Mixed-Conifer Management

In the mountainous regions of the Western United States, increasing wildfire activity and climate change are putting forests at risk of regeneration failure and conversion to non-forests. During periods with unfavorable climatic conditions, locations that are suitable for post-fire tree regeneration (regeneration refugia) may be essential for forest recovery.

Accurate estimates of available live crown fuel loads are critical for understanding potential wildland fire behavior. Existing crown fire behavior models assume that available crown fuels are limited to all tree foliage and half of the fine branches less than 6 mm in diameter (1 h fuel). They also assume that this relationship is independent of the branchwood moisture content.

Fire exclusion and past management have altered the composition, structure, and function of frequent-fire forests throughout western North America. In mixed-conifer forests of the California Sierra Nevada, fire exclusion has exacerbated the effects of drought and endemic bark beetles, resulting in extensive mortality of fire-adapted pine species.

Tree regeneration is a critical mechanism of forest resilience to stand-replacing wildfire (i.e., where fire results in >90 % tree mortality), and post-fire regeneration is a concern worldwide as the climate becomes warmer.

Climate change and disturbance are altering forests and the rates and locations of tree regeneration. In semi-arid forests of the southwestern USA, limitations imposed by hot and dry conditions are likely to influence seedling survival.

High-severity fires and short-interval reburns strongly influence forest structure and composition and may overwhelm forest ecosystem resilience and catalyze persistent shifts to non-forest conditions.

Dry conifer forests in the western US historically experienced frequent fire prior to European American colonization. Mean fire return interval ranged from about 5–35 years, with the majority of fires burning at low-to-moderate severity.

Climate warming, land use change, and altered fire regimes are driving ecological transformations that can have critical effects on Earth's biota. Fire refugia—locations that are burned less frequently or severely than their surroundings—may act as sites of relative stability during this period of rapid change by being resistant to fire and supporting post-fire recovery in adjacent areas.