Hydraulic segmentation does not protect stems from acute water loss during fire

Area of Science:

• Plant Physiology
• Fire Ecology
• Forest Science

Background:

• The fire plume hypothesis suggests heat from fires causes tree water loss, potentially leading to hydraulic failure.
• It remains unclear if trees can sustain high water loss during fire events due to the integrity of their water transport systems.

Purpose of the Study:

• To investigate water uptake in Magnolia grandiflora branches exposed to varying fire intensities.
• To determine factors influencing water uptake post-fire.

Main Methods:

• Branches of Magnolia grandiflora were subjected to controlled fire intensities.
• Water uptake was measured during and after fire exposure.
• Factors affecting post-fire water uptake were analyzed.

Main Results:

• Burning induced a 22-fold increase in water uptake, with maximum loss at high intensities consuming leaves.
• High water loss rates suggest steep water potential gradients, likely causing xylem cavitation.
• Post-fire water uptake occurred, primarily due to tissue rehydration, especially after moderate burns that killed but did not consume leaves.

Conclusions:

• The fire plume hypothesis is supported across a broader range of fire conditions.
• Trees sustain high water loss rates during fires, even when foliage is severely damaged or destroyed.
• Hydraulic integrity and rehydration dynamics are critical factors in tree survival post-fire.