Abstract
Post-fire soil erosion risk assessment is not exempt of uncertainties. In many parts of the world post-fire soil erosion can have devastating effects over forest ecosystems, infrastructures and human life. However, in the Mediterranean countries, it has been defined as “low” and it was attributed to a long history of intense land use. This review paper integrates the last research assessing post-fire runoff and soil erosion as well as mitigation techniques focussing inPortugal. In the case of north-centralPortugal, recent research assessing wildfire and ground preparation effects leads to the conclusion that post-fire soil losses was as high as 5-10 Mg ha-1yr-1, while ground preparations soil losses doubled these figures. Since those values are higher than the estimates for tolerable soil losses, further considerations must be taken in order to guarantee a sustainable land use. The advantages of post-fire soil erosion control with straw mulching are well known worldwide. Recently, other treatments were assessed in recently burnt eucalypt and pine plantations in Portugal: 1) the eucalypt chopped bark mulch; 2) the slash logging mulch (unchopped twigs, stems and leaves); 3) the hydromulch, a mixture of water, organic fibres, seeds, nutrients and a surfactant with good performance in cut slopes rehabilitation; and 4) the polyacrylamides (PAM), a chemical agent with good performance in agricultural soil erosion control and high potential due to its low application rate. The more effective treatments were those increasing the ground cover, one of the most important key factors for soil erosion. For this reason, the eucalypt chopped bark mulch and the hydromulch reduced the runoff in 50% and the soil erosion in 80-90%, while the PAM did not achieved the required reduction effect. In areas where the ground cover was high (due to the presence of a needle carpet) the slash logging mulch was not effective since soil erosion was already low in the untreated areas.
Highlights
Once post-fire soil erosion risk has been determined, the second step is to implement mitigation techniques of proven effectiveness
The eucalypt chopped bark mulch and the hydromulch reduced the runoff in 50% and the soil erosion in 80-90%, while the PAM did not achieved the required reduction effect
The hydromulching applied at the pine site in Colmeal (Fig. 8) by Prats et al (2013) was highly effective, reducing runoff in 70% and soil losses in 80%
Summary
Once post-fire soil erosion risk has been determined, the second step is to implement mitigation techniques of proven effectiveness. In the case of Portugal, once straw availability is lacking in many parts of the country, the first field trial on the effectiveness of post-fire soil conservation measures was based on the application of heavy loads of eucalypt logging litter (Shakesby et al, 1996). They demonstrated that these forest residues were highly effective for reducing soil erosion in burnt eucalypt as well as maritime pine plantations, but surprisingly, they received very little public attention. To compare its costs and analyze the suitability of applying these treatments to reduce post-fire soil erosion
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