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Using Indigenous Plants to Conserve Indigenous Fauna

John Reid

Approaches to using plants for gardens and landscaping projects have evolved considerably over the previous 30 years or so. Among the changes are the greater use of Australian native plants since the sixties and the increased interest in indigenous plants since the eighties.

However, to a large extent fundamental principles of gardening and other plantings remain more or less unchanged. Plants are used primarily for amenity, utility and decoration. Many plantings, particularly those in gardens, are collections of numerous different species brought together from many different Australian and overseas localities. They are treated as static in space and time with little or no opportunity for plants to reproduce themselves on-site or interact genetically (via pollination and seed dispersal) with plants on other sites. Gardens and other plantings are considered as separate entities that have no need to be congruent with their surroundings. Generally we retain and plant the species we want (or are able to obtain) with little or no consideration for the habitat requirements of indigenous species of plants and animals that occupied our site before European settlement. In such settings, natural elements and processes are to be controlled or eliminated, especially those considered unattractive (e.g. 'untidy' or prickly plants) or harmful (e.g. mistletoes, leaf-eating insects).

The purpose of this paper is to offer some ideas that extend traditional approaches to using Australian plants for gardening and landscaping to more adequately meet the needs of indigenous fauna. My emphasis is on indigenous plants for the many reasons discussed elsewhere (e.g. Edwards et al. 1988, Buchanan 1989, SGAP Maroondah 1991), but most important here is the contention that indigenous vegetation provides the greatest range of habitat options for indigenous fauna because they have evolved together. 'Indigenous' is difficult to define precisely, but for this paper, a plant or animal species is regarded as indigenous to a site if it is believed to have occurred there immediately prior to European settlement. For example, Cootamundra Wattle, Acacia baileyana is indigenous to the Cootamundra - Wagga Wagga area of New South Wales, whereas outside that area, e.g. in Melbourne gardens, it is regarded as a native plant but not an indigenous one. 'Fauna' refers to animals including mammals, birds, reptiles, frogs, insects and spiders, and is used interchangeably with 'animals'. Similarly, 'flora' is used interchangeably with 'plants'.

The urban context

The urban environment, such as that of Greater Melbourne, is the context for the ideas discussed here. However, most will be generally applicable to the rural environment also.

Indigenous vegetation is extremely fragmented in urban areas. Some municipalities have virtually no remnant vegetation. Even in municipalities that retain some 'bushy' atmosphere, bushland remnants with a reasonable complement of indigenous plant species represent only a fraction of the pre-European vegetation with most sites isolated from one another by residential, industrial and formerly agricultural land uses. A recent study of remnant bushland in the City of Maroondah recognised 82 sites ranging in size from 0.1 ha. to 33.5 ha and representing in total just under 5% of land in the municipality (Lorimer et al. 1996).

The future conservation of such sites depends partly on connections being restored between them by appropriate revegetation to enable bushland remnants to be extended and thereby more protected from outside disturbances. Connections between sites will also enable animals and plants (via seeds and pollen) to move from one site to another. This will be impossible to achieve if all land between bushland sites is managed as an alien environment. The types of plantings that occur in private gardens and public reserves can make a major contribution to improving links between bushland remnants and to extending the amount of habitat for indigenous plants and animals in a particular area.

Relationships between flora and fauna

Animals depend on plants for survival in many ways. Some awareness of plant-animal relationships is useful if a gardener, landscaper or other land manager is attempting to provide habitat for indigenous fauna. The examples for discussion here fall into three broad categories: food relationships; shelter for protection and nesting; and habitat corridors for migration, dispersal and recolonisation. Some examples of specific plant-animal relationships are provided in Tables 1 to 4. There are many more that are known and probably an even greater number yet to be discovered. Although limited, the examples given should be useful as a starting point for considering fauna in garden and landscape planning. The examples listed and discussed here are for the Greater Melbourne area. Different examples will be found in rural areas and other urban centres but the general concepts will be similar.

Food relationships

Animals feed directly on plants in many ways. These relationships have co-evolved over time and also benefit plants in different ways including pollination, seed dispersal and nutrient cycling. Some examples are given in Table 1.

Many animals eat plant-feeding animals. A major benefit to plants is the control of herbivores, especially insects. Some examples are given in Table 2.

Shelter for protection and nesting

Living and dead vegetation provides a range of refuges and nesting sites for animals. Some examples are given in Table 3.

