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bioweb.sungrant.org » Technical » Biomass Resources » Agricultural Resources » New Crops » Short Rotation Woody Crops » Hybrid Poplar

Hybrid Poplar	Printer Friendly

Hybrid poplars (Populus spp.) are fast growing, short rotation trees being developed for fiber and bioenergy uses. Hybrid poplars are crosses between native cottonwoods (the most common being Populus deltoids crossed with Populus trichocarpa) and are close relatives to aspens. Hybrid poplars can be produced throughout the U.S. where sufficient water is available. The U.S. Department of Agriculture Forest Service began work to develop hybrid poplars in the early 1970’s which in 1979 became the foundation for the U.S. Department of Energy’s Biomass Feedstock Development Program efforts to develop hybrid poplar as a bioenergy crop (ORNL Fact Sheet).    Hybrid poplars have short production cycles—6 to 8 years in the Pacific Northwest, 8 to 10 years in the Midwest, and 10-12 years in the Southeast. They are typically planted at spacings ranging from 8 x 8 feet to 12 x 12 feet (wider in the Pacific Northwest, narrower in the Southeast; 300 to 700 trees/acre). Yields range from 4 to 10 dry tons of wood/acre/year. Native forests typically grow at a rate of less than 1 dry ton/acre/year and managed pine plantations generally produce about 2.5 dry ton/acre/year. The higher yields have been achieved in the Pacific Northwest and Midwest. Yields in the southeast tend to be at the lower end. Hybrid poplars can resprout from their roots after harvest (coppice), but the management approach generally recommended is to replant to take advantage of improved varieties and to minimize potential insect and disease problems (ORNL Fact Sheet).   Hybrid poplars prefer well-drained slightly alkaline soils (pH 5 to 7.5). The soil is generally plowed to a 10 inch depth and cuttings (about 10 inches long) are planted either manually or mechanically with just the top bud showing. Weed control in the first year is essential and likely some weed control in the 2nd and possibly 3rd years may be needed (depending on spacing and tree growth--once canopy closure occurs, weed control is not needed). Fertilizer needs are low.  Nitrogen is generally applied only if the nitrogen levels in the leaves fall below 3 percent on a dry weight basis. Typically this means that 1 to 2 applications of nitrogen at levels of up to 50 lbs N/acre are required during the entire production cycle. Hybrid poplars are susceptible to leaf rust caused by Melampsora spp. and stem canker caused by Septoria musiva. Hybrid poplars are harvested with standard forest harvesting equipment (i.e., feller bunchers, skidders, forwarders, chippers, etc.) (ORNL Fact Sheet).    A recent economic analysis using a dynamic model of the U.S. agricultural sector (POLYSYS), estimated that when competing for cropland acres with existing crops (i.e., corn, soybeans, etc.) as well as other potential bioenergy crops (i.e., switchgrass, willow), hybrid poplar was less competitive as a dedicated bioenergy crop than switchgrass (De La Torre Ugarte, 2003; Walsh 2003). This result was due largely due to higher production costs and lower yields for hybrid poplar relative to switchgrass so that even though poplars have a slightly higher energy content than switchgrass, at any given energy price ($/btu) switchgrass was more profitable than poplars under most conditions examined. Estimates of the cost of producing hybrid poplar vary substantially, but for the purpose of this analysis costs ranged from $917 to $1051/acre ($1998) and expected harvested yields ranged from 34.5 to 46.3 total dry tons/acres depending on region.   The U.S.D.A. Forest Service (using POLYSYS and the North American Pulp and Paper Model) examined the potential of hybrid poplar as a future fiber crop (years 2000 to 2036), rather than bioenergy crop, under a number of technical, economic, and forest industry assumptions (Ince, 2001). Depending on the scenario, they estimated that a total of 15 to 800 million cubic meters (6.4 to 343 million dry tons based on an assumed density of 24 dry lbs/cubic foot) of hybrid poplar could be harvested for pulpwood over the 36 year time period, mostly in the period following 2020 (an annual harvest of 50 to 60 million cubic meters (21.4 to 25.7 million tons) under the highest scenario). Production occurred in the Southeast under the low production scenarios, and spread to the Midwest, and then to the Pacific Northwest under the higher production scenarios. The production levels correspond to 0.1 to 1.8 million hectares (0.247 to 4.45 million acres) of hybrid poplar production. The study did not include the potential to use Conservation Reserve Program acres. The level of production in this study bounds the results obtained from a previous analysis using the NAPAP model and FASOM (Forest and Agricultural Sector Optimization Model) which estimated 0.6 to 1.0 million hectares (1.48 to 2.47 million acres) of land could be converted to poplar production. More recent analysis by the Forest Service estimates approximately 0.1 billion cubic feet (1.2 million dry tons) of hybrid poplar could potentially be produced annually for fiber by 2050 (Haynes, 2003).   An analysis of poplar production for fiber uses on agricultural lands in the Southeast (Gallagher, 2006), estimated delivered breakeven costs to a pulp mill (assumed transport distance of 50 km) of $75.58 to $89.28/dry ton depending on delivered form (i.e., roundwood or chips) and the year of harvest (years 5 through 10) for yield levels that are currently achievable (20 green tons/hectare/year) and $57.42 to $68.92/dry ton for the same scenario but yields of 30 green tons/hectare/year. The analysis assumes irrigation and includes the cost of installing irrigation lines. Land costs are also explicitly included. Other costs include site preparation, cutting costs, weed and insect control, fertilizer, irrigation costs, labor, a custom harvest charge, and transport costs.   A recent Department of Energy study estimates that by mid-century, 9.2 million dry tons of short rotation wood crops could be available for bioenergy use (Perlack, 2005). The estimate is based on the assumption of short rotation woody crop production on 5.1 million acres of non-Conservation Reserve Program acres, an average yield of 8 dry tons/acre of fiber, and 25 percent of the production being available for energy with the remainder used for fiber. No economic analysis was conducted.   Over 90,000 acres of hybrid poplar have been planted for commercial production--most in the Pacific Northwest for fiber rather than energy, but also 5,000 acres in Minnesota as part of two large-scale demonstration projects and smaller acreage in the midwest and southeastern U.S. (Kroll, 1995; Downing, 1996).

