous species in upland and lowland woods. Treatments compared removal of second-year plants in mid-March (early treatment) or mid-May (late treatment) to a control. We recorded first-and second-year plants and native herbaceous species percent cover on April 19 and 20. First-year plant cover was higher on control than treatment plots; however, in the upland woods only control and late treatment plots differed significantly. First-year plant cover was less in removal than control plots, indicating reduced seed input; however, we found no difference in cover of second-year plants between late treatment and control plots. Results suggest second-year plants strongly compete with younger conspecifics, and their removal decreases first-year plant mortality. Removal of second-year garlic mustard did not significantly affect total cover of native herbaceous species. Second-year plants complete vegetative growth before late May and might impact early developing native species more than later growing species. We tested effect of removal of garlic mustard on native species in 2 phenological categories: spring-and summer-dominant species. We found no treatment effects on summer-dominant species. However, early treatment plots had significantly more cover of spring-dominant plants than late treatment and control in the upland woods. Indicator Species Analysis indicated a majority of spring (75%) and summer (50%) dominant species maximized performance in the early treatment.

Comparison of the non‐native herbAlliaria petiolatawith dominant native herbs in microhabitats of a Midwestern forest

“…1, 2). These results support previous results we have obtained at this site (Davis et al 2012(Davis et al , 2014(Davis et al , 2015, as well as observational studies and removal experiments in other locations, which generally indicate weak, inconsistent, or non-existent associations between A. petiolata and native plant abundance and diversity in natural habitats (McCarthy 1997, Stinson et al 2007, Rodgers et al 2008a, Van Riper et al 2010, Herold et al 2011, Rooney and Rogers 2011, Dornbush and Hahn 2013. This is superficially at odds with experimental studies demonstrating strong potential resource competition by Alliaria (Poon and Maherali 2015), and strong allelopathic effects of Alliaria on mycorrhizal community structure and function and growth of host plants (Wolfe et al 2008, Cantor et al 2011, Lankau 2011a, Cipollini and Cipollini 2016 in the laboratory.…”

“…, Herold et al. , Rooney and Rogers , Dornbush and Hahn ). This is superficially at odds with experimental studies demonstrating strong potential resource competition by Alliaria (Poon and Maherali ), and strong allelopathic effects of Alliaria on mycorrhizal community structure and function and growth of host plants (Wolfe et al.…”

“…, Herold et al. ), and nutrient depletion by one cohort can negatively impact growth and competitive ability of the next (Poon and Maherali ). These negative autecological effects are thought to underlie the demographic cycling present in many natural populations of Alliaria (McCarthy , Nuzzo , Meekins and McCarthy , Winterer et al.…”

“…Alliaria also appears to have self-inhibitory tendencies due to strong intra-specific competition. In dense populations, adult plants inhibit growth of first-year plants (Winterer et al 2005, Herold et al 2011, and nutrient depletion by one cohort can negatively impact growth and competitive ability of the next (Poon and Maherali 2015). These negative autecological effects are thought to underlie the demographic cycling present in many natural populations of Alliaria (McCarthy 1997, Nuzzo 1999, Meekins and McCarthy 2002, Winterer et al 2005, Pardini et al 2009, Van Riper et al 2010).…”

Experimental evidence for indirect facilitation among invasive plants

“…Alliaria invasions can suppress spring ephemeral flora and tree seedlings, likely not only through direct interactions, but also indirectly through suppression of mycorrhizal fungi communities (McCarthy 1997;Stinson et al 2007;Herold et al 2011). Like Microstegium, Alliaria can also reduce the diversity and abundance of insects and alter abiotic soil properties (impacts of Alliaria invasion reviewed by Rodgers, Stinson & Finzi 2008).…”