Conservation and reclamation

The number of vascular plant species considered to be in danger of extinction is roughly estimated to be about one-tenth of the total number of plant species in the world. It is not just the extinctions that are a cause of concern, but the time scale within which they are occurring. Plants cannot evolve fast enough to withstand habitat destruction by, for example, bulldozing, forest cutting, overgrazing, or damage by pollutants. Indeed, the problem is growing ever more critical as the human population on earth increases.

The plant world is essential to all animal life, including humans, as the base of the food chain. All our food, from cereal crops to grazing livestock, is directly or indirectly a plant product. In addition, plants protect soil from erosion and, frequently, nourish it; they also play a major role in the world’s climate and carbon dioxide balance.

The three major arguments for conservation are economic, climatic, and esthetic. Of them all, the economic one has the greatest immediate impact. This argument is also the strongest in justifying land reclamation. If species are to be conserved in their original habitats, then less land must be developed to cope with human population expansion and the consequent agricultural needs.

Cattle now graze on Montana land reclaimed after strip coal mining.

Economics of conservation

In the United States it has been estimated that nearly one-quarter of all drugs obtained on prescription in any year are obtained from plants. They include tincture of arnica (from mountain arnica, Arnica montana), atropine (from belladonna, Atropa belladonna), codeine and morphine (from the opium poppy, Pa-paver somniferum), and quinine (from the bark of the Cinchona tree). About 80 per cent of major drugs probably can be derived from plants more cheaply than they can be made in the laboratory.

But many plant species that are potential sources of drugs are in danger of becoming extinct before we learn to exploit their special properties. One example is a member of the periwinkle family Apocynaceae, Catharanthus coriaceus, which is found in Madagascar in very small numbers and is threatened by grazing and burning. The Catharanthus coriaceus plant could be of great use although its medical value has not yet been thoroughly investigated—its genus is known to contain 70 alkaloids, some with clinical value in the treatment of cancer.

Plants provide many products other than drugs, including rubber and gums (see previous articles), tanning agents, dyes, fibers, insecticides, perfumes, waxes, cosmetics, preservatives, turpentine, and oils. This last product has seen an interesting development; sperm whale oil was used from the 1930’s for several years as a high-pressure lubricant and had no equal. By the late 1960’s these whales were greatly reduced in number and approaching extinction. Fortunately, it had been discovered that oil from the jojoba bean (Sim-mondsia californica) can replace the sperm whale oil as a lubricant and so reduce the need to hunt these animals, which are now protected.

Forests, being the richest sources of timber, are being exploited everywhere. For example, the equivalent of several square miles of forest is cut down in Malaysia every day for export. In 1950, 35 per cent of the earth’s land surface was covered in forest; today it is about 30 per cent. Apart from supplying the timber industry, wood is still a major source of fuel— it provides 31 per cent of the world’s fuel needs and plays a large role as a source of energy, mainly in developing countries. But in many forests, once the plant cover is removed, the soil is easily washed away, and the ground is left infertile.

Unlike fossil fuels, wood is renewable; it can also be converted to various other fuels and, thus, be competitive in a world economy. Controlled and artificial regeneration of trees is, therefore, desperately needed to ensure that stocks of timber will be replenished for future generations and that, with care, forests will always provide what is required.

Yet another economic need is that of soil conservation. The removal of plant cover almost inevitably results in soil erosion to some degree; for example, heavy rains can gradually turn a deforested hillside into a bare rocky slope, washing away all the soil and depositing it in rivers or lakes. In river watersheds this erosion can cause rivers to silt up; similarly, reservoirs and lakes may silt up, preventing their use for either water supply or hydroelectricity. But it is not only in watersheds that the removal of the native vegetation brings problems of erosion. The removal of plant cover on plains may lead to wind erosion of the soil and the creation of dust bowls, similar to what happened in the United States during the 1930’s, when farmland of the Middle West was damaged. Conversely, however, it is often possible to reduce erosion by introducing plants to protect the soil from the effects of wind and rain.

Pets and domestic animals have also caused a great deal of destruction. Grazing may prevent seed formation, and overgrazing can kill off plants or at least keep them at subsistence level so that they die without seeding or even managing to reproduce vegetatively. The presence of grazing animals, such as goats, on small islands with endemic plant species has had a drastic effect on the plant life there. Proper grazing rotation could conserve some grasslands as pasture and is now practiced in certain areas. Controlled burning is encouraged in these areas because it causes the leaf litter to release its nutrients and thus help to increase nutrient levels in the soil, as well a,s to stimulate new plant growth. The addition of artificial fertilizers also helps to maintain the vegetation.

Hybridization often uses the gene pool in wild crop plants to improve cultivated varieties. Research has been done into the possibility of breeding a perennial variety of corn (Zea mays, left). The dominant gene (P) in the wild perennial variety is bred with the recessive gene (a) in the cultivated annual variety. When the hybrids (Pa) cross-fertilize, three out of four will be perennial. Similarly, rice (Oryza sp.), which occurs naturally in tropical and subtropical regions, can now be grown in Portugal (right), where it provides a staple crop, having been bred to withstand temperate conditions. The need to conserve wild plants for their genetic importance is slowly being acknowledged.

Conservation for food

Food must also take its place in any economic consideration of conservation. About 3,000 plant species have been recorded as providing humans with food, but most present-day agriculture is based on fewer than 30 species. Of these, three plants are of particular importance: rice (Oryza sativa), wheat (Triticum sp.), and corn (Zea mays); about half of all arable land in the world is taken up with their cultivation. The dependence on such a small number of crops is potentially disastrous, because monocultures are more susceptible to disease and climate variation than mixed crops.

