Potential Impacts of Biomass Harvesting on Forest Resource Sustainability. Contact Information:

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1 Potential Impacts of Biomass Harvesting on Forest Resource Sustainability Scott M. Barrett a, W. Michael Aust b, and M. Chad Bolding c Contact Information: a Extension Associate, VA SHARP Logger Program Coordinator, sbarrett@vt.edu b Professor of Forest Hydrology, waust@vt.edu c Assistant Professor of Forest Operations/Engineering, bolding@vt.edu Department of Forest Resources and Environmental Conservation 228 Cheatham Hall Virginia Tech; Blacksburg, VA ABSTRACT Due to current woody biomass demand, some loggers have added small chippers to their harvesting operations to produce biomass fuel chips from logging residues such as limbs, tops and otherwise non-merchantable material. Numerous facilities throughout the Southeast and the nation, have announced intentions of converting biomass to energy. Assuming that utilization of biomass increases in the future, additional removals of logging residues will be necessary. Utilizing logging residues for energy has positive benefits for both loggers and landowners. However, there are also some concerns that increased utilization of logging residues will potentially cause negative impacts on the long-term sustainability of forest resources. Concerns over potentially negative effects generally fall into issues regarding removals of nutrient and organic pools or concerns regarding increased erosion losses and water quality effects due to increased bare soil. A review of past studies indicates that nutrient removal rates from biomass harvesting are generally not great enough to cause long term site productivity declines. In instances where the effects on nutrient pools are greater, fertilizer application would be sufficient to ensure future nutrient pools. Nutrient removal rates for a case study site in Virginia that harvested fuel chips indicated that average fuel chip nutrient content of 2.56, 0.27, and 1.33 pounds per green ton of nitrogen, phosphorous, and potassium, respectively. Erosion rates estimated on the case study site ranged from 3.2 to 8.6 tons per acre per year and indicate that additional studies are needed to determine if conventional BMP s are adequate for biomass harvesting operations. Introduction The use of woody biomass for the production of energy is expanding rapidly and has the potential to offset a portion of the non-renewable fuels used for energy production in the United States. This can potentially reduce dependence on foreign oil as well as reduce usage of other fossil fuels which are net emitters of carbon dioxide. Utilizing woody biomass from forests to produce energy is generating significant interest in Virginia and throughout the nation. Numerous facilities are already using woody biomass for energy and additional facilities have announced plans to begin construction. Although a variety of positive benefits associated with utilizing woody biomass for energy exist, there are also some concerns. Typical biomass

2 harvesting operations utilize logging residues such as limbs, tops, and otherwise nonmerchantable material by adding a chipper to a conventional logging operation (Westbrook et al., 2007). Compared to conventional harvesting, biomass harvesting removes additional branches, foliage, and other logging residues from the site. Removing additional biomass from the site leaves less protective cover on the forest soil which has the potential to increase erosion and sedimentation. Removing limbs and foliage that would have been left on site in conventional harvests is a concern because it removes a disproportionate quantity of nutrients and could potentially decrease long term site productivity by reducing available nutrients. As interest in biomass utilization intensifies, questions about emerging markets and products have increased and VA Tech Forestry Extension has been actively involved in biomass educational programs throughout the state. In addition to the interest over potential new markets, forestry professionals and others attending these workshops commonly express concern over the potential environmental impacts of utilizing biomass from logging residues. Therefore, the objective of this paper is to provide the forestry community information regarding the concerns of nutrient removal, erosion, and sedimentation when logging residues are utilized for bioenergy. Specifically the goal was to assess current information, determine its relevancy to biomass utilization as practiced in Virginia, and identify areas where future research may be needed. Study Site and Methods A 20 acre study site was located in Bedford County, VA in the Piedmont physiographic province. This area has well developed local markets for biomass fuel chips as well as pulpwood and hardwood sawtimber. The market for biomass fuel chips is dominated by an 80 Megawatt wood fired electrical generation facility near Altavista, VA. In addition, two paper mills purchase boiler fuel, including whole tree chips on the open market to produce heat and steam for their manufacturing facilities. The combined consumption of boiler fuel purchased on the open market by these three facilities is approximately one million tons per year, the majority of which is from whole tree chips. The case study site was a pine plantation that involved a clearcut harvest. The harvesting contractor was operating a mechanized logging crew with a feller buncher, 2 grapple skidders, a Morbark Model 22 Chiparvestor disc chipper, and a single loader loading roundwood and feeding the chipper. Products produced on the site were double bunk pine pulpwood and fuel chips. Hardwood stems, small diameter pine stems, tops and branches were chipped for biomass fuel chips. Chip samples were collected from chip vans on site. Nine chip samples were collected with two subsamples of each for a total of 18 samples analyzed. Samples were sealed in a plastic bag on site then later transferred to a paper bag prior to drying. A green weight was obtained, and then samples were placed in a drying chamber. After dry weight was obtained, moisture content was calculated for each sample. Dried chip samples were ground in a Wiley mill until they passed through a 1 millimeter screen. After grinding, the samples were analyzed for Carbon, Nitrogen, Phosphorous, and Potassium content. Erosion rates on site were estimated using the Universal Soil Loss Equation (USLE) as modified for forests (Dissmeyer and Foster, 1984).

