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 g m(-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. Copyright (C) 2015 John Wiley & Sons, Ltd.