Effects of mastication of burned non-commercial Pinus pinaster Ait. trees on soil compaction and vegetation response

Abstract Mastication is commonly used as a fuel reduction treatment to minimize severe wildfires in fire-prone areas worldwide. Although mastication of non-commercial burned trees has become common practice in NW Spain in recent years, little is known about the possible effects on fuels, soil physical properties and vegetation recovery. In this study, sites in NW Spain (Arbo and Soutomaior) where non-commercial Pinus pinaster Ait. stands burned in August 2016 in NW Spain were selected for study. In both sites the fires scorched tree crowns and caused moderate soil burn severity. In January 2017, burned trees in 15 plots (10 in Arbo and 5 in Soutomaior) were masticated using a steel track tractor with a front mounted rotating toothed drum. In addition, five plots in Arbo were masticated using a walking excavator with a mulching head. In the 10 remaining plots (5 in each site) the trees were cut with a chainsaw and manually moved offsite. The fuel distribution categories were determined immediately after mastication. Soil penetration resistance and soil shear strength were measured immediately after wildfire, and also immediately, six months and one year after mastication. Species cover and pine seedling density were measured six months and one year after mastication. Percentage masticated material cover ranged from a mean of 60% (s.e. = 1.5) after mastication by tractor in Soutomaior to a mean of 81% (s.e. = 6.0) after mastication by walking excavator in Arbo. 64–75% of material was shredded after mastication. Mastication had no effect on soil shear strength or soil penetration resistance, and it also did not affect total vegetation cover. Species cover was not significantly affected by any of the environmental variables or masticated material cover. Mean pine seedling density was 0.2 seedlings m −2 in masticated and non-masticated plots, irrespective of the equipment used. Mastication did not favour the establishment of non-native species. Mastication after wildfire does not appear to be detrimental to soil conservation and vegetation recovery although further research is needed to confirm this.