Fig. 3

A conceptual model of the interaction of herbaceous and shrub (woody) fuels with fire weather severity in sagebrush ecosystems that are not experiencing pinyon-juniper expansion. Fuel composition is displayed on the y-axis and fire weather condition is displayed on the x-axis. Low fire weather severity is characterized by high fuel moistures, high relative humidity, low temperature, and low wind speeds, while extreme fire weather is characterized by the opposite conditions. As shrub fuel loading increases (low on the y-axis) or fine fuel loading increases (high on the y-axis), fuel continuity increases, and less severe fire weather is required for large wildfires. Annual grasses, represented by the area in yellow in the upper left, produce fine fuels that can fill interspaces between native fuels (shrubs and grasses) and are particularly problematic. Extreme fire weather conditions, which are projected to increase in the future, can override the influence of fuel loads and continuity. Figure modified from Strand et al. (2014)