Effects of Wildfire on Wood Properties of Surviving Ponderosa Pine in the Plumas National Forest

Wildfires are increasing in frequency and severity across western U.S. forests, affecting tree survival and wood quality. Ponderosa pine (Pinus ponderosa Dougl.) is adapted to frequent, low-intensity fire. Its thick bark and fire tolerance allows mature trees to survive wildfire; however, survival does not mean the tree is unaffected. Fire may cause scars, bark scorch, crown damage, and changes in wood properties. These impacts are hidden inside the stem and may alter density, stiffness, and strength.

Despite increasing interest in fire’s impact on forest structure, the effects of wildfires on wood properties of surviving ponderosa pine remain poorly understood. This study addresses that gap by examining the effects of wildfire frequency on wood density, modulus of elasticity (MOE), and modulus of rupture (MOR) in surviving ponderosa pine trees. Eighteen trees were sampled from the Plumas National Forest, with three fire-treatment classes: six trees from an unburned control plot, six from a one-burn plot, and six from a two-burn plot. Small, clear specimens were prepared from each tree for density and mechanical testing following ASTM standards.

Preliminary results indicate that wildfire history affects wood properties. Density differed significantly between the two-burn and one-burn treatments but did not differ between the two-burn and control trees. Mechanical properties showed stronger fire-related impacts, with MOE and MOR displaying greater variability in burned trees, especially those exposed to multiple fires. Control trees exhibited more uniform radial trends, while burned trees had inconsistent profiles, suggesting heightened structural variability following fire. The study shows that surviving ponderosa pine trees experience measurable internal changes in wood quality after wildfire, particularly when exposed to repeated burns. These findings underscore the importance of considering fire history when assessing wood quality in fire-affected forests and highlight the need to account for radial variation in future evaluations of fire-surviving trees.