The fire effects on Pinus ponderosa sapling physiology

Event Details

Nov 21 2019, 11am - 12pm

2019-2020 Seminar Series

Requel Feltrin, University of Idaho

Longer periods of drought and warmer global temperatures has favored the occurrence of wildfires in forest ecosystems. With predictions of increase in severity and extent of wildfires due to climate change, understanding how fire affects trees and the causes that lead to post-fire tree mortality are urgently needed. Previously, cambium, foliage, and bud damage due to fire have being studied. However, the physiological mechanisms that lead to tree death after a forest fire is not understood. In the last decade, xylem hydraulic failure has been proposed to be the main cause of post-fire tree mortality due to deformation of xylem conduits and increases in vapor pressure deficit (VPD) during forest fires. In this study, two separate experiments were conducted with wellwatered Pinus ponderosa saplings exposed to fire. Xylem hydraulic conductivity was assessed one day and 21 months after fire exposure to better understand the effects of fire in the short- and long- term. In experiment 1, saplings were divided in two treatments: unburned and burned with a lethal fire intensity of 1.4 MJ m-2. In experiment 2, plants were placed in three treatments: unburned and burned with 0.7 and 1.4 MJ m-2. Native percentage loss of conductivity (nPLC), vulnerability to cavitation, and deformation of xylem tracheid were assessed. nPLC was not affected in either experiment. Plants evaluated one-day post fire did not show any evidence of being more vulnerable to xylem cavitation. However, we found that plants were more vulnerable to cavitation after 21 months. In neither experiment we did observe deformation of the xylem of plants exposed to the fire. We conclude that hydraulic failure was not the main cause of post-fire tree mortality and suggest that other physiological mechanisms such as depletion of carbohydrates could lead to tree mortality. We also did not find any evidence of conduit deformation that has been proposed as the consequence of hydraulic failure and vulnerability to cavitation in post-fire trees. However, saplings exposed to the fire are more vulnerable to cavitation after 21 months, thus we suggest that the irregularity of the newly grown xylem cells closer to the wound caused by the heat can contribute to plants that survive fires being more vulnerable to xylem embolism.

Missoula Fire Sciences Laboratory

Rocky Mountain Research Station (RMRS)
Fire, Fuel, and Smoke Science (FFS) Program

The fire effects on Pinus ponderosa sapling physiology