Vegetation communities
Garlic mustard does not appear to require disturbance to become established, making it a threat to mature forests. It can enter, establish itself, and become the dominant plant in the forest understory in 5-7 years. It actively displaces native spring ephemeral wildflowers through direct competition and/or through changes to the soil/leaf litter.
Forest ecosystems and wildlife
Garlic mustard is allelopathic; the chemicals produced in the roots have been shown to prevent the growth of other plants and grasses. These chemicals also affect the growth and regeneration of arbuscular mycorrhizal fungi (AMF), beneficial fungi in the soil that help trees and plants absorb nutrients and water into their roots. The reduced AMF in forests inhibits growth of most native tree seedlings and plants, which depend on AMF. Loss of AMF changes the forest ecosystem. Non-native species are able to grow and displace native seedlings, including those which would eventually become canopy trees such as maples and oaks. This effect can last for years after garlic mustard has been removed.
Ontario’s forests have evolved to depend on leaf litter, which provides a layer of slowly decomposing organic matter on the forest floor. Garlic mustard leaves have a high nutrient content. When they die, they accelerate the rate of decay of native leaf litter, altering the natural decomposition cycle and changing the structure and function of forest ecosystems.
This effect is compounded by non-native earthworms which have also caused ecosystem changes to Ontario’s forests by reducing the amount of leaf litter available. Garlic mustard is able to establish itself in these low-leaf litter environments, whereas many native species cannot. By changing the composition of the litter layer on the forest floor, garlic mustard reduces habitat for ground-nesting birds and affects habitat for salamanders and other forest floor-dwelling animals.