System-level changes following invasion caused by disruption of functional relationships among plant and soil properties

The ecological impacts of invasive plants have served to justify the cost of their management, which is estimated to exceed $1 billion annually in the US alone. However, our understanding of the ecological impacts of most invasive plants is extremely limited, and when known, interpretation is confounded with varied measurements and methods. While this can provide important information about specific components of ecosystem function, it limits our understanding of the broader scope of impacts any one species may have. Using Japanese stiltgrass (Microstegium vimineum) as a study system, our objectives were to (1) survey a broad suite of 29 important ecological impact metrics (EIMs), (2) identify invader cover-EIM relationships, and (3) test if the comparative reference (uninvaded or invader removal) influences interpretation. Japanese stiltgrass had the strongest effect on the plant community, followed by soil properties, soil nutrients, and other abiotic/biotic factors. Many EIM values differed among reference types, and plant community EIMs were reduced with increasing Japanese stiltgrass abundance. For example, plant biodiversity was lower in the invasion when compared to both removed and uninvaded sites; however, soil organic matter was higher only in the uninvaded site when compared to the invasion. The integrative ecosystem metric E(c) also showed that the system overall was impacted by the Japanese stiltgrass invasion, and this varied among sites. Interestingly, relationships among EIMs were also changed by the presence of Japanese stiltgrass. For example, a strong correlation between pH and soil organic matter disappeared when Japanese stiltgrass was present. Together this suggests that this invaded ecosystem functions in a different way through both individual and correlated alterations to ecosystem properties.