Agroforestry is playing a role in the early days of a new black walnut industry developing in western Oregon. Among the first private landowners who have planted black walnut on their farms for timber are several innovators experimenting with intercropping as a means of improving the growth and economics of the tree crop.
Those involved in the new industry are optimistic that the Northwest can develop a market niche based on the unique properties of their home-grown black walnut. The oldest business in Oregon specializing in walnut wood is Goby Walnut Products. The business was started in 1975 by Gary Goby, who is also President of the Oregon Chapter of the national Walnut Council.
A member of the Oregon Chapter, Peter Kenagy, is experimenting with a variety of trees, forages and crops for interplanting in black walnut plantations on his 420 acre Willamette Valley farm.
In one of his first plantings of black walnut four years ago, Kenagy interplanted a wildlife forage mix between rows of trees planted at 10 X 20 ft. spacing. The 10 ft. wide forage strips, which include sorghum, sudan grass, buckwheat and sunflower, are intended to attract birds and other wildlife. Plastic tree guards (political signs creatively recycled) protect the walnut trees both from herbicides sprayed along the tree row to reduce moisture competition, and also against rodent damage. Kenagy plans to maintain the wildlife forage for 6 to 7 years until the trees achieve canopy closure.
In a recently cleared area, Peter Kenagy has tried intercropping black walnut with sweet corn. He planted pre-germinated nuts in rows 20 ft apart, sprayed once for weed control, and then drilled corn seed between the tree rows. The same traveling boom spray gun was used to irrigate the walnut/corn trial as for crops in the adjacent fields. Kenagy said that the corn produced about the same yield as in his other fields and provided the economic justification for irrigating the new black walnut plantation.
Kenagy is also testing several fast-growing, short-rotation tree crops for interplanting with black walnut. Hybrid poplar and paulownia act as a nurse crop to force straighter growth of the black walnut and also provide a source of income early in the walnut rotation. Poplar has proved to be too competitive when planted at the same time as walnut in Kenagy's trials, so he now plans to plant black walnut at double the final density two or three years prior to planting poplar or paulownia.
Another Northwest innovator is J.T. Lowe who intercrops black walnut with Douglas fir that are managed for Christmas trees on his farm near Portland. The firs are planted at 5 X 5 ft. spacing, within walnuts planted at 15 X 15 ft. spacing, and harvested for Christmas trees at after 7 years. However, in older stands of healthy walnuts, Gary Goby has seen evidence of juglone induced growth inhibition of young interplanted fir trees when their roots intertwine with the black walnut.
Rather than utilizing eastern black walnut (Juglans nigra), strains recommended by the Oregon Chapter of the Walnut Council for farm planting in the Northwest are hybrid crosses of eastern black walnut and California black walnut (J. hindsii). Originally developed as rootstocks for English walnut, these interspecific hybrids are well adapted to the Willamette Valley of Oregon. There the hybrids grow almost twice as fast as eastern black walnut, according to Gary Goby, and produce better quality timber than the California black walnut. Some of the larger trees planted by early settlers exceeded 5 ft. in diameter at harvest, he said, and yielded high grade lumber in large dimensions.
Favorable growing conditions in western Oregon, mineral content of the soil, and the absence of damaging storms as in the Midwest, contribute to special colors and grain patterns in the wood. Gary Goby frequently finds orange tones in the wood he processes, along with black highlights. His wood inventory contains examples of a wide variety of decorative figures, particularly desirable for furniture, gunstocks and musical instrument making. Local trees are capable of producing much larger timbers than are commonly available from Eastern sources; Goby has produced top quality "clears" exceeding 8/4 (2 inch thick) X 10 ft. long X 28 inches wide. He has observed the beginning of heartwood formation after 18-20 years in the Oregon crosses, compared to only 9-10 years in eastern black walnut. Furthermore, Goby does not steam sapwood to sell as heartwood, a common practice among eastern sawmills.
Goby travels throughout western Oregon and Washington, buying trees offered to him by private landowners. After the logs are first processed on contract by a sawmill near Lacomb west of the Cascade Mountains, he drys and resaws the rough lumber at his own custom drying and milling operation near Albany. Goby Walnut Products offers a variety of products, including kiln dried lumber in 4/4 to 8/4 (1-2 inch) thicknesses, air-dried 10/4 to 16/4 (2-4 inch) lumber, gunstock blanks, musical instrument stock, resawn veneers and turning stock. Milling about 30,000 BF (board feet) of timber per year, the company sells to both national and international markets.
Although the black walnut trees harvested today come from rural homesteads and suburban homes, Goby sees increasing interest among rural landowners in planting black walnut woodlots specifically for timber. This is a difficult, long-term decision for many, he said, since 50-80 years are typically required to grow trees of sufficient size (at least 28 inch diameter) for maximum return on their investment. While commercial veneer manufacturers are not interested in black walnut at present because of concerns about saw-damaging metal objects hidden inside old farmstead trees, Goby foresees a valuable veneer market developing for plantation-grown trees in future.
Planting black walnut for timber is "not for selfish people," Goby believes. "This is stewardship in its most basic definition." Nevertheless, for landowners (and their families) able to initially invest about $1000 per acre to establish a black walnut plantation, and to wait 50-80 years for final harvest, the potential rewards are attractive. Goby pays a higher rate of sawlog stumpage to the landowner, at least $1 per BF, than in the eastern US, where the going rate for stumpage is closer to 35 cents per BF. In the future, he believes the price of carefully grown black walnut timber can only increase. "Young men plant radishes," he says, "old men plant trees."
A study comparing the costs and returns of black walnut to Douglas Fir, the Northwest's most common timber species, as farm tree crops was prepared in 1992 by a private forester. Based on a 100 acre plantation of each species, the estimated value for walnut harvested at age 80 years was projected to be $10 million compared to only $1.5 million for fir, even including a pre-commercial thinning for the fir.
Agroforestry could make the economics of black walnut culture more attractive in the Northwest as it has done in the Midwest. Many possibilities are being demonstrated locally through the efforts of Peter Kenagy, Joