Effectiveness of Polyacrylamide, Wood Shred Mulch, and Pine Needle Mulch as Post-Fire Hillslope Stabilization Treatments in Two Contrasting Volcanic Soils

Jonay Neris,Jesús Notario Del Pino,Carmen Arbelo,Stefan Doerr,Antonio Rodríguez-Rodríguez

doi:10.3390/f8070247

Abstract

Post-fire hillslope stabilization treatments aim to reduce runoff-erosion risks following forest fires by counteracting the impact of fire on key soil and hillslope properties. Here we evaluate the effectiveness of wood shred mulch, long-leaved pine needle mulch, and polyacrylamide (PAM) in reducing post-fire runoff and erosion in two volcanic soil types of contrasting wettability using rainfall simulations (55 mm h−1 for 30 min) at the microplot (0.25 m2) scale. The cover provided by the wood shreds and pine needles led to a reduction of runoff and erosion in both the wettable—(62% and 92%, respectively, for wood shreds, and 55% and 87%, respectively, for needle mulch) and the extremely water-repellent soils (44% and 61%, respectively, for wood shreds). In contrast to what might be expected, PAM did not reduce runoff or erosion when applied to the extremely water-repellent soils, suggesting that PAM should not be applied in this terrain type. Although more research is needed to determine whether the high effectiveness of pine needle mulch and wood shred mulch fully translates to coarser scales, the results are encouraging in terms of these materials’ ability to provide effective and relatively economic mitigation treatments for fire-induced runoff-erosion risks in volcanic soils.

Highlights

Wildfire can substantially enhance the hydrological and erosional response of forest areas with sometimes serious consequences for the environment, infrastructure, and population, such as flooding, debris flows, and the contamination of rivers and reservoirs [1]
This study aimed to address the research gaps identified above by evaluating the impact of fire and the performance of three different post-fire hillslope stabilization treatments in fire-affected volcanic soils of contrasting water repellency
While soils at Candelaria were classified as non-water repellent, those at Vilaflor were extremely water repellent (p < 0.001)

Summary

Introduction

Wildfire can substantially enhance the hydrological and erosional response of forest areas with sometimes serious consequences for the environment, infrastructure, and population, such as flooding, debris flows, and the contamination of rivers and reservoirs [1]. This response is typically triggered by an enhancement of soil water repellency together with a reduction in soil aggregate stability and a decrease in ground cover [1]. Several post-fire hillslope stabilization treatments have recently been developed, including wood-based and agricultural straw mulches. Wood-based mulches (chips, shreds, or strands) show advantages when compared to straw mulches such as: (i) higher density, reducing their redistribution by wind; (ii) free of weed seeds, and; (iii) lower

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