The Impacts of Brush Packs on Landscape Function in a Paddock in Temperate, Mesic Southeastern Australia

Abstract

This study investigated the impacts of brush packs on landscape function, focusing on nutrient cycling at a degraded, heavily grazed paddock with a temperate, mesic climate in southeastern Australia. It addressed a gap in the existing research which has largely focused on the impacts of brush packs in semi-arid and arid environments. Brush packs, constructed from Leptospermum branches, were established in 2018 during a period of drought to restore function at a dysfunctional, heavily grazed, mostly bare ground site. The impacts of brush packs on function were assessed at both the landscape-scale and fine-scale using the Landscape Function Analysis (LFA) method, and direct measurements of nutrient cycling: soil respiration and carbon levels. Soil chemical properties, pH and electrical conductivity (EC), were also measured to determine if brush packs had any influence on these important soil properties. Based on previous research, it was expected that brush packs would increase LFA scores in all three indices: stability, infiltration, and nutrient cycling, as well as increase soil respiration rates and carbon levels. It was also expected that brush packs would not change pH or EC levels. A total of twenty brush packs were established randomly across five transects, with six additional transects established as controls. LFA measurements were taken in 2018, both before and after brush pack establishment, and again in 2019 and 2024. In 2024, measurements of soil respiration, carbon levels, and chemical properties were taken, with carbon and chemical properties compared across four depth intervals (0-1, 1-3, 3-5, and 5-10cm) and carbon fractionated into three fractions (particulate organic carbon, aggregate carbon, and mineral-associated organic carbon). Unexpectedly, brush packs gave no improvements in function at the landscape-scale relative to control (pasture) transects. At the fine-scale, they showed improvements in all three indices relative to control interpatches. However, brush packs did not improve soil respiration and carbon levels relative to control patches. During the study both brush pack and control patches experienced significant functional improvements due to substantial pasture growth driven by a rare three-year La Niña event. The natural recovery across the site likely overshadowed any additional benefit provided by the brush packs. No significant differences in pH or EC levels were observed. These findings indicate brush packs may have limited utility as a rehabilitation technique in resilient, mesic landscapes. LFA data collected one year after the brush packs were established and before the three-year La Niña event drove natural recovery suggests brush packs likely had a head start in terms of functional recovery. If conditions were to shift towards dysfunction, such as during a period of drought and intense grazing the relative functionality of the brush packs may increase, if they persist. Therefore, future research could explore whether the brush packs in this study offer lasting benefits to landscape function under drought conditions.