| Abstract | 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 the V. dubia invasion and examine how these
differ between V. dubia and other problematic non-native annual grasses, Bromus
tectorum and Taeniatherum caput-medusae; and (2) determine how burning influences
relationships between V. dubia and 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
of V. dubia cover, elevations, biophysical classes, and fire severities. We investigated
relationships between V. dubia, wildfire, environmental, and plant community characteristics
using non-metric multidimensional scaling and linear regressions.
Results: Ventenata dubia was most abundant in sparsely vegetated, basalt-derived
rocky scablands interspersed throughout the forested landscape. Plant communities
most heavily invaded by V. dubia were largely uninvaded by other non-native annual
grasses. Ventenata dubia was abundant in both unburned and burned areas, but negative
relationships between V. dubia cover and community diversity were stronger in
burned plots, where keystone sagebrush species were largely absent after fire.
Conclusions: Ventenata dubia is expanding the overall invasion footprint into previously
uninvaded communities. Burning may exacerbate negative relationships between
V. dubia and species richness, evenness, and functional diversity, including in
communities that historically rarely burned. Understanding the drivers and impacts
of the V. dubia invasion 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.
|
