Global Ecological Problems and Issues

When a tropical forest is cleared and transformed to a field or pasture, the amount of carbon stored in the vegetation is usually reduced between 90 and 99 per cent. This contributes to the problem of global warming. Transforming fields and pastures to multi-storey home gardens, on the other hand, removes large amounts of carbon from the atmosphere. Some types of multi-storey home gardens can store hundreds of tons of carbon per hectare.

According to John Sholto Douglas and A.J. de Hart only about 8-10 per cent of the world's land area is currently being cultivated, but this area already includes a very large majority of all existing good-quality farmlands. Tree crops, however, could theoretically be grown on at least 75 per cent of the world's land area. Trees can be grown also on lands that are not suitable for conventional field farming, including arid and semi-arid lands, steep hill-slopes and rainforest lands.

In arid ecosystems the land may become almost like a desert during the dry season, but the vegetation recovers quickly with the rains. Only if the soil has continuously been losing nutrients through erosion so that the natural recovery has been prevented, can we talk about actual desertification.

In areas that have a very uncertain rainfall the security of food production is the number one consideration of the poorer segments of the population. In such areas tree crops are especially important because trees are likely to provide a crop even during bad drought years, when all the (rainfed) annual crops will fail.

The world has altogether 6.1 billion hectares of drylands if hyper-arid, arid, semi-arid and sub-humid lands are all included. Already about one billion people live on drylands and they will most probably have to feed a growing percentage of the world's population in the future. Because the trees and other plants growing on arid places have never received the attention of plant breeders, people moving to drylands usually attempt to cultivate familiar plants which require large or relatively large amounts of water to survive and produce crops. This results in very insecure food crops: in drought years there may be no crop at all. For this reason already 90 per cent of all international food aid is going to drylands.

The domestication of various wild fruit and nut trees growing on drylands might be the most important single answer to these problems.

Tree crops and multi-storey home gardens are likely to constitute the agricultural technologies best suited for very arid conditions. Food-producing trees can be grown also on lands that cannot be used to conventional field farming. Moreover, food-producing trees can probably produce much more protein, fat and carbohydrates per hectare than any other food crops that can be grown on dry lands.

Because their longer root systems the trees are able to utilize moisture and nutrients that lay far beyond the reach of the annual crops. Many of the trees that have evolved in the dry areas produce fruit crops even during the worst drought years. And properly managed tree plantations can provide good and permanent soil cover - both directly and through their litter production.

In the super-humid tropical rainforests the topsoil contains practically no nutrients: all the nutrients have been washed down to the deeper soil layers by the heavy rainfall. Most of the available nutrients are contained by the vegetation itself, and they are continuosly being recycled by the trees. If the trees are replaced by annual crops or by pasture, most of these nutrients will be lost in a very short period of time.

When the land is transformed to pasture, it is usually cleared by burning. This creates a transient fertility that will wear off in a year or two. After this the land is invaded by weeds, many of which are poisonous to cattle. The only practical way to fight the weeds is to burn the area again, but the repeated burnings further deplete the fertility of the soil.

After three or five more years the land has to be abandoned, and left for a fallow for a much longer period of time. And a substantial part of its fertility has been lost on a permanent basis: because all the trees have been cut down, most of the nutrients have been leached into the deeper soil layers, so that they can no longer be captured even by the trees that will grow on the land during the fallow period. Slash-and-burn agriculture can also produce a similar degradation of the land, if the burning and cultivation periods become prolonged or if they are repeated too often.

The answer, again, is to mix perennial crops with annual plants.

If there is, permanently, a large enough number of trees growing on each hectare of land, the nutrients will not be leached into the deeper soil layers. Instead, they will be captured by the innumerable small branches of the trees' root systems and recycled back to the farming system.

As long as the rapid recycling of nutrients, the actual basis of the whole rainforest ecosystem, is maintained crops can be grown on rainforest land on a permanent basis, for thousands and thousands of years. In theory it should be possible to continue this kind of cultivation even much longer than this: some rainforests have probably existed for a hundred million years or more.

If cultivated by conventional farming methods or turned to pasture, rainforests are among the world's poorest and most unproductive lands. However, when multi-storey home gardening in practised, and a permanent tree cover is maintained, they can be extremely productive, because of the combination of high temperature and extreme humidity. Tropical rainforests are situated in areas that would anyway receive a lot of rain, but in some cases the amount of rainfall is doubled or multiplied by the trees. Rainforest trees evaporate huge amounts of water. At the same time they produce aerosols (tiny particles) that contribute to repid cloud formation over the forest. The researchers have found out, that some rainforest areas have an ability to circulate up to 75 per cent of the rainwater back to the atmosphere. The super-efficient, super-fast recycling of nutrients (and water) leads to very high biological production.

In one study the natural rainforest of Panama was found to produce about 40 tons of fruit (with a net dry weight of eight tonnes) per hectare in a year. This is a lot, when we remember that not all the trees growing in the rainforest produce fruit.

At its height the Mayan civilization supported populations of 700-1150 people per square kilometre on rainforest land in the densely populated parts of their empire. According to Clive Ponting: "Excavations in the outer areas of Tikal suggests that, at its height, the population was at least 30 000 and possibly as high as 50 000 (of the same order as the great cities of Mesopotamia). Other cities, though not quite so large, would have followed the same pattern of dense urban settlements and so it seems likely that the total population in the Maya region at its peak might have been near to five million in an area that now supports only a few tens of thousands."

Contd...

For Hindi click here

Copyleft. Any part of the content on this site can be used, reproduced, or distributed freely by anyone, anywhere and by any means. Acknowledgement is appreciated.

Designed and maintained by CAPITAL Creations, New Delhi. Phone 91-11-26194291