Contemporary fires are less frequent but more severe in dry conifer forests of the southwestern United States

How do you study forest fire history?

After a forest fire, surviving trees will continue to grow new layers of wood to heal fire injuries. As tree rings provide information about the growth history and age of trees, scientists can use tree-ring fire scars to obtain information about the year, season, severity, frequency, size, and fire-climate relationships of fires that occurred centuries to millennia prior to modern records. 

In this study, researchers quantified modern fire severity at hundreds of tree-ring fire-scar sites across the Southwest. They specifically chose sites which had historically burned frequently with low-severity fire for centuries prior to human-driven fire exclusion. 

Wildfires have become less frequent but more severe

Researchers found that, even with the increase in fire in recent decades, dry conifer forests are burning at less than 20% of historical levels. In addition, they found these forests are now burning at greater fire severity, often killing forests that survived many fires in the past. 

Moreover, suppressed wildfires tended to burn more severely than prescribed burns and wildfires managed for resource benefit. These findings inform the restoration of low-severity fire to dry conifer forests to increase resilience to increasing high-severity fire.