3 Nutrient Removal Samples of fuel chips were analyzed to determine nutrient content and if current logging residue utilization standards on this job produced similar nutrient removal rates compared to other previously published studies. Samples were analyzed for moisture content, carbon, Nitrogen (N), Phosphorus (P), and Potassium (K). Pine fuel chips had an average moisture content of 57 percent and contained 53.8 percent carbon. Average nutrient content of the fuel chips indicated nutrient concentrations of 0.297, 0.032, and percent N, P, and K respectively as shown in Figure 1. Figure 1. Average percent nutrient content of fuel chips. Figure 2. Average pounds of nutrients removed per green ton of fuel chips.

4 Average quantities of nutrients removed per green ton of biomass were calculated and indicate that for this study site approximately 2.56 pounds of Nitrogen, 0.27 pounds of Phosphorous, and 1.33 pounds of Potassium are removed per green ton of fuel chips removed from the site as shown in Figure 2. Nutrient removals per ton of harvested material may be useful for estimating additional nutrient removals for biomass harvests when compared to conventional harvests. Table 1 provides an example loblolly pine site on a 25 year rotation showing Nitrogen inputs, outputs, and net changes with differing levels of logging residue harvest. Loblolly pine bole only Nitrogen content was estimated at 103 pounds per acre (Pritchett and Fisher, 1987), inputs from natural processes was estimated at 155 pounds of N over the course of a 25 year rotation (Carter and Foster, 2003), and Nitrogen content of residues were based on average values calculated from sample chips in this study. Example residue removal rates were based on reported values of harvest rates for logging residues plus understory material in a pine plantation of 10.8 tons per acre (Westbrook et al., 2007) and a theoretically more intense utilization rate of 20 tons per acre. Inputs and outputs will vary for each site but this example shows the relative quantities of nutrients removed based on our estimates of nutrient content of logging residues and a sample pine plantation system. In this specific example, residue removal rates greater than 20 tons per acre would cause declines in the quantity of available nitrogen over the course of the next rotation. It also serves to illustrate that while it will vary by site, increased residue removal has the potential to decrease site productivity. Table 1. Nitrogen pools and transfers for 25 year rotation of loblolly pine (pounds/acre). Treatment Boles Residues Total Inputs Net Change Bole only pulpwood harvest Pulpwood plus 10 tons residues Pulpwood plus 20 tons residues Although nutrient removal associated with biomass harvesting on forest sites can be a concern, nutrient removals from similar whole tree harvests have been researched in the past. Many early whole tree chipping studies date back to the early 1970 s when an earlier energy crisis focused research on biomass energy. A recent comprehensive literature review by Eisenbies et al. (in review) on intensive utilization of harvest residues in southern pine plantations concluded that as long as the forest floor remains intact, harvesting logging residues will probably not have long term negative effects, especially on more fertile sites. However, they also noted that even in cases where nutrient removal might cause productivity declines, fertilization could feasibly be used to offset nutrient losses. It should be noted that some studies of whole tree harvesting of hardwood stands revealed additional concerns related to calcium depletion (Boyle et al., 1973; Swank and Reynolds, 1986). As a result, additional research may be warranted for hardwood logging residue utilization and calcium removal. Erosion and Sedimentation Compared to conventional harvesting, biomass harvesting removes a higher percentage of above ground biomass including, branches and foliage and therefore could provide less protective cover for the soil. The additional bare soil could potentially result in increased erosion and nutrient loss from the site. In addition to the productivity losses associated with soil erosion, the erosion could reach water bodies and cause water quality concerns. Forestry Best Management Practices

