THE world is moving from a period of energy problem to one of the material shortage. Pakistan like other developing countries has a shortage of wood.

The share of forestry in the GDP was 0.35 per cent in 1983-84, which has decreased to 0.11 per cent in 1998-99. Similarly, there is a decline in the annual growth rate of the firewood from 8.8 per cent (during 1988-93) to 2.9 per cent during 1993-998.

There is a small area under forests in Pakistan including Azad Kashmir and Northern Areas, around 4.22 million hectares out of the total area of 87.98 million hectares. Out of this the contribution of private plantations (farm forestry) is 2.256 million hectares. During 1999-2000, the forests contributed 425,000 cubic meters (m3) for timber and 443000 m3 for firewood and Pakistan earned Rs1.5 billion from the export of various wood products, except the sports goods. The import of round and sawn wood during 1998-99 was 391,562 m3, while other wood products were 317,175 metric tons.

Apart from all-out efforts for increasing the production in state forests, attention has been focused on the agro-forestry as an effective supplementary source of fuel and timber wood. A decade ago the promising remedy of shortage of wood has been coming up by the use of eucalyptus species.

Eucalyptus is native to Australia, New Zealand, Tasmania, and nearby islands. The genus has more than 500 species. In Australia the eucalypti are commonly known as gum trees or stringy bark trees. The eucalypti grow rapidly, and many species attain great height of about 90 meters (300 feet) and a circumference of 7.5 metre.

Eucalyptus is popular among the farmers and people engaged in forestry and landscaping due to its adaptability to diverse and adverse environmental conditions, its resistance to various pests and pathogens, its ability to coppice (reproduction of harvested stem) and fast growth rate as compared to that of an indigenous species i.e. Dalbergia sissoo (shisham), Acacia nilotica (kikar), Albizzia procera (siris/sharin), Morus alba (mulberry/shahtoot) and Cedrus deodara (deodar). Farm-grown timber is characterized by the smallness of size due to short rotation, frequency of knots due to wider spacing and more branching. Proper silvicultural management can overcome these defects. But post-harvest problem of wood are more serious and cause rejection for value-added products. These problems are twisting, surface cracks and end split due to excessive shrinkage in wood upon drying. Collapse is a phenomenon described by the transverse caving-in of wood cells during drying above the fibre saturation point. Collapse formation and the associated development of internal checks are common phenomena in low to medium density eucalyptus timber. Collapse-shrinkage can be substantially recovered by steam reconditioning, thereby restoring the lost volume.

After a three-year research, the author ultimately reached to the solution of these problems to a great extent. New uses for presently under-utilized species were an important component of the strategic studies to investigate the suitability of E.camaldulensis for the manufacture of high quality furniture. There is an urgent need to understand and find out ways for the successful employment of eucalyptus wood for various traditional uses by enhancing its stability through research on the quality of dried wood in Pakistan.

The major worldwide end-uses of eucalyptus reported so far are in; railway ties, sports goods industry, plywood industry, particle-boards industry, furniture, shuttering and scaffoldings, firewood, construction material etc. As a timber eucalyptus is straight, tall, medium to high density, naturally preserved and general-purpose timber. It is ideal for pulp and paper, rail ties and other domestic usage. Till now eucalyptus wood has not been commercially used because of the lack of information about its technological properties and the seasoning problems.

Its market is still in a developing position. Wood quality can be comprehensively circumscribed by the wishes, ideas and expectations with which customers invest. Optimum marketing success cannot be achieved unless these properties meet wood purchasers’ specifications as accurately as possible. Seasoning is an essential preparation of lumber and wood. Proper seasoning reduces the magnitude of the dimensional changes due to shrinkage and swelling, protects wood from micro-organisms, prepares better for most finishing and preservation methods, and increases its strength. Good seasoning practices involve minimum time-interval between the felling, pre-drying, sawing, and the protection of sides and tops of air-drying stacks.

A reduction in seasoning time or an improvement in the quality of seasoned lumber offers potential economic benefits. A greater understanding of the seasoning process can facilitate improvement in wood seasoning process. In Pakistan wood seasoning is done through crude traditional methods. Wood is kept in water pond or stream for a long time almost round the year and then put under shade or sun for drying for months.

The same is the fate of eucalyptus that results in star shake, end split and other wood defects. Due to these reasons the buyers and the end-users have developed poor opinion about the timber and dislike it. Under such circumstances the gravity of the problem has increased to many folds. At one hand there is a severe shortage of timber, while on the other buyers and consumers are averse and dislike eucalyptus because of the few defects.

With increasing economic pressure on forest industries to improve the profitability, maximum productivity is constantly being pursued worldwide through increasing growth rates and shorter rotation times. This project was taken up to explore the extent and reasons of wood degradations during the seasoning and to find out suitable pragmatic remedial measures.

The wood is taken from the farm trees grown at Post Graduate Agricultural Research Station, University of Agriculture, Faisalabad. It is processed and treated in the laboratory of the Department of Forestry, Range Management and Wildlife. Among the pre-seasoning treatments are water soaking, boiling in water, and freezing and in another experiment the effect of chemical treatments for dimensional stabilization are studied. The effects of various pre-seasoning, and seasoning treatments on the dimensional stabilization of farm-grown eucalyptus wood were studied. There are several means of reducing the dimensional change of wood resulting from the changes in moisture contents. Approaches to reducing dimensional change are:

1. Freezing and boiling pre-seasoning treatments were considered effective. Preventing moisture absorption by coating the product, and preventing the dimensional change by restraint (under load/weight) that makes movement difficult or impossible were much useful. This may result in distortion of shape e.g. buckling in few cases.

