Soil hydrological and erosional responses in areas of woody encroachment, pasture and woodland in semi-arid Australia

Abstract

In arid and semi-arid areas, woody encroachment is the increase in density, cover, extent and/or biomass of woody plants. Woody encroachment is often associated with increased runoff and soil erosion. Hydrological and erosional responses of woody encroachment and of pastures established after management of encroachment in semi-arid Australia are not well understood. This study compared the hydrological and erosional responses across vegetation states comprising woody plant encroachment (>1200 stems ha⁻¹), recently established pastures (<23 years of age), long-established pasture (50–100 years of age) and open woodland (<330 stems ha⁻¹) in semi-arid eastern Australia. Responses were measured using rainfall simulation with intensity of 35 mm h⁻¹ for 30 min applied on 1 -m² plots. Runoff and sediment production did not differ significantly between vegetation states. Average runoff in woody encroachment was 9.0 mm h⁻¹, followed by recent pasture (8.2 mm h⁻¹), long-established pasture (5.9 mm h⁻¹) and open woodland (4.2 mm h⁻¹). Total sediment production in recent pasture was 11.6 g m⁻², followed by woody encroachment (9.0 g m⁻²), long-established pasture (7.3 g m⁻²) and open woodland (4.3 g m⁻²). Runoff and sediment production were significantly lower at one pasture site (0.9 mm h⁻¹ and 1.3 g m⁻²) where rotational grazing and minimum tillage had been implemented than in the adjacent paired woody encroachment site (10.3 mm h⁻¹ and 6.5 g m⁻², respectively). This example of a pasture that had been managed to increase ground cover illustrated the effect of pasture management on reducing runoff and sediment production. Across all vegetation states, small scale runoff and sediment production were minimal or zero where total ground cover was 73% or higher.