Stand water use status in relation to fire in a mixed species eucalypt forest

Abstract

Previous research on seed-regenerating eucalypt species (e.g. ash-type eucalypts) posits that water use by regenerating forests increases quickly after fire and may exceed that of mature forests (by as much as 100%) for periods of many decades. This hypothesis has not been tested in forests dominated by re-sprouting eucalypts. We examined the effect of fire on tree and stand-level water use in a resprouting mixed species eucalypt forests close to Stanley in north-east Victoria, Australia.In general, rates of water use in regenerating mixed-species eucalypt forests 3years after fire were very similar to those for adjacent unburnt mature forests (0.48±0.14 in regenerating vs. 0.66±0.17mmday−1 in unburnt forest, mean±0.95 CIs). This clear difference between resprouters and seeders corresponds to: slower sap flow in resprouting trees; a comparatively limited increase in sapwood area index (22% compared to 70% in Alpine ash forests); and a 20% decrease in total leaf area index after the fire. While the general climate differed little amongst study forests due to their close spatial proximity, vapour pressure deficit within unburnt was greater than regenerating forest and was the main control of tree water use, irrespective of species. Midday leaf water potential and measures of leaf physiology (except stomatal conductance) derived from gas-exchange measurements were similar between mature and resprouting trees, but the stomata of resprouting trees maintained a greater conductance to water vapour than mature leaves.A few years after crown-removing fires, water use by resprouting mixed-species eucalypt forests was little different to nearby mature forests. These results strongly contrast post-fire patterns in water use for the seeder (ash-type) eucalypt forests.