- Author: Elise S Gornish
One of the most devastating characteristics of invasive plants is their ability to enhance further invasion by con- and heterospecifics, as well as to limit native recolonization into previously invaded areas. Invasives can accomplish this through a variety of ways that include the modification of nutrient cycling dynamics, a change of water availability, the attraction of novel herbivores, and an increase in soil acidity. One of the most common ways that invasives enhance further invasion is through the modification of the soil microbiome (the bacterial and fungal community). This has direct relevance for management because if an invasive plant is cultivating a soil microbiome that facilitates future invasion and restricts native plant recolonization, habitats with a history of invasion will likely require a larger contribution of resources in order to limit invasion and enhance native establishment compared to habitats without such a history.
In California, managers are interested in developing a more comprehensive understanding of the invasion dynamics of Medusahead (Taeniatherum caput-medusae), a noxious annual grass that has caused dramatic declines in the environmental and economic value of natural and working landscapes. Several management approaches, including herbicide and prescribed fire, have demonstrated utility in controlling small populations of Medusahead. As a result, a particular pressing question for Medusahead management is: Are areas that were previously invaded by Medusahead more likely to be reinvaded by the future? Preliminary data in a collaborative study between the University of California, Davis and the University of Colorado, Boulder might provide an answer. Sequence data of soils across a Medusahead invasion gradient suggest that the soil microbiome is not changed by the presence of Medusahead or the magnitude of invasion. Further, a greenhouse study suggests that Medusahead growth rate is similar whether grown on previously invaded soils or non-invaded soils (of the same type and from the same location). Although additional research is required in order to develop a more complete understanding of the potential relationship between Medusahead and the soil microbiome, this preliminary work suggests that managers do not necessarily need to invest more resources in historically invaded sites compared to ecologically equivalent uninvaded sites in order to inhibit Medusahead invasion or restore native biodiversity.
Stay tuned for updates on this research as it develops.