Aspects of the Ecology of an Invasive Plant, Garlic Mustard (Alliaria petiolata), in Central Illinois

Abstract

Alliaria petiolata (garlic mustard), an exotic plant species, has invaded woodlands in several areas in mid‐western and northeastern United States and adjacent Canada, and it is displacing the indigenous under‐story flora. This study was conducted to provide information about the species' biology that might be useful in controlling its spread in native woodlands. The plant is a strict biennial in North America, spending the first year of growth as a basal rosette. This period of relatively slow growth is followed by a period of rapid shoot elongation (1.9 cm/day) during early spring of the second growing season. The plant is capable of cross‐ and self‐pollination, although pollination and stigma receptivity occur before the flower is open, so autogamy is the most likely breeding system. Garlic mustard invests 20.4% of its biomass in reproductive effort, with an annual seed rain of 15,000 seeds/m2. Seed dispersal from fruits begins in early July and continues into October. Most seeds germinate in the spring following the year in which they were produced. Seedling recruitment is high (8.3–18.0 seedlings/cm2), but only about 7.5% of the plants survive to maturity. The success of the plant in invading woodlands appears to be related to (1) its autogamous breeding system that allows a single individual, or a few individuals, to establish populations of genetically similar but interfertile individuals; (2) high seed production, permitting establishment of large numbers of individuals; and (3) rapid growth during the second growing season, which increases its competitive ability. Because of garlic mustard's ability to occupy understory habitats successfully, it may be unrealistic to expect to eliminate the plant from many habitats it has already invaded.

Testing the mutualism disruption hypothesis: physiological mechanisms for invasion of intact perennial plant communities

“…In garlic mustard-invaded sites, the continuous presence of garlic mustard rosettes and/or adults, its high seedling and rosette mortality throughout the year (Davis et al 2006), and a 2-month period of intense leaf litter input as adults senesce (Anderson et al 1996, Cantor et al 2011) likely contribute to the year-round release of allelochemicals into the soil. Given the significant physiological suppression shown by our short-term pulse experiments, we anticipate that longer-term exposure of AMF-dependent plants to garlic mustard allelochemicals could affect carbon storage and resource allocation.…”

“…AMF external hyphae associated with understory herbs typically exhibit peak growth in mid to late summer (Brundrett and Kendrick 1990). This peak coincides with garlic mustard adults' senescence (Anderson et al 1996) and the release of allelochemicals (Cantor et al 2011), making the AMF mutualism in false Solomon's seal particularly susceptible to disruption by garlic mustard. Finally, false Solomon's seal's roots grow at shallow depths (2-4 cm below the soil surface; A. Hale, personal observation), which increases their probability of encountering allelochemicals leaching from garlic mustard leaf litter or root exudates.…”

Efficacy of Treatments against Garlic Mustard (Alliaria petiolata) and Effects on Forest Understory Plant Diversity

“…Seeds fall within two meters of the parent plant, with most seeds germinating within one meter creating thick patches that compete with native vegetation [3,4]. Additionally, adult plants grow rapidly in early spring when many native plants are still dormant [5]. In Michigan, garlic mustard is commonly found invading deciduous forests, roadsides, and urban areas [6].…”

A seasonal, density‐dependent model for the management of an invasive weed

“…Garlic mustard is an obligate biennial with a life cycle strongly coupled to the seasons (e.g., Cavers et al 1979, Roberts and Boddrell 1983, Anderson et al 1996, Nuzzo 2000, Pardini et al 2008. As shown in Fig.…”

“…Garlic mustard (Alliaria petiolata; Brassicaceae) is a Eurasian herb that invades North American forests and edge habitats, forming dense monotypic stands and producing allelopathic toxins that displace native flora (Cavers et al 1979, Nuzzo 1991, Anderson et al 1996. Because of its tolerance to many growth conditions, extensive seed dispersal, and ability to self-fertilize, this species has become a pervasive weed in the midwestern and northeastern United States and some parts of Canada (Nuzzo 2000).…”