The report, Biomass as Feedstock for a Bioenergy and Bioproducts Industry: The Technical Feasibility of a Billion-Ton Annual Supply (generally referred to as the Billion-Ton Study or 2005 BTS), was an estimate of 'potential' biomass based on numerous assumptions about current and future inventory, production capacity, availability, and technology. The analysis was made to determine if conterminous U.S. agriculture and forestry resources had the capability to produce at least one billion dry tons of sustainable biomass annually to displace 30% or more of the nation's present petroleum consumption. An effort was made to use conservative estimates to assure confidence in having sufficient supply to reach the goal. The potential biomass was projected to be reasonably available around mid-century when large-scale biorefineries are likely to exist. The study emphasized primary sources of forest- and agriculture-derived biomass, such as logging residues, fuel treatment thinnings, crop residues, and perennially grown grasses and trees. These primary sources have the greatest potential to supply large, reliable, and sustainable quantities of biomass. While the primary sources were emphasized, estimates of secondary residue and tertiary waste resources of biomass were also provided. The original Billion-Ton Resource Assessment, published in 2005, was divided into two parts-forest-derived resources and agriculture-derived resources. The forest resources included residues produced during the harvesting of merchantable timber, forest residues, and small-diameter trees that could become available through initiatives to reduce fire hazards and improve forest health; forest residues from land conversion; fuelwood extracted from forests; residues generated at primary forest product processing mills; and urban wood wastes, municipal solid wastes (MSW), and construction and demolition (C&D) debris. For these forest resources, only residues, wastes, and small-diameter trees were considered. The 2005 BTS did not attempt to include any wood that would normally be used for higher-valued products (e.g., pulpwood) that could potentially shift to bioenergy applications. This would have required a separate economic analysis, which was not part of the 2005 BTS. The agriculture resources in the 2005 BTS included grains used for biofuels production; crop residues derived primarily from corn, wheat, and small grains; and animal manures and other residues. The cropland resource analysis also included estimates of perennial energy crops (e.g., herbaceous grasses, such as switchgrass, woody crops like hybrid poplar, as well as willow grown under short rotations and more intensive management than conventional plantation forests). Woody crops were included under cropland resources because it was assumed that they would be grown on a combination of cropland and pasture rather than forestland. In the 2005 BTS, current resource availability was estimated at 278 million dry tons annually from forestlands and slightly more than 194 million dry tons annually from croplands. These annual quantities increase to about 370 million dry tons from forestlands and to nearly 1 billion dry tons from croplands under scenario conditions of high-yield growth and large-scale plantings of perennial grasses and woody tree crops. This high-yield scenario reflects a mid-century timescale ({approx}2040-2050). Under conditions of lower-yield growth, estimated resource potential was projected to be about 320 and 580 million dry tons for forest and cropland biomass, respectively. As noted earlier, the 2005 BTS emphasized the primary resources (agricultural and forestry residues and energy crops) because they represent nearly 80% of the long-term resource potential. Since publication of the BTS in April 2005, there have been some rather dramatic changes in energy markets. In fact, just prior to the actual publication of the BTS, world oil prices started to increase as a result of a burgeoning worldwide demand and concerns about long-term supplies. By the end of the summer, oil prices topped $70 per barrel (bbl) and catastrophic hurricanes in the Gulf Coast shut down a significant fraction of U.S. refinery capacity. The following year, oil approached $80 per bbl due to supply concerns, as well as continued political tensions in the Middle East. The Energy Independence and Security Act of 2007 (EISA) was enacted in December of that year. By the end of December 2007, oil prices surpassed $100 per bbl for the first time, and by mid-summer 2008, prices approached $150 per bbl because of supply concerns, speculation, and weakness of the U.S. dollar. As fast as they skyrocketed, oil prices fell, and by the end of 2008, oil prices dropped below $50 per bbl, falling even more a month later due to the global economic recession. In 2009 and 2010, oil prices began to increase again as a result of a weak U.S. dollar and the rebounding of world economies.
Productivity and cost par ton are predicted for tvo in-voods chippers (Xorbark 20 and 27) vhere DBH. species groups, and moisture content are varied. Keyw rd: Transpirationai drying Typical iogging operations in the South average rcoving Less than A52 of the aboveground biomass (CSFS 1983). The buik of the biomass produced must be deait vith in site preparation and re-estahiishaent of the stand. If a market for this residue biomass is avaflable, a case can be nude for harvesting this aterial that is normaliy left on tSe site. The cost of recovering this residue or ;ocentiai residue, minus the value of the residue to a ut iiizing facliicy xs t be iess than the cost of re-cstabiishnent &hen the material is left on the s i t e . Tvo types of residue are found on a site foiioving ciearcut iogging. There are the tops of zerchantabie stems and the underscory steas which do not meet the specifications for the material being harlested. ‘:e have observed naturai pine stands with up to 60 tons of understory material par acre and pine piantations vith as much as 60 tons of this materiai. The key to the ccst effectiveness of any intensive utiiizatlon operation is the l conomicai handiinp of scaii stems. Our previous work has shown that skidding can be cost effective when ut:iizing snaii steGls if there is a sufficient quantity of these stems avaiiabie on the sire to Take a fuii ioad for each skidder turn (Stokes et i, Yfiier et ai. 1985 Watson et l L. 1386). %~~‘~~~s true for a prehaweit operation vhen oniy the understory stem iiere taken as well as for an operation in which the merchanrabie overstov and the underscory stems vere ta’kan in a single pass. PeLLi>g t h e smaii stgls econonicaLLy’is possibie with sore o f the currentiy a v a i i a b i e equipment and if iarge quantities of underscory aateriai are avaiiabie on the site. Feiler-bunchers vith high speed heads, which are highly maneuverabie. and have a fast travel speed, can perform very veil when harvesting the understory. 