Effects of mulching and post-fire salvage logging on soil erosion and vegetative regrowth in NW Spain

Abstract

Mulching is frequently used to reduce runoff and erosion following high-severity wildfires. In commercial forest stands, post-fire salvage logging is common practice, although it can lead to increased erosion losses in recently burned areas. Field research concerning the effects of post-fire salvage logging on sediment production is limited and the effects of clearcutting in areas previously treated by mulching are not known. In this study, 36 experimental plots were established in three experimental sites affected by crown fires that caused moderate-high soil burn severity in the summer of 2013. Immediately after the fire, bark strands mulch was applied in 18 of the plots. Salvage logging took place at the end of the first winter following fire. Post logging treatments were: mulching+salvage logging, no mulching+salvage logging and no mulching+no logging. The objectives of the study were to determine whether mulching mitigates soil erosion caused by fire and salvage logging and also to assess the possible effects of wildfire and salvage logging, with and without mulching, on vegetation recovery. During the six month period lapsed between the wildfire and salvage logging, precipitation was higher than the annual mean in the area, and the average soil loss in the untreated burned soils was 18.5Mgha−1. In that period, mulching significantly reduced soil loss (84%). In the 18-month period following salvage logging and in the absence of mulch, there was no increase in erosion due to logging (8.7Mgha−1) compared with the unlogged treatment (7.0Mgha−1) whereas mulching reduced significantly soil losses even after logging (2.3Mgha−1). Neither mulching nor salvage logging had any detrimental effects on the regeneration of natural vegetation. Our results showed that the mulching just after a fire can substantially reduce the subsequent erosion due to post-fire salvage logging without any significant adverse effects on vegetative regrowth. In addition, leaving the standing burned trees seemed not to be a feasible management option to reduce post-fire erosion and enhance vegetation recovery in those kind of stands.