We examined the biodiversity impacts of fencing remnant vegetation to prevent livestock grazing in the Western Australian wheatbelt.
Untested conservation measures
Southwest Western Australia's wheatbelt retains an extraordinarily rich biological diversity that is threatened due to fragmentation, weed invasion, salinisation and degradation associated with widespread land clearing and intensive agricultural use.
For over 30 years, natural resource management programs have supported restoration activities in the wheat and sheep farming district of southwest Western Australia.
Despite this, the effectiveness of one of the oldest and most widespread conservation measures – fencing remnant vegetation to exclude livestock grazing – has rarely been evaluated.
Investigating the effect of fencing on biodiversity
Working with colleagues from the University of Western Australia , we investigated the impact of livestock exclusion fencing on biodiversity in the Avon catchment in Western Australia.
To do this, we compared 29 unfenced and 29 fenced (paired) sites, and 11 reference sites in York gum–jam woodlands within the catchment. These woodlands are rated high priority for biodiversity conservation. Sites had been fenced for between two and 22 years. Reference sites were selected as benchmarks; these were the least degraded woodlands we could find.
We tested two hypotheses:
- Fencing facilitates recovery of degraded York gum–jam woodlands towards conditions of the reference woodlands.
- Recovery of degraded woodlands after fencing to reference condition is constrained by ecological or other limits.
Fencing enhances biodiversity values
We found that on average, fenced sites had significantly higher native plant richness and abundance than unfenced sites. As well, weed abundance declined and the number of young wattle trees increased with time since fencing.
On the other hand, fenced sites usually had lower native plant species diversity than the reference sites, and sites with high soil nitrogen were slow to recover from weed invasion. Young eucalypts were uncommon in most sites, but did occur in sites that had been fenced and burnt or flooded.
We concluded that fencing to exclude livestock grazing is valuable for biodiversity conservation in remnant York gum-jam woodlands. However, additional conservation measures are likely to be needed in some cases, particularly where there is a lack of native seed, or where elevated soil nutrients and weeds prevent native species recovery.
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