Study the effect of fire on aggregate stability, surface visible features and vegetation cover at the different scales in forests of south western coastal zone of the Caspian Sea

Degradation of forest lands by fire is one of the major bioenvironmental problems in northern Iran that significantly changes the vegetation attributes and visible features at the soil surface and therefore, affects aggregate stability against erosive forces. The complete information from aggregate stability at the micro scale and type of features related to soil erosion at the plot and watershed scales leads to a perfect judgment about erosion risk in an area. The objective of this study was to evaluate the effect of fire on aggregate stability, surface visible features and vegetation cover at the micro, plot and watershed scales in some parts of forest lands in west northern zone of the Guilan province.
Material and In parcels separated in 15 fire-affected forests and 15 unburned forests adjacent to the fire-affected forests, in five geomorphological units, aggregate stability indices at the micro scale and microtopographic erosion features and litter percentage at the plot scale were measured. In addition, some vegetation attributes, drainage density index, and the presence of some morphodynamics features of soil erosion were evaluated at the watershed scale.
The results of analysis of variance showed that all aggregate stability indices as well as litter percentage and drainage density had significant differences within subjects (within burned and unburned forests). Among studied parameters, only litter percentage showed significant differences between subjects (geomorphological units). Results also revealed that the time reversibility for aggregate stability indices and drainage density to condition before fire was about four to five years. Also, increasing the fire severity from low to high and changing of fire type from surface to canopy had the most effect on mean weight diameter of aggregates. Assessment of microtopographical erosion features at the plot scale revealed that some of them had variations in burned sites compared with the control sites. At the watershed scale, the rills, gullies and landslides were more abundant in the burned sites than the unburned sites. The correlation coefficients between measured properties related to different scales showed that there were significant correlations between some of them at the various scales.
The soil aggregate stability indices are very useful to evaluate the power of formation of many microtopographic and morphodynamics features of soil erosion at the plot and watershed scales. The results of this study can be used for assessment of soil erosion risk in forest lands and can be useful for management of woodland.