Do wildfire and slope aspect affect soil water repellency in eucalypt plantations? – A two-year high resolution temporal dataset

• Published in: Catena (Giessen) Vol. 189; no. C; p. 104471
• Main Authors: Martins, Martinho A.S., Verheijen, Frank G.A., Malvar, Maruxa C., Serpa, Dalila, González-Pelayo, Oscar, Keizer, Jan J.
• Format: Journal Article
• Language: English
• Published: Germany Elsevier B.V 01.06.2020; Elsevier
• Subjects: Eucalypt plantations; Slope aspect; Soil moisture content; Soil water repellency; Temporal pattern; Wildfire; Wildfire; Soil water repellency; Slope aspect; Temporal pattern; Eucalypt plantations; Soil moisture content
• ISSN: 0341-8162; 1872-6887
• DOI: 10.1016/j.catena.2020.104471

•Soil Water Repellency is high under eucalypts regardless wildfire or slope aspect.•Comparing to the unburnt site, wildfire reduced SWR in the first post-fire years.•SWR is higher and less spatially variable under unburnt eucalypts in dry periods.•Comparing to the unburnt site, slope aspect had minimum impact on SWR after burning.•Wildfire causes greater, or quicker, temporal changes in soil moisture content. Wildfire can induce, enhance, or destroy natural soil water repellency (SWR) depending mostly on soil burnt severity, soil and vegetation types, soil organic matter (SOM) content and type, soil texture, peak soil temperature and remaining time and, antecedent soil moisture content (SMC). In Portugal, SWR in eucalypt stands has been shown to increase surface runoff under dry antecedent SMCs in both burnt and unburnt sites, thereby enhancing soil erosion. Despite the many hydrological implications of SWR, intensive field monitoring under a wide range of SMCs is still limited. This study aimed to improve our understanding of the role of slope aspect and wildfire on the temporal evolution of SWR in Mediterranean environments, which will be helpful for hydrological modelling and post-fire soil erosion risk assessment. In this sense, two burnt eucalypt plantations (wildfire of July 2010) were selected along a neighbouring, long-unburnt eucalypt stand, in north-central Portugal, in order to assess SWR and SMC’s in a high temporal resolution. During the first two post-fire years, at 1–2 week intervals, surface (2.5 cm depth) SWR and SMC were monitored using the “molarity of an ethanol droplet” (MED) test and a soil probe, respectively. The results showed that the observed annual SWR was very high to extreme (80% of measurements ≥ 6 ethanol class) for all three sites. Wildfire reduced the annual median SWR by one class (extreme to very high) for both post-fire years. During prolonged dry periods the unburnt site was significantly more repellent (P < 0.01) and less spatially variable (P < 0.01) than the recently burnt site, while in the wet periods there was no significant difference. After burning, slope aspect did not have a strong impact on the annual median SWR class. However, the north-west aspect site recorded significantly (p < 0.01) greater annual frequencies of extreme repellency than the south-east aspect site (70–73% vs. 51–55%).