Sanctuary Fences and their Local Impacts

Fox- and cat-proof fences are being built across Australia because they are one of few currently viable options to maintain introduced predator-sensitive fauna species and therefore restore whole ecosystems. Most fox-proof fences are circa 2 m high with a floppy top, embedded in the ground and some also have electric wires on them. In the case of Mulligans Flat Woodland Sanctuary, we have constructed circa 22 km of fox- proof fences using two similar designs. With the designs we used we experienced short-term construction impacts which were not dissimilar in scale to the construction of farm fences with the addition of trenching, and ongoing impacts relate to fence maintenance and the established fence filtering fauna in the landscape.

The short-term construction impacts can be largely mitigated with fencing alignment (building on existing fence lines or tracks and avoiding sensitive natural and cultural values) and rehabilitation of any construction impacts (e.g. through seeding with native flora).  It should also be noted that although the Sanctuary woodlands are relatively in good condition compared to many other sites, they have been impacted by decades of agricultural management, and are not considered either ‘pristine’ or ‘wilderness’.

The continuing influence of the fence in the landscape is two-fold – (1) restricting movements of unwanted species that are removed from the Sanctuary area (e.g. foxes, rabbits, cats); and (2) restricting movements of non-target native species (e.g. turtles, dingos, large lizards, wombats, large macropods like kangaroos). It should be noted these fences are not strictly ‘predator-proof’ – a raft of predation occurs within Sanctuary areas by species for whom the fence has no direct impact (e.g. frogs, lizards, snakes, sugar gliders, owls, goshawks, etc.), and many of these predatory species will be beneficiaries of not having foxes in their environment.  We prefer to use the language ‘fox-proof’ as this is the main threat to the maintenance of the threatened species we are recovering.

In our temperate woodland setting that is already depauperate of ‘critical weight range ’mammals (those between 35 and 5500 g, that have been most affected by introduced predators) there may be 20 species whose local or migratory movements are potentially negatively impacted by the fence’s continuing presence – for example, the Eastern Long Neck Turtle, Swamp Wallabies, Red-neck Wallabies, Wallaroos, Goannas, Dingos, Spotted Tail Quoll, Koala, Wombat, and Echidna. Some of these species’ local populations also benefit from having a safe-haven from fox predation (e.g. Echidna, Goannas, macropods, reptiles including turtles) but their long-term management in a Sanctuary context in the absence of larger predators requires attention.

Some of these movements across a Sanctuary fence can be facilitated or managed by design (e.g. the wombat gates being trialed at Wandiyali near Queanbeyan NSW) or programmatically (e.g. volunteers at Mulligans Flat help turtles cross the fence – although always with some reluctance when they are put outside to face the challenges of roads and foxes), and for wide ranging species some of these barriers are probably of no consequence given the scale of these Sanctuary environments in the broader landscape matrix. It is also important to note that species within also benefit from the absence of predation by introduced predators, so may in fact experience a net-gain in population size (further below).

There are tens-of-thousands of species in a Box-Gum Grassy Woodland environment, and for the vast majority of those species the presence of the conservation fence itself is unlikely to be of direct consequence.

Benefits of Conservation Fences

Whilst conservation fences are often considered an ‘expensive’ conservation asset, most people don’t often consider that alternatives also cost money. If we accept that landholders have an obligation to control pest animals on their properties, and conservation agencies have an obligation to save and foster endangered species, then the costs of the alternative options can stack-up considerably. Once established, Sanctuary areas can be rid of feral animals. Unfenced control programs are not always effective for threatened native species, and gains can be lost if pest control stops (even briefly) or there is a landscape-scale increase in introduced predators e.g. a surge in fox numbers in some years.

In the original sanctuary context, we have eradicated foxes, hares, and rabbits and had our fences up before the deer and goats arrived. In our original Sanctuary area, it is now 10+ years since we have spent any money on fox management (other than surveillance) and coming up to 5 years since we have spent money on rabbit management. In our Sanctuary expansion area, the removal of rabbits has likely cost us circa 10% of the original forecast expense. In both areas, ongoing surveillance will be important, but money saved from rabbit and fox management can be invested in conservation. To achieve the reductions in fox and cat predation required over vast areas to enable species to recover and be reintroduced at the Sanctuary scale, the alternative to building a fence, would also be a scale of expenditure over a long period of time that would quickly pay for the fence.

Finally, the do-nothing-until-its-nearly-too-late option ultimately becomes much more expensive, requiring either the emergency deployment of large feral animal control programs, or the recovery of the final individuals of a species for incorporation into a zoo or captive breeding program, where the objective is always putting the species on a pathway to recovery back to the wild, though seldom achieved. This approach has been tried throughout the world, and has been found to be ultimately very expensive and often not effective.

Many of the locally extinct species had critically important roles in the function of Box-Gum Grassy Woodlands of our region, and some of the research we have supported at Mulligans Flat has demonstrated this. The flora and fauna of these woodlands has co-evolved over millennia. For example, it is often not realised that every native tree over 120 years old in our region, germinated in soils that were dug over by bettongs, bandicoots or potoroos. Returning species such as these is integral to restoring the whole Box-Gum grassy woodland ecosystem.

