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

Full description

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.

Methods

For full details of methods, see Scarff et al (2021). Effects of plant hydraulic traits on flammability of live fine canopy fuels. Functional Ecology, in press, and the associated Supplementary Information.

Usage Notes

This archive contains hydraulic trait data for 62 species of vascular plant from south-eastern Australia.

The sheet 'Metadata' lists abbreviations for response variables, codes used to classify species regeneration strategy and species codes.

The sheet 'Raw data, shoots' shows pressure volume curves for distal shoot samples.

The sheet 'Trait data by species, shoots' records hydraulic trait data for distal shoots, and regeneration strategy.

The sheet 'Trait data by species, twigs' records hydraulic trait data for twigs, showing results for 30 of the 62 species addressed in the shoot study.

The sheet 'Trait effect on moisture' shows how the range in water loss associated with variation in hydraulic traits, can be expressed as a range in water content at TLP or at midday. In turn, this range in moisture content is expressed as a range in ignition time for a leaf or twig. See Methods section 'Numerical model of leaf ignition' in main paper (Scarff et al 2021 Functional Ecology) for details. The sheet consists of 3 parts: A, B and C. These address calculations for traits that modify water loss (A), for MC100 (B) and for ψPD (C).

The sheet 'Ignition model validation' shows how the numerical model of biomass ignition predicted ignition times for leaves. Part A shows predictions for 43 species tested by Gill & Moore (1996), based on leaf thickness, density and moisture content. Part B shows how ignition time changes as leaf thickness and moisture content are systematically varied.