The Role of Wildfire in the Establishment and Range Expansion of Nonnative Plant Species into Natural Areas A review of current literature

2006 FOREWORD Discussions of nonnative plant species and wildfire present excellent opportunities to integrate knowledge from different disciplines, but they also present significant challenges. As both wild-fire and nonnative plant species elicit emotionally charged reactions, researchers are challenged to provide quantitative information to replace current opinions and dogma based on emotion and conjecture. The conventional wisdom is that many notorious nonnative plant species will dramatically increase and change future fire frequency following wildfire. A surprising number of papers draw conclusions about nonnative plant species and wildfire using this conventional wisdom as the null hypothesis, rather than using the more traditional and testable null hypothesis that the abundance of nonnative plants is not altered by wildfire. We set out to review the scientific literature on the response of nonnative plant species to wildfire. We were focused on an objective assessment of responses based on quantitative data. That is, we did not accept conclusions not well supported by data and statistical analysis. We intentionally did not use information from the grey literature; in fact, we used information only from quantitative studies published in journals, proceedings, books, and websites. We held the null hypothesis that there would be no response by nonnative species following wildfire, and looked for evidence that would allow one to reject this null hypothesis. Thus, we may have erred on the side of conservatism with regard to integrating nondata-based knowledge that often finds its way into conclusions. However, one can be certain that our assessment was as objective as possible. We hope this review will provide context for researchers to determine which issues need to be studied and how best to conduct those studies to further contribute to this important issue. Which nonnative plant species are most invasive after wildfire in natural areas? In natural areas with predominantly native vegetation, do existing nonnative plant populations increase or decrease after wildfire? Which existing nonnative plant populations increase or decrease after wildfire? Do wildfires contribute to the dominance of nonnative plant species in