Runoff and Inter‐Rill Erosion Affected by Wildfire and Pre‐Fire Ploughing in Eucalypt Plantations of North‐Central Portugal

Increases in post‐fire runoff and erosion have been reported worldwide, but little is known about the combined effect of wildfires and pre‐existent ploughing operations. A previous study using simulated rainfall found a similar runoff for an unploughed and a pre‐fire ploughed site, but clearly showed lower erosion for the pre‐fire ploughed site. This study measured post‐fire runoff and erosion at the same two sites, with the same experimental design, but under natural rainfall conditions. Four micro‐plots were installed on each of two eucalypt stands, one of which was rip‐ploughed 20 years before the fire. The rainfall amount was 35% lower during the first post‐fire year than during the second, but the runoff coefficient was approximately 20% for both years and sites. The sediment losses were significantly higher on the unploughed than on the pre‐fire ploughed site during the first year (378 vs. 112 g m−2 y−1) and especially during the second year (552 vs. 67 g m−2 y−1). Half of the eroded sediments consisted of organic matter. On the unploughed site, both the natural and the extreme‐intensity simulated rainfall produced specific sediment losses of 0·35 gm−2 mm−1 rain, whereas the high‐intensity simulated rainfall produced approximately half (0·16 g m−2 mm−1 rain). At the pre‐fire ploughed site, the natural, high, and extreme‐intensity simulated rainfall produced similarly low‐specific sediment losses (0·07 g m−2 mm−1 rain). These low rates and the absence of differences between methodologies and simulated intensities suggested a depletion of soil stocks 20 years after the rip‐ploughing.