Long-term erosional responses after fire in the Central Spanish Pyrenees

This paper reports the results of a study on how fire effects water and sediment losses in the Central Spanish Pyrenees where land abandonment results in an increase of the scrubland and fire-affected surfaces. In 1991, two plots (control and burnt) were installed to collect runoff, suspended sediments and solutes. One of the plots was burnt (burnt-1) and the other was covered by shrubs and herbs (control). During 1993, another burnt plot was installed (burnt-2). Data was collected from the three plots until 1999 and is used as the basis for assessing the soil erosion changes after the fire. Runoff, solute and suspended sediment concentration and erosion rates were slightly greater during the first 2 years following fire on burnt-1 compared to the control plot. The average runoff coefficients during the 8-year study period were 4.2% and 7%, the total sediment concentrations were 189 and 181 mg l−1, and the erosion rates were 89 and 143 kg ha−1 year−1 for the control and burnt-1 plots, respectively. In contrast, burnt-2 plot responded differently than burnt-1 plot to fire, although these two plots were designed to be replicated treatments. The average runoff coefficient for burnt-2 plot was two times greater than that for the control plot. Likewise, total sediment concentration was 649 mg l−1 and erosion rate was 566 kg ha−1 year−1, which are 3.6 and 4.5 times greater than the control plot. Differences between burnt and control plots were analysed at hourly, daily, monthly and yearly temporal scale. Both burned plots began to recover after the fire. However, burnt-1 plot had a recovery time of 2 years compared to burnt-2 plot; while 7 years after the fire, the runoff sediment concentration and erosion rates from burnt-2 were higher than those for the control plot. Water and sediment losses from the two burnt plots were markedly different.