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Humus form development and hillslope runoff, and the effects of fire and management, under Mediterranean forest in NE-Spain

1989; Elsevier BV; Volume: 16; Issue: 4-5 Linguagem: Inglês

10.1016/0341-8162(89)90028-3

1872-6887

J. Sevink, A.C. Imeson, J.M. Verstraten,

Hydrology and Sediment Transport Processes

Study of a series of plots on acid to intermediate rocks under well preserved mediterranean type forests in NE Spain showed that soils have well developed mor or moder type humus forms. Mor type humus forms were observed in soils with a shallow lithic contact or an abrupt textural change, and consist of an ectorganic layer (L, Fq, H) abruptly overlying a generally water repellent Ae or E horizon. Moder type humus forms, with a gradual transition between the ectorganic layer (L, Fa and the Ah horizon, were found in soils with more favourable rooting and soil moisture conditions, indicating that these conditions have a strong control over humus form development. Quantities of organic matter (ectorganic layer + Ah/Ae) ranged from about 5 kg/m2 in mor to about 10 kg/m2 in moder humus forms, the difference being due to the presence of a well developed Ah horizon in the latter. Rainfall simulator experiments showed that slopes with mor type humus forms are likely to produce hillslope runoff during summer rain storms in spite of the relatively high storage capacity of the ectorganic layer. This is due to the hydrophobicity of the mineral top soil (if dry), which hampers infiltration. Furthermore, during the wet season the soils commonly have a perched water table, inducing saturated overlandflow. Slopes with moder type humus forms, on the contrary, are very unlikely to produce any hillslope runoff, because of the high storage and infiltration capacity of the soils. On slopes with mor type humus forms, traditional management (cutting of the undertsory) leads to erosion of the ectorganic layer and thus to a reduction of its storage capacity. Forest fires have similar effects, since they lead to the (partial) destruction of the ectorganic layer and destroy the existing vegetation. As evidenced by the rainfall simulation experiments, in both cases hillslope runoff will strongly increase, inducing erosion of the mineral soil, in particular after fire. On slopes with moder type profiles the effects of fire and traditional management will be far more limited, because of the high storage and infiltration capacity of these soils, and hillslope runoff is not likely to increase, if occurring at all.