Between 100 and 200 million acres of U.S. forest lands are estimated to be at high risk for catastrophic wildfires due to overcrowded conditions and the build-up of diseased and dead materials. The removal of this material offers a potentially new source of forest materials for bioenergy and bioproducts. The Healthy Forests Initiative and the Healthy Forests Restoration Act of 2003 (P.L.108-148) include provisions to remove and utilize excess woody biomass material to produce a full range of wood fiber products and bioenergy and bioproducts.
The quantities that need to be removed could be substantial. Rummer (2003) estimates that in 15 western states, as much as 346 million dry tons of biomass could be removed at harvesting costs ranging from $35 to $62/dt depending on species, terrain, density, and diameter among other factors.
Skog (2005) identified areas in 12 Western States (AZ,CA,CO,ID,MT,NM,NV,OR,SD,UT,WA,WY) where thinning could substantially reduce fire hazards and provide revenue from wood products to help offset treatment costs. Acres with low fire hazards, areas without roads, and acres with minimum removable merchantable volume of less than 5 tons/acre were eliminated from the analysis such that the total acres examined ranged from 6.7 to 15.1 million depending on whether thinning operations involved only the removal of smaller and younger trees or included older trees of various age and size. The estimated quantities of biomass that could be removed were 178 and 445 million dry tons respectively with harvest costs ranging from $250 to $2500/acre.
Due to the high cost of mechanically removing biomass from high fuel load areas, removal of some merchantable timber for conventional fiber uses in addition to small diameter trees and dead, rough, or rotten material has been suggested as a means to subsidize the cost. However, the harvest of substantial quantities of merchantable timber can have a significant impact on local and national fiber markets. Ince (2006) examined these implications for public lands only in the 12 states evaluated by Skog which further reduces the total acres to 5.6 (small diameter trees) and 10.9 (larger trees) million acres. The estimated amount of biomass potentially available was 9.9 and 23.2 and billion ft3 (~ 124 and 290 million dry tons assuming an average density 25 dry lb/ft3 for pine species) for small and larger diameter tree thinning operations respectively. Annual wood removal levels ranged from 0.5 billion ft3 (about 6.25 million dry tons) to 1.5 billion ft3 (about 18.75 million dry tons) and involved treatment of 3.4 to 8.4 million acres depending on scenario and fuel treatment approach. The economic costs and impacts of fuel treatment removals from 2005 to 2020 were examined for a number of scenarios. Increased quantities of timber from public lands displaced timber harvests from private lands and for all scenarios examined, reduced projected stumpage prices for timber.
Excessive fuel loading also occurs in the eastern U.S., and thus the total quantities of fuel treatment resources that could be available for bioenergy and bioproducts could potentially be significantly higher.
Perlack (2005) estimated the annual availability of 59.6 million dry tons of fuel treatment thinnings (30% for bioenergy) by mid-century, but did not estimate the cost of removing the material or evaluate the economic implications of displacing traditional fiber sources.
The USDA Forest Service (USDA-FS, 2007) reports that from 2001 to 2007, 6.802 million acres of forest land was mechanically thinned, and that of the 1.3 million acres thinned in 2007, material from 23% of the acres were used for fiber, bioenergy, and/or bioproducts.