1. TREES AND THE ENVIRONMENT
In times of drought, a few shade trees in the vicinity of watering places will reduce the amount of water needed by livestock.
Forests and plantations of trees can, and have been used to dispose of treated sewage effluent. The effluent whilst biochemically safe still contains high concentrations of nitrates and phosphates in solution. If these effluents are discharged into rivers and lakes in large quantities the growth of algae is stimulated and the lake environment becomes degraded with the death of fish and other adverse side effects.
Trees in cities moderate local temperature variations and provide a restful antidote to acres of concrete, steel and glass.
- WOOD AND ITSUSES
At a time when there is a worldwide concern over the rate of depletion of non-renewable resources, such as oil, coal and many metals, wood begins to assume a new and greater importance. Apart from food crops it is the major raw material which is renewable. Wood was one of the earliest materials used by man for tools and transport in the form of dugout canoes, and when mechanical principles begun, he turned to wooden disc wheels. Plastic is made from oil and coal, and metals are mined from the ground – but the Earth only possesses fixed amounts of these materials – which are non-renewable and will become scarcer and cost more. Wood, because it is a renewable resource and a very versatile material is perhaps beginning a new era of importance in man’s history. All wood can be wrought and shaped mechanically. It can be nailed, screwed, mortised and glued and used for walls, roofs, furniture and most delicate sculptures, then mechanically broken down and reconstituted into new materials, such as particle board, hardboard and newsprint. Importantly wood can be chemically modified and altered either to make pulp from which all kinds of paper and cardboard containers can be made, cellulose from which rayon fibre for clothing is produced and even alcohols and sugars which can serve as raw material for a variety of chemicalindustries.
WOOD USED AS WOOD
Wood is used in the round for transmission poles, telephone poles and fence posts for which expensive steel would have to be used. The gum and wattle wood used will not withstand termite attack or rot but has the property of being permeable to preservatives such as creosote which is forced into the wood under pressure to give a long life in contact with the ground. Slabbed round wood is used as ‘mat packs’ in the mines to support the roofs in the mining stopes. A useful property here is that these wood supports creak and groan before they give way, a warning not given by steel or concrete.
Sawn wood as boards, beams and battens is used in all sorts of construction work from roof trusses to tile battens and ceiling boards. Also made are wooden cases for packing agricultural produce, such as tobacco andfruit.
Resilience is another valuable property of wood. Australian tallow wood is a highly prized material for dance floors because of this property. Toughness is a particular quality of some wood such as ash andhickory.
FORESTRY: LEARNER GUIDE
When it is combined with flexibility and the ability to be permanently bent, using steam, as in ash, the timber is especially suitable for sports goods such as tennis racquets and bentwood furniture.
The willow used for cricket bats is 40% lighter than Ash but only about 15% less tough which makes it ideal for thisuse
Thick plywood, or cardboard, is a composite made up of sawn components with veneer faces, and used and re-used as shuttering for concrete work. Wooden matches are cut from veneer having the same thickness as the matchstick. For this poplar wood is used which peels well and gives strong match splints which easily soak up the wax used to make the splints burn evenly. Plywood is widely used in the furniture industry where the face veneer is usually a particularly decorative wood like mukwa or teak.
The cheapest form of paper is newsprint made by mechanically grinding wood into fibre without any chemical treatment. Paper packaging has two important advantages over plastic. The first is that it is much easier to re-use or re-cycle and the second that it rots down instead of remaining unaltered for years. Unsightly and sometime dangerous litter as is the case with plastics.
Cellulose from wood is also dissolved, reconstituted and spun as rayon fibre or made into cellulose acetate fibre. Wood cellulose is also used to make photographic film and nitrocellulose in explosives. Rayon yarn forms 15% of the total world textile production. Cotton, wool and rayon are the fibre materials made from renewable resources as opposed to nylon and terylene, produced from non- renewable oil and coal.
Figure 1: A Kiaat Tree
