Exotic plant invasions are a growing challenge to the management of native biodiversity, ecosystem functioning, and fuels and fire management. Exotic annual grasses that alter fire regimes are recognized as some of the most important ecosystem-altering species on the planet. Grasses such as cheatgrass and medusahead are negatively impacting millions of hectares across the Great Basin by fundamentally altering the ecosystems in which they invade. A similar threat is developing in the forestlands of the interior Pacific Northwest region with a relatively new invasive annual grass, Ventenata dubia (ventenata, North Africa grass). Ventenata thrives at higher elevations than does cheatgrass, where it threatens native forest biodiversity and is creating ecosystem-level changes. We are conducting a multi-phased landscape scale project focused on the Blue Mountain Ecoregion (BME) of Oregon, Washington, and Idaho (all lands) to examine the extent of ventenata invasion and associated ecosystem change. In this first phase, we will map ventenata distribution across the BME by developing spatially explicit predictive models that relate georeferenced field and survey data of ventenata occurrence and abundance to satellite imagery and existing ancillary geospatial data characterizing biophysical variables (gridded climate, topography, and soils).
Results/Conclusions
Initial assessment of georeferenced occurrence data showed that ventenata largely occurs in open meadows and scablands (less than 5% canopy cover) interspersed within the forest matrix. Spatial data from our first training data area in the BME, the Starkey Experimental Forest, showed that about 27% of the forest was classified as open grasslands/scablands. The average patch size of these open areas was about 68,000 m2 (range 1000-1,600,000 m2). Plots surveys in these open areas showed that ventenata was the dominant species in 90% of the plots. The infilling of these open areas, once dominated by low statured native species, bare soil and cryptograms, represents a major change in fuel structure. The spatial arrangement of fuels across the landscape is a critical driver of wildland fire behavior. The ventenata invasion may lead to rapid fire spread across the landscape due to fire carrying through open areas once largely not vulnerable to burning. For the second and third phases of our research, we will examine how fuels, fire regimes, and fire effects have shifted across the region and how these changes might affect management. We will also depict alternative future scenarios of ecosystem change associated with future climate change and management actions.