Soil Water Repellency Severity and its Spatio‐Temporal Variation in Burnt Eucalypt Plantations in North‐Central Portugal

Abstract

Soil water repellency (SWR) is a dynamic soil property that influences soil hydrology. The main goal of this work was to determine in situ spatial and temporal variations in SWR in six recently burnt eucalypt stands with different pre-and post-fire management. The severity of SWR was measured in the field using the "molarity of an ethanol droplet test" during 1-2 years, at intervals of 1-2 weeks. Measurements were taken for the ash layer, soil surface and three different soil depths (2-3, 7-8 and 14-16 cm). The volumetric soil moisture content (SMC) was measured at the three deepest layers. The results showed that ploughing operations carried out several years before the fire did not have major impacts on the severity of SWR. The ash layer was predominately wettable, whereas the other soil layers were dominated by strong to extreme severity SWR. Furthermore, and starting at a soil depth of 3 cm, the severity of repellency decreased with increasing depth. The spatial variability within a slope was significant on half of the sampling days, indicating that wettable patches were present under median severely repellent conditions, possibly increasing hydrological connectivity within the slopes. Temporal SWR patterns were inversely related to antecedent rainfall and SMC. The SWR patterns were similar between sites, as well as for the different sampling depths within each site. Major changes in the median levels of repellency were registered in periods as short as 1-2 weeks, but measured rainfall and/or soil moisture conditions were insufficient to explain these changes.

Physically‐Based Modelling of the Post‐Fire Runoff Response of a Forest Catchment in Central Portugal: Using Field versus Remote Sensing Based Estimates of Vegetation Recovery

“…(). In 2009, SWR followed the expected patterns (Keizer et al ., ; Malvar et al ., ) with low values in winter when soils were wetter, and high values in spring, summer, and autumn when soils were drier. In 2010, however, repellency in the pine stand was much lower than in the first year, although still stronger in the dry seasons; while in the eucalypt stand it increased throughout the year.…”

Afforestation, Subsequent Forest Fires and Provision of Hydrological Services: A Model‐Based Analysis for a Mediterranean Mountainous Catchment

“…Northwestern Portugal has been the focus of research on hydrological and erosion processes in burnt areas (Ferreira et al ., ; Malvar et al ., , ; Shakesby et al ., ); impacts of postfire management on hydrological processes and erosion (Martins et al ., ); postfire stream water quality (Campos et al ., ; Ferreira et al ., ; Silva et al ., ); hydrological and erosion processes in unburnt forest plantations (Boulet et al ., ; Hawtree et al ., ; Santos et al ., ); and hydrological modelling in burnt and unburnt forests (Nunes et al ., ; Rial‐Rivas et al ., ; Tavares Wahren et al ., ; Vieira et al ., ). The Macieira watershed has also received some research attention: Ferreira () studied erosion after the 1991 fire, and Nunes et al .…”

“…However, fires can be considered to have a larger impact. The increase in the effect of soil water repellency when compared with unburnt plantations (Nunes et al, 2016c) can lead to increased runoff and erosion (Malvar et al, 2016). Also, fires can lead to subsequent disturbances such as salvage logging and replanting, as happened in Macieira, which can add to the impacts of the fire itself .…”

Short-time phosphorus losses by overland flow in burnt pine and eucalypt plantations in north-central Portugal: A study at micro-plot scale

“…This could be explained by the typically stronger soil water repellency in eucalypt stands than in pine stands in the study region (Doerr et al, 1998;Keizer et al, 2005a, b;Santos et al, 2013), which was likely to have promoted overland flow and the associated sediment and P losses at the BES site. The possible existence of a water repellent ash layer overlying a strongly to extremely repellent topsoil at the BES site could have further enhanced the differences in overland flow and erosion between the eucalypt and pine site (Bodí et al, 2011(Bodí et al, , 2014Dlapa et al, 2013;Malvar et al, 2015b). An alternative explanation would be the needle cast cover due to spontaneous mulching from the partially scorched pine crowns at the BPS site reducing overland flow and erosion (Table 3), as also reported by prior post-fire erosion studies (Cerdà and Doerr, 2008;Knoepp et al, 2005;Kutiel and Shaviv, 1992).…”