Showing papers by "Artemi Cerdà published in 2008"

The effect of ash and needle cover on surface runoff and erosion in the immediate post-fire period

Abstract: Hillslopes are thought to be most susceptible to enhanced surface runoff and erosion immediately following wildfire due to removal of protective vegetation and litter cover, and in many cases a fire-induced reduction in soil wettability. This enhanced susceptibility declines as vegetation and litter layer recover. For logistical reasons, however, few studies have been able to examine the responses of burnt terrain immediately following burning and little is therefore known about the effect of the wettable ash layer that often covers the ground until it is redistributed or removed by wind or water erosion. Here we quantify the effects of ash and needle cast ground cover on surface runoff generation and soil erodibility in the immediate post-fire period (2–10 days) following a severe wildfire in an Aleppo pine forest over calcareous soils in Mediterranean eastern Spain. A homogenous vegetation cover and lack of wind during the fire resulted in 100% ash cover (36 mm mean depth) across the study area. The ground fire did not consume the tree crowns, but its high intensity caused complete tree mortality, leading to subsequent needle fall. Hydrological and erosional responses were measured for fifteen 1-hour rainfall simulations (55 mm h− 1) on 0.25 m2 circular plots for each of three terrain types: (i) ash and needle covered, (ii) ash-only covered and (iii) bare. Furthermore, ash and needle cast cover were monitored over an eleven-week period on otherwise undisturbed terrain to examine its evolution during the first critical months following burning. The soils exhibited no or slight post-fire water repellency. The overlying wettable ash layer had a porosity of 83%, providing a water storage capacity of ∼ 30 mm. A third of the plots with ground cover did not generate any surface runoff. Ash-needle and ash-only plots showed 25- and 18-fold reductions in surface runoff respectively compared to bare terrain. Mean sediment yield from covered plots was more than two orders of magnitudes lower than from bare plots. The ash cover remained unchanged during the first two weeks while overlying needle cast more than doubled. Heavy rainfall (153 mm) over a subsequent six-day period removed the ash almost entirely where no needle cast was present, whereas on ash and needle covered ground only a limited redistribution and accumulation into litter dams occurred. The results quantify the potential importance of ash deposits on the susceptibility of hillslopes to surface runoff and erosion immediately following fire. The combination of ash and needle cast appears particularly effective in reducing hillslope responses. The outcomes demonstrate clearly that the widely held notion of landscapes being most susceptible to surface runoff and erosion directly after burning is not correct where a fire has resulted in substantial ash deposition. Instead, the susceptibility will be greatest following a storm event of sufficient severity to remove this protective layer and before the onset of vegetation recovery.

The influence of ants on soil and water losses from an orange orchard in eastern Spain

Abstract: Herbicide applications have greatly reduced plant cover, and increased soil erosion on a new orange orchard planted on valley slopes in eastern Spain. This has increased the importance of soil fauna, such as ants, in regulating soil erosion processes. Ants increase water infiltration rates by forming soil macropores during nest construction, but new soil brought to the surface by ant activity could increase the sediments available for erosion. Simulated rainfall experiments were conducted on 20 paired plots (20 with ant activity and 20 controls) to study the impact of ants on surface water flow and sediment movement in an intensively managed orange orchard near Valencia, Spain. Simulated rainfall was applied to each plot at a rate of 55 mm/h on a 0.25 m 2 area for 1 h. We found a reduction of soil bulk density, an increase in soil organic matter, and an increase in macropore flow in ant-affected soils, as compared to soil without ant activity. These ant-induced soil changes increased water infiltration rates and runoff discharge. However, the fresh, unconsolidated soil brought to the surface during nest construction resulted in greater soil loss on two plots than their ant-free controls. Ants can be an important factor in soil erosion processes when surface vegetation is removed by intensive herbicide use.

Erosión del suelo en plantaciones de cítricos en laderas. valle del riu canyoles, valencia.

Abstract: During the last decades the citrus orchards in the Mediterranean has moved from the lower topographical positions to the hillsides searching a free frost climatic areas. All this has been possible since the introduction of the drip-irrigation, promoted by the urban development pressure on the coastal land and valley bottoms, and fomented by the cost reduction in the groundwater pumping. The new plantations occupy now spaces of high slope angles where the losses of soil are high. In spite of the change in the location of the orchards -from plains to hillsides - the soils are being intensely ploughed or applying herbicides in order to eliminate the weeds. The conservation and organic farming agriculture can help to detain the high losses of soil. Experiments with simulated rainfall (60 mm h-1) in citrus fi elds on the Montesa’s valley (Valencia) where herbicides have been applied, on straw mulch and cash crops applied were carried out to quantify very different rates from erosion according to the applied management. The rate of erosion was negligible on the straw mulch and cash crops, meanwhile on the ploughed fi eld reached 10 g m-2 h-1, whereas in those with herbicides the loss of soil ranged between 37 and 58 g m-2 h-1.