Rainfall influence on plot-scale runoff and soil loss from repeated burning in a Mediterranean-shrub ecosystem, Valencia, Spain

Abstract

The effect of a repeated burning on soil hydrology and erosive parameters was studied on a Mediterranean forest soil (Rendzic leptosol) with the aim of identifying the effects of the fire and climatic parameters related to the post-fire runoff and soil loss. The study was carried out in an Experimental Permanent Field Station (La Concordia), close to Valencia (Spain). This field station is located on a calcareous hillside facing SSE, and is composed of nine erosion plots (20 x 4 m). Firstly, experimental fires were performed in June 1995 with two fire treatments (T1 or high severity fire and 12 or moderate severity fire) and a control one (unburnt, T3). The repeated fire (low severity) was carried out in July 2003. The studied period was focused from 18 months before the repeated fire (July 2003) until 18 months after it. Rainfall characteristics of each single event were recorded, which allowed us to statistically distinguish four time periods according to the rainfall intensity and duration: periods I (March 2002 to May 2003) and III (December 2003 to early May 2004) with low intensity and long duration rainfalls, and periods II (June 2003 to November 2003) and IV (late May 2004 to December 2004) with high intensity and short duration rainfalls. Before the 2003 fire, the partial recovery of soil and vegetation from the previous burning in 1995 led to a diminution in the runoff rates (6.5 Lm(-2) in burned plots and 1.8 Lm(-2) in unburnt ones). Six months later (period II), runoff increased in one order of magnitude (23.9 Lm(-2) in burnt plots and 1.1 Lm(-2) in the unburnt ones) due, in part, to the short time elapsed from fire until high intensity rainfalls. These differences in runoff production were maintained during the whole post-fire period. Fire effects were reflected in the erosion rates. Soil losses prior to the 2003 fire, in both fire treatments and in the control one, were scant relative to post-fire levels. However, six months after the repeated fire (period II) and almost one year later (period IV), soil losses increased into two orders of magnitude coinciding with the post-fire bare soil augment. The repeated fire impact and rainfall intensity magnified runoff and soil loss. Significant linear relationships between rainfall intensity, runoff and soil loss, were obtained for the burned plots. In the burned areas, rain intensities increased to 20 mm h(-1) augmenting the runoff and soil loss in one and two orders of magnitude, respectively.