Expanding The Invasion Footprint:Ventenata Dubiaand 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 challenging previous conceptions of community resistance in forest mosaic communities in the Inland Northwest. However, little is known of the drivers and potential ecological impacts of this rapidly expanding species. Here we (1) identify abiotic and biotic habitat characteristics associated with theV. dubiainvasion and examine how these differ betweenV. dubiaand other problematic non-native annual grasses,Bromus tectorumandTaeniatherum caput-medusae; and (2) determine how burning influences relationships betweenV. dubiaand plant community composition and structure to address 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 110 recently burned and nearby unburned plots. Plots were stratified to capture a range ofV. dubiacover, elevations, biophysical classes, and fire severities. We investigated relationships betweenV. dubia, wildfire, environmental, and plant community characteristics using non-metric multidimensional scaling and linear regressions. Results Ventenata dubiawas most abundant in sparsely vegetated, basalt-derived rocky scablands interspersed throughout the forested landscape. Plant communities most heavily invaded byV. dubiawere largely uninvaded by other non-native annual grasses.Ventenata dubiawas abundant in both unburned and burned areas, but negative relationships betweenV. dubiacover and community diversity were stronger in burned plots, where keystone sagebrush species were largely absent after fire. Conclusions Ventenata dubiais expanding the overall invasion footprint into previously uninvaded communities. Burning may exacerbate negative relationships betweenV. dubiaand species richness, evenness, and functional diversity, including in communities that historically rarely burned. Understanding the drivers and impacts of theV. dubiainvasion and recognizing how these differ from other annual grass invasions may provide insight into mechanisms of community invasibility, grass-fire feedbacks, and aid the development of species-specific management plans.