5 (BMP s) for Water Quality are widely implemented and their effectiveness at preventing erosion and sedimentation is well documented (Aust and Blinn, 2004). However, current BMP guidelines were typically developed for conventional harvesting operations (Shepard, 2006) where logging residues were left on site. Little research has been done to determine what additional impacts there may be from harvesting woody biomass for energy and what additional BMP recommendations may actually be needed for biomass harvesting operations. A number of states have already altered BMP guidelines to reflect additional recommendations for biomass harvesting. However, little research has directly compared water quality impacts from current biomass harvesting operations versus conventional harvesting operations. We collected preliminary data at the case study site for the Universal Soil Loss Equation (USLE) as modified for forests (Dissmeyer and Foster, 1984). We collected representative samples from the harvested area, deck, and haul road and these data indicated that average erosion rates across this site ranged from 3.2 to 8.6 tons per acre per year immediately following harvesting. These data contrasted with values of < 1 to 5 tons per acre per year for a similar conventional harvest in the piedmont. A visual assessment of the site indicated that the increased removal of logging slash left considerably more bare soil than a typical conventional harvest and indicated that further investigation of the impacts of biomass harvesting on erosion and sedimentation is justified. Conclusions Nutrient removal and erosion rates are among the top potential concerns related to biomass harvesting that are voiced by forestry professionals. Significant prior research has been conducted regarding nutrient removals and whole tree harvesting. Based on current utilization standards for biomass and known nutrient removal rates, for most stands, long term productivity will probably not be a wide spread problem. However, there are infertile sites where additional nutrient removals from biomass harvesting could impact productivity. For these potentially nutrient limited sites, standard fertilizer application rates could feasibly offset nutrient removal impacts. Additional research may be needed to identify sensitive sites where nutrient removals from biomass harvesting could potentially decrease productivity. The other primary concern related to biomass harvesting relates to erosion, sedimentation and water quality. When logging residues are harvested for fuel chips, less protective cover is left on the forest floor and the potential exists for increased soil erosion. Some states have begun to implement additional BMP s for biomass harvesting and other states are considering the possibility of additional BMP s. Implementation of additional BMP s can add significant costs to harvesting operations, yet little research has been conducted to determine if conventional BMP s are effective at protecting water quality on biomass harvesting operations. Before additional BMP s for water quality are recommended for biomass harvesting operations, research should compare and contrast water quality impacts of conventional harvesting versus biomass harvesting operations. These comparisons will determine if current BMP standards are adequate, and if not, what additional BMP s may be necessary. As with any area of forest operations, sustainability of the resource is a top concern of forest managers. Previous studies indicate that for most sites, utilizing logging residues for bioenergy

6 is a sustainable and desirable use of the forest resource. Additional research in the future should focus on identifying sites of special concern where harvesting logging residues could potentially cause productivity declines, and in determining what if any additional BMP s may be necessary to protect water quality. References Aust, W. M., and C. R. Blinn, Forestry Best Management Practices for timber harvesting and site preparation in the eastern United States: An overview of water quality and productivity research during the past 20 years ( ). Water, Air, & Soil Pollution: Focus. 4-1: Boyle, J. R., J.J. Phillips, and A.R. Ek Whole Tree Harvesting: Nutrient Budget Evaluation. Journal of Forestry. December Carter, M.C. and C. D. Foster Prescribed burning and productivity in southern pine forests: a review. Forest Ecology and Management. 191, Dissmeyer, G. E. and G.R. Foster A guide for predicting sheet and rill erosion on forest land. USDA Forest Service Technical Publication R8-TP 6. 40pp. Eisenbies, M.H., E.D. Vance, W.M. Aust, and J.R. Seiler. In review. Intensive utilization of harvest residues in southern pine plantations: Quantities available and implications for nutrient budgets and sustainable site productivity. Pritchett, W. L. and R.F. Fisher Properties and management of forest soils. Second Edition. John Wiley and Sons. New York. p Shepard, J. P Water quality protection in Bioenergy production: the US system of forestry Best Management Practices. Biomass and Bioenergy 30 (2006) Swank, W. T. and B.C. Reynolds Within-tree distribution of woody biomass and nutrients for selected hardwood species. Proceedings of the 1986 Southern Forest Biomass Workshop, Knoxville, TN. pp Westbrook, M. D. Jr., D.W. Greene, and R.L. Izlar Utilizing Forest Biomass by adding a Chipper to a Tree-Length Southern Pine Harvesting Operation. Southern Journal of Applied Forestry. 31 (4)