2. Treating wood with material that replaces all or part of the bound water in the cell wall is a commercial means of stabilization. Such treatments are applied when it is still green. These treatments add up to 35 per cent to the weight of the product and are generally expensive.

3. Cross-linking; treating wood to produce mutual cross-linking of the hydroxyl groups in the cell wall has been used experimentally with success. It reduces the hygroscopicity of the wood and prevents swelling. One of the main reasons to modify wood chemically is to reduce the free swelling or shrinking of a modified unloaded specimen submitted to humidity change as compared to the swelling of untreated wood under like conditions. Several methods are used to improve the dimensional stability of wood, including the resin impregnation to replace water in cell walls and treatment with various chemicals to eliminate the binding sites for water molecules.

The study focuses on the use of different stabilizing materials such as:

Sucrose: It is cheap, non-toxic, non-corrosive and slightly hydroscopic, non-sophisticated and inexpensive equipment is needed, no heating is necessary, the wood keeps its natural colour, is easy to clean after impregnation and its composites can be treated and lastly the dimensional stabilization achieved is good.

Impregnation with the PEG: In intact cell walls low molecular weight (200-600) PEG can partly replace the water within the cell walls and thus keep them in swollen state when the residual water evaporates. Once the cell walls have lost their integrity and mechanical strength a high molecular weight PEG (MW>1500) is needed to bulk the cell lumen at least to a certain degree and thus prevent the tissue from collapse.

In Pakistan there is quiet low level of consumption of wood treated with “impregs”. Eucalyptus heartwood is difficult or very difficult to penetrate with the stabilizers applied by conventional treatments (i.e. through diffusion). Diffusion treatment of green heartwood to produce an envelope of treated wood is practicable and is useful for sawn building timbers.

The DEG, sugar and paraffin resulted as effective and environmentally safe chemicals for dimensional stabilization. The LRF percentage value for total lumber recovery after removing all defects of the treated samples was 93 per cent, 90 per cent and 68 per cent for the DEG, sugar and paraffin treatments and control respectively.

During the seasoning the effect of end-coating, full-coating, loading seasoning stacks, and coating along with load treatments were studied. Further effect of wood sample sizes on seasoning quality with single step seasoning and two-step seasoning with staggered sawing were studied. End coating with load treatment was considered most feasible and effective means for the control of dimensional instability and reduction of warp. The LRF percentage value for total lumber recovery after removing all defects of the treated samples was 82 per cent and 80 per cent for load treatment and coating with load treatments respectively.

The boiling treatment of timber before seasoning has long been considered as a way of reducing drying times and quality-improvements, as well. The hot water soaking reduced the drying time without further degrades.

The reasons to modify wood chemically is to improve its dimensional stability, i.e. to reduce the free shrinking of a modified unloaded specimen as compared to the shrinking of untreated wood under the like conditions. The study mainly focused on the use of different stabilizing materials, quantify their suitable concentration and method of application. Thirteen chemicals were used namely, polyethylene glycol (PEG), diethylene glycol (DEG), paraffin, sucrose, sodium silicate, borax, ferrous ammonium sulfate, zinc sulfate, polyvinyl acetate, diesel oil, alginate, diammonium phosphate, and urea. The chemicals especially the PEG, the DEG, sugar and paraffin used for the dimensional stability of eucalyptus wood gave some promising results.

From the silvicultural point of view it is important to know that at what stage the eucalyptus tree must be harvested. As eucalyptus is a fast growing tree and farmers are eager to get early income from their produce this study helped us to decide, the right age of tree/diameter gain, when the felling is desirable for all purpose end-uses. It can be felled at any age from 5 years and onward. The wood is equally defect-prone and needs stabilization treatments irrespective of the age group. It should be sawn into end-use component’s shape immediately after felling and then treated and dried. Before felling, the grain orientation of the standing trees must be visualized and it should be straight if it has to be used as sawn-wood and smaller components. The farmers selecting eucalyptus for woodlots should choose species suitable for multiple end-uses, some species show considerable potential for the production of high value appearance-grade timber suitable for furniture manufacture.

When eucalyptus wood is used as panel wood, after sawing some boards show more defects than the others within the same log. Hence it was questionable whether which part of the wood in a log is more favourable for use after seasoning and quantitatively how much wood is destroyed (or how much of each board in each lumber grade is defective?). For utilization purposes, the most important defect factor is the degree of difficulty a defect presents to the wood processor trying to obtain available rough dimension parts from a board. Visual inspections are central to many wood processing decisions.

Pre-freezing, a less known pretreatment has been used successfully to reduce the shrinkage and associated drying defects. The process involves freezing the green wood before air or kiln drying.

Manufacturing products from eucalyptus wood by the saw, dry, and rip method attracts attention because warp is reduced, less crook and greater lumber recovery, but greater shrinkage in thickness in some cases.

New industrial drying techniques and equipments have been developed. Research on solar-heated wood drying has continued through the world. In the kiln drying of green timber, temperature should not exceed beyond 45 degrees centigrade with high relative humidity to avoid too rapid seasoning. The object of good seasoning practice should be the limitation of defects to a level acceptable in the intended product.