A Colonizing Species Has High Fitness on Soils with an Exotic Species Legacy When Conditioning Effects Are Mitigated

Plant interaction with soil can create feedbacks that influence intraspecific and interspecific performance. These feedbacks can either be short term, within-season soil conditioning called priority effects, or longer-term influences called soil legacies. Negative effects of exotic species include soil conditioning and soil legacies that prevent effective restoration after weed removal. In this experiment, I compare the historic soil effects in a California annual grassland on the performance of a colonizing native annual forb, California plantain. At locations dominated by California plantain and at locations dominated by exotic annual species but that had historically housed California plantain, I compared California plantain fitness with and without soil conditioning agents by using areas in each location that were cleared at the start of the current growing season (soil conditioning present) or had been kept clear of vegetation starting early the previous growing season (soil conditioning absent). The soil legacy of the exotic-dominated community doubled California plantain fitness compared to when both the soil legacy and soil conditioning from exotic community were present. While soil conditioning and soil legacies can impact restoration success, these effects may be mitigated by keeping areas clear of vegetation for one growing season prior to planting.