A Sanctuary is not a Zoo – predation in Sanctuary Settings

The species in the Sanctuary are considered ‘as-wild’ – once a reintroduction process has been successful the animals are not fed or cared for in any way different to wild animals.  Naivety to predators of critical weight range mammals in sanctuaries has been recognised as significant. Accordingly, we are fostering predation in the Sanctuary (e.g. via the Eastern Quoll and Spotted Tail Quoll) to ensure that populations of our threatened species are predator-aware, maintain predator avoidance behaviours, and healthiest possible populations are maintained.  This has several benefits – traits for the fittest individuals are supported, and unhealthy individuals are quickly eaten (meaning for example they can’t spread disease), and it enables the development of populations that are more likely to persist outside fenced Sanctuaries where fox control programs are active.

See the Mulligans Flat Woodland Sanctuary Strategy – Flourishing Nature | Flourishing Culture which highlights the approach we are taking to rebuild a functional food web which guides our reintroduction programs.

Regeneration of Fauna Populations

One of the pleasantly surprising aspects of building a fox- and cat-free sanctuary area is the observations of non-target species’ populations regenerating. In our instance at Mulligans Flat we have observed populations of Sugar Gliders, Possums, Echidnas, Swamp and Red-neck Wallabies, Shingleback and Bearded Dragon lizards, and Antechinus respond positively to the absence of foxes – evidenced most obviously by their ongoing paucity in the landscape surrounding the Sanctuary.

This highlights simply our lack of awareness and appreciation of the impacts of foxes and cats in this landscape and as a society, our ‘shifting baseline’ and lowering of expectation regarding the nature rich quality of the landscape for which we are custodians.

Reintroduction Opportunities

In any area absent of foxes and cats there will be opportunities for re-introductions of species that were once in the locality or the region. In the Mulligans Flat Box-Gum Grassy woodland system, our colleagues examined fossilised owl deposits from the Capital Region, and combined with habitat modelling, habitat suitability assessment and historical records to determine what species could have occurred in our woodland environment. Our selection and development of a pipeline of species for reintroduction then takes into account, strategic, operational, policy, community engagement and practicality considerations to determine what and when to reintroduce a species. In each instance where we choose to reintroduce a species, we do it using adaptive tactics framework that commits us to several years of learning and doing to achieve reintroduction success.

Reintroductions without a fox- and cat-proof fence are possible, for example on islands, peninsulas or otherwise fox-controlled areas, but the deployment of a fence is often considered on the balance of risk and certainty to be a favoured tactic.

Opportunities for meta-population management of rare species

With the growing network of Sanctuaries and interest in new Sanctuaries in the ACT, NSW and Victoria, we have an emerging opportunity to manage threatened species in these sanctuary environments as ‘meta-populations’ . To help manage population genetics, expose populations to a variety of habitat and climate types, foster growing populations, we are keen to support a matrix of sanctuaries in temperate woodland environments that can support and share populations to mitigate local risks and maximise conservation success at local, regional and national scales. The species that we consider to be appropriate for consideration in this context include:

•  Eastern Bettong

• Bush Stone-curlew

• Eastern Quoll

• New Holland Mouse

• Eastern Chestnut Mouse

• Rosenburg’s Goanna

• Brush-tailed Phascogale

• Koala

• Spotted-tailed Quoll

• Australian Bustard

• Southern Brown Bandicoot

Research into Macropods and their Management

Aboriginals likely harvested kangaroos for tens of thousands of years. Recent research from Namadgi National Park highlights the impact of foxes on juvenile kangaroos. Establishing an agricultural landscape with watering points has likely fostered kangaroo populations and enabled recruitment in periods when it would otherwise not have occurred.

Establishing a fox-free environment requires a commitment to manage macropods and/or total grazing pressure to mitigate impacts on flora and flow-on impacts on the ecosystem. Potential long-term solutions include initially excluding large macropods, releasing macropods, harvesting macropods, fertility control, and the reintroduction of predation pressure (and some combination therein).

Long-term Experiment, Monitoring and Adaptive Management

The ecosystem restoration process is long-term, so research and monitoring also has to be on that timescale. In 2005, we established the ‘Mulligans Flat – Goorooyarroo Woodland Experiment’ to follow the impact of conservation management interventions on biodiversity. When we built the predator-proof fence, we were also able to conduct research on the reintroduction of lost native species. To date, this research has produced over 55 peer-reviewed papers, and informs our management of Mulligans Flat Woodland Sanctuary and other sanctuaries and nature reserves in Australia.

Floristic Benchmarks and Ecosystem Condition

Most ecological work in Box Gum Grassy Woodlands in Australia is impact assessment for development applications.  These processes rely on floristic descriptions of woodland condition to identify whether an area ‘is’ or ‘is not’ officially considered Box Gum Grassy Woodland, and the quality of that patch.  Unfortunately these benchmarks are entirely floristic based, and silent on the presence or absence of fauna and its role in a healthy woodland ecosystem.  Further, the benchmarks used were developed in and after 1980s , which we know represents a state that has been devoid of the influence of key ecosystem engineers (e.g. Eastern Bettongs) for 100 years or so – a period that represents many generations of many of the species used to define the condition of the site.

At the Sanctuary we are addressing the phenomenon of shifting baselines, and trying to generate new baselines that take into considered a more holistic ecosystem approach – how do floristics and condition change as we re-build a woodland ecosystem with its missing faunal components?

Is Mulligans Flat ‘Rewilding’

‘Rewilding’ is a very popular new movement in conservation, where natural processes are harnessed to restore ecosystems to as wild a state as possible. A new international study identified 10 guiding principles of rewilding. Mulligans Flat Woodland Sanctuary meets all ten of these guiding principles, so yes, we are ‘rewilding’ at Mulligans Flat.