Biological diversity is essential for the health of the planet and plays a vital role in agricultural productivity, yet agriculture is adversely impacting on the conservation of natural biodiversity. Biological diversity involves the totality of all life forms on the earth ranging from genes to species and the community of species found in natural ecosystems. Beatley [1994] goes further to suggest that the loss of biodiversity and the extinction of numerous species is the greatest global threat to the disruption of the environment and is a strong indicator of the worsening health of the earth and its declining sustainability. In view of the assertion that one quarter of all the species on earth could well be extinct by the year 2000 [Reid, Miller, 1990], it could be argued that the reduction of the earth's biodiversity and species extinction is a natural part of the evolutionary process Beatley [1994] due to the domination of the human race over all the other species and could be the epitome of Darwin's theory of the survival of the fittest. If this is the case we should be very concerned about it, as this raises an ethical dilemma which is a serious challenge to our society as it is today.

In Australia biodiversity in agriculture is a major issue for two reasons. Firstly, agriculture's continued productivity depends on biodiversity and will continue to impact on the conservation of native biodiversity. The sustainability of agriculture in part depends on the protection of biodiversity that in turn relies upon a diverse genetic base, which is needed to increase the likelihood of finding new high value agricultural plants and animals. However, in order to improve productivity ongoing breeding programs tend to narrow the genetic base [Commonwealth et al. 1991A]. For example, since the nineteenth century out of an original 7,098 North American apple varieties, 6,121 have disappeared [Bierbaum, 1991].

Reeve [1990] refers to Vietmyer's [1986] observations that it is extremely ironic that genetic diversity should be sought using genetic engineering when there are over 20,000 edible species of plants on the earth, of which 3000 have been used in the past. Today the bulk of the present food supply comes from only twenty species with just four, rice, wheat, corn and potato, accounting for over half of the total food supply.

Agroecosystems do have a reduced biodiversity and are simplified ecosystems, which have inherently made them less stable and more vulnerable to disruptions by insect or fungi attacks than natural ecosystems. The use of monocultures has been linked to an inherent instability within agroecosystems as they have historically been responsible for initiating a food crisis and no doubt history will repeat itself again, particularly due to the fact that our genetic plant resources are vanishing [Richardson, Stubbs, 1978].

The second reason why biodiversity is a major issue to agriculture is that agriculture has and will continue to impact on the conservation of native biodiversity. Agricultural development practices have cleared land, changed habitats and modified fire patterns resulting in the loss, endangerment and extinction of native plants and animal species. It has also adversely affected the environment by contributing to land degradation, increased chemical waste and air and water pollution and loss of habitats. Domestic stock if not controlled can also selectively eat out the most palatable plants and leave the poorer plants. This will cause an ecological succession of plants and woody weeds which can start to invade pastoral land [Savory, 1988].

Agricultural development has had a very great impact on the earth's landscape and has been responsible for changing biodiversity. The changes to biodiversity and to landscapes have been subtle and dramatic. An example of dramatic change was the removal of a third of the earth's forests, half of which were lost between 1950 and 1990 which was done in a relatively unobtrusive manner [Meadows et al. 1992].

Subtle changes from one generation to the next pass almost unnoticed and become lost in time as generations accept the current reality that has slowly changed before their 'unseeing' eyes. A problem arises when changes slowly take place over a farmer's lifetime, such as tree decline and increased erosion, because properties may slowly decline in productivity or a whole farming region may decline from land degradation. Farmers and their land are so closely connected on a daily basis that changes cannot always be clearly recognised [Commonwealth et al. 1991A].

A further example of these broader changes in ecological processes can be shown through the selection, harvest and removal or clearing of indigenous trees. The wholesale removal of forests is very evident and can be easily recorded. What, however, is more subtle is the selective harvesting of trees with suitable commercial characteristics. When trees are individually selected over a period of time the indirect effect can be the removal or loss of the commercially superior genetic material from that ecosystem, resulting in the reproduction of commercially inferior genetic material in its place.

Having discussed some of the issues involving biodiversity the question remains as to why biodiversity is declining and ecological processes are collapsing? Allsopp [1972 ] attributes this to a lack of ecological morality, which is an awareness of the world as an organism in which all the living parts contribute to the whole. Many of the current difficulties in relation to society can be resolved, because of the fact that the health of the whole requires the cultivation of all the parts [Allsopp, 1972]. To this extent the maintenance of ecological processes is essential to protect not just the fringe of an ecosystem or a few components, but rather an entire ecosystem to maintain its productivity, structure and diversity [Commonwealth et al. 1991A].

Recognition of the global dimension

Within the debate about sustainable development it is apparent that the recognition of the global dimension is increasingly being emphasised, as the scale of sustainability [Campbell, 1994] broadens to incorporate the global dimension. There is only one earth and it is the largest known ecosystem. Many environmental issues now have a global dimension so there is a need for joint actions by all nations [Bierbaum, 1991]. In simple terms humanity is taking natural and exhaustible resources into a "throughput" economy and producing desirable products for human activity as well as negative outputs of pollutants from which we cannot escape. Boulding [1970] describes, in the concept of "Spaceship earth", that a spaceship economy is needed whereby a circular flow of materials occurs and recycling becomes part of the economic system on a global scale [Boulding, 1970] as pollution and other environmental problems know no state or national boundaries. A further observation is that although there is widespread concern over the use of non-renewable resources because they are infinite and non-sustainable, there is not enough consideration given to the by-products of the resources used as they enter 'planetary sinks' as wastes and pollutants [Meadows et al. 1992]. Although humanity is concerned about the exhaustion of resources, part of the consequence of using resources is invariably pollution in some form or another and this may be a greater threat to humanity than dwindling resources [Meadows et al. 1992].

The human race is a major force in the ecology of the earth and has the capacity to conserve or destroy most life forms and processes on the earth. There is a basic distinction between these two opposites. Allsopp [1972] believes that we are in a position of trusteeship in nature that can be exercised as stewardship. Pessimists believe that the pursuit of the Western philosophy of wealth at all costs by continued exploitation promises an outcome of ecological disaster on a global scale [Allsopp, 1972, Bierbaum, 1991]. By considering a global scale Campbell [1994] takes up this challenge in his hierarchy of sustainability which is considered later.

In summary, the issues of biodiversity, the global dimension and intergenerational equity act as a background to gain a better insight into sustainable development. It is assumed that the issues of biodiversity and the recognition of the global are two dominating themes that are relevant to sustainable agriculture. Having considered some of the issues and assumptions of sustainable development a new focus will be taken in regard to sustainable agriculture which has evolved out of the philosophy and application of sustainable development.