Using Hotspot Analysis and Detection of Early Season Invasives (DESI) to analyze the temporal and spatial dynamics of invasive cheatgrass (Bromus tectorum).

The invasion of exotic annual grasses during the last century has transformed plant habitats and communities worldwide. Cheatgrass (Bromus tectorum) is a winter annual grass that has invaded over 100 million acres of the western United States (Pellant and Hall, 1994. Pellant, 1996). Cheatgrass quickly utilizes available resources especially after a disturbance to the landscape. A major impact of invasion is the increased frequency in fires (D’Antonio and Vitousek, 1992). As cheatgrass is highly successful at invading open and disturbed landscapes at a rapid pace it increases the frequency and severity of fires in arid landscapes (Brooks, 2005). Cheatgrass’ prolific seed production and flammability allows it to competitively exclude native plant species (Seabloom et al., 2003). The successful life strategy of cheatgrass gives a unique spectral image reflectance that can allow the use of remote sensing platforms to track and locate invasions

Using sUAV imagery to map litter of invasive annual grass in dry environmental conditions

Invasive annual grasses pose a severe threat to drylands of the United States by increasing habitat degradation and the occurrence and severity of wildfires, while simultaneously outcompeting native species. Advances in technology and accessibility of small uncrewed aerial vehicles (sUAV) provide the opportunity for small preserve managers to map and monitor plant invasions in critical habitats for rare and endemic plant species. Many remote sensing techniques rely on the invasive plants' different phenological signals to distinguish them from native plants and habitats. However, invasive annual grasses in the western United States have high variability of interannual productivity and may not green up each year. Therefore, our objective was to use an sUAV (quadcopter drone) to map invasive annual grass regardless of phenological stage in critical Mojave Desert habitat. The study locations were White Dome, a small habitat preserve, and Beehive Dome in Washington County UT, USA. These areas are critical habitats for several endangered and threatened plant species and are covered with sensitive biological soil crusts, making on-the-ground measurements destructive. Using imagery collected with an sUAV we created red, green, blue (RGB) orthomosaics and calculated the Visible Atmospherically Resistant Index (VARI) across these areas. We successfully mapped the litter of invasive annual grasses at one of the two sites. At White Dome, we attained 95.2 % and 84.3 % Producer's and User's Accuracy in mapping invasive annual grasses based on the RGB spectral signature of invasive grass litter. At Beehive Dome, the heterogeneous nature of the edaphic and topographical features made it difficult to accurately map (<20 %) using VARI and RGB alone. Here, we propose plans to increase accuracy in these dryland systems to be able to map invasive annual grasses regardless of year or environmental conditions

Data from: Loss of biotic resistance and high propagule pressure promote invasive grass-fire cycles

1. The spread of invasive grasses across Earth are modifying fire cycles resulting in state changes in arid ecosystems. Disturbance, biotic resistance of native biological communities and propagule pressure, are likely important factors influencing the spread of invasive grasses and their influence on changing fire regimes. 2. Over a five-year period (2011-2016), we tested how the potential loss of biotic resistance of native plant and native rodent communities related to fire and rodent exclusion treatments, in concert with increased propagule pressure affected the establishment of Bromus tectorum L. (cheatgrass) and the spread of secondary fires. 3. Our study results suggest that native plant and native rodent communities contribute to biotic resistance against cheatgrass invasion and that fire and high propagule pressure act to diminish biotic resistance by native communities. Five years into the study, cheatgrass establishment was 11-fold greater in burned plots than in unburned plots (with native plant communities still intact), 2.4-fold greater in rodent exclusion plots than rodent access plots, and 1.8-fold greater with increased propagule pressure. At the start of the experiment in 2011 and into 2012 there was very little cheatgrass in the experimental blocks (<1 plant m-2). However, by 2016, burned-rodent excluded plots were fully invaded (1625 stems m-2). High propagule pressure released cheatgrass from biotic resistance of rodent communities in post-fire conditions but had minimal effects on the biotic resistance of native plant communities in unburned plots. Fire in combination with either rodent exclusion or high cheatgrass propagule pressure produced higher density cheatgrass stands that were positively correlated with the spread of secondary fires that are characteristic of invasive grass-fire cycles. 4. Synthesis. Loss of native plant cover or reduction in rodent populations due to fire, extreme climatic events or disease outbreaks, which are increasing with human activity, may provide windows of opportunity for invasive grasses to escape biotic resistance and reinforce invasive grass-fire cycles

Data from: Loss of biotic resistance and high propagule pressure promote invasive grass-fire cycles

1. The spread of invasive grasses across Earth are modifying fire cycles resulting in state changes in arid ecosystems. Disturbance, biotic resistance of native biological communities and propagule pressure, are likely important factors influencing the spread of invasive grasses and their influence on changing fire regimes. 2. Over a five-year period (2011-2016), we tested how the potential loss of biotic resistance of native plant and native rodent communities related to fire and rodent exclusion treatments, in concert with increased propagule pressure affected the establishment of Bromus tectorum L. (cheatgrass) and the spread of secondary fires. 3. Our study results suggest that native plant and native rodent communities contribute to biotic resistance against cheatgrass invasion and that fire and high propagule pressure act to diminish biotic resistance by native communities. Five years into the study, cheatgrass establishment was 11-fold greater in burned plots than in unburned plots (with native plant communities still intact), 2.4-fold greater in rodent exclusion plots than rodent access plots, and 1.8-fold greater with increased propagule pressure. At the start of the experiment in 2011 and into 2012 there was very little cheatgrass in the experimental blocks (<1 plant m-2). However, by 2016, burned-rodent excluded plots were fully invaded (1625 stems m-2). High propagule pressure released cheatgrass from biotic resistance of rodent communities in post-fire conditions but had minimal effects on the biotic resistance of native plant communities in unburned plots. Fire in combination with either rodent exclusion or high cheatgrass propagule pressure produced higher density cheatgrass stands that were positively correlated with the spread of secondary fires that are characteristic of invasive grass-fire cycles. 4. Synthesis. Loss of native plant cover or reduction in rodent populations due to fire, extreme climatic events or disease outbreaks, which are increasing with human activity, may provide windows of opportunity for invasive grasses to escape biotic resistance and reinforce invasive grass-fire cycles

Hotspot Analysis Reveals Large Landscape Controls Over Cheatgrass (Bromus tectorum) Persistence Across Arid Landscapes

The invasion of exotic annual grasses during the last century has transformed plant habitats and communities worldwide. Cheatgrass (Bromus tectorum) is a winter annual grass that has invaded over 100 million acres of the western United States (Pellant and Hall, 1994. Pellant, 1996). Cheatgrass has relatively rapid growth rate and has been shown to invade particularly in post-disturbance landscapes (Germino 2016). A major impact of invasion is the increased frequency in fires (D’Antonio and Vitousek, 1992). Cheatgrass’ prolific seed production and flammability allows it to competitively exclude native plant species (Seabloom et al., 2003). The successful life strategy of cheatgrass gives a unique spectral image reflectance that can allow the use of remote sensing platforms to track and locate invasions