The interaction between climate and fire may further alter vegetation communities. The effect that climate change will have on fire regimes strongly depends on the vegetation type—fires in particular vegetation types can be limited by fuel moisture or fuel availability, or both. For example, spruce-fir forests, which are relatively wet forests, naturally experience infrequent, high-severity fires, usually during drought. Therefore a shift to more arid conditions would result in more severe fires (Schoennagel et al. 2004). The fire severity in mixed conifer forests, which typically occur along a complex moisture gradient on elevations between spruce-fir forests and ponderosa pine forests, is controlled by both climate and fuel availability. Drier conditions would result in a mosiac of fire effects on the landscape, where the fire regimes of the wetter sections of the forests would be more influenced by extended drought (Schoennagel et al. 2004). Ponderosa pine forests, which are typically drier and occur at lower elevations than spruce-fir and mixed conifer forests, historically experienced frequent, low-intensity fires that were limited by the availability of fine fuels. However, 20th century fire suppression has resulted in increased tree density; therefore, the fires that occur are high severity, stand-replacing fires (Schoennagel et al. 2004). The fire regimes in pinyon-juniper woodlands are not as well studied as the fire regimes in higher elevation plant communities. Large, stand-replacing fires in pinyon-juniper woodlands have been occurring more frequently since the 1980s, but not enough evidence on historical fire regimes exists to determine whether this increase in large fires is due to climate (Romme 2009). While the recent increased frequency of large wildfires across the West is associated with earlier spring snowmelts or spring or summer temperatures, this is not the case in the Southwest, likely because extended drought is not the only influence on severe fires in the major forest types of the region (Westerling et al. 2006).