Many species can live in moderately-altered landscapes that retain most of their trees, shrubs and grasses. However, a few species survive only where their habitat has been fenced to prevent grazing, trampling and rooting by feral or domestic animals.
Fences can be used to help keep buffalo and pigs out of monsoon rainforest patches that contain delicate plants such as Mitrella and Tiwi Islands Waxflower, or livestock from wetlands that support Swamp Twig-Rush, Caldwell's Clubrush or Australian Painted Snipe. They can be used to prevent pigs from eating the seeds and crowns of Armstrong Cycads, from raiding the nests of Gulf Snapping Turtle or from denuding the wetlands used by Howard Springs Toadlet.
Fencing to exclude livestock is recommended to prevent overgrazing of Tobermorey Melon or physical damage to ancient Waddy Wood trees, and can also be used to exclude cattle from the riparian habitats of Purple-Crowned Fairy-Wrens. Rabbit-exclusion fences in strategic areas will allow the regeneration of Tjilpi Wattle.
Strategic fencing around port facilities, combined with vigilance in checking loads, should help prevent cane toads from stowing away on boats, and so keep them off islands that support populations of Northern Quoll. Strategic fencing has proved successful to date on Groote Eylandt. On the negative side, fences that exclude Wild Dogs and Dingoes may contribute to the loss of threatened species. Populations of cats and foxes can increase, and Wild Dogs and Dingoes are more effective predators of small mammals and reptiles, so they can to multiply.
When planning a fenced area, consider what the fence design should achieve. For example: there is no point in fencing a wetland to exclude cattle, if pigs are the main animals causing damage to the wetland. It is better to use the available funds to fence a small area effectively, than to fence a larger area ineffectively.
While fencing may slow down the entry of new pigs or other grazing animals from sections of water frontage or coastal environments, it will not completely exclude them. Follow-up management is required to remove any trespassers. Fences to exclude cats and foxes for the protection of small mammals, such as Plains Mice or Mala, are really only an option on conservation reserves, where there are intensive management and monitoring programs for the threatened species of concern.
Different construction design and types of wire will be needed to keep out different types of animals. Three or four strand barb-wire fencing is generally sufficient to exclude buffalo, cattle and horses. Electric fencing is recommended for buffalo, and flagging or extra droppers are recommended to make the fence more visible in areas of high buffalo or horse traffic.Progressively smaller sizes of mesh are required to exclude pigs, rabbits and mice. Other considerations, such as the most suitable type of posts and gates to use, the height of fences and whether to bury the mesh have been well researched, and details can be found in the attached reading list.
In the case of species being translocated to within fences, the design must also be sufficient to keep to your target species inside. For example, you do not want burrowing species to dig out of the fenced area, leaving a hole behind them. Habitat contained within the fence must be sufficient to support species that cannot get out, particularly in the case where there are few or no predators and the population is likely to reach unnaturally high levels. Indicators of overstocking should be developed with mitigation strategies available to reduce population pressure when overstocking levels are being reached.
Management of fenced areas
Long term upkeep is also important if fences are to achieve their conservation purpose. Fences require monitoring and maintenance. The frequency of fence checking depends on the type of fence and what you are trying to keep out. For example high mesh fences may require weekly checking to ensure that large animals, such as kangaroos have not hit the fence and damaged it. Frequent monitoring is particularly important when fences are first erected, as animals that use the area inside and outside the fence are more likely to hit or attempt to get inside the fence when it is new. This can result in injuries and damage to fences. Fences should also be checked after weather events such as storms that might bring down trees, or floods and any required maintenance undertaken.
Where fenced areas exclude livestock, increased grass growth may allow wallaby and kangaroo populations to multiply to unsustainable levels. Where possible, prevent this happening by turning off artificial waters in and near the fenced area and allow dingos to remain at healthy levels. Prevent overgrazing of fenced areas by ensuring that animals that accidentally get inside are able to escape.
Animal welfare should be considered at all times. Fenced areas should be checked regularly to ensure any trapped animals do not go hungry. Also, if there is any chance of an animal being trapped inside the fence, water must be provided.
Horse, cattle and camels are all known to use spear traps, or one way gates, to get out of fenced areas, so installing these will help address both conservation and animal welfare issues. In large fencing projects, spear traps into small, watered holding paddocks can be used to muster animals for later harvest or extermination.
Fenced areas also need to be actively managed for fire and weeds. Where grazing pressure has been removed, grass growth may proliferate, increasing fuel load and fire hazards. Increased grazing pressure just outside the fence by animals attracted to this grass growth may form a barrier to wildfires. Fire management within the fenced area should be to benefit the threatened species for which the fence has been erected.
This may involve fire exclusion for rainforest species, or periodic burning to maintain wetland health. Weeds may also proliferate when grazing is excluded, as is the case when cattle have been taken off wetlands containing Para Grass. Weeds may also thrive in areas disturbed by fence building or by increased grazing pressure surrounding the fence. Weed management within the fenced area should also benefit the threatened species for which the fence has been erected.
There may be a temptation to use paddocks fenced for conservation purposes for production uses instead - especially in lean years, or when there are extra animals needing a holding paddock just after a muster. Brief periods of grazing may be acceptable in some situations, but should be disclosed in the planning stage if this is an ulterior motive for building the fence.
Taking into account all these factors, consider whether fencing may simply cause one environmental problem while solving another. It is a good idea to take photographs of habitat condition before erecting fences, and then a follow-up series of photographs from the same place to track any improvement or change. Measures of other features, such as ground cover or bird numbers are also useful to demonstrate improved habitat value. Funding bodies are often prepared to assist with fencing materials and/or labour.