Heating effects on water repellency in Australian eucalypt forest soils and their value in estimating wildfire soil temperatures

Abstract

Wildfires can induce or enhance soil water repellency under a range of vegetation communities. According to mainly USA-based laboratory studies, repellency is eliminated at a maximum soil temperature (T) of 280–400°C. Knowledge of T reached during a wildfire is important in evaluating post-fire soil physical properties, fertility and seedbed status. T is, however, notoriously difficult to ascertain retrospectively and often based on indicative observations with a large potential error. Soils under fire-prone Australian eucalypt forests tend to be water repellent when dry or moderately moist even if long unburnt. This study aims to quantify the temperature of water repellency destruction for Australian topsoil material sampled under three sites with contrasting eucalypt cover (Eucalyptus sieberi, E. ovata and E. baxteri). Soil water repellency was present prior to heating in all samples, increased during heating, but was abruptly eliminated at a specific T between 260 and 340°C. Elimination temperature varied somewhat between samples, but was found to be dependent on heating duration, with longest duration resulting in lowest elimination temperature. Results suggest that post-fire water repellency may be used as an aid in hindcasting soil temperature reached during the passage of a fire within repellency-prone environments.

Distinctiveness of wildfire effects on soil erosion in south-east Australian eucalypt forests assessed in a global context

“…O'Loughlin et al, 1982;Mitchell and Humphreys, 1987;Burch et al, 1989;Crockford et al, 1991;Zierholz et al, 1995;Prosser and Williams, 1998;Doerr et al, 2004;Howell et al, 2006). They show that repellency is widespread and usually attains high intensities not only in sandy and sandy loam soils but even in sandy clay loams with up to 40% clay from south-east New South Wales in the Upper Yass Representative Basin (Crockford et al, 1991; Fig.…”

Wildfire impacts on hillslope sediment and phosphorus yields

“…Old growth tree density in this plateau area was 120-140 stems per hectare with larger trees reaching 20-25 m height. Within each site (Table 1), zones of contrasting fire severity were identified semiquantitatively by on-the-ground reconnaissance of vegetation consumption (cf Shakesby et al 2003;Doerr et al 2004;Chafer et al 2004) namely: (a) severely burned where observations of vegetation destruction implied consumption of all ground and shrub vegetation, canopy While semi-quantitative assessment of fire severity is not without its limitations, the differences identified between these broad categories were considered to be distinct enough for meaningful comparisons to be made. Heterogeneity in burn severity in the study area permitted severe, moderate, and unburned zones to be identified within close proximity to each other.…”

Comparing the effectiveness of seeding and mulching+seeding in reducing soil erosion after a high severity fire in Galicia (NW Spain)

“…Fire can also alter the soil structure, by affecting bulk density, and total porosity; thus, reducing infiltration and promoting overland flow (De Bano et al, 1998;Neary et al, 2005;Mataix-Solera et al, 2011). Changes in water repellency promoted by fire can also greatly contribute to runoff generation and soil erosion (Doerr et al, 2004;Keizer et al, 2008;Rodríguez-Alleres et al, 2012).…”