Effects of fire and vegetation cover on hydrological characteristics of a Mediterranean shrubland soil

An experimental study based on the effects of fire on soil hydrology was developed at the Experimental Station of 'La Concordia' (Valencia, Spain). It is located on a calcareous hillside facing SSE and composed of nine erosion plots (4 x 20 m). In summer 2003, after eight years of soil and vegetation recovery from previous fires in 1995 (with three fire treatments: T1 high-intensity fire, T2 moderate intensity, and T3 not burnt), experimental fires of low intensity were again conducted on the plots already burnt, to study the effects of repeated fires on the soil water infiltration, soil water content and runoff.Infiltration rates and capacities were measured by the mini-disk infiltrometer method (MDI), assessing the effects of vegetation cover by comparing the under-canopy microenvironment (UC) and its absence on bare soil (BS), immediately before and after the fire experiments. Soil properties like water retention capacity (SWRC) and water content (SWC) were also determined for the different fire treatments (T1, T2 and T3) and microsites (UC and BS). Hydrological parameters, such as runoff and infiltration rate, were monitored at plot scale from July 2002 to July 2004. In the post-fire period, data displayed a 20% runoff increase and a decrease in infiltration (18%).Differences in the steady-state infiltration rate (SSI) and infiltration capacity (IC) were tested with the MDI on the different treatments (T1, T2 and T3), and between the UC and BS microsites of each treatment. After fire, the SSI of the UC soil declined from 16 mm h⁻¹ to 12 mm h⁻¹ on T1, and from 24 mm h⁻¹ to 19 mm h⁻¹ on T2. The IC was reduced by 2/3 in the T1 UC soil, and by half on T2 UC soil. On the BS of T1 and T2, the fire effect was minimal, and higher infiltration rates and capacities were reached. Therefore, the presence/absence of vegetation when burnt influenced the post-burnt infiltration patterns at soil microscale. On the T3, different rates and capacities were obtained depending on the microsites (UC and BS), with higher SSI (25 mm h⁻¹) and IC (226 mm h⁻¹) on BS than on UC (SSI of 18 mm h⁻¹ and IC of 136 mm h⁻¹).The SWRC and SWC were recovered from 1995 to 2003 (prior to the fires). The 2003 fire promoted high variability on the SWC at pF 0·1, 2 and 2·5, and the SWRC on burnt soils were reduced. To summarize, the IC and SSI post-fire decreases were related to the lower infiltration rate at plot scale, the significant differences in the SWRC between burnt and control treatments, and the increase in the runoff yield (20%).According to the results, the MDI was a useful tool to characterize the soil infiltration on the vegetation patches of the Mediterranean maquia, and contrary to other studies, on the UC soil, the infiltration rate and IC, when soil was dry, were lower than that obtained on BS. Once the soil gets wet, similar values were found on both microenvironments.