Mastication of burned non-commercial P. sylvestris L. stands: Effects on soil erosion and vegetation recovery

Abstract

Forest mastication is frequently used as a fuel reduction treatment aimed at minimising severe wildfires in fire prone areas worldwide. In recent years, mastication of non-commercial burned trees has become common practice in NW Spain, as a way of providing cover on the burned soil and preventing erosion. However, little is known about the possible effects on soil conservation and vegetation recovery. In this study, 20 experimental plots were established in a Pinus sylvestris L. plantation affected by a crown fire that caused moderate-high soil burn severity in the summer of 2016. Immediately after the fire, burned trees were masticated in half of the plots, while burned trees were left standing in the other half of the plots during the first two years after the fire. The objectives of the study were to determine how mastication affected soil erosion, soil physical properties (soil penetration resistance, soil shear strength, soil bulk density) and vegetation recovery. The masticated material covered 43% of the burned soil. During the first year after wildfire + mastication, precipitation was lower than the annual mean level in the area, and the mean soil loss in the untreated burned soils (5.7 Mg ha−1) was not significantly different from that in the masticated plots (5.0 Mg ha−1). Mastication did not have any detrimental effects on either the soil physical properties analysed or on the regeneration of natural vegetation. The results indicated that in addition to mastication of severely burned non-commercial trees, extra mulch should be applied to reduce the risk of soil erosion. Mastication after wildfire is not detrimental to soil conservation. No advantage was obtained by leaving the standing burned trees on site, in relation to reducing soil erosion or enhancing vegetation recovery.