Overland Flow, Soil Erosion and Stream Water Quality in Forest Under Different Perturbations and Climate Conditions

Abstract

Forest cover and its management and perturbations could significantly affect the surface runoff (part of the precipitation that does not penetrate into the soil and not accumulate on its surface), overland flow (surface runoff and streams), soil erosion, and runoff water quality. These effects are strongly related to climatic conditions. The overall objective of this chapter was to describe and discuss the relationships between forest and climate conditions, and their effects on surface runoff, overland flow, soil erosion and runoff water quality, when subjected to various managements and perturbations. Three different climate types were studied in this chapter: (1) a Mediterranean, semi-arid climate with annual precipitation of ∼500 mm; (2) a semi-humid northern climate with annual precipitation of ∼600 mm and freezing temperatures and snow conditions in the winter; and (3) a mild, humid climate with average annual rainfall of ∼1,800 mm and no freezing temperatures or snow conditions. With respect to water issue, the watersheds were divided into two main types: (1) those under water-limited conditions (watersheds in the Mediterranean semiarid region); and (2) those under non-water-limited conditions (watersheds in a semi-humid northern climate and in a mild, humid climate). In the Mediterranean semiarid region, the effects of different soil covers (bare soil, cover of annual plants, mulched soil, and cover of plants canopies) on surface runoff and soil loss amounts and runoff water quality were studied and discussed. In the semi-humid northern climate, the effects of various perturbations (clear cutting and land drainage) on cumulative and seasonal overland flows and their qualities at the outlet of different, small, upland forested catchments were studied. In contrast, in a mild, humid climate, the effects of successive perturbations of a moderate surface wild fire, clearcutting, a rotation based on coppice and coppice sprout selection, and an attack by G. scutellatus Gill on an increase of overland flow and its quality from Eucalyptus globulus catchment were presented and discussed.