The harvest and subsequent regeneration of trees is a serious business for the forest industry. As a result, any claim that whole trees are used for anything less than their full potential is wildly frustrating. Landowners manage forests to maximize tree growth, and subsequently, return on investment. Forest products companies use the trees they buy from those landowners to the fullest extent possible.
In the US South, pine trees are considered mature at 25-40 years old. Plantations are typically thinned when trees are 12-15 years old to promote the growth and improve the quality of the most desirable trees in a stand. Trees that remain are often thinned again when they reach 18-22 years of age.
When trees reach a diameter large enough to produce high-value wood products, a final harvest takes place. Three raw materials come out of a harvest: sawtimber, pulpwood, and harvest slash.
Sawtimber is the portion of a mature tree that runs from the stump through the smallest diameter used to produce valuable lumber and plywood. Trees with straight trunks are needed to produce these high-value wood products, so trees with bends in their trunks are removed during a thinning.
These smaller trees with bends, twists, or other defects are considered pulpwood. The portion of mature trees too small in diameter to make lumber is also considered pulpwood.
Pulpwood is used to make a wide range of products. Oriented strand board used in home construction is manufactured from chipped pulpwood. A variety of pulp and paper products, including cardboard boxes and other packaging materials that can be recycled, are made from pulpwood as well. The pulpwood portion of the tree can also be chipped to produce energy.
The remainder of the mature tree - its top, limbs and pine needles - is often called harvest slash. Mills use this residual material to generate heat and electricity to run their operations. A portion of harvest slash is also left on the forest floor to prevent erosion, nourish the soil and provide wildlife habitat.
Environmental groups claim whole trees are used to produce energy, and in some cases, they may be right. Where they are wrong, however, is in their claim that forests are clear-cut solely to obtain whole trees for energy. Basic forest economics and industry best practices simply do not allow for this scenario.
Consider, for example, the price differential between sawtimber and pulpwood. In the two-month period of September/October 2013, the southwide volume weighted average price for pine sawtimber with a 14” diameter at breast height (DBH) was $24.72 per ton. The southwide volume weighted average price of pine pulpwood price (DBH varies, generally from 4” to 8”) was $10.58 per ton.
Landowners do not harvest small trees at $10.58 per ton when they can harvest mature trees at $24.72 per ton. Not to mention, the additional growth in the tree in the intervening years results in many more tons of sawtimber that can be sold at the higher price.
Energy producers using wood to produce fuel do not pay $24.72 for sawtimber when pulpwood is available at $10.58. More importantly, energy producers do not pay pulpwood prices when the price of harvest slash is negligible. Our blog post on capacity to pay offers further evidence of why whole trees are simply not sourced for energy purposes.
If a whole tree is used to produce energy, it is because the tree is an otherwise unmerchantable pulpwood-sized tree that took 12-15 years to grow. The Environmental Protection Agency recognizes pre-commercial thinnings that remove these and other trees as a best practice and considers trees taken in first thinnings to qualify as biomass under the renewable fuel standards (RFS).
Consider also the practices the industry has implemented to create maximum value from harvested trees. In the 1990s, it took 5.0-5.2 green tons of wood to make 1,000 board feet (1 mbf) of lumber. Today, sawmills have adopted laser technology to improve the average to 3.5-4.0 green tons of wood to make 1,000 board feet.
In addition, companies throughout the industry have implemented ways to use the wood waste their operations create through boilers that use bark, harvest slash, and other mill residues to generate the heat and electricity needed to dry lumber or run paper machines.
Quite frankly, the allegation that the forest products industry allows the use of whole trees for energy insults both landowners who invest a great deal of time and money into their trees and wood products companies whose long-term viability relies on their ability to maximize the potential of harvested trees.