We are using Japanese stiltgrass as a test case to develop our model for invasive species spread. Japanese stiltgrass, officially known as Microstegium vimineum, is one of the most rapidly spreading invasive species in eastern U.S. forests. It spreads primarily along corridors, such as roads, trails, and waterways and grows well in disturbed locations. These traits are similar to many other invasive species, making it an excellent model system.
Japanese stiltgrass is native to Asia and was first recorded in the United States in 1919 in Tennessee. It is believed to have been introduced in packing material from China.
Japanese stiltgrass was first reported as spreading in 1987 (Barden 1987). Shortly thereafter it began spreading rapidly through eastern forests and now occurs in at least 22 states. It is currently spreading northward with an approximate northern boundary from central Illinois through central New York state. Our study sites in Indiana are at the edge of its current range.
Japanese stiltgrass frequently invades forest understories, particularly where there are light gaps or litter disturbance. It is also very common in floodplain areas, along streams, and other areas of overland water flow. It produces prolific seeds and can reproduce in as low as 5% sunlight.
Japanese stiltgrass produces two types of flowers: open, outcrossing (chasmogamous, "CH") flowers and closed, self-pollinating (cleistogamous, "CL") flowers. CH flowers are only produced at the tips of stems but CL flowers can be formed at every leaf juncture.
Seeds from CH flowers generally fall from the plant as soon as they are mature. Seeds from CL flowers tend to stay in the dried thatch of the plants. If this litter is moved (e.g. by flooding, wind) the seeds move with it. This can occasionally transport seeds long distances.
Japanese stiltgrass grows late in season
Japanese stiltgrass germinates in late spring (April - May in Indiana) but does not become a dominant part of the plant community until late July through September. It flowers in early fall and sets seed approximately three weeks later (September - October in Indiana).
It can affect species that grow later in the season through its dominant growth, but also can affect early spring species by its dense thatch that decomposes slowly.
Because Japanese stiltgrass is an annual plant, it must re-establish from seed each year. Stopping seed production is the most important aspect of management.