Some potential crop plants, however, are threatened species, such as the Yeheb bush (Cordeauxia edulis), which grows on the Somali-Ethiopian border and is being killed off by overgrazing. It produces nuts that have a very high protein content and are, therefore, a valuable food source. It can grow in the most arid parts where other legumes cannot survive, and, once planted, it needs no tending. It is, therefore, very suitable as a crop for the nomadic populations of the area.

These and other wild crop plants bear the characteristics that make it possible to develop new and better varieties of crops by breeding in disease-resistance or greater yield. This is done genetically using a repository of genes (a gene pool). These gene pools survive in places such as uncultivated grasslands and rain forests that are of inestimable value as a gene bank—a value which disappears as these areas are destroyed.

Land reclaimed from the sea has for centuries been turned over to pasture, arable farming, or horticulture. One of the largest such reclamation projects—the Zuider Zee scheme—has been undertaken in the Netherlands. Over the decades, this country, which covers 16,163 square miles (41,863 square kilometers), has reclaimed about 3 per cent of that area. But in the 199ffs, the Netherlands began allowing some of this land to be flooded once again.

Climatic conservation

The presence of vegetation and its removal is thought to affect the climate. A forest, for example, is continually giving off water vapor into the air that may affect the amount of rainfall over the forest. Its destruction may have more than just a local effect on rainfall. There may be, for this reason, a desperate need to conserve the world’s rain forests, which are being irrevocably destroyed.

Plants also remove carbon dioxide from the atmosphere and store it. After deforestation, and the loss of humus by erosion, carbon dioxide is released into the atmosphere and accumulates there, leading to a “greenhouse effect.” It is thought that if the carbon dioxide content of the atmosphere is raised by even a small amount it will cause the average annual temperature to rise by a few degrees. This increase in temperature could melt the polar icecaps, which would raise the sea levels and cause climatic conditions to alter.

At present, 22,000 million tons of carbon dioxide are added to the atmosphere every year. Afforestation and the conservation of forests is needed to remove and store it. It has, therefore, been suggested that large-scale afforestation of fast-growing trees be undertaken and, indeed, there are 250 million acres (101 million hectares) of newly created forest today—a figure that could be doubled by the end of this century.

Another alarming fact that impresses on us the need for plant conservation is that 50 to 60 per cent of the oxygen on this planet is produced by terrestrial and freshwater plants (the balance comes from marine algae). Were this source to be depleted, it would have serious consequences for living organisms.

Esthetic conservation

There is no doubt that plants are visually appealing to many people and, while satisfying horticultural needs, can often be combined with recreational areas. Forests and gardens, for example, have been places of leisure activity for centuries. The commercial value of forests need not be reduced by conservation or recreational needs. Botanic gardens and nature reserves also serve as reservoirs for endangered species, in which they can maintain genetic variability and act as a gene pool for future hybrids. Wildlife is closely associated with vegetation and in conserving large tracts of vegetation, we maintain wildlife habitat.

Algae farming is an alternative means of producing feed and fertilizers and indirectly may protect plants from exploitation. Bacteria in ponds feed on waste, producing carbon dioxide that is used by algae in the water, together with sunlight, in photosynthesis. The algae are skimmed off the water, filtered, dried, and then used.

Reclamation

The conservation of plants is the first step in preserving our plant world, but there is also a pressing need for more space for expanding human populations, their food, and that of their livestock. Some space can be retrieved from coastal dunes and marshes, deserts, and disused quarries and mine dumps.

Land has been reclaimed from the sea for centuries. These days, the Dutch method of empoldering is most often employed in western Europe. Sediments formed from alluvial gravel, sand, silt, and decaying vegetation are carried in by the tide, accumulate behind artificial dikes, and the enclosed land is drained. Gradually rain leaches most of the salt out of

the highly fertile soil, which can then be used for agriculture. In Germany in this century alone, about 30,000 acres (12,000 hectares) of marine alluvium have been reclaimed in this way.

In tropical and equatorial regions, however, many marshes are high in sulfides, which when exposed to the air become sulfates, making the soil too acid for crop production.

In southeastern Asia and India, rice is grown economically on such soils by not totally draining the land and avoiding the use of heavy machinery on it, which would break up the soil.

Coastal and desert dunes can be stabilized in several ways—for example, by planting grasses or succulents on them, by spraying resins onto the sand surface, or by covering it with polyethylene sheeting. Once stabilized they can be planted with crops, with trees for timber, or even forage plants. In the Wellington province of New Zealand, for example, pampas grass (Cortaderia selloanna) has been grown on stabilized sand as a food reserve for cattle. Desert reclamation has combined stabilization of the sand with various methods of irrigation and the addition of fertilizers and chemicals.

Apart from shores and deserts, some areas of land devastated by industrial machinery and strip mining have also been reclaimed. In parts of the Australian desert, for example, the sand has been heavily mined for mineral salts, and the soil structure has consequently been destroyed. The toxic mining wastes reduced the possibility of natural reclamation of the area, but with the application of at least 4 inches (10 centimeters) of topsoil vegetation could be established. Banksia seedlings were planted together with sorghum to hold the topsoil. Nitrogen and phosphate fertilizers were applied, and wattles {Acacia spp.) and gums (Eucalyptus spp.) were then planted.

The reclamation of land for recreational purposes is an increasing trend. Here, for example, disused gravel pits have been filled with water to provide facilities for sailing and other water sports. This is a suitable reuse of land that has been disturbed by quarrying and that is not easily converted to agricultural use. In a small way it meets the demands of expanding populations.