HABITAT CORRIDORS FOR WILDLIFE
Why create a wildlife corridor?
Large areas of indigenous vegetation have been cleared for housing, agriculture, industry, and other uses, hence there is greatly reduced habitat left for native wildlife. Many of these native vegetation fragments are often small and isolated from one another by barriers such as open pasture, housing, roads, and water bodies (eg. dams). These are sometimes known as "island" habitats.
It should be noted that wildlife is more than just birds and mammals. It also includes insects, reptiles, spiders and micro fauna such as earthworms. Without this diversity of smaller animals, many larger animals will not be able to survive.
Wildlife constantly move:
- Looking for seasonally available and new sources of food.
- Looking for shelter/protection
- Searching for mates
- Dispersal of young to new ranges
In island habitats there may be no adjacent habitat to forage in, or for animals to roam and disperse. They may not provide all the resources an animal species requires (e.g. food, water, shelter/protection and breeding). Island plant communities are also vulnerable to catastrophic events, such as pests, diseases, clearing, bush fires, and to gradual changes, such as inbreeding or climatic variation.
Habitat corridors provide links between these isolated island communities. This allows migration to replenish a declining wildlife population (increasing numbers giving better chance for some to survive and reduce inbreeding) and also allows recolonisation where a species may have become locally extinct (extend the local range).
Other Benefits of Wildlife Corridors
There are not only benefits for indigenous vegetation and wildlife, but also considerable benefits to local land owners. Creating such corridors can also:
- Help reduce erosion (e.g. in gullies, stream banks, on exposed ridges)
- Help reduce salinity problems
- Reduce nutrient runoff into streams
- Provide windbreaks or shelter belts for stock and crops:
- Greatly improved yields due to reduced heat or cold stress of stock
- Reduce physical damage to plants (eg. young seedlings, flowers on fruiting plants) by wind (direct wind effects and sandblasting effects)
- Increase birth rates of stock (up to 50% increases recorded in lambing rates in some areas.
- Provide timber and firewood
- Help improve water quality
- Help mitigate floods
- Improve recreational fishing
Where to Establish Wildlife Corridors
- Corridors may exist anywhere between habitat islands of any size, even as little as a few old remnant Eucalypt trees that may provide valuable hollows, or linking smaller patches to perhaps a larger state forest.
- Remnant wetland environments (eg. marshes, swamps, lakes) can also be linked with other vegetation corridors, providing improved access for wildlife to important water sources.
- They are best designed where possible to follow natural contours (eg. rivers, ridges).
- They might incorporate other farm plantings (eg. windbreaks, timber lots).
Types Of Wildlife Corridors
- Natural corridors that follow land contours (eg. ridges, streams, gullies).
- Remnant vegetation such as those along roadsides, railway reserves and disused stock routes. These corridors often follow straight lines.
- Planted corridors include such things as farm shelter breaks and windbreaks. These are generally created for purposes other than creating wildlife habitat, but this can be incorporated into the design through careful selection of plant species.
Wildlife Corridor Design
- Preserve or restore natural corridors (eg. gully lines, stream banks). Stream sides are high value areas for wildlife. Limit stock access to riverbanks to prevent erosion, and allow for regeneration of riverside vegetation.
- Wherever possible build onto or restore existing corridors as they will have existing populations of local flora and fauna, increasing the rate of species spread.
- The wider the corridor the better (eg. at least 30 – 100 m wide) (see section on "edge" effects).
- Corridors are more effective when they link up with large larger habitats with few or no gaps (eg. roads cutting through).
- Use local (indigenous) plants. These are adapted to local conditions (eg. soil, climate, fire regimes), and local fauna are adapted to them. Also preserves the biodiversity of local flora. Indigenous plants generally have low establishment costs in comparison to introduced species and have minimal weed potential.
- Incorporate all forms of vegetation (eg. shrubs, grasses, rushes, ground covers, climbers), not just trees. In some grassy forests of northeast Victoria, for example, there may be four species of Eucalypts and between 70 and 100 under storey species. This means that the under storey represents over 90% of the biodiversity of the vegetation in this ecosystem.
- A network of corridors is more effective than single links. They increase opportunities for migrations and reduce the risk of links being broken (eg. bush fires, subdivision and subsequent clearing of some blocks).
- Fencing to restrict grazing of corridor vegetation by domestic stock is very important, but be careful not to restrict movement of wildlife.
- Consider habitat (eg. rocks, hollow logs, leaf litter) for animals that may be slow in migrating (eg. small ground dwellers such as lizards and snakes). Consider the provision of artificial nest boxes, or placement of hollow logs within new plantings.
- Cooperative action between local landowners may be necessary. Such cooperative efforts can make the best use of available resources, and allow for the most effective links between remnant patches.
- Agroforestry projects can be be positioned to link remnant vegetation patches, and also to act as a buffer around larger remnant vegetation patches.
"Edge effect" is a term used to describe what occurs with regard to vegetation and wildlife when one type of vegetation shares a border with another. They may occur naturally (eg. forest grading into woodland, or streamside vegetation to drier nearby slopes, and burnt and unburnt areas); or they can be man-made, such as pasture abutting forest, or roads through forest. Some edge effects can be positive in terms of native flora and fauna, but most tend to have negative effects. Edge effects are most likely to have an influence on narrow strips or small remnant areas. In terms of corridor plantings the wider the corridor the less the impact of "edge effects".
What Can Happen At Edges?
- Solar radiation, air and soil temperature, wind speed, humidity levels can all be altered leading to stresses on existing vegetation, and change in the types of plant seeds germinating.
- As vegetation patterns change near edges, so usually do the types of wildlife that inhabit those areas. Edges can be important for some species, providing shelter, nest sites, perching and observation points (eg. parrots feeding on grass and grain seed, eagles on rabbits, kangaroos and wallabies on grasses).
- Species with wider tolerances take over near edges, while less tolerant species only survive in "core" areas away from edges. In narrow corridors or small remnant patches these core species are generally absent.
- Aggressive edge-dwelling species such as Noisy and Bell Miners may invade and displace former inhabitants.
- Pest animals such as foxes, cats and dogs tend to move along and hide out near roads, tracks and cleared areas.
- Invasive (weed) plants can readily move into remnant vegetation and corridor plantings from adjacent agricultural, industrial or residential areas.
- Chemicals and fertilizers can drift from agricultural areas into edge areas.
- Erosion and altered water runoff characteristics (eg. drains) can damage and undermine the soil in edge areas.
- Stock can trample and graze edge areas.
- Litter (eg. from roadsides) can pollute habitat areas.
- Noise and movement from traffic and agricultural activities can disturb animals that require quiet to breed and feed.
- The longer the edge, the larger the area that is vulnerable to disturbance.
- The more angular the edges the greater the edge effect. Corners increase disturbance. Rounded corners and regular shapes minimise edge effects.
- The smaller the area the greater the risk of impacts occurring throughout the vegetation, with the 'core' habitat being destroyed.
(Ref: P. Johnston and A. Don, Grow Your Own Wildlife, Greening Australia Ltd.)
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