High Tonnage Harvesting and Skidding for Loblolly Pine Energy Plantations

The southeastern United States has a promising source for renewable energy in the form of woody biomass. To meet the energy needs, energy plantations will likely be utilized. These plantations will contain a high density of small-stem pine trees. Since the stems are relatively small when compared with traditional product removal, the harvesting costs will increase. The purpose of this research was to evaluate specialized harvesting and skidding equipment that would harvest these small stems cost efficiently. The feller-buncher utilized was a Tigercat 845D with a specialized biomass shear head. The skidder was a Tigercat 630D equipped with an oversized grapple. This equipment was evaluated in a 4-hectare stand with characteristics of a southern pine energy plantation. During the study, the feller-buncher achieved an average production rate of 47 green tonnes/productive machine hour (gt/PMH) and the skidder had an average production rate of 112 gt/PMH. A before-tax cashflow model was used to determine a cost per ton for each machine. The feller-buncher costs were $3.85/gt over a 10-year life span, whereas the skidder costs were $1.95/gt over the same 10-year life. The results suggested that the current system working in a southern pine energy plantation could harvest and skid small stems for approximately $5.80/gt. The topic of declining fossil fuels and the need for renewable energy sources is evident in today’s society. Because of this necessity, researchers and politicians have assembled different ideas in which renewable fuels will be a major part of the US energy portfolio. Some of the framed ideas include the ‘‘US Billion-Ton Update’’ (US Department of Energy [DOE] 2011), ‘‘25x25’’ (25x’25 2007), and the Energy Independence and Security Act of 2007. The billion ton study (DOE 2011) illustrates how different areas of biomass feedstocks are allocated to the renewable fuel portfolio in a sustainable manner. The ‘‘25x25’’ states that 25 percent of our energy consumed must come from biomass by the year 2025. The one policy that has been enacted is the Energy Independence and Security Act of 2007 (http://www.gpo.gov/fdsys/pkg/PLAW-110publ140/ html/PLAW-110publ140.htm). Included in the Act are standards in which biofuels will play a major role in ensuring national energy security and the reduction of greenhouse gases. One of the main goals of the Act is to have 36 billion gallons of biofuels produced annually by 2022. The common attributes of all of these ideas are that they require a tremendous amount of biomass in a relatively short time period. A great deal of this material is expected to be sourced from woody biomass. Woody biomass is available in such forms as urban residues, mill residues, dedicated energy crops, and logging residues. Currently, mill and logging residues supply the woody biomass market, but they are not sufficient to meet the large-scale quantities set forth. Eventually, dedicated energy crops will likely be utilized by the United States to meet the requirements for biomass feedstocks. Shortrotation woody crop (SRWC) supply systems were first described in the late 1960s and early 1970s as a means of rapidly producing lignocellulosic fiber for use in the wood products industry and for energy (Tuskan 1998). Studies have been completed to determine optimum species, silvicultural techniques, fertilization, genetics, and irrigation to make the crop successful (Tuskan 1998). The barrier with SRWCs is the immense amount of inputs needed for high growth rates. This poses economic and environmental issues that may hinder the introduction of a biofuel market. These two issues happen to be important considerations when choosing a crop for biomass production. Another aspect that should be taken into account is the volatile risk associated with the biofuel market. The need for biomass feedstocks The authors are, respectively, Graduate Student and Associate Professor, School of Forestry and Wildlife Sci., Auburn Univ., Auburn, Alabama ([email protected], tgallagher@ auburn.edu [corresponding author]); Research Engineer, USDA Forest Serv., Southern Research Sta., Forest Operations Unit, Auburn, Alabama ([email protected]); and Professor and Professor, School of Forestry and Wildlife Sci., Auburn Univ., Auburn, Alabama ([email protected], [email protected]). This paper was received for publication in June 2014. Article no. 1400055. Forest Products Society 2016. Forest Prod. J. 66(3/4):185–191. doi:10.13073/FPJ-D-14-00055 FOREST PRODUCTS JOURNAL Vol. 66, No. 3/4 185 for energy has not been constant in the past. To mitigate risk, the biomass feedstock crop should be flexible in its ability to produce different products for the landowner to make a profit from his or her initial investment. Correspondingly, the crop should be well known in different areas such as nursery management, stand management, and disease and pest control. Southern pine stands have the potential to provide significant feedstocks for the biomass energy market (Scott and Tiarks 2008). Pine plantations have played a major role in the success of the forest products industry in the United States but specifically in the southeastern United States. The Southeast produces more industrial timber products than any other region in the world (Allen et al. 2005). This can be attributed to the Southeast climate and knowledge of intensive southern pine plantation management. The stands proposed for the energy plantations will predominately be composed of loblolly pine (Pinus taeda) planted at a density between 2,470 and 2,960 trees per hectare (TPH). Stands will be grown for 10 to 15 years, after which they will be harvested by the clear-cut method. Typically, stands at this age are not merchantable in today’s market because of the small stem dimensions at this young age. The shorter rotations will be attractive to landowners looking for a quick return on investment when compared with other timber product types that require much longer rotations. The problem lies in the logistics of felling the smalldiameter stems and delivering them to the mill in a form that is economically feasible (Spinelli et al. 2006). Harvesting systems must be balanced for the characteristics of the forest, machine types, and intensity of the harvest to reflect the equipment’s productivity (Akay et al. 2004). The main issue in the logistics process is the production costs associated with harvesting and handling the smaller stems. In the Southeast, conventional whole-tree harvesting systems incorporate a feller-buncher to fell and bunch the trees while a rubber-tired grapple skidder drags the bundle (several bunches from the feller-buncher laid together) of trees to the loading deck (Wilkerson et al. 2008, Soloman and Luzadis 2009). These two machines are essential to the operation and must be productive for profitability. The stems are processed at the loading deck into logs, tree-length material (delimbed and bucked), or chips. In full tree systems, the residues such as foliage, limbs, bark, and tops are typically left on the loading deck or the skidder distributes the slash back into the harvested stand. These residues, along with the main bole of the tree, provide a large amount of low-cost biomass. Additionally, large amounts of logging residues could potentially hinder future operations such as site preparation (Visser et al. 2009). In an energy plantation setting, the conventional whole-tree harvesting system configuration will follow traditional harvesting techniques and the whole tree will be chipped. When chipping, the equipment should be utilized to maintain wood flow for the highly productive chipping application. Using a whole-tree chipping system aids the harvesting process in several areas. Investment in biomass harvesting productivity research studies have been minimal since the late 1980s because of the low interest in biomass feedstocks, resulting in a gap in the understanding of production potential of modern harvesting machines. On the basis of an unpublished benchmarking study of a current harvesting system operating in south Alabama, the US Department of Agriculture Forest Service found that current felling and skidding costs range from $5.44 to $8.21 per green tonne (gt; Klepac 2011). The use of more specialized and technologically advanced equipment could lower the cost per unit. Also, it is essential that the harvesting system be composed of as few machines as possible to save money in maintenance and labor costs, moving costs, and reduced interference delays (Klepac and Rummer 2000). These systems do not need to be capital intensive to lower costs, but must have the flexibility and capability to be used for conventional round wood production in case of a biomass market collapse. Because of the high volume and low product value, a highly productive operation that uses an economy-of-scale approach must be developed. High production rates lower the fixed costs by spreading the costs over more units harvested. The system designed for this study is a high-speed, high-accumulation feller-buncher and a modified high-capacity rubber-tired skidder. A small case study was performed on this new equipment to analyze productivity and costs associated with owning and operating the machines.