Post‐fire soil erosion mitigation at the scale of swales using forest logging residues at a reduced application rate

Abstract

Mulching with forest residues has proved to be highly effective in reducing post‐fire soil losses at the plot scale. However, its effectiveness has not been quantified at the application rates that are typically used in operational post‐fire land management (2–3 Mg ha‐1 using straw), as well as at scales larger than 100 m2. The present study compared post‐fire erosion rates for six convergent hillslopes or swales of 500 to 800 m2, three of which were left untreated while the other three were mulched immediately after the fire with shredded eucalypt bark at a rate of 2.4 Mg ha‐1. Erosion rates were monitored at irregular intervals during the first three post‐fire years, whilst ground cover was assessed yearly. Selected topsoil properties (0–2 cm) such as organic matter content and aggregate stability were determined at a single occasion – two years after the wildfire, for three micro‐environments separately: bare soil, and under mulch/litter and vegetation. Soil losses on the untreated swales decreased with post‐fire year from 2.2 to 0.4 and 0.11 Mg ha‐1 yr‐1 (respectively for the first, second and third post‐fire years), while the mulched swales produced 84%, 77% and 38% less soil losses than the untreated swales. Soil losses also depended on slope aspect, with the north‐facing swales producing less erosion than the west‐facing ones. This could be linked to their significant differences in bare soil, vegetation and stone cover, or a combination thereof. The type of micro‐environment also played a significant role in topsoil properties (stone content, bulk density, resistance to penetration/shear stress, porosity and organic matter content). The present results add to the increasing evidence that forest residues should be duly considered for operational post‐fire land management. Forest residues were highly effective in reducing erosion from swales at application rates as low as the typical 2 Mg ha‐1 of post‐fire straw mulch. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.

Projecting Future Impacts of Global Change Including Fires on Soil Erosion to Anticipate Better Land Management in the Forests of NW Portugal

“…In fact, when our results were only compared during the three years of post-fire disturbance, the efficiency of mulch application decreased runoff by 7% and SY by 40%. Compared to Prats et al (2019Prats et al ( , 2012 where mulch application reduced runoff by 15%-25% and SY by more than five times, our results were more conservative probably because our burnt field area only represented 10% of the watershed area; while Prats et al (2012, 2019) calculated SY at the field area scale and they burned 100% of the area while in our case 10% of the catchment burned. Moreover, our simulations ran over 20 years vs. 5-10 years in other studies [32,61].…”

“…Concerning sediment reduction caused by mulching, Shakesby et al (1996) [63], showed that Eucalyptus logging litter reduced soil erosion by 95%. The average reduction was five times in Prats et al (2019Prats et al ( , 2012; it should be noted that, in the latter study, maximum erosion rates were lower than in our study site. As previously said, the study site of Prats et al (2012) also presents smaller temporal and spatial scales.…”

“…These measures include the application of organic residues to the soil surface (i.e., mulching, with straw or forest logging residues), log and shrub barriers, infiltration enhancement through scarifying or plowing or re-seeding and ecological restoration [17,[26][27][28][29]. However, it is typically impractical to treat all burnt areas entirely, thus requiring knowledge of the effectiveness of these measures under different fire and post-fire conditions [29][30][31][32][33][34].…”

Can straw-biochar mulching mitigate erosion of wildfire-degraded soils under extreme rainfall?

“…The experiment revealed, indeed, that it was the lowest effective straw application rate. Other materials, such as wood strands and forest residues are known to be more resistant to be blown away by wind (Robichaud et al, 2014;Prats et al, 2019).…”

“…The first can be achieved by using post-fire mulching. The application of a layer of straw of 2 Mg ha -1 over the soil is the most effective soil erosion mitigation treatment and its effectiveness has been extensively monitored in the USA (Robichaud et al, 2014;2020) and Europe (Fernandez & Vega, 2016;Prats et al 2019). However, the perception of forest managers is that post-fire mulch is expensive and they are reluctant to use straw mulching and most post-fire expenditures are used for logging, barrier-based or planting/seeding solutions instead.…”