3e cost of faiiing understory has been found to be reasonabie provided there is ample quantity of -ateriai to be fei>ed (Watson ec ai. 1986). :ovtl~Ie r, t+e Ceiling costs become prohlbltive when :&e-e i s Less than 15 green cons of macerfai co be 1 ?resrnted at the 9th annual Council on Forest Engineering Meeting. !!obiie, Al. September 29 Ccr,ker 2. 1986. 2 The allthors are Associate Professor and ?esearch Assisrant, Department of Forestry, Yississippl Scare Cnivers icy, and Research Engineer. USFS Andrevs Forest Sciences Lab, Auburn. AL. cut per acre (YilLer et ai. 1985) . Ihe feliar-buncher spends much more of its time in traveling cycie when there is iov voiume of this =teriaL on the site. Chipping is the predominant method of handling the small stems once they have been moved to a loading area. Chippfng allows for the r e d u c t i o n in airspace that is necessary for the l conomicai tramport of srmll stems. lhe soie current use of this understory materiai is for fuel, thus chipping or hogging the material vouid be necessary In preparing the stems for burning. The results of a study that was conducted to investigate the l conomfes and productivity of chippers in processing seuil stems are reported in this paper. The poucr required for converting smail stems to chips should not be as great as for the conversion of Large stems to chips. Xost companies producing chips In the South are using chippers in the 650 horsepower class. Ke f irst set out to determine if these Larger chippers vere necessary if only small stems vere being processed. Some companies are using transpirational drying to reduce the moisture content of wood for fueL. By felting the trees and aiioving the stems to dry for severai veeks. one can gratiy increase the net Btu yleid from the wad. Hovever, processing the dried materiai requires that the knives be changed more often and it vas feit that the chippers were ioslng productivity on a productive h o u r bas is when handling this drier materiai . Thus, the impact of moisture content of the stems processed on productivity was a iso examined.
Abstract Eight combinations of skidder tires, ranging in total width from 0.7 m to 2.2 m, were evaluated for rut formation potential on two soils in south-central Alabama. One was a mixed pine-hardwood bottomland; the other was an upland, predominantly pine stand. Each soil/tire combination was replicated twice. Changes in soil profile after one, three, seven, and nine loaded passes were used as indices of soil disturbance. The number of skidder passes was the most significant factor influencing rut formation. The effect was linear up to nine passes on both test sites. The first pass on the upland site accounted for half the average rut depth and area. The magnitude of the displacement after one pass was related to tire width. Each subsequent pass caused a uniform smaller increment in depth and area. The magnitude of the increase was independent of tire width. On the bottomland site, however, each pass resulted in an increment in both depth and area the magnitude of which was a function of tire width. Average rut cross-sectional area on the bottomland site ranged from 0.13 m2 to 0.75 m2 for nine passes. Depth of ruts ranged from 1.7 cm to 3.6 cm for nine passes on the upland soil, and from 1.4 cm to 21.2 cm for nine passes on the bottomland soils. Soil physical properties were not affected by skidder traffic regardless of tire width.
Sixteen stands were harvested at intensities (proportion of basal area removed) ranging from 0.27 to 1.00. Logging contractors used chain saws and rubber-tired skidders. Harvested sites were similar in slope and tree size. Harvest cost per hundred cubic feet of wood (CCF) was inversely related to harvest intensity and tree size. Harvesting profitability per CCF was near zero when removing trees averaging less than 8 inches diameter at breast height (DBH). Harvest intensity had the greatest influence on profitability in small-diameter timber. Harvest profitability was greatest when removing large trees at high levels of harvesting intensity. Because of the differences in average tree size removed by different harvesting prescriptions, some prescriptions were more profitable than others. Most profitable for harvesting contractors in our study was single-tree selection in an uneven-aged stand. Less profitable were selection in an even-aged stand, clear cutting, and shelterwood harvests, in that order. Selection at low removal intensities with small trees removed would always be the least favored harvest method with the equipment spreads we observed. Average removed tree size needed to be at least 8 inches DBH to break even.
Abstract Three stands were harvested by either clearcut, shelterwood, or single-tree selection methods. The single-tree selection method consisted of a light thinning in an even-aged stand as the initial basal area reduction cut required to convert the stand to uneven-aged structure. The contractor used two skidders (one grapple, one choker) and production chain saws to harvest all three tracts. Harvested sites were all similar in slope (10-15%), average dbh (12-14 in.), and preharvest number of stems by dbh. In the felling study, fell, walk, and limb-top time were all greater for the single-tree selection method. Time to process a tree was lowest for the clearcut, intermediate for shelterwood, and highest for single-tree selection method. For skidding, bunch building time was highest for the single-tree selection and lowest for the clearcut method. Average volume per cycle was consistently higher for the grapple skidder than the choker skidder; volume per cycle was lowest for the single-tree selection and highest for the clearcut method for both skidders. Time per cycle was consistently lower for the grapple skidder than the cable skidder. Time per cycle was lowest for the clearcut and highest for the single-tree selection method. Factors that affected felling productivity (in decreasing order) were: dbh of harvested stems, intertree distance, and method of harvest. Factors that affected skidding productivity (in decreasing order) were: skidder type, pull distance, average volume per cycle, and the method of harvest. Costs of felling and skidding were highest on the single-selection stand and lowest on the clearcut stand. Total percentage of stand area trafficked was lowest for the single tree stand. However, the total area disturbed to meet a wood procurement budget was lowest for the clearcut and highest for the single-tree method. South. J. Appl. For. 18(4): 168-174.
