Snowpack thermal patterns in pre- and post-bushfire Snow Gum forests

Abstract

Forests exert control on snowpack properties and processes through their modification of energy balance and micrometeorological conditions. Though forest disturbance by fire is increasing in frequency and severity in many warm regions containing seasonal snowpacks, increases are also expected in high latitude and altitude regions as a result of climate change. The influence of fire on snowpack internal thermodynamics, particularly at the snowpack – tree stem interface has yet to be examined. This study measured tree stem temperatures, horizontal snowpack temperatures surrounding tree stems, vertical internal snowpack temperatures, and micrometeorological variables to determine snowpack thermodynamics in undisturbed and fire-disturbed Eucalyptus pauciflora (Snow Gum) forests in the Australian Alps. Analysis focused on average snowpack temperature characteristics of each area and the micrometeorological drivers of internal snowpack temperatures. Shortwave radiation at the fire-disturbed forest was ~ 700% higher than that of the undisturbed forest, with stem temperatures exceeding ambient air temperature by an average of 5.3 °C. By comparison, average stem temperatures at the undisturbed forest were an average of 1.8 °C lower than ambient air temperatures. Increased stem temperatures were associated with tree wells of more uniform development in size, shape, and distribution within the fire-disturbed forest. Increased shortwave radiation and ambient air temperature at the fire-disturbed forest coincided with greater diurnal variation in snowpack temperature. In general, snowpack temperature was heavily dependent on location in the snowpack surrounding the stem and snowpack depth. Ambient air temperature was found to be the primary meteorological driver of horizontal snowpack temperature changes when examining variable importance from a Random Forest regression model. This study finds that changes in snowpack dynamics at the scale of individual tree stems is very important when considering fire impacts on hydrological processes in forested regions.