Interacting Effects of Native Plant Diversity and Resource Availability on Plant Community Invasibility and Invader Impact

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ABSTRACTMaron, JohnUniversity of MontanaThe invasion of native plant communities by non-native plants is an increasing ecological and economic concern. Non-native plants degrade native communities; removal of these damaging non-native species from native communities conservatively costs this country over $8 billion annually. A major challenge for ecologists is to understand the factors that promote invasion by non-native species into native communities so that native systems can be managed to reduce the likelihood that exotic weeds can establish and spread. Our research will explore whether species-rich native grasslands are more difficult for non-native plants to invade than grasslands that contain fewer native species. Furthermore, we will examine how water availability interacts with native species diversity to influence community susceptibility to invasion and the magnitude of impact that non-native species have on native plants. We will create plant assemblages that vary in the number of native species within them. We will then introduce seeds of St. John's Wort (Hypericum perforatum), sulfur cinquefoil (Potentilla recta) and spotted knapweed (Centaurea maculosa) into these assemblages. These widespread weeds are economically and ecologically damaging throughout the western U.S. Plots will receive ambient or supplemental water, a critically limiting resource in dry grasslands of the intermountain west. By manipulating resource availability in the context of a diversity-invasibility study, we will explore how native plant diversity and resource availability jointly influence the ease with which non-native species can enter native assemblages and the subsequent effect that these non-native species have on native plants.