How do fires kill plants? The hydraulic death hypothesis and Cape Proteaceae “fire-resisters”

The actual mechanism which causes plant death after having been burned has been poorly studied. One possibility is that fire causes direct, or indirect, fatal damage to plant hydraulic systems. If true, this suggests that burned plants ultimately die of drought. This hypothesis was tested on the post-fire response of a “fire-resister” species of the Cape Proteaceae, as well as by analysing its morphology. Fire-resisters are plants which are incapable of resprouting, but nevertheless survive some fires. Mortality of the studied fire-resister appears to be compatible with a hydraulic death hypothesis because i) most post-fire mortality occurred within days, ii) it occurred from the base-upwards and iii) correlated negatively with stem diameter rather than plant height. Higher levels of survival of the fire-resister is probably due to absolutely thicker bark than co-occurring re-seeder species of the same age. Since this bark has not evolved to protect buds, it has probably evolved to protect stem hydraulic systems.

Research Highlights
► Plants die rapidly after fire and from the base upwards.
► Plant death after fire may be due to hydraulic death rather than meristematic death.
► Plants protect themselves from hydraulic death by absolutely thick bark rather than relatively thick bark.