Presence Of Garlic Mustard Research Articles

Regional Patterns of Floristic Diversity and Composition in Forests Invaded by Garlic Mustard (Alliaria petiolata)

The impacts of invasive species on native plant communities are often studied on small spatial scales but may vary across regionally heterogeneous landscapes. Comparisons of vegetation across several similar sites with and without an invasive species present can be logistically challenging but highly informative to both scientists and land managers. We examined regional geographic variation in the diversity and composition of 8 replicate northeastern forest-understory plant communities invaded by the non-native species Alliaria petiolata (Garlic Mustard). Despite variation in underlying soil conditions and horizon development, several native species and their associated functional groups were either negatively or positively associated with Garlic Mustard invasion at the regional scale, and soil moisture and pH were higher in invaded plots across all sites. Most tree species were less common at invaded sites, but high tree-seedling abundances at some sites led to regionally higher seedling abundance in the presence of Garlic Mustard. Our study highlights the importance of species-specific responses, as well as site-specific soil conditions, for better understanding potential impacts of invasion.

Increased Springtail Abundance in a Garlic Mustard-Invaded Forest

Alliaria petiolata (Garlic Mustard) decreases diversity of native plants and introduces novel litter inputs to forests, but whether Garlic Mustard's presence influences detritivores is unclear. Our goal was to determine if Garlic Mustard alters springtail (detritivore) densities during early invasion. We obtained epigeal (litter, humus, and soil) cores from invaded and uninvaded areas in a Pinus strobus (White Pine) forest and used high-gradient dynamic sampling to extract springtails. Invaded areas contained nearly three times more springtails than uninvaded areas, attributable to two springtail morphospecies from Collembola families Tomoceridae and Entomobryidae. Higher pH in invaded epigeal samples correlated with increased springtail abundance. pH alkalization also correlated with increased proportion of juvenile rosettes in mixed stands. Our results suggest a possible role for pH modulation of springtail abundance in response to Garlic Mustard invasion.

The impact of garlic mustard on sandy forest soils

Garlic mustard (Alliaria petiolata), an exotic biennial herb invasive to North American forests, has potential to affect resource availability in invaded soils. Garlic mustard produces a suite of toxic chemicals that impact diversity both above and belowground and thus likely alter ecosystem processes. To examine the effects of garlic mustard on soil biota and ecosystem processes, we sampled soil from invaded and uninvaded stands at a pine plantation on sandy soils in central Illinois. Several of the pine stands were also planted with the N2-fixing tree black locust (Robinia pseudoacacia). Results indicate that pine soils underlying garlic mustard have higher pH, and exhibit higher rates of N mineralization, relative nitrification and soil respiration compared to soils without garlic mustard. Nitrogen turnover on pine invaded stands is more similar to pine soils with the black locust trees present than to uninvaded pine stands without black locust. Garlic mustard cover was much greater in stands with black locust trees planted, suggesting that garlic mustard may be attracted to high N sites. Catabolic response profiles, which provide a measure of soil microbial function, indicated a shift in substrate use for one of the substrates tested in the presence of garlic mustard. While many of the soil characteristics measured did not differ between invaded and uninvaded stands, the differences with regard to N turnover were striking and will likely have long term effects on soil nutrient status, with potential to feedback to forest health.

Competitive and allelopathic effects of garlic mustard (Alliaria petiolata) on American ginseng (Panax quinquefolius)

The purpose of this study was to test competitive and allelopathic effects of invasive garlic mustard on American ginseng (Panax quinquefolius) seedlings under natural conditions. For comparative purposes, we also examined the potential effects of the native striped violet (Viola striata). In order to partition effects of resource competition and chemical suppression via allelopathy, field soils were amended with activated carbon or left unamended. Activated carbon positively affected ginseng growth as well as biomass of competitors. Ginseng mortality tended to increase with garlic mustard presence, though activated carbon alleviated this response. Garlic mustard had no significant effect on ginseng seedling growth, while striped violet suppressed shoot length in the absence of activated carbon. Our results showed a surprising effect of activated carbon on plant growth, a potential allelopathic effect of the native striped violet and suggest that newly invaded ginseng populations with low densities of garlic mustard may be able to withstand its effects. However, recruitment within invaded populations may decline.

Influence of the Invasive Herb Garlic Mustard (Alliaria petiolata) on Ground Beetle (Coleoptera: Carabidae) Assemblages

Garlic mustard, Alliaria petiolata (Bieb.) Cavara and Grande, is a widespread invader that has aggressively colonized woodland edges and forest interiors across North America, yet its ecological impacts remain scantily documented. We evaluated the effects of garlic mustard on ground beetle (Coleoptera: Carabidae) assemblages and their invertebrate prey by comparing carabid captures and species richness and invertebrate abundance in invaded and noninvaded areas of two forests in central New York. Geostatistical techniques were used to model ground beetle distribution and to determine spatial correlation between carabids, garlic mustard, ground beetle prey availability, understory plant species richness, and litter depth. Data were collected from April to September 2002, using a grid of 64 by 64 m, with 89 sampling points arranged in nested grids to capture the spatial correlation within and between each variable. Garlic mustard invasion had no effect on carabid captures and species richness or on invertebrate abundance. Ground beetle abundance and biomass were spatially correlated, but their distribution was independent of garlic mustard and all other environmental factors we recorded. Our data on carabid assemblages and their invertebrate prey clearly show that absence or presence of garlic mustard did not influence these organisms at our study sites. It is possible that garlic mustard invasion has negative ecosystem impacts; however, the biennial nature of the plant and its pattern of spread may produce subtle ecological effects that are difficult to quantify or are easily confounded by other dominating factors.

Invasion Pattern of Herb Garlic Mustard (Alliaria petiolata) in High Quality Forests

The invasion of non-indigenous plant species poses a severe threat to native plant communities. Garlic mustard (Alliaria petiolata) is a naturalized European biennial herb that has spread rapidly through the eastern US and adjacent Canada. To determine garlic mustard rate of spread, eleven permanent plots (50×25 m) were located in seven high quality (relatively undisturbed) forests in the early stages of invasion. Garlic mustard presence was recorded within six 50×2 m permanent belt transects, and density and percent cover by age class were recorded in 36 permanent 1 m2 quadrats, between 1989 and 1992, and again in 1997. Garlic mustard spread at an average rate of 5.4 m per year between 1989 and 1992, in all plots combined. Within individual plots rate of spread varied substantially, with location of the front increasing up to 36 m and decreasing as much as 18 m between years. While the front alternately advanced and retreated, over time garlic mustard consistently advanced through all forests. Rate of spread was influenced by establishment of satellite populations, and disturbance (wind-throw and flooding). The pattern of spread within plots was one of a ragged advancing front, supplemented by establishment of satellite populations 6–40 m distant from the front, which then coalesced with the main population. Garlic mustard presence between 1989 and 1997 increased significantly within all plots, and in each age class within each plot. The greatest increases occurred in plots where this plant was initially rarest. Garlic mustard cover and density varied nonsignificantly during the same time period. These results indicate that after garlic mustard invades a forest it becomes a permanent part of the community, annually increasing in presence but fluctuating in cover and density. Garlic mustard maintains a low profile under low disturbance conditions, but increases rapidly with periodic disturbance. This study monitored garlic mustard invasion in high quality relatively undisturbed forests, and may underestimate the rate of spread in low quality highly disturbed forests.