Expanding the invasion footprint: Ventenata dubia and relationships to wildfire, environment, and plant communities in the Blue Mountains of the Inland Northwest, USA

Questions: A recently introduced non-native annual grass, Ventenata dubia, is challengingprevious conceptions of community resistance in forest mosaic communitiesin the Inland Northwest. However, little is known of the drivers and potential ecologicalimpacts of this rapidly expanding species. Here we (1) identify abiotic and biotichabitat characteristics associated with the V. dubia invasion and examine how thesediffer between V. dubia and other problematic non-native annual grasses, Bromustectorum and Taeniatherum caput-medusae; and (2) determine how burning influencesrelationships between V. dubia and plant community composition and structure toaddress potential impacts on Inland Northwest forest mosaic communities.Location: Blue Mountains of the Inland Northwest, USA.Methods: We measured environmental and plant community characteristics in 110recently burned and nearby unburned plots. Plots were stratified to capture a rangeof V. dubia cover, elevations, biophysical classes, and fire severities. We investigatedrelationships between V. dubia, wildfire, environmental, and plant community characteristicsusing non-metric multidimensional scaling and linear regressions.Results: Ventenata dubia was most abundant in sparsely vegetated, basalt-derivedrocky scablands interspersed throughout the forested landscape. Plant communitiesmost heavily invaded by V. dubia were largely uninvaded by other non-native annualgrasses. Ventenata dubia was abundant in both unburned and burned areas, but negativerelationships between V. dubia cover and community diversity were stronger inburned plots, where keystone sagebrush species were largely absent after fire.Conclusions: Ventenata dubia is expanding the overall invasion footprint into previouslyuninvaded communities. Burning may exacerbate negative relationships betweenV. dubia and species richness, evenness, and functional diversity, including incommunities that historically rarely burned. Understanding the drivers and impactsof the V. dubia invasion and recognizing how these differ from other annual grassinvasions may provide insight into mechanisms of community invasibility, grass-firefeedbacks, and aid the development of species-specific management plans.