Using heat plumes to simulate post-fire effects on cambial viability and hydraulic performance in Sequoia...

Area of Science:

• Plant physiology
• Forest ecology
• Fire science

Background:

• Low severity fires can cause mortality in trees.
• Xylem and vascular cambium injury are proposed causes, but their relative importance is unclear.
• This study investigates the role of xylem dysfunction versus cambium necrosis in fire-induced mortality.

Purpose of the Study:

• To simultaneously evaluate the xylem dysfunction and cambium necrosis hypotheses.
• To determine the relative impact of heat exposure on vascular cambium viability and xylem hydraulic conductivity in Sequoia sempervirens.
• To assess the effect of heat stress on post-fire vulnerability to embolism.

Main Methods:

• Simulated low severity fire conditions using a drying oven (70 and 100 °C for 6-60 min) on Sequoia sempervirens shoots.
• Assessed cambial viability using Neutral Red stain.
• Measured water transport capacity by calculating loss of hydraulic conductivity and constructed vulnerability curves.

Main Results:

• Vascular cambium necrosis occurred rapidly at 100 °C (6 min) and survived longer at 70 °C (15 min).
• Heat exposure significantly reduced hydraulic conductivity (e.g., 40% at 70 °C for 60 min; 100% at 100 °C for 45 min).
• Heat treatments caused irreversible hydraulic conductivity loss but did not significantly alter post-fire embolism susceptibility.

Conclusions:

• High temperatures damage vascular cambium more rapidly than xylem.
• Xylem remained functional under treatments that caused complete cambium death.
• Vascular cambium viability appears more critical for post-fire survival in Sequoia sempervirens than xylem function.