SMALL-SCALE SITES
The small-scale sites varied more than the large-scale sites with regards to Soil types, Implementation( expert input) and the landholders’ Focus on improving land condition( Grazing management)( Table 2). Nevertheless, the discussion will be presented around the same key questions:
1. How long did it take for the small-scale sites to stabilise?
2. What were the primary causes of reduced success / soil stability at the sites and how can these be remedied?
3. What changes to planning and design are recommended to improve small-scale gully remediation?
4. What maintenance schedules and maintenance costs should be embedded in the remediation plan?
How long did it take for the small-scale sites to stabilise?
Catchment only works
The results of this study indicate that, if remediation works are implemented following standard soil conservation guidelines and near average weather conditions follow, renovated catchments of gullies in Sodosol soils are likely to stabilise within three years. Gully catchments in the Open Downs land type with Vertosol soils may take only two years. This is expected given that catchments tend to still have sufficient topsoil to support vegetation, and when released from excessive grazing pressure, land condition improves. This is not the case when the thin, but essential topsoil has eroded away.
Gully remediation works
For the remediated small-scale gullies, results suggest that, if soil conservation officer’ s plans are followed and there are average weather conditions after the work, a site is likely to be‘ mostly stable’ within three years( Table 3, 9 / 12 sites, Figure 14 with sites removed if poorly implemented / plans not followed). All the sites were monitored in years 3-5 following the works, 2022-2024, but the last two years of monitoring recorded few improvements. More often than not there was a slight reduction in stability / land condition and this coincided with the re-introduction of grazing( Table 3, Appendix 2 and Figures 13 and 16). This will be discussed further in the next section. The two sites deemed to be stable were in Vertosol soil of the Downs country land type. Notably, these results cast doubt on the ability for small gullies in Sodosols to achieve full stability.
What were the primary causes of reduced success / soil stability at the sites and how can these be remedied?
The main drivers of reduced stability at the remediated small-scale sites( catchments and gullies) were:
• presence of erosion( sheet and rill erosion);
• reduced ground cover( e. g. < 70 per cent, there was a pasture deficit due to overgrazing at 19 / 58 LCATs across six sites, five attributed to cattle grazing, one wallaby grazing); and
• lack of biodiversity( Indian couch, Bothriochloa pertusa dominated at almost half of the LCATs 28 / 58 over nine sites)( Table 3).
These three causes of reduced land condition, recorded through the land condition assessments, reflect the observations made at the small-scale sites across the three years. It is expected that, for most sites, the impact of these three drivers of land condition would be eased by a more concentrated focus by land managers on improving land condition at the recovering site.
In 2022, the first year of monitoring, sites had typically been protected from regular grazing for two or three years, vegetation biomass was relatively high, some desirable pasture species present and bare areas seemed to be reducing. Some remediated catchments were in B condition and the remediated gullies were mainly in C condition. Over the next two years of monitoring, sites in the Vertosol and Kurosol soils tended to continue to improve in stability, despite a return to light or moderate grazing. However, the condition of sites in the Sodosol soils tended to dip for the treated catchments( Figure 12) and plateau for the treated gullies( Figure 16). This dip coincided with when most graziers reintroduced grazing to the
46 GULLY MAINTENANCE AND MONITORING TECHNICAL REPORT