Initial success of native grasses is contingent on multiple interactions among exotic grass competition, temporal priority, rainfall, and site effects

Kurt Vaughn and Steve Fick seeding the experimental plots at the Hopland site in November 2011. Photo by T. Young

Throughout the western United States, native perennial grasses are being supplanted by aggressive non-native annuals. In a recent study published in AoB PLANTS, Young et al. show that giving native grasses just a two-week germination ‘head start’ over exotic invasive grasses shifts the competitive edge strongly in their favour. They also show that the strength of this advantage differs strikingly depending on the site at which the experiment is carried out, and the weather in the initial weeks of the experiment. These results a) give insight into the reasons for the competitive advantage that annuals usually demonstrate, and b) are an example of the likelihood that ecological experiments often produce results that are limited to a particular time and place, and less general than we might wish to believe.