Determining carbon in timber products

• The moisture content of the tree biomass is about 35%.
• The dry matter conversion rate from a tree is 65%. -Source
• Carbon constitutes 50% of the dry mass of trees.
• "The carbon content of vegetation is surprisingly constant across a wide variety of tissue types and species. Schlesinger (1991) noted that C content of biomass is almost always found to be between 45 and 50% (by oven-dry mass)." -Source: FAO

• The allocation of above ground and below ground biomass.
• It varies among biomes. See Figure 5 in this paper on New Pytologist
• Woody: 80% above ground (leaf+stem) and 20% below ground (root)
• Tundra: 35% above ground (leaf+stem) and 65% below ground (root)
• Grassland: 20% above ground (leaf+stem) and 80% below ground (root)
• Shrubland/desert: 50% above ground (leaf+stem) and 50% below ground (root)
• For timber products which come from woody products, we think the roots consitute 20% of the total biomass. Therefore the conversion ratio from the woody tree mass to the total biomass is 120%.
• The timber used for wood products are air dried after forest clearing. 
• The conversion ratio of the air dry mass to the oven dry mass is 88% -Source
• How about we only have the volume of the fresh weight? The timber product density is between 500 kg to 1000 kg per cubic meter, depending on the types of product and its origin biomes (Coniferous or not)
• The newest and most comprehensive FAO conversion brochure: PDF
• FAO Forest Resources Assessment WP 82