Can simple, on-ground vegetation and soil measures reliably indicate the health of rangelands? An application in Australia’s semi-arid woodlands

Sustainably managing grazing lands is aided by monitoring and responding to simple and reliable indicators of how well the vegetation and soils of these landscapes are functioning to capture scarce resources such as water and nutrients. Indicators are needed because direct measurement of resource capture is time consuming and costly. Our aim was to assess how simple measures of vegetation patch cover and size, and soil surface condition, would apply to patchy (run-on/run-off) semi-arid landscapes being grazed at different intensities. We used the grazing gradient design where distance from water serves as a surrogate for grazing intensity, which is a combination of herbage consumption and trampling. From 0.5 to 8.9 km distance from water, we measured vegetation and soil indicators of landscape function on 12 sites, six along a grazing gradient in a mulga (Acacia aneura) woodland and six in a gidgee (Acacia cambagei) woodland. We found the size of tree groves, at both mulga and gidgee sites, declined near water, indicating a loss in the capacity of these groves to capture mobile resources in run-off. Enhancing this capacity at sites in ‘good’ rangeland condition was the presence of a thick band of grass upslope of tree groves. The number of soil erosion features (rills) was also a reliable indicator of landscape function at both gidgee and mulga sites. Soil surface condition indices of stability, infiltration and nutrient cycling had no detectable trends with distance from water at gidgee and mulga sites, but these three indicator values were always significantly higher within groves than inter-groves, confirming the important role of maintaining healthy groves of trees and upslope bands of grass within these semi-arid rangelands.