Historical Fire and Ventenata dubia Invasion in a Temperate Grassland

Ventenata (Ventenata dubia L.) is an invasive annual grass that has rapidly expanded its range across temperate grassland and shrub-steppe ecosystems in western North America. However, there is little published regarding its ecology, especially its relationship with fire on rangelands. The objective of this study was to examine the effect of fire on ventenata invasion in the Pacific Northwest Bunchgrass (PNB) Prairie. Given the influence of fire on the invasion of other annual grasses such as cheatgrass ( Bromus tectorum L.), we expected that fire would facilitate the spread and increase in abundance of ventenata. In addition, we considered that annual variation in precipitation might mask the effect of fire and drive the year-to-year variation in production of ventenata. Therefore, we resampled 56 plots in 2015 and 2016 where frequency and foliar cover of ventenata had been recorded in 2008 and where 12 of these plots had burned in the past 15 yr. We then compared ventenata abundance (frequency and foliar cover) be- tween burned and unburned plots within each sampling yr (2008, 2015, and 2016), as well as the change in abundance over time. Our data revealed that ventenata frequency and cover increased on all plots. However, there was not significantly higher abundance in burned plots in any of the sampling years. In addition, ventenata abundance did not increase more in burned plots over time. Our findings suggest that, unlike cheatgrass, fire may not be a driving factor in the spread and increase of ventenata across the PNB Prairie. This finding has important implications for the management and control of ventenata, as well as the conservation of the PNB Prairie.