Sources
Popular Poplars: Trees for many purposes, Oak Ridge National Laboratory, Biomass Feedstock Development Program Fact Sheet, http://bioenergy.ornl.gov/misc/poplars.html. Thomas Kroll and Mark Downing, 1995, Large scale biomass plantings in Minnesota: scale-up and demonstration projects in perspective, In Proceedings, Second Biomass Conferences of the Americas: Energy, Environment, Agriculture, and Industry, Portland, OR, August 21-24, pp. 21-29 De La Torre Ugarte, Daniel G., Marie E. Walsh, Hosein Shapouri, and Stephen P. Slinsky, The Economic Impacts of Bioenergy Crop Production on U.S. Agriculture, U.S. Department of Agriculture, Agricultural Economic Report Number 816, February 2003. Walsh, Marie E., Daniel G. de la Torre Ugarte, Hosein Shapouri, and Stephen P. Slinsky, Bioenergy Crop Production in the United States--Potential Quantities, Land Use Changes, and Economic Impacts on the Agricultural Sector, Environmental and Resource Economics, vol. 24, pp. 313-333, 2003. Peter J. Ince and Alexander N. Moiseyev, 2001, Some forestry implications of agricultural short-rotation woody crops in the United States, In Global Initiatives and Public Policies: First International Conference of Private Forestry in the 21st Century, Atlanta, GA, Mary 25-27, 2001. Mark Downing, Dan Langseth, Ron Stoffel, and Tom Kroll, 1996, Large-scale hybrid poplar production economics: 1995 Alexandria, Minnesota establishment cost and management, In Proceedings of BIOENERGY ’96-The seventh national bioenergy conference: Partnerships to develop and apply biomass technologies, Nashville, TN, September 15-20, 1996. Robert D. Perlack, Lynn L. Wright, Anthony F. Turhollow, Robin L. Graham, Bryce J. Stokes, and Donald C. Erbach, April 2005, Biomass as feedstock for a bioenergy and bioproducts industry: the technical feasibility of a billion-ton annual supply, Oak Ridge National Laboratory, ORNL/TM-2005-66. Richard W. Haynes, February 2003, An analysis of the timber situation in the United States: 1952 to 2050, U.S. Department of Agriculture Forest Service, General Technical Report PNW-GTR-560. Tom Gallagher, Bob Shaffer, and Bob Rummer, 2006, An economic analysis of hardwood fiber production on dryland irrigated sites in the U.S. Southeast, Biomass and Bioenergy 30 (2006): 794-802.