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As part of the Seeding the Future Program, I undertook a PhD Internship with Bush Heritage Australia to study the changes in soil properties in response to destocking on Bon Bon Station Reserve, Antakirinja Matu-Yankunytjatjara Country.
Bon Bon Station Reserve, which is in the South Australian rangelands, is a former sheep property that was established as a nature reserve by Bush Heritage in 2008.
Despite making up 80% of all land in Australia, rangelands often endure extensive degradation and yet remain relatively understudied. So, with the help of Dr Patrick Taggart, we designed a study to ascertain differences in soil physicochemical properties and biology around destocked and active watering points in the South Australian rangelands.
To do this, we used Bon Bon Station Reserve vegetation where all stock were removed 14 years ago. As soil types are often determinants of vegetation communities, we selected our sites at watering points within a common Chenopod shrubland habitat. This included six decommissioned watering points on Bon Bon, and 10 active points on an adjacent sheep station.
At each site, we created a transect running away from the watering point to capture a gradient of decreasing stock impact. The most heavily impacted areas in landscapes are those immediately at watering points where stock congregate, with increasing distance from artificial watering points typically said to be less impacted. Along this transect we sampled at 0, 25, 50, 100, and finally, 200 metres from the watering points. At each distance we measured groundcover and collected soil samples from the top 10cm of the soil profile. Back at the laboratory these samples were run through a series of physicochemical and biological tests.
Our results were promising. Bon Bon showed several signs of recovery. This was demonstrated by lower nutrient loading relative to the adjacent pastoral property.
Total dissolved solids (a measure of dissolved substances such as minerals, salts, and organic matter) were also lower on Bon Bon relative to the pastoral property. Bon Bon also has a higher percentage of ground cover and litter abundance, which is a positive sign of recovery.
Another positive aspect of our results was that almost all measured soil properties were equivalent on Bon Bon and the pastoral property beyond 50m from watering points. This suggested to us that the impacts of stock on soil properties are highly localised around high-impact, high-traffic areas and are not widespread across the broader landscape, at least for the soil properties measured.
On a slightly less positive note, we also observed several soil properties that were in a poorer state on Bon Bon relative to the adjacent pastoral property. For example, phosphorus concentrations remained high on Bon Bon, as did bulk density. This suggested a lack of recovery from compaction on Bon Bon, although bulk density measures were challenging to interpret due to differences in soil composition between the two properties. These poorer values for some measured soil properties on Bon Bon may be, in part, due to the low rainfall and productivity in these systems leading to slow soil recovery in arid environments.
Overall, our study demonstrated that the soils on Bon Bon are on a positive trajectory to recovery. Despite this, after 14 years of no stock, some legacy effects on soils remain in areas close to historical watering points that were highly impacted by stock.
Arid environments are slow to recover, but Bon Bon Station Reserve is here to stay and so environmental improvement will undoubtedly continue.
