Effects of plant hydraulic traits on the flammability of live fine canopy fuels in 62 Australian plant species

Plant species vary in how they regulate moisture and this has implications
for their flammability during wildfires. We explored how fuel moisture is
shaped by variation within six hydraulic traits: saturated moisture
content, cell wall rigidity, cell solute potential, symplastic water
fraction and tissue capacitance. Using pressure-volume curves, we measured
these hydraulic traits distal shoots (i.e. twigs + leaves) in 62 plant
species across four wooded communities in south-eastern Australia. For a
subset of 30 of those species, we also measured hydraulic traits of twigs
using moisture-release curves. Moisture content of fine fuels was then
estimated for circumstances typical of fire weather. These projections
were made assuming that under the hot, dry, windy conditions typical of
large wildfires, leaves and fine twigs would function at internal water
pressures close to wilting point (i.e. turgor loss point, TLP). The effect
of different moisture contents at TLP on ignition time was then modelled
using a fully mechanistic, finite element model of biomass ignition based
on standard principles of physical chemistry. We also measured predawn
water potential, an indication of plant access to soil water that is
influenced by root architecture. These data were used to model how root
traits influence fuel moisture and ignition time.