The authors found that in ponderosa pine forests, low- and moderate- severity resource benefit fires more effectively reduced basal area and crown fire potential more so than prescribed fires. Areas burned multiple times for resource benefit maintained stand structure and fuel loads more consistent with historical forest conditions. Low severity fire in pinyon-juniper woodlands did not have an effect on forest structure and fuels, however, moderate severity fire did have beneficial effects on these ecosystems.

The authors found that topography had a stronger influence on burn severity than climate (temperature and precipitation), but that climate before and during the fire was still a significant predictor of burn severity. The authors suggest that climate conditions can overwhelm topographic limitations on area burned and fire severity during dry years with widespread fire. 

The author found that extreme fire weather values are most strongly associated with circulation patterns of high gradient, southwest flow across the Southwest creating strong winds. Early season variability in the relative humidity also related strongly to increased levels of fire danger. Seasonal changes in relative humidity levels, strength of height gradient, and geopotential heights were all important in modeling the relationship between synoptic circulation patterns and extreme fire-weather days.

Climate change projections suggest a shift toward hotter and drier conditions across the west resulting in an approximately 50 to 500% increase in area burned across the western U.S. Fire will continue to play an important role in shaping future forests affected by climate change. Forest restoration based on historical reference conditions is consistent with resilience to the changing climate and an increase in fire. 

The authors found that stands affected by bark beetle outbreaks had higher surface fuel loadings, but lower canopy fuel loadings than unaffected stands. The bark beetle outbreaks were partially driven by tree stress due to drought conditions. The authors suggest that future trends toward more frequent and longer-term drought may result in increases in bark beetle activity, alterations to fuel loads and subsequent increases in fire hazard.

Overall, the authors found that fire and fire exclusion is unlikely responsible for the change in mortality rates in the coniferous western forests of the western U.S. and British Colombia, Canada. Instead, the authors suggest that warming and subsequent hydroclimate changes is directly responsible for the increased mortality rate.

The authors found no significant difference between their models of fire-climate relationship before and after 1600 CE suggesting that the historical range of variation drawn from fire chronologies from c. 1600 to 1900 CE are useful analogs for current and future restoration and management purposes. The authors also found that a dry year preceeded by a wet year 1-3 years earlier was a strong predictor of fire activity throughout the fire record (572 – 1987 CE). An atypically long fire-free period occurred between 1360 to 1455 CE during an unusually wet period. This was followed by high-severity fires during the Medieval Climate Anomaly in the late fourteenth or fifteenth century likely driven by drought conditions and the increase in fuels from the prior century.

Gambel oak can survive in forests dominated by frequent fire regimes, although top kill by fire is common. However, it is a prolific resprouter and will survive even intense wildfire and may even become the dominant species if frequent high-severity wildfire eliminates competing vegetation. The frequency and intensity of prescribed fire could be used as a tool to alter the species composition of pine-oak forests by maintaining a variety of oak growth forms. Several tactics may enhance survival of large oaks during prescribed fire: keeping pine slash away from oak boles, avoiding lighting near oaks or reducing fire intensity near oaks, and raking fuels away from oak boles.

The authors found that low- or moderate-severity fires generally regulated subsequent fires to similar severities, similar to historical patterns of frequent, low-severity fires in dry coniferous forest systems. Smaller burns created openings in both the understory and overstory vegetation, which adds diversity to the landscape, provides mechanisms for plant succession, and promotes differential tree establishment. In contrast to small burns, they found that large burns may create a homogeneous setting of burned areas which may not enhance species diversity following fire. Finally, the authors suggest that although typically previous fires kept the spread of subsequent fires in check most of the time, climate and weather can override fuel limitations and spread into recently burned landscapes.

The authors found that periods of drought were significantly related to fire occurrence during El Niño oscillations; however, this trend was interrupted in the 1940’s and 1950’s, likely by the introduction to logging and livestock grazing in the area. This interruption of the fire regime also resulting in an increase in tree establishment, especially oak and other broadleaf tree species.