Since the mid-1980's, large plantations of hybrid poplar have become a common sight in the Pacific Northwest. A combination of favorable climate and soils, short rotation intensive culture (SRIC) and advanced breeding techniques have made these highly productive “fiber farms” an important source of hardwood fiber for paper manufacturing. The experience gained from large-scale plantations will also aid nonindustrial private growers wanting to grow poplars for higher-value wood products.
During the recent annual convention of the Society of American Foresters in Portland, OR, participants had the opportunity to tour the Lower Columbia River Fiber Farm (LCRFF) operations of Fort James Corp. Representatives of Fort James and researchers from the University of Washington were on hand to show the entire process, from genetic selection, site preparation, tree management, to harvesting.
Fort James is one of several forestry companies that are growing hybrid poplar for pulp chip production. Approximately 65-70,000 acres of poplar plantations are currently in production in the Northwest. Most of this acreage is located on the drier east side of the Cascade range within 100 miles of the Columbia River. However, Fort James has developed its plantations, totaling over 11,000 acres planted since 1985, west of the Cascades on the fertile flood plain of the lower Columbia River northwest of Portland.
Through its Landowner Assistance Program, the company has lease agreements on an additional 2500 acres of private farmland, providing technical assistance and an assured market to private growers. The entire acreage is currently devoted to furnishing chips to its mill in Wauna, OR for the production of intermediate-grade printing paper.
Fort James operates its own proprietary poplar breeding program, centered at the Westport Research Station. Interspecific hybrids are bred through controlled crosses between three Populus species: P. trichocarpa, P. deltoides and P. maximowiczii. The aim is to develop disease-resistant, fast-growing clones for deployment in the company plantations.
In contrast to the drier east side, diseases of poplar are a major problem on the wetter west side, particularly Melampsora poplar rust and Venturia shoot blight. While these diseases rarely kill trees outright, they do lower productivity. Disease resistance of new clones may only last 8-14 years since new rust strains that can attack them soon evolve. Thus the company must try to keep one step ahead of the rust by continually breeding newer clones.
Of the 3000-5000 seedlings from controlled crosses that are introduced annually to the company’s tree improvement process, only 6-8 clones will be operationally deployed at the end of a four-step selection process that lasts up to 15 years. Clones are selected on the basis of diseaseresistance, size and form, growth rate, and wood qualities. The objective is to provide chips to the paper mill with desirable fiber characteristics at the lowest possible cost.
In addition to Fort James’ own breeding program, researchers at the University of Washington are pursuing both basic and applied research on poplar with other public and private organizations through the Poplar Molecular Genetics Cooperative (PMGC) and the Tree Genetic Engineering Research Cooperative (TGERC). Major projects include the development of over 15,000 new hybrid clones, identification of DNA markers for clonal “fingerprinting”, and breeding of transgenic clones that are resistant to either herbicide or insect attack. Experimental clones that are resistant to glyphosate herbicide or cottonwood leaf beetle (incorporating a form of Bt) are currently being tested in cooperation with Fort James and other coop members.
The LCRFF is located on land that has near-ideal climate and soil conditions for poplar, with a watertable that averages only 2-5 feet deep. The plantations are harvested and replanted on a 7-year rotation; most of the company’s acreage is currently in its second rotation. Rather than allowing coppice regrowth, the land is re-planted with the latest clones developed through the breeding program. After site preparation to remove stumps and prepare raised planting beds, unrooted 12 inch cuttings are planted by hand at 7 X 10 foot spacing. The raised beds provide warmer and better-drained soil conditions and thus help speed growth in early spring.
Since hybrid poplar is very sensitive to moisture competition from weeds, intensive weed control measures are employed during the first 2-3 years of establishment. A combination of cultivation and both preand post-emergence herbicides are used. Clones are selected for rapid development of wide crowns that shade out weeds and shorten the need for weed control. Another management priority is animal damage control to reduce depredation by voles, deer, beaver and other mammals. Clonal differences have been observed in browsing preference by deer; “feed tree” clones may be interplanted to divert deer away from other clones. No fertilizer or irrigation are applied on the LCRFF.
Harvesting operations are highly mechanized and closely coordinated with the paper mill to maintain a constant supply of chips. Poplars are transformed from standing trees to paper products in three days or less. Trees are cut with feller-bunchers, logs are carried by skidders to a flail debarker on site, and are then processed by a chipper which feeds chips into enclosed vans for transport to the mill. Average yields on the LCRFF have increased by 31% over the last ten years due to improved clones and cultural practices. As much as 2500 bone dry tons per month are harvested to meet demand year-round. About 70% of the total harvested biomass is recovered as clean chips.
In response to a dip in pulp chip prices, Fort James and other companies are also investigating the feasibility of growing poplars on a longer rotation for higher-value wood products. A small sawlog trial started 10 years ago on a portion of the LCRFF. Trees are planted at 10 X 12 foot spacing in anticipation of harvesting logs with an average 10 inch DBH and a 6 inch top on a 10 year rotation for both solid wood and chips. All trees are pruned to increase the volume of knot-free clearwood that could be used for millwork (e.g. molding). Poplar may also be used for plywood cores and composite panels (e.g. oriented strand board), but markets for these products are still in their infancy in the Northwest.