Land use has significant effects on the erosion process, since it influences the soil detachment capacity by causing an overland flow (D_c). The effects of different land uses on the rill detachment capacity have not been explained in depth, and the hydraulic parameters providing accurate estimates of this soil property have not been completely identified. This study quantifies D_c at low flow rates in woodland and forestland, compared to two other land uses (cropland and grassland), in the Saravan watershed (Northern Iran), and develops prediction models of D_c and rill erodibility (K_r). D_c was measured on undisturbed soil samples, collected in the four land uses, and characterized in terms of the main physico-chemical properties in a flume experiment, simulating five slopes and five shallow water flows. The results showed that D_c was significantly lower in woodland and forestland compared to cropland and grassland, as the consequence of the changes in the main soil properties and the more developed vegetation cover and structure. D_c was positively correlated to clay and silt contents of soils, and negatively correlated to sand content, aggregate stability, root density, and organic matter. The stream power and unit stream power were found to be very accurate predictors of D_c in woodland and forestland, respectively. K_r values, which assumed the lowest values in woodland and forestland, were provided by interpolating D_c and the shear stress of water flow. Overall, this study has confirmed that vegetation cover and improved soil properties in forestland and woodland may help to reduce erosion in delicate environment ecosystems, such as the forests of Northern Iran.

Rill detachment capacity is a key parameter in concentrated flow erosion. Rill erosion generally turns into gully erosion with severe environmental impacts. Changes in land use and human activities can have heavy effects in rill formation, particularly in forests subject to deforestation; soil morphology plays a significant role in these effects. However, literature reports few studies about rill detachment rates and their implications on soil quality in forest and deforested soils with different morphological characteristics. To fill these gaps, this study has evaluated the rill detachment capacity (D_c) and the main soil quality indicators in three areas (upper, middle and lower slope) of forest and deforested (for 10 years) hillslopes exposed to the north and south in Northern Iran. The variations of D_c have been measured on soil samples under laboratory conditions through a flume experiment at three slope gradients (12 to 19%) and five flow rates (0.22 to 0.67 L m⁻¹ s⁻¹) with four replications. The large and significant (p < 0.05) difference (about 70%) detected for D_c between forest and deforested hillslopes was associated to the higher organic matter content of forest areas; as a consequence, these areas also showed higher aggregate stability, porosity, root weight density, microbial respiration and available water. In the deforested hillslopes exposed to the south, the soil erodibility was higher by 12% compared to those exposed to the north. The differences in the monitored soil quality indicators were instead less noticeable and not always significant (p < 0.05). Conversely, D_c did not significantly change (p < 0.05) among the upper, middle and lower hillslope areas investigated in this study. Simple but accurate models to predict the rill detachment capacity, erodibility and critical shear stress of soils from indicators of soil quality or the unit stream power using regression equations are suggested. Overall, the results can support land planners in prioritizing the actions for soil conservation in deforested hillslopes exposed to the south as well as in the extensive application of the proposed equations in erosion prediction models.

Wildfire heavily impacts the quality of forest soils, and the precipitation occurring immediately after fire can determine high runoff and erosion rates, which may lead to noticeable soil degradation. Mulching is commonly used to limit the hydrological impacts of wildfire and climate, but this post-fire management technique may alter the erosion–deposition dynamics at the hillslope scale and, consequently, alter soil quality. In order to explore the magnitude and significance of these changes (little was studied in the literature until now), this communication reports the first results of a field activity that evaluated the changes in soil quality in areas affected by a wildfire and subjected to different post-fire treatments in Mediterranean forests. The main properties of sediments eroded from burned and untreated soils, and mulched soils (using a straw dose of 0.2 kg/m² of dry weight), were measured after the first rainstorm (height of 37 mm and maximum intensity of 11.6 mm h⁻¹) occurring two months after a wildfire (occurred on 30 June 2016) in a pine forest of Castilla-La Mancha (Spain). This event produced a runoff volume of 0.07 ± 0.02 mm in mulched soils and 0.10 ± 0.10 mm in non-mulched soils; soil loss was 0.20 ± 0.06 g/m² in the mulched area and 0.60 ± 0.60 g/m² in the non-mulched area. In comparison to burned and non-treated areas, this study showed: (i) increases in salinity, and reductions in organic matter, nutrients, nitrates, and micro-elements in burned and untreated soils; (ii) reductions in runoff (−20%) and in soil erosion (−60%) as a result of mulch cover; (iii) effectiveness of mulching in limiting the declines in soil quality detected in burned and eroded areas; and (iv) transport of low amounts (less than 10–15%) of some compounds (organic matter and nutrients) downstream of the fire-affected areas (both mulched and untreated). Phosphorous runoff toward valley areas and nitrate incorporation into the soil, detected in both mulched and untreated areas, require attention, since these processes may cause eutrophication of water bodies or nitrate pollution in groundwater.