Civil Engineering Reference
In-Depth Information
Flax, a plant of diversity
Flax is one of the oldest cultivated plants. The seeds can be pressed to produce oil for use
in painting and for producing linoleum. Its fibres can be woven into very valuable textiles,
pressed into strips for sealing joints around doors and windows, braided into light insula-
tion matting or compressed into building boards.
Flax fibres are twice as strong as polyester fibres - they are considered the strongest
of natural fibres, about 50-75 per cent stronger than cotton (Andersson, 1986). It is even
stronger when wet. It is naturally resistant to most insects. It is relatively fire-proof and can
be used as insulation in fire doors. If it does ignite, it smoulders and does not emit poiso-
nous gases.
Plants are renewable resources that can be cultivated and harvested at regular
intervals. With sensible methods of cultivation, they are a constant source of raw
materials.
Pollution problems that have arisen in this area during recent years are a wor-
rying development. In the Czech Republic and Poland more than half of the
forests are dead or dying. Investigations into forest deaths in the USA show that
productivity of American pine has declined by 30-50 per cent between 1955 and
1985. There are similar situations in Siberia (Brown, 1990) and in Scandinavia.
Coniferous trees have suffered more from pollution than deciduous trees; other
species of plants are also affected. The most damaging pollutants are considered
to be ozone, sulphur and oxides of nitrogen, and the main producers are heavy
industries and cars. The picture is made more complex because certain forms of
pollution actually stimulate growth in the forest for a short period. This is espe-
cially relevant to nitrogen oxides - growth stops when the forest becomes satu-
rated, and the apparent vitality ceases.
The importance of trees and plants to the global climatic situation has begun
to be realized. They break down carbon dioxide (the dominant greenhouse
gas) into oxygen. From this perspective it is amazing that the rain forests are
threatened not only by pollution but also by clearing for development. This
happens also in larger areas of Australia, Russia and the USA, where timber is
felled without the necessary replanting. Siberia is in a very critical situation,
forests of larch trees are being cleared in order to solve Russia's economic
crisis.
Timber from the tropics
The first shipments of tropical timber came to Europe via Venice during the fifteenth and six-
teenth centuries. This timber was mainly extracted from the rain forests, which covered
about 14 per cent of the Earth's surface at the beginning of the twentieth century. This has
now been reduced to 6-7 per cent. The consequence of this is likely to be an increased
greenhouse effect, more frequent flooding, the extinction of rare animal and plant species
and an increase in the areas of desert.
Tropical timber is used for window and door frames, interior panelling, floors and fur-
niture as solid timber and veneers. Some timbers, e.g. azobè, iroko and bankiria, have
