Native plants said no match for invaders

Given enough time, invasive plant species will eliminate native plants growing in the wild, despite recent reports to the contrary, Canadian researchers say. Ecologists at the University of Toronto with colleagues from the Swiss Federal Institute of Technology in Zurich, writing in the Proceedings of the National Academy of Sciences, report that recent statements that invasive plants are not a concern are often based on incomplete information, with insufficient time having passed to observe the full effect of invasions on native biodiversity. "The impacts of exotic plant invasions often take much longer to become evident than previously thought," lead author Benjamin Gilbert of Toronto's department of ecology and evolutionary biology said. "This delay can create an 'extinction debt' in native plant species, meaning that these species are slowly going extinct but the actual extinction event occurs hundreds of years after the initial invasion." Despite recent findings that competition from introduced plants has driven remarkably few plant species to extinction, pushing them instead to patchy, marginal habitats unsuitable to their non-native competitors, the researchers said survival in marginal habitats doesn't guarantee long-term persistence for the native plants. "Of particular concern is the possibility that short-term persistence of native flora in invaded habitats masks eventual extinction," Jonathan Levine of the Zurich institute said. The researchers studied a California reserve where much of the native plant diversity exists only in marginal areas surrounded by invasive grasses. "Invasion has created isolated 'islands of native plants' in a sea of exotics," Gilbert said. "This has decreased the size of native habitats, which reduces seed production and increases local extinction."