WSU-Puyallup

Department of Energy, Small Business Technology Transfer Program, Carbon Management.

CARBON SEQUESTRATION BY HYBRID POPLARS IN THE PACIFIC NORTHWEST

The burning of fossil fuels for energy generation has resulted in the steady increase in atmospheric carbon dioxide concentration over the last century, beginning with the industrial revolution. Continued increases in atmospheric CO₂ may have profound effects on the global environment and economy, resulting from the global warming brought on by the greenhouse effect. We are interested in developing a mitigation strategy to enhance biological conversion of CO_2, an important greenhouse gas, into a stable form to provide for long term sequestration of carbon.

The project addresses the issue of increasing plant and soil carbon sequestration by altering existing ecosystems through the conversion from low productive, unimproved pasturelands to fast growing hybrid poplar plantations in the Pacific Northwest. Average above-ground productivity of unimproved pasture in western Washington and Oregon is about 4 Tonnes/ha/year (Hafenrichter et al. 1973). In contrast, the average above-ground productivity of a 4 year-old hybrid poplar plantation was estimated to be 28 Tonnes/ha/year (Heilman and Stettler 1985). Values of total plant productivity, i.e. carbon sequestration amounts, are less certain due to lack of good data for below-ground biomass and the fact that the pasture grass is an annual (at least the above-ground portion) and the poplars are a long-lived woody perennial plant. If one assumes that the above-ground biomass represents 50% and 70% of the total standing biomass for pasture and poplar, respectively, then total productivity would be 8 and 40 Tonnes/ha/year. These values do not include any soil carbon derived from the plants. Presently there are approximately 24,000 hectares (60,000 acres) in hybrid poplar plantations in the PNW that represents a carbon sequestration rate of over 960,000 tonnes per year. The available land for non-irrigated poplar plantations in this region could be as high as a million hectares while the possibility of irrigating the plantations could increase the potential land base 3- to 5-fold. Additionally, sequestration value of the poplar wood is much greater than the pasture, which is rapidly returned to the soil while the poplar wood is used for paper and wood products representing a long-term carbon sequestration system.

This project will utilize rapidly growing hybrid poplar clones from the Washington State University Poplar Research Program, coupled with the development of a poplar growers association to provide the technical assistance needed for the conversion of available pasturelands into productive poplar plantations. In Phase I, the available land area will be determined for both non-irrigated and irrigated plantations in the PNW based on soil type, topography and pH, and the feasibility of forming a poplar growers association to provide technical information for plantation establishment and management will be assessed. Important biological questions will also be addressed in Phase I including selection of hybrid poplar clones based on growth rates, wood density and lignin content, and initial studies to determine rates of below-ground carbon sequestration in tree and soil carbon pools.

In Phase II, the growers association will be formed with existing poplar growers and additional landowners will be identified, brought into the growers association, and provided economic incentives and technical assistance to establish poplar plantations on their lands. The biological research will be continued to further develop estimates of carbon sequestration rates, both in controlled environment and field situations, with an emphasis on understanding and modeling below-ground processes of woody root growth, fine root turnover and contribution to soil carbon pools. Depending on the results of the wood density and lignin analysis in Phase I, breeding for or genetic engineering of, high lignin content clones for deployment in new plantations would be pursued.

Anticipated benefits would include the potential of sequestering large amounts of carbon, upwards to 40 million tonnes annually by year 2010, an active poplar growers association to deal with cultural and marketing issues, an economically viable crop for landowners that could be harvested every 10 to 12 years, and logs that could be used for a variety of wood and paper products resulting in long-term carbon sequestration. Additional scientific benefits will be accrued from the better understanding and modeling of below-ground processes and application to long-term carbon sequestration by other forest ecosystems.

In order to sequester significant amounts of carbon using hybrid poplars, a number of issues need to be addressed in the Phase I research. One is to identify the land base in the PNW to support the planting upwards of one million hectares to hybrid poplar. Another is to develop a means to provide economic and technical assistance to the owners of these lands in order to get these lands planted in poplar and to maintain high levels of carbon sequestration. On the scientific side, identifying those clones that will have the fastest growth while sequestrating the maximum amount of carbon into stable compounds such as cellulose and lignin. Understanding the fate and amount of carbon that is translocated below-ground into storage such as in woody roots or lost to the soil carbon pools through root turnover or exudation is needed to fully determine carbon sequestration by poplars and other trees.

Determine the amount of land in the Pacific Northwest potentially available for growing hybrid poplar, with and without supplemental irrigation based on soil-site criteria (Broadacres Nursery).

Determine the feasibility of creating a poplar growers association in the PNW to aid plantation establishment, address cultural and marketing issues, targeting existing growers and owners of land identified in 1. (Broadacres Nursery).

Screen and select poplar clones based on growth rates, wood density and lignin content (WSU-Puyallup) to be used in plantation establishment.

