The Committee pointed out in Chapter 2 that biodiversity operates at genetic, species and ecosystem levels.40 It relates to the diversity of species indigenous to the location and natural ecosystems. Any process that reduces the natural diversity of populations or ecosystems diminishes biodiversity.
The Committee identified activities that can be associated with utilisation of native plants and animals and pose a threat to biodiversity. These include:
a) translocation of native species to areas where they have not previously occurred;
b) genetic pollution and impoverishment;
c) habitat loss and modification; and
d) depletion of populations.
Translocation
Translocated species or populations are organisms that may be native to some parts of Australia, but have been introduced beyond where they naturally occur. This includes introduction of individuals of species that may occur in the new locality, but have "genetic stock and/or populations that are distinct from those in the source area".41 Where they affect populations indigenous to the area and ecosystems, this can impact on biodiversity.
Translocated species may establish as feral populations in the new location. An example noted by the Committee is Sweet Pittosporum (Pittosporum undulatum). This species, which is indigenous to coastal hills of eastern Victoria and NSW, has been introduced as a garden plant to more westerly areas. It is now invading forests of central Victoria.42 Prickly acacia (Acacia paradoxa), a native of all mainland States, has been introduced to Tasmania, where its spread over dry hillsides is considered to be excessive.43
Escape of organisms from the site to which they are introduced is difficult to prevent.44 With plants whose seeds are carried by birds or other animals the risk is particularly high. Consequently it is reasonable to assume that, if such a plant is introduced into a new area, it will enter local ecosystems.
Aquatic species, once released into a waterway, are likely to move throughout streams within the catchment. Because of this the `Flora and Fauna Guarantee - Scientific Advisory Committee' has recommended listing the stocking of fish as a potentially threatening process where the species, though native to Australia, or even Victoria, was not previously part of the aquatic community in the location of the release; that is:
[the] deliberate or accidental introduction of live fish into private waters within a Victorian river catchment in which the taxon to which the fish belong cannot reliably be inferred to have been present prior to the year 1770 AD.45 In line with this concern, introduction of marron into Victoria from Western Australia is currently prohibited because of its likely impact as predator of, and competitor to fresh-water species (particularly yabbies) in Victoria's streams and rivers.
For animal species in general, the risk associated with their translocation depends on the likelihood of their escaping from the site to which they have been introduced, as well as the probability of their establishing in the wild should they do so.
Introduction of pathogens is also a hazard. The spread of phytophthera dieback to Western Australia has been attributed to the introduction of infected plants from the eastern States. As the Committee mentioned in Chapter 4, it is because of the risk of introducing disease that permission to introduce barramundi to Victoria has so far not been given.
A code of practice has been developed under the National Translocation of Live Aquatic Organisms Policy to deal with the translocation of aquatic species.46 The Code includes the following points:
a) consideration should be given to local species first, to see if any can do the required job instead;
b) full information is required on the current biology and ecology of the candidate for translocation: an assessment of the likely impact of the new species in light of this information and impacts of other similar introductions;
c) should the translocation be allowed, initial quarantine is required to determine if parasites or pathogens are present - total restriction should apply until approval has been given;
d) introduction should be a one-off event; and
e) public education is needed to ensure that the public understands reasons for restrictions. 47
However, translocation of a species at risk (particularly fish species) may be appropriate where the natural habitat of the species has been so degraded that "translocation of the fish species may be the only means of saving wild populations".48
Genetic Pollution and Impoverishment
Biodiversity is concerned with maintenance of the genetic character of local populations.49 The Maroondah City Council pointed out that genetic variation between different populations of the one species can be considerable.50 Such genetic diversity within and between populations represents a resource on which future generations of the species can draw to meet changes and new hazards. In the long term it may be a resource that is useful to people as well. Introduction of individuals from populations with different genetic characteristics will change the genetic (and ultimately the physical) character of a wild population. This is referred to as genetic pollution.
The genetic character of a population is a product of past evolution. Consequently the processes that the Committee discussed above in relation to evolution ultimately impact upon biodiversity.
Utilisations of native species that incur the risk of genetic pollution include introduction of populations or genetic material (for example pollen, seeds, eggs) from other localities and release of individuals or genetic material that have been modified by deliberate selection or genetic engineering. 51
Breeding and selection are necessary aspects of cultivation of native species. The Committee was told that the high yields and suitability of conventional crop and pasture species to agricultural production has been achieved through great expenditure of time and effort. 52 Similar effort committed to native plants may achieve just as much in terms of productivity and suitability, while capturing advantages inherent in these species.53 However, native species subject to selection for farming or cultivation become genetically dissimilar to wild populations.54 Should such populations be released or escape to the wild there is a risk of genetic pollution of wild populations. 55 Features that make a species desirable when used commercially may be less than desirable in the wild. For example, selection for disease resistance could, in the wild, lead to a weedy strain of a plant.56
The Committee notes that native-plant farming may have a higher potential for genetic pollution of natural populations than native-animal farming because cross-fertilisation between commercial cultivars and wild species of plants is difficult to prevent. On the other hand, the point of view has been put to the Committee that most selections for cultivated production would disadvantage the plant in the wild (for example need for fertiliser or irrigation to attain best growth) and so few selected varieties would be likely to survive in the wild.57
The Australian Conservation Foundation has proposed a number of strategies to achieve reduced genetic pollution from native crops.58 They have suggested selecting crops that are reproductively incompatible with, or flower at different times from, wild populations; growing crops at sufficient distances from wild populations to prevent pollination by wind or other vectors; and making the survival of crops contingent on artificial conditions within the farm system, such as water or fertiliser.
The Committee also understands that, because of genetic changes brought about by breeding and selection, cultivation and farming of native species cannot be viewed as a primary conservation tool. Conservation and the preservation of biodiversity are most fully addressed by protection of species in situ, within their natural habitats and with their natural genetic composition.
Introduction into the wild of individuals from a wild population that is not local can also impact on the genetic diversity (and character) of indigenous populations. 59 This practice was referred to in evidence presented to the Committee by the Royal Botanic Gardens.60 In the case described, introduced blue gums, commonly from Tasmania, can hybridise with local Victorian sub-species. Other examples reported to the Committee were the release or escape of emus imported from Western Australia61 and the stocking of waterways with fish62 and eels63 derived from interstate.
Habitat Loss and Modification
Habitat loss, modification and fragmentation are generally regarded as the main threat to the maintenance of the diversity of animal and plant species.64 It is widely accepted that habitat loss and fragmentation have played a large part in the decline, and (sometimes) extinction, of many small mammals within Victoria.65
Clearing of Victorian bushland continues to reduce and degrade habitats. Improved satellite monitoring has shown that an average of 2,544 hectares per year in Victoria were cleared in the period 1990-95, 60 per cent higher than estimates of clearing made for the national greenhouse emissions inventory.66
Native grassland habitats appear even more vulnerable to destruction or degradation. A recent study found that 44 per cent of grassland sites recorded in western Victoria in 1986 had, within a decade, been destroyed, severely degraded or are planned for destruction. A further 30 per cent have been degraded to some extent.67
Placing commercial value on native species was proposed by the Senate Inquiry68 and others as a method for protecting wildlife habitats, and hence, the wildlife species themselves.69
The importance of habitat has been acknowledged by many of the submissions and other evidence presented to the Committee. Birds Australia emphasised that loss of habitat is the main cause of decline in populations of many species in Victoria.70 This is true of plants and aquatic species as well as of land animals. For example conversion of natural ecosystems to grazing exotic pastures led to a substantial decline in the native yam or murnong (Microseris lanceolata).71 Damming and other modification of Victoria's waterways have caused the decline of native fish such as the trout cod.72 Conversion of forested land to agriculture has reduced the status of the Gippsland giant earthworm to `endangered'.73 The needs of this species were explained to the Committee during its study tour of South Gippsland.
Several larger mammals that have been described to the Committee as `super-abundant', have been much less effected or apparently even advantaged by changes brought about by modern land use.74 However, some of these abundant species have in fact also experienced contraction of populations in parts of Victoria, due to loss of habitat.
For example the common wombat is in decline in western Victoria. Though cull may have contributed to this decline, it has been attributed, in the first instance, to the loss of native grasses that produce a flush of summer growth in the wombat's breeding season.75
The range of the eastern grey kangaroo has been altered by changes to its habitat.76 It occurs in widely varying densities, from between 24.6-42.2 per square kilometre in the protected Coranderrk Bushland, Healesville, to zero on intensively cultivated land.77 Over Victoria's large areas of developed farmland and cropland, densities are generally much less than where there is native vegetation. These, and the other large kangaroos, are usually restricted to areas where remnant forest and woodlands provide cover.
An interesting exception to the widespread loss of habitat is the situation of the black wallaby. This species has increased its range into western Victoria.78 This is a result of expansion of its preferred habitat of dense understory regrowth - an expansion caused by logging and changed fire regimes.
Habitats of fish and other aquatic species have also been altered substantially as a result of changes to catchments and riparian vegetation, modification of the waterways by desnagging, dredging and changing alignments, and use of water for irrigation and urban supply. Consequently many aquatic species are also under stress.
In many Victorian streams the feeding habits of the introduced European carp exacerbated this problem. During its study tour of South Australia the Committee observed the improvement in water quality and resultant growth of native water plants and animals that resulted from removal of European carp.
Depletion of Populations
Destruction of individuals through harvesting, by-catch, road kill, or deaths associated with the mechanics of harvesting can represent an unsustainable drain on populations that are already stressed by loss of habitat.
The Senate Committee stated that:
The risk of over-harvesting should be low and legal harvesting should be set at a level well below the scientifically calculated off-take rate. Where a legitimate increase in quota is indicated, it should still incorporate a safety margin. There should be a low risk of `by-catch' [or destruction] of non-target species.79
Over-harvesting
The present Committee has already noted that responses of populations to removal of individuals can be unpredictable and impacts are subject to time lags. Consequently, sustainable levels of harvest or cull are difficult to determine. Good and regular assessment of populations is needed to determine whether a species is secure or in decline. Such assessments have not, and are not generally, undertaken in Victoria, except for some fish species.80 As a result, a population can be severely reduced before it is realised that numbers are falling.
For example, earlier this century common wombats were considered to be so numerous that they had a bounty on them. More recently, though protected under the Wildlife Act 1995, they were declared `unprotected'. No assessment of their numbers was made and culling continued throughout Victoria until it was finally realised that populations were seriously depleted in the west of the State. Only then were they returned to `protected' status. Wombats remain unprotected in the east of Victoria, although there is still no assessment of total population size or any changes that may be occurring.81
During the last half of the nineteenth century, koala populations appeared to increase rapidly in many areas to the extent that:
By the turn of the century huge numbers were being killed for their pelts, and koala fur became the staple of an important export industry. The population then declined greatly in the early decades of [the twentieth] century, due to both commercial harvesting and widespread habitat destruction. Disease, including ophthalmic disease and pneumonia, was also claimed to have had a widespread effect. By the 1920s grave fears were held for the survival of the species in Victoria, with estimates of the total population being as low as 500.82
Again, protected measures were only applied when population sizes had plummeted. Only an active breeding and relocation program has restored the koala population to its former range in Victoria.83
Impacts of over-harvesting can be long lasting. Populations of the Australian fur seal were severely depleted by exploitation in the nineteenth century.84 Although all hunting was outlawed by 1923, the population of this once-abundant animal is still well below its original size - nearly 100 years later.
This issue is considered further by the Committee in Chapter 9.
By-catch and Incidental Damage
As the Committee described in Chapter 4, non-target species can also be killed or damaged during harvest, hunting and recreational activities.
Attributing commercial value to a particular species, as advocated by the Senate Committee, may enhance protection of that species at the expense of others. For example, rather than conserving remnant bushland within which commercially valuable plants occur, a landowner might manage the bushland in a way that favours those plants, thus changing the ecosystem. Alternatively, bushland may be cleared altogether to establish a plantation. In this case many native species are lost from the site.