Habitat corridors for migration, dispersal and recolonisation

Habitat corridors linking patches of remnant and planted vegetation (including private gardens) need to be an integral part of vegetation management and planning if individual sites are to remain viable in the longer term. Corridors of vegetation along streams, roads, railway lines, easements etc. provide valuable habitat, especially in urban and rural areas where remnant vegetation is extremely fragmented. They also enable animals and plants (via seeds) to move between patches of habitat that would otherwise be isolated. Genetic material of animals and plants (via animal pollinators) also moves with animals along corridors.

The regular seasonal movement of some bird species, e.g. Fan-tailed Cuckoo, Rufous Whistler, Sacred Kingfisher, Olive-backed Oriole etc. is well known. Both anecdotal and quantitative evidence (Baker 1989) suggests that migratory bird species continue to visit remnant sites that are connected by habitat corridors but decline in isolated sites. It is highly likely that other animals such as mammals and insects also use corridors to move from one remnant site to another. Habitat links between sites also enable animals and plants to recolonise sites depleted during catastrophes such as fires and droughts.

Butterfly food plants

The ecology of butterflies is relatively well known compared to other insects. Adult butterflies feed on nectar from the flowers of a variety of plants, both exotic and native. Among the indigenous flora of Greater Melbourne various plants including Sweet Bursaria, Bursaria spinosa, and Burgan, Kunzea ericoides, are attractive to adult butterflies (and other insects). However the food plants used by butterflies when they are caterpillars (larvae) are much more specific and consequently of greater conservation significance. A list of some indigenous butterflies of Greater Melbourne and some of the indigenous plants eaten by their caterpillars is provided in Table 4.

This sort of information is not as well known for other insect groups. Including a butterfly food plant list is not meant to imply that butterflies are more deserving of conservation. It is included to give some idea of the range of plant-animal relationships that are possible in a diverse and healthy ecosystem. It should be noted that the plants listed are not indigenous to all parts of the Greater Melbourne area.

Other aspects of butterfly ecology also illustrate the complexities of establishing fauna habitat using indigenous plants. Some butterflies (e.g. Imperial White, Wood White, Common Dusky Blue) have caterpillar food plants that are parasitic (e.g. mistletoes, Cherry Ballart, dodder laurels). Parasitic plants are probably considered undesirable or impractical for most current garden or landscaping projects.

The Common Imperial Blue and Blue Jewel butterflies both use Black Wattle and Blackwood as caterpillar food plants but utilise them at different stages of the plant's life. Caterpillars of the Common Imperial Blue usually occur on relatively young plants under two metres high whereas Blue Jewel caterpillars occur on large trees infested with wood-boring insects (Common and Waterhouse 1982). This illustrates the need to provide different age classes of vegetation in a healthy ecosystem. The Blue Jewel requirement of wattle trees starting to decline due to insect activity is another example of a habitat feature probably not normally considered desirable in a garden or landscaping project.

In addition to the correct food plants the caterpillars of some butterflies (e.g. Common Imperial Blue, Blue Jewel, Dark Purple Azure) have mutually beneficial relationships with certain species of ants and need them to be present on the food plant (Common and Waterhouse 1982).

The habitat approach: How much is possible?

At least some of the habitat requirements discussed in this paper can be provided in gardens and other urban plantings. The extent to which the full range of bushland habitat options can be provided in the urban context is limited by the highly altered nature of the urban environment. Competing land uses, such as houses, schools, shops, factories, roads, footpaths, etc., inevitably limit the amount of space available for flora and fauna habitat. Many other factors, including varied land ownership, conflicting aesthetic and other personal preferences, safety considerations, lack of local knowledge and suitable indigenous plant material, limit what is possible in the urban environment.

However, any degree of progress towards the pre-European condition of vegetation will increase its value to indigenous fauna. Every contribution by gardeners and landscapers towards using indigenous plants to create fauna habitat is valuable. This process is like gradually putting pieces back into a disturbed jigsaw puzzle. Just as urban areas have been made incrementally alien to indigenous plants and animals over time, this process attempts to incrementally reverse that trend. The realisation that we cannot exactly replicate the original ecosystem should not stop us trying to do so. From an indigenous ecosystem perspective, the closer we get the better.

While a diverse habitat providing for a wide range of fauna is desirable, not all the needs of local fauna can be met in a suburban garden or other small-scale planting. The habitat approach to planting will be most effective if integrated with surviving remnant vegetation or linked to similar plantings on nearby sites. Cooperative arrangements between adjoining private properties to protect and plant with local species would provide the kind of coverage that will make a real difference. Some suburban streets in Melbourne still have remnant trees growing along them that provide some cohesion from one private garden to the next. Despite representing only part of the former natural ecosystem these concentrations of remnant trees provide a strong basis for habitat conservation across private boundaries. Coordinated planning and management is required to stop the 'cryptic loss' (described by Reid (1996) as tree decline due to lack of on-site seedling recruitment) of urban remnant trees and to restore middle and ground strata species where possible.

