Limitations to the soil impacts of tree regrowth in improved cattle pasture

Abstract

Tree regrowth plots are often utilised to reduce soil erosion and increase soil organic carbon (SOC) as well as providing shade for cattle. However, unfenced tree regrowth plots have been found to make limited improvements in soil health in grazing lands. To better inform land management decisions, the impact of an unfenced tree regrowth on soil erosion rates and soil properties was analysed for an improved (i.e., sown with introduced species) cattle pasture in Eastern Australia. Soil cores were collected to 20 cm depth for two paired transects: one with improved pasture and a tree plot, and one consisting only of improved pasture. Samples were analysed for soil organic carbon and soil properties and soil erosion rates were determined using the diffusion and migration model (DMM) and Revised Universal Soil Loss Equation (RUSLE). Maximum DMM erosion rates were similar for the two transects at 2.7 (tree plot) and 2.3 (pasture) t.ha−1.yr−1, with the tree plot not having a statistically significant effect. RUSLE erosion rates showed less similarity for the transects at 5.58 (pasture) and 3.08 (tree plot) t.ha−1.yr−1. SOC was lower within the tree plot compared to the rest of the transect, while it was significantly higher in the pasture than the tree plot transect (4.93% compared to 3.72%). To examine if the tree plot is buffering against higher erosion caused by this, the RUSLE cover factor was substituted for that of the pasture transect. However, no such effect was observed. Overall, the tree plot had no significant effect on SOC and erosion in this improved pasture grazing system. This has implications for the design of tree plots and their location, which is significant due to their perceived role in regenerative agriculture practices.