Short- and long-term effects of fire on stem hydraulics inPinus ponderosasaplings

Understanding tree physiological responses to fire is needed to accurately model post-fire carbon processes and inform management decisions. Given trees can die immediately or at extended time periods after fire, we combined two experiments to assess the short- (one-day) and long-term (21-months) fire effects onPinus ponderosasapling water transport. Native percentage loss of conductivity (nPLC), vulnerability to cavitation and xylem anatomy were assessed in unburned and burned saplings at lethal and non-lethal fire intensities. Fire did not cause any impact onnPLC and xylem cell wall structure in either experiment. However, surviving saplings evaluated 21-months post-fire were more vulnerable to cavitation. Our anatomical analysis in the long-term experiment showed that new xylem growth adjacent to fire scars had irregular-shaped tracheids and many parenchyma cells. Given conduit cell wall deformation was not observed in the long-term experiment, we suggest that the irregularity of newly grown xylem cells nearby fire wounds may be responsible for decreasing resistance to embolism in burned plants. Our findings suggest that hydraulic failure is not the main short-term physiological driver of mortality forPinus ponderosasaplings. However, the decrease in embolism resistance in fire-wounded saplings could contribute to sapling mortality in the years following fire.

Automated summary

Understanding tree physiological responses to fire is crucial to accurately model post-fire carbon processes and inform management decisions. Two experiments were conducted to assess short- and long-term fire effects on Pinus ponderosa sapling water transport. While fire did not impact native percentage loss of conductivity and xylem cell wall structure, surviving saplings were found to be more vulnerable to cavitation 21 months post-fire, suggesting decreased resistance to embolism in fire-wounded plants may contribute to sapling mortality in the years following fire.