Runoff and erosion in woody encroachment, pasture and woodland vegetation in semi-arid New South Wales, Australia

Abstract

Woody encroachment is the increase in density, cover, extent or biomass of woody plants. It has been reported from arid and semi-arid areas around the world. Woody encroachment is the result of changes in factors such as weather and climate, grazing pressure, fire regimes, and combinations of these. The most widely recognised effects of woody encroachment are the decline in herbaceous forage production and carrying capacity for livestock, decreased biodiversity and socioeconomic value of affected areas, and, in some cases, increased runoff and soil erosion. The eco-hydrological responses of areas of woody encroachment and of pastures established after removing the woody vegetation are not well understood in semi-arid Australia. The aim of this thesis was to investigate runoff, erosion and associated factors in woody encroachment, and how these compare with other vegetation states in semi-arid Australia from an eco-hydrological perspective. ... Overall, the study showed that runoff and erosion in the four vegetation states are mostly site-dependent. Hydrological and erosional responses in woody encroachment were generally not significantly different from those in recently and long-established pastures and woodland. The study showed that ground cover type and amount and its spatial distribution largely determine runoff and erosion responses in the studied systems. There is potential in using high resolution satellite imagery and spatial modelling to apply accepted concepts of semi-arid patchiness to link small-scale eco-hydrological and erosional responses to larger scales appropriate for management. The study showed that factors related to gully erosion in woody encroachment areas are related to topographic thresholds that can be used for the identification of areas susceptible to gullying.