Initiate physiological studies to determine carbon sequestration rates, especially carbon associated with below-ground processes (WSU-Puyallup at Broadacres Nursery).

Andrews, J.A., D.D Richter and W.H. Schlesinger. 1996. Belowground CO₂ dynamics in a loblolly pine ecosystem: Insights from the FACE-forest prototype study. Supplement to the Bull. Ecol. Soc. Am. 77:13.

Ceulemans, R. and M. Mousseau. 1994. Effects of elevated atmospheric CO₂ on woody plants. Tansley Review No. 71. New Phytol. 127:425-446.

Curtis, P.S., D.R. Zak, K.S. Pregitzer and J.A. Teeri. 1994. Above- and belowground response of Populus grandidentata to elevated atmospheric CO₂ and soil N availability. Plant and Soil 165:45-51.

Eamus, D. and P. Jarvis. 1989. The direct effects of increase in the global atmospheric CO₂ concentration on natural and commercial temperate trees and forests. Adv. Ecol. Res. 19:1-55.

Idso, S.B. and B.A. Kimball. 1991. Effects of two and half years of atmospheric CO₂ enrichment on the root density distribution of three-year-old sour orange trees. Agric. and For. Meteor. 55:345-349.

Hafenrichter, A.L., D.S. Dougals and F.L> Brooks. 1973. Hay and pasture seedings for the Pacific Coast States. Chapter 47 in Forages (ed. M.E. Heath, D.S. Metcalfe and R.F. Barnes), Iowa State Univ. Press, Ames, IA.

Heilman, P.E. and R.F. Stettler. 1985. Genetic variation and productivity of Populus trichocarpa T. and G. and its hybrids. II. Biomass production in a 4-year plantation. Can. J. For. Res. 15:384-388.

Heilman, P.E., T.M. Hinckley, D.A. Roberts, and R. Cuelemans. 1996. Production physiology. Pp. 459-490. In Biology of Populus, (ed. R.F. Stettler, T.Bradshaw, P.E. Heilman, and T.M. Hinckley), NRC Research Press, Ottawa, Canada. 539 p.

Korner, C. and J. Arnone. 1992. Responses to elevated carbon dioxide in artificial tropical ecosystems. Science 257:1672-1675.

Leavitt, S.W., E.A. Paul, B.A. Kimball, G.R. Hendry, J.R. Mauney, R. Rauschkolb, H. Rogers, K.F. Lewin, J. Nagy, P.J. Pinter and H.B. Johnson. 1994. Carbon isotope dynamics of free-air CO₂-enriched cotton and soils. Agric. and For. Meteor. 70:87-101.

Lewis, J.D., R.B. Thomas and B.R. Strain. 1994. Effect of elevated CO₂ on mycorrhizal colonization of loblolly pine (Pinus taeda L.) seedlings. Plant and Soil 165:81-88.

Norby, R.J., C.A. Gunderson, S.D. Wullschleger, E.G. O'Neill and M.K. McCracken. 1992. Productivity and compensatory responses of yellow-poplar trees in elevated CO₂. Nature 357:322-324.

Norby, R.J. 1994. Issues and perspectives for investigating root responses to elevated atmospheric carbon dioxide. Plant and Soil 165:9-20.

O'Neill, E.G. 1994. Responses of soil biota to elevated atmospheric carbon dioxide. Plant and Soil 165:55-65.

Rogers, H.H. and S.A. Prior. 1992. Cotton root and rhizosphere responses to free-air CO₂ enrichment. Crit. Rev. Pl. Sci. 11:251-263.

Stettler, R.F., L.Zsuffa and R. Wu. 1996. The role of hybridization in the genetic manipulation of Populus. Pp. 87-112. In Biology of Populus, (ed. R.F. Stettler, T.Bradshaw, P.E. Heilman, and T.M. Hinckley), NRC Research Press, Ottawa, Canada. 539 p.

Thomas, R.B. and B.R. Strain. 1991. Root restriction as a factor in photosynthetic acclimation of cotton seedlings grown in elevated carbon dioxide. Plant Physiol. 96:629-634.

van Veen, J.A., E. Liljeroth, L.J.A. Lekkerkerk and S.C. van de Geijn. 1991. Carbon fluxes in plant-soil systems at elevated atmospheric CO₂ levels. Ecol. Applic. 1:175-181.

Vogt, K.A. and H. Persson. 1991. Measuring growth and development of roots. Pp. 477-501. In Techniques and Approaches in Forest Tree Ecophysiology (ed. J.P. Lassoie and T.M. Hinckley), CRC Press. 599 p.

Zak, D.R., K.S. Pregitzer, P.S. Curtis, J.A. Teeri, R. Fogel and D.L. Randlett. 1993. Elevated atmospheric CO₂ and feedback between carbon and nitrogen cycles. Plant and Soil 151:105-117.