Forest Products, Utilization and Wood Science
Forest Products, Utilization and Wood Science tests wood structure, properties, processing and the economics of timber and non-timber forest products. Nepal's answers should connect species to end use.
Core rules and concepts
- Hardwoods have vessels; softwoods have tracheids. Heartwood is darker and more durable; sapwood conducts water.
- Moisture content (MC) = (wet weight minus oven-dry weight) divided by oven-dry weight, multiplied by 100. Fibre saturation point is about 28-30%; below it, wood shrinks, and above it, free water is lost first.
- Density and specific gravity affect strength; shrinkage is anisotropic, with tangential greater than radial greater than longitudinal.
- Processing: felling, bucking, sawing, seasoning by air or kiln, preservation with CCA or borax, and grading.
- Composite products include plywood, particleboard, MDF and veneer. Nepal's commercial species include Sal, Sissoo, Khair, Teak, Chir and Uttis; NTFPs include lokta, chiraito, tejpat, allo and yarsagumba.
Worked example
A wood sample weighs 480 g when green and 400 g when oven-dry. MC = (480 - 400)/400 x 100 = 20%. If its green volume is 500 cubic centimetres and oven-dry weight is 400 g, basic density = 400/500 = 0.80 g per cubic centimetre. The reasoning: moisture content is always expressed on oven-dry weight, not green weight; basic density uses oven-dry weight over green volume.
Traps
Calculating MC on green weight overstates the result. Do not confuse density with specific gravity, which is dimensionless. Do not assume shrinkage is equal in all directions. Do not ignore preservation and seasoning when explaining why local timber fails in service.