Feeding the fire: Annual grass invasion facilitates modeled fire spread across Inland Northwest forest?mosaic landscapes

Invasive annual grasses are a growing global concern because they facilitate larger and more frequent fires in historically fuel-limited ecosystems. Forests of the western United States have remained relatively resistant to invasion by their subsequent impacts. However, where forests adjacent invaded areas, increased fire spread across ecotones could alter behavior ecosystem resilience. In Inland Northwest, USA, recent grass ventenata (Ventenata dubia) has fine fuel loads continuity nonforest patches embedded within forested landscape. Despite ventenata's rapid American West management concern, little is known regarding how influences vegetation types or its potential landscape-scale practices. Here, we examine alters simulated forest-mosaic landscapes 7 million ha Blue Mountains Ecoregion using large simulator (FSim) with custom landscapes: present-day versus historic uninvaded. Invasion mean size, burn probability, flame lengths throughout ecoregion, strength these impacts varied location scale. Changes at ecoregion scale were modest given that fuels only 2.8% types. strong localized changes (primarily dwarf-shrublands) facilitated into nearby forests. Within patches, probabilities 45%, higher required strategies shift from direct indirect attack, requiring machinery. 25% neighborhood experienced 28% increase probability 16% experiencing likely produce crown (flame >2.4 m). Increased canopy loss severe implications for forest resilience invasive can heavily invade early seral dry conifer limit postfire recovery. Our study demonstrates influence despite primarily invading nonforested highlights as an important issue expansive ecosystem.