The habitat approach also attempts to circumvent personal prejudices that may affect species choice. To try and replicate natural processes in gardens is to accept some natural features that would usually be frowned upon by gardeners, such as foliage and sap feeding by insects and parasitism of trees and shrubs by mistletoes and dodder laurels. The habitat approach uses local bush remnants, where available, to guide species choice. By its nature, this approach is a more ecologically integrated way of selecting plants for landscaping projects than an approach based on non-ecological criteria such as aesthetics (e.g. large, brightly coloured flowers) and ease of supply.

The habitat approach: Some design ideas

The following ideas may be useful when designing plantings to provide habitat for indigenous fauna.

• Retain any existing remnant vegetation on the site, including dead trees where possible.

• Use indigenous plants grown from local seed sources for additional plantings.

• Investigate and implement opportunities for indigenous plantings to form links between existing bush remnants.

• Consider the planting as an integrated plant community or vegetation association (or part of one).

• Plan species choice for indigenous plantings by examining bushland remnants on similar sites, talking to Friends groups and other local enthusiasts and by checking local reports, vegetation maps and plant lists. Local councils are generally a good starting point when seeking this information. Note that a plant that is indigenous to a particular area or municipality may not be indigenous to all sites within that municipality, e.g. a eucalypt species from a dry north-facing slope may not grow naturally next to a permanent creek.

• Use indigenous plants in numbers and combinations that resemble the structure of local remnants, e.g. clumps or thickets of the same species, rather than one each of numerous different species. Where possible plant different strata, e.g. trees,. shrubs, grasses and sedges, ground cover.

• Assist remnant vegetation to spread onto the site naturally where possible rather than planting. On some sites, seedling recruitment will be possible from seed shed by nearby remnant plants or from seed already stored in the soil. Various management techniques such as protection by fencing, exclusion of mowing and grazing, removal of exotic trees, weed control and use of fire may enable natural seed regeneration to occur. Some species, e.g. Swamp Paperbark, Melaleuca ericifolia, will spread from root suckers into cleared sites if mowing is excluded and weeds are controlled.

• Transplant indigenous species from sites that are about to be cleared to nearby safe sites, providing they genuinely have no chance of survival where they are growing.

• Provide food plants for a range of fauna (including mammals, birds and insects), not just for conspicuous species such as honeyeaters.

• Provide a permanent water source for birds that is safe from cats. The Bird Observers Club of Australia consider this to be the single most important factor in attracting birds to gardens (Wilson 1996).

• Avoid using poisons to control insects. Aim to use suitable habitat to attract healthy fauna populations (e.g. birds, insects and spiders) to keep pests in check.

• Where possible, avoid using poisons to control weeds.

• Promote indigenous plantings and fauna habitat with signs in private gardens and public reserves.

The habitat approach: Some related issues

Listed here are a few additional points that also relate to the concepts discussed so far.

• Bushland areas are being invaded by Australian plants used in gardens outside their indigenous distribution, e.g. Bluebell Creeper, Sollya heterophylla, and Cootamundra wattle, Acacia baileyana. Environmental weeds such as these contribute to the reduction of indigenous vegetation in remnant sites. Use of indigenous species in plantings will help to reduce this occurrence.

• Indigenous fauna is disturbed and preyed on by pets (e.g. cats and dogs). Without control of introduced predators are we creating habitat that lures indigenous animals to their death?

• The introduced Common Myna and Common Starling compete with indigenous fauna for nesting sites in tree hollows.

• Habitat for aquatic and wetland fauna (e.g. insects, fish, frogs, various birds, Water Rat, Platypus) should be considered in the design of gardens and other plantings, where possible.

• Appropriate seed sources for indigenous revegetation projects should be chosen with consideration for the correct genetic provenance, making sure that remnants are not degraded by over collection.

• Suitable nursery facilities and realistic timeframes are necessary for planting projects so that appropriate indigenous species are available when required.

• How can plantings be managed as dynamic systems where there is an opportunity for self-replacement over time and for different age classes of the same species to provide different habitat requirements for fauna?

• How can we integrate land that is under different management and ownership (public and private)?

Acknowledgments

Thanks for various assistance in preparing this paper to Graeme Lorimer, Elizabeth Balogh, To Hindley and Glen Jameson.

References

Further Reading

Also recommended is Land for Wildlife News, the newsletter of the Land for Wildlife Scheme, a joint project of the Department of Natural Resources and Environment and the Bird Observers Club of Australia Melbourne.

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Australian Plants online - March 2000
Association of Societies for Growing Australian Plants