Soil properties on a chronosequence of landslides in montane rain forest, Ecuador

To assess the impact of landslides on soil fertility in south Ecuador, we compared the properties of shallow translational debris slides with those of adjacent undisturbed soils. A chronosequence of four small landslides, ca. 0.5, ca. 2–3, ca. 8–10, and ca. 20 years old, was selected on a 30–50°, forest-covered, east-facing slope of the eastern cordillera at 1900–2300 m above sea level (a.s.l.). All soils were Dystric Cambisols. The mean mass of the soil organic layer (sum of all O horizons) increased in the order landslide head (46 t ha−1)<central part (“track”, 101 t ha−1)<foot (102 t ha−1)<reference soils (291 t ha−1), implying a variation in nutrient storage of the same order. In the head area, only the oldest landslide had an organic layer. All mineral soils were acidic (pH in H2O of the A horizon: 3.4–5.2), the effective CEC of the A horizon ranged from 22 to 141 mmolc kg−1, and the base saturation from 13% to 54%; none of these properties was consistently different between landslide and reference soils. The A horizons of the soil in the landslide foot area had greater concentrations of most nutrients than those in the landslide head area. However, differences were not significant. The nutrient concentrations in the landslide foot area resembled those in the A horizons of the reference soils. Thus, the most obvious change in soil properties caused by the landsliding was partial or complete removal of the organic layer, which was not restored during the ca. 20 years covered by the chronosequence. This decreased the topsoil fertility of the landslide area.