Mixed-Conifer Management

The stability of seasonally dry Western mixed-conifer forests is threatened by the history of fire suppression, logging, and now increasing climate-driven aridity. Durable aboveground carbon storage in living trees–a key ecosystem service of these fire-adapted forests–is at risk due to the disruption of natural fire cycles.

Background

Successive catastrophic wildfire seasons in western North America have escalated the urgency around reducing fire risk to communities and ecosystems. In historically frequent-fire forests, fuel buildup as a result of fire exclusion is contributing to increased fire severity.

Fire-caused tree mortality has major impacts on forest ecosystems. One primary cause of post-fire tree mortality in non-resprouting species is crown scorch, the percentage of foliage in a crown that is killed by heat. Despite its importance, the heat required to kill foliage is not well-understood.

Gap-based silviculture, which we define as the creation and maintenance of multi-aged stands through the periodic harvesting of discrete canopy gaps, provides a potential mechanism for converting previously high-graded stands into more heterogeneous, multi-aged structures.

In many parts of the western United States, wildfires are becoming larger and more severe, threatening the persistence of forest ecosystems. Understanding the ways in which management activities such as prescribed fire and managed wildfire can mitigate fire severity is essential for developing effective forest conservation strategies.

In recent decades, bark beetle outbreaks have caused mass tree mortality in western US forests, which has led to altered wildfire characteristics, hydrological processes, and forest carbon dynamics.

Wildfires and other disturbances play a fundamental role in regenerating lodgepole pine forests. Though severe, stand-replacing fires are typical of this ecosystem, they can have dramatic impacts on soil properties and biogeochemical processes that influence the rate and composition of vegetation recovery.

Fire exclusion over the last two centuries has driven a significant fire deficit in the forests of western North America, leading to widespread changes in the composition and structure of these historically fire-adapted ecosystems.

Fire and drought are expected to increase in frequency and severity in temperate forests due to climate change. To evaluate whether drought increases the likelihood of post-fire tree mortality, we used a large database of tree survival and mortality from 32 years of wildland fires covering four dominant western North American conifers.