Abstract
Wildfires can create or intensify water repellency in soil, limiting the soil's capacity to wet and retain water. The objective of this research was to quantify soil water repellency characteristics within burned piñon–juniper woodlands and relate this information to ecological site characteristics. We sampled soil water repellency across forty‐one 1,000 m2 study plots within three major wildfires that burned in piñon–juniper woodlands. Water repellency was found to be extensive—present at 37% of the total points sampled—and strongly related to piñon–juniper canopy cover. Models developed for predicting SWR extent and severity had R 2 adj values of 0.67 and 0.61, respectively; both models included piñon–juniper canopy cover and relative humidity the month before the fire as coefficient terms. These results are important as they suggest that postfire water repellency will increase in the coming years as infilling processes enhance piñon–juniper canopy cover. Furthermore, reductions in relative humidity brought about by a changing climate have the potential to link additively with infilling processes to increase the frequency and intensity of wildfires and produce stronger water repellency over a greater spatial extent. In working through these challenges, land managers can apply the predictive models developed in this study to prioritize fuel control and postfire restoration treatments.
Highlights
Since the late 19th century, global temperature has increased by 0.85°C (IPCC, 2013), models predict even more abrupt temperature changes occurring by the end of the 21st century (Fischer & Schär, 2010; Ganguly et al, 2009; IPCC, 2013)
Woods et al (2007) intensively studied the continuity of soil water repellency (SWR) at multiple spatial scales and concluded that whenever water-repellent soils comprise more than 75% of sampled points (i.e., 75% SWR extent) within a slope or watershed, there is a high probability that continuous overland flow will be generated
Postfire SWR is widespread within piñon–juniper woodlands and is almost always found in the tree mound zones of piñon–juniper individuals or closely adjacent
Summary
The highly positive water entry pressure of water-repellent soil degrades infiltration and percolation rates (DeBano, 1971; Doerr & Thomas, 2000; Doerr et al, 2003; Madsen, Zvirzdin, Petersen, et al, 2011; Pierson, Robichaud, & Spaeth, 2001) This initiates a cascade of ancillary effects including reduced soil moisture (Madsen, Zvirzdin, Petersen, et al, 2011; Wallis & Horne, 1992), enhanced runoff and erosion (Benavides-Solorio & MacDonald, 2001; DeBano, 2000; Leighton-B oyce, Doerr, Shakesby, & Walsh, 2007; Martin & Moody, 2001), and reduced postfire restoration success (Letey, 2001; Madsen et al, 2012; Wallis & Horne, 1992). It was hypothesized that SWR would have a close association with piñon and juniper trees and that soil attributes and topography would play important roles in defining SWR extent and severity and thickness of the water-repellent layer
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