The functions of the agro-ecosystem are clear and unambiguous. The primary function is to feed people. There are also secondary functions that include feeding livestock, and supplying various industrial products, such as fibres, rubber, and industrial feedstock. Because of agriculture, the human species has increased the carrying capacity of its environment to many times that of our pre-hunting, pre-scavenging, food-gathering ancestors. By using cultural developments, such as the use of clothing, buildings, and fire, the human species has also increased its total environment, and has been able to spread into otherwise uninhabitable environments. More recently, medical science has greatly reduced the death rate, unfortunately without achieving a corresponding decrease in the birth rate. As a consequence, the human population now exceeds six billion people. The total world-population of pre-agricultural, pre-herding, hunter-gatherers has been estimated at between one and five million. The total human population has been able to increase by more than a thousand-fold because of its cultural achievements.
The world's reserve of food covers only a few months of total human consumption. This reserve is being constantly replenished, but the supply of food could easily be interrupted. An obvious example is a major volcanic eruption such as that of Tambora, in Indonesia, in 1815, that produced 'the year without a summer'. There was so much dust in the atmosphere that an entire summer was effectively lost. The dust produced spectacular sunsets that were vividly recorded on canvas by Joseph Turner. If a comparable eruption today were to reduce the world agricultural output by, say, twenty percent, about one billion people would die of starvation. A failure of the food supply could also trigger a chain reaction of many other failures. A loss of electric power, for example, could lead to a loss of the water supply, a collapse of the retailing system, and so on. The world was given a taste of this in 1998 when an abnormal ice-storm in Canada and the Northeast United States cut power to more than one million homes in the dead of winter. A major disaster was only narrowly averted, particularly in large towns such as Montreal. (Note: This book was completed before the events of September 11th which have added another factor to this fragility).
Our agro-ecosystems are fragile for biological reasons also. They have too much uniformity, and they have inadequate resilience and stability. For example, 80% of the wheat in the non-industrial world consists of cultivars bred by CIMMYT (International Maize and Wheat Improvement Centre, Mexico). These cultivars all have temporary resistances to some of their parasites. The appearance of one new 'super-race' (i.e., complex vertical pathotype) of a major parasite could lead to a resistance failure in most, or even all, of these cultivars. This would cause a major reduction in both the yield and the quality of all of this wheat. A similar disaster could occur with the rice cultivars produced by IRRI (International Rice Research Institute, Philippines). The green revolution is vulnerable. But so too, to a lesser degree, is the whole of modern crop husbandry.
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