Above-average rainfall stimulates short-term, passive recovery of ungulate mediated soil scalds in Australian mesic savanna

The quality of savanna habitats across the globe has declined due to increased grazing pressure from introduced ungulate species. High grazing pressure can result in a loss of perennial grass cover, which can lead to the formation of “soil scalds” on clay soils. Scalds are maintained by the formation of a soil crust, which impedes water penetration and increases runoff. Scald formation can have significant negative ecological impacts on savanna ecosystems, yet the reversibility of this process remains uncertain. In this study, we examine perennial grass decline in a north Australian savanna, where historic grazing pressure has resulted in formation of soil scalds. We tested the reversibility of scald formation by implementing a soil treatment, which involved ripping the soil to a depth of 5−10 cm and placing erosion matting on the soil surface. In addition, ungulate exclusion fencing was erected to test if the presence of feral ungulates impacted scald recovery. After a year of above-average rainfall, both control and soil treatment plots showed significant recovery in perennial and annual grass cover, as well as a significant decline in bare ground cover. However, the degree of recovery was greatest in soil treatment plots, mainly due to increases in annual grass cover. This short-term study suggests that passive recovery of scalds is possible under favorable conditions and confirms that soil mediation can accelerate revegetation. In contrast, fencing was not found to have a significant effect on vegetation recovery, which is likely due to the low ungulate density present during the study. It is important to note, however, that our results are from a single season and a long-term study is required to confirm ongoing recovery.