The differential response of surface runoff and sediment loss to wildfire events

Wildfires are of primary importance in determining ecosystem function and geomorphological process in most of the forested landscapes across the globe. Following a fire event in a maquis forest located at the Carmel mountain range in northern Israel, we monitored the eco-geomorphic response of the system, in an attempt to explain runoff and sediment yield dynamics. Specifically, we assessed growth of vegetation cover, and monitored runoff and sediment yield in relation to three controlling factors: fire severity, slope aspect, and slope steepness. Fourteen 10m² plots were constructed in different combinations of aspect, fire severity and steepness, which were monitored for a period of 24months.Analysis of vegetation cover indicated that initial growth was faster on the north aspects, but by the end of the study period vegetation cover was similar to that of pre-fire levels on both aspects. Runoff and soil loss amounts from the burnt sites were commonly significantly higher on the south slope, steep gradients and high fire severity, compared to the counterpart plots. Temporal analysis indicated that sediment yield from the plots significantly decreased between the first and second winter seasons, whereas no statistically significant decrease in runoff was observed. Applying regression analysis methods we investigated the response of sediment yield to runoff, vegetation cover, soil moisture, rain intensity and precipitation, with respect to each of the controlling factors. In all cases runoff appeared to be a significant variable, as was vegetation cover, with the exception of the moderate burnt plots.We suggest that vegetation plays a complex role in determining the response of the geomorphic system to wildfire perturbations. While the mere presence of vegetation is sufficient to reduce soil loss, it is not sufficient to significantly affect runoff, most likely due to the different architecture of the newly regenerated vegetation. Additionally, vegetation seems to be an important factor in the harsher environments where more intensive soil movements occur, as the conditional effect of vegetation is more pronounced, and its contribution to the reduction of soil movements is higher.