Live Fuels, Foliar Moisture, and Fire Behavior

The central theme is of this ongoing body of research is that live fuels should not be treated as static fuel categories. Vegetation responds to seasonal conditions, water availability, drought stress, and physiological change. These responses can affect the amount of moisture retained in foliage and the way live vegetation ignites and burns. Understanding these processes can improve descriptions of wildland fuels and support more accurate assessments of fire potential.

Photo Credit

Photo courtesy of Mike Lehman, Wisconsin DNR.

Ground-level view of a typical red pine crown fire. 

Research on red pine and jack pine demonstrates that foliar moisture, chemistry, density, and flammability vary throughout the year. These seasonal changes may help explain periods of increased crown-fire activity, including the spring decline in foliar moisture—often referred to as the “spring dip”—observed in the Great Lakes region of the United States. This work provides a scientific basis for examining the relationship between seasonal foliar conditions and crown-fire behavior.

The pyro-ecophysiological framework further connects plant physiology with combustion. It recognizes that characteristics such as plant water status, tissue moisture, and physiological stress can influence the flammability of live vegetation. This approach provides a foundation for understanding how biological processes affect the behavior of live fuels during wildland fire.

More recent research applies this framework to both conifers and common shrubs. By combining ecophysiological indicators with combustion-related traits, these studies seek to improve predictions of live-fuel moisture content across different vegetation types. Improved prediction of live-fuel moisture can support better fuel characterization, fire-danger assessment, and fire-behavior modeling.

Together, this research advances an integrated understanding of live fuels as dynamic components of the wildland fuel complex. It links seasonal vegetation change, plant physiology, foliar moisture, and combustion behavior to improve understanding of when and where live fuels may contribute to increased fire activity. The work also supports continued development of methods for monitoring live fuels and incorporating their changing characteristics into fire-management applications.