Effect of forest floor characteristics on water repellency, infiltration, runoff and soil loss in Andisols of Tenerife (Canary Islands, Spain)

Given its singular properties and location, forest floor (litter+duff) is a key factor in hydrological processes. Water infiltration research was carried out for the present study in Andisols at ten sites, six of which had coverings of pine forest and four of rainforest. Rainfall simulations were conducted on gentle, moderately-steep and steep slopes (10, 30 and 50%) to determine infiltration, runoff and soil loss as a function of the forest floor characteristics. The duff on the pine forest soils consists of moderately porous, extremely hydrophobic and consistent semi-decomposed organic material, which is rich in fungi hyphae. The duff on the rainforest soils is formed by highly porous, loose, semi-decomposed organic material. The study results highlight the influential role played by the forest floor in infiltration and runoff. Infiltration barely reaches 20mm h^-1 in pine forest, compared to 50mm h^-1 in rainforest. As a consequence, the pine forest runoff is twice that recorded in rainforest sites. The wetting front on gentle and moderately-steep slopes evidences the influence of the duff on infiltration. In pine forest, most of the rainwater remains in the duff and infiltration depends little therefore on the underlying mineral soil properties. In rainforest, the wetting front extends below the duff and the well-developed soil structure is a major factor in water infiltration. The differences noted in the two parameters are not found on the steep slopes. No soil loss differences are observed between the two vegetation covers and forest floors despite the greater runoff in pine forest. The results demonstrate the protective effect of the organic covering and how the stability of the Andisols helps combat water erosion processes.