Tree Mastication and Helimulching: Two Alternatives for Mitigating Soil Erosion and Carbon Loss After Wildfire

Abstract

Abstract The use of masticated tree debris to protect burned soil from post-fire erosion is not common and very little is known about its effectiveness in reducing the risk of erosion after fire. The main objective of this research was to assess the effects of agricultural straw helimulching and tree mastication on soil and carbon losses and recovery of vegetation during 2 years after fire in two wildfire-affected areas in northwestern Spain. Eighteen plots were established in each experimental site for monitoring the following treatments: helimulching, mastication, and control (untreated burned soils). Salvage logging was carried out in the first spring after fire in one of the experimental areas, thus enabling study of whether the application of mulch after fire also protects the soil during logging. Mean soil cover in helimulched areas was more than 90% in both experimental sites, whereas masticated slash from juvenile pine trees covered around 60% of the burned soil. In both study sites, soil and carbon losses were significantly higher in the untreated soils than in the helimulched and masticated soils. Mulching was effective in reducing soil and carbon losses even after salvage logging. Study Implications: The use of mulches to protect burned soil from post-fire erosion is becoming common in fire-prone areas. Agricultural straw is the most common material, whereas other alternatives such as the use of masticated tree debris to reduce soil erosion risk after fire is not as common. The results obtained in this study show that mastication of noncommercial trees is a feasible technique to reduce post-fire soil erosion, although cover of more than 60% must be achieved to reduce soil erosion and carbon loss to sustainable values. Application of straw mulch is effective to protect burned soil during salvage logging.