Ecological processes include flows of matter and energy, interactions between organisms, evolution of species and maintenance of the physical environment on which plants and animals depend.
Energy Flow and Nutrient Recycling
Only plants containing chlorophyll and some micro-organisms can capture energy directly from the sun.1 These organisms can also obtain mineral nutrients in inorganic form from soil or water.2 All other organisms must obtain energy by consuming other organisms or the partly decomposed remains of other organisms. They also gain many important nutrients in the same way.
At each feeding or trophic level the maximum amount of energy that can be converted to growth is less (and generally much less) than 10 per cent of the energy consumed. Consequently the total mass of organisms at each trophic level in an area is less than the mass of organisms in the trophic level below it. The mass of herbivores is much less than that of the plants and the mass of carnivores that feed on herbivores (primary predators or scavenges) is much less than that of the herbivores. The mass of secondary predators or scavengers is still less than that of the animals on which they feed.
If a species is to survive, there must be an adequate supply of the animals or plants on which it feeds. This influences the interactions between species. Interactions are discussed in more detail in the next section.
The productivity of an area is set, in the first instance, by its capacity to grow plants. This in turn is related to soils, climate and total grazing pressure. `Total grazing pressure' is the sum of the plant material removed by all the grazing animals on a site. If it exceeds the growth capacity of the plants the amount of plant material left to capture energy from the sun declines. The ecosystem enters a downward spiral in which productivity continues to fall until total grazing pressure is reduced through death or removal of the grazing animals.
Scavengers (for example yabbies and ravens) and saprophytes (organisms which gain energy by decomposing dead organic material) depend on the remains of plants or other animals.3 When native animals are harvested, rather than killed by predators or other natural means, populations of predators, scavengers and saprophytes are all affected, as their energy source is diminished.
Scavengers and saprophytes also play an important role in returning nutrients to soil and water for re-use, and in incorporating organic matter into soil.4 Where plants or animals, whether native or exotic, are removed from the ecosystem, nutrients in them are lost from the locality. These must eventually be returned or the productivity of the ecosystem will decline.
Total Grazing Pressure
Locally native animals, particularly the large kangaroos, wallabies, possums, koalas and some native birds, can contribute to total grazing pressure, and hence to overgrazing and reduced productivity. Fragmentation of their habitats plays a large part in the periodic build-up of large numbers of these animals by denying them the opportunity to move to new feed.5 The native animals concerned all require some native tree and shrub cover in their habitat.6 They do not normally range far from such cover.
While native animals may contribute to total grazing pressure, so also do domestic stock and pest animals such as rabbits, hares and feral goats. Overgrazing provides one argument for the cull or harvest of native animals, but other responses can be appropriate. These could include eliminating the feral pests and, as graziers commonly do, reducing stocking of farm animals during periods of drought.7 For most valuable crops, such as lucerne or vegetables, kangaroo-proof fencing could be considered.8
In some districts it may be practical to locate crops on a property beyond the main feeding range of the native animal - that is, remote from the tree and shrub cover that forms an essential part of their habitat.9
Relocation of native animals has proved effective where there are suitable habitats in which to place them.10 The Committee notes that the relocation of koalas has been used to reduce excessive local browsing and restore populations to habitats from which koalas had died out. The success of this program is creating some problems. Populations are now so widely established and successful that additional suitable sites for relocation are now difficult to find.11 Alternative methods, such as contraception, for control of koala populations are being investigated.12
Several submissions, as well as evidence at the Inquiry's public hearings,13 refer to the `waste' of kangaroos and other culled animals left on properties under Victorian regulations. However a contrary view has been put that, from an ecological point of view, nothing is truly wasted: every dead organism becomes a source of energy and nutrients for other organisms.14
One submission also drew attention to the impact of nutrient loss through the removal of animals or plants. Nutrients removed through harvest of plants or animals must lead eventually to the need for replacement of the nutrients lost.15 The advantage of native plants - their ability to grow in low-nutrient soils - has limits.
Interactions Between Species
As the Committee indicated in the preceding section, reducing the population of one species can have impacts on other species of animals or plants. These interactions may be subtle and it may take some time for the effects to become obvious. Because of the complexity of ecological systems, "incipient change may not be detected until an ecosystem has been irreversibly altered".16
When prey species such as kangaroos or possums are removed, the consequence in the short term can be that predators such as dingoes and red foxes turn to different prey.17 These may be other native mammals or domestic stock.18 In the longer term, predator numbers may decline so that one of the controls on the native-prey population (as well as introduced pests such as rabbits) is weakened.
On the other hand, increase in populations of herbivores, such as kangaroos, leads to increase in the population of predators.19 This, in turn, tends to reduce the populations of herbivores. The Committee understands that the destruction or exclusion of dingoes has probably contributed to increasing numbers of kangaroos in some areas.20 In Victoria predation by feral dogs would provide some balance to the loss of dingoes.
Recher, Lunney and Dunn, in The Natural Legacy, illustrate the consequences of these complex interactions:
European impact on wildlife was not always immediately detrimental ... Kangaroos and wallabies, which were not reported to be numerous in the Great Dividing Range in New South Wales [and Victoria] before it was settled ... were so abundant in the 1870s, that pastoralists petitioned the governor for help in controlling them. From 1880 ... tens of thousands were killed. By the late 1890s kangaroo numbers had fallen ... As kangaroo numbers fell, ... wallabies and the introduced hare increased in abundance for about 20 years and then declined. Bettongs ... flourished with, or shortly after the wallabies, but as rabbits then foxes increased they too dwindled. ... The lesson to be learned ... is that an abundance of wildlife can be transient. Even the most common species can disappear as the environment is progressively altered.21
Similar interactions occur in aquatic ecosystems. For example, Mosquito fish (Gambusia affinis), introduced in the 1920s, competes with, and prey upon, native fish. In some Australian streams this species has succeeded in excluding native fish altogether.22
Build-up of nutrients in water bodies can alter interactions between species. The process of nutrient accumulation, known as eutrification, can lead to excessive growth of micro-organisms which can reduce the availability of light and oxygen for larger plants and animals and consequently they may become less abundant.
Interactions occur between members of the one species as well as between different species. This may be indirect - for example where excessive population growth leads to a reduction in food supply. With native species this usually leads to reduced fertility and death of young animals and other weaker individuals.23
In more gregarious species there is normally a clear social organisation. Among Australian fur seals, for example, "the largest and most aggressive males compete vigorously for a place in the area frequented by adult females, each bull defending an individual territory ... unsuccessful bulls and bachelor males are completely excluded from the breeding area."24 Dominance of a few males is common in other species as well, for example among the large kangaroos and common brushtail possums.25 Most of the time the dominance of these individuals is accepted and there is little disruption of the population. Removal of dominant males, as with cull or harvest, is likely to cause increased aggression and dislocation of populations.26
Interactions within plant communities are equally complex. The removal or reduction in the population of one species can have substantial impacts on other species. The role that tree ferns play in the re-establishment of moist forests after disturbance provides an illustration. A study by the Department of Natural Resources and Environment (DNRE) has shown that a percentage of tree ferns survive and rapidly resprout fronds after wildfire. These provide a microclimate and a substrate for the establishment of other species. 27
Time lags in environmental responses make decisions based on short-term observations hazardous. This effect also creates a limitation on adaptive management approaches. The complexity of interactions between, and within, species suggest that a cautious approach to utilisation of native plants and animals is desirable. Studies of the interactions between the target and other species prior to utilisation, and if accompanied by ongoing research into long-term impacts, would assist in addressing such issues.
Population Evolution
The attributes of a species in a particular location have been produced by the evolutionary pressures in that locality.28 These equip the local population to live in that area. Wild-harvest of plants and animals produces a new set of selective pressures. For example, if the object of killing kangaroos is commercial harvest, the largest animals are the most likely target. These will normally be the dominant and fittest individuals. These would, in the natural environment, be most successful at mating. If the objective is population control for damage reduction, reproductive females will be targeted. In either case it is the weakest and least fit that are favoured. In the long term this will lead to a population less well adapted to survive in the natural environment. Only the objective of culling to enhance the population itself would promote normal evolution.29 This, as described by the RSPCA, is culling of weak and old individuals.30
Among plants, selection of individuals for yield or attractiveness will also produce unnatural selection pressures. The individuals removed are those which, because of their vigour or superior capacity to attract pollinating animals, would in all probability have produced the greatest quantity of seed. Thus their genetic material would have given them an evolutionary advantage. Harvest shifts this genetic advantage to less attractive or vigorous individuals.
At the same time, an alternative to culling of wildlife populations suggested by Animals Australia would also present a major disruption to the process of evolution.31 This alternative is contraception. At present contraception is practical only for captive animals, but research is being undertaken into a possible viral form of contraception. Mass contraception, if it were to become practical, would interfere severely with the process of evolution.32
Maintenance of the Physical Environment
Soil, air and water are important components of the physical environment. Several practices associated with utilisation of native species have impacts similar to those of more conventional cultivation and processing of exotic species. These include the use of chemicals and resultant pollution hazard, and soil erosion.33
Use of Chemicals
Native-flower crops are subjected to a number of environmentally damaging post-harvest treatments to increase vase life, or during fumigation for export. Two commonly used post-harvest treatments, silver thiosulfate (STS), used as an anti-ethylene treatment, and methyl bromide, an ozone-depleting substance used to control insect, bacterial and fungal pests, are being phased out around the world due to serious concerns over their environmental impacts. Alternatives to these chemicals are currently being investigated. MCP (1-methylcyclopropene) is showing promise as a replacement for STS.34 There is currently no suitable replacement for methyl bromide. The preserves and dyes used in the production of dried flowers are also coming under increasing scrutiny. The Committee understands that a move away from toxic chemicals currently used to treat cut flowers is an important, and sometimes overlooked, step towards achieving ecologically sustainable development of the industry.
Soil Erosion
Soil erosion results when the soil surface is exposed to the action of water or wind.35 Any activity that removes the protective cover of plants or plant litter exposes soil to erosion. Soils, once stripped of the most productive few centimetres of topsoil, can be very slow to recover.
Though hard-hoofed domestic stock and burrowing rabbits do much more damage to soil than do kangaroos (partly because the hard hoofs of the former can damage both plants and soil surface, and the latter burrow and chew roots) native animals can contribute to total grazing pressure. Total grazing pressure has been mentioned in relation to loss of plants. By contributing to unsustainable grazing pressures they may also exacerbate soil erosion and, as a consequence, affect water quality.36
In Victoria the density of native animals in the wild is usually insufficient to contribute much to the erosion risk. However, densities of farmed animals (specifically emu) can be sufficient to cause erosion if they are kept on erosion-prone land.37 Methods to manage soil erosion are, however, well understood in Victoria. Sound site selection and management can deal with this issue.38
Human trampling, access roads, paths and tracks can lead to soil compaction and erosion.39 This is one of the more common impacts of recreational activities, but wild-harvesting of native plants can also lead to erosion.
