Wildfire effects on physiological properties in conifers of central Idaho forests, USA

Key message Conifers which substantially lost foliage in wildfires were also reduced in their relative hydraulic capacity, resulting in little change in water use efficiency. Wildfires are a natural and ubiquitous component of many forests. Fire-induced damages can lead to immediate tree mortality or a prolonged state of decline. However, physiological mechanisms behind the phenomenon are not well understood. We investigated physiological properties of conifers that survived wildfire 2 year post-fire in central Idaho, USA. In 2005, we set up a burned plot at each of three sites, where the independent wildfires damaged dominant conifers in 2003, paired with a comparable adjacent control plot without any fire damage. At each burned plot, we assessed physical damages in the burned conifers. At each plot in a given site, we repeatedly measured physiological characteristics in five trees of a dominant conifer species ( Pseudotsuga menziesii or Pinus contorta ) to compare burned and control plots across the three sites during the 2005 growing season. Growth of the burned conifers was significantly reduced post-fire. Leaf area of burned conifers was significantly reduced due to scorching, which, in theory, should have led to increased stomatal conductance ( g s ) and leaf specific conductance ( K L ). However, we did not find significant differences in K L between burned and control conifers, and g s was sometimes even lower in burned than control conifers. These results indicate the wildfires reduced capacity of hydraulic apparatus in the surviving conifers, partly due to reduced sapwood area associated with the decreased stem growth post-fire. This was supported by our finding that integrated water use efficiency, assessed via δ 13 C of woody materials and foliage, was not significantly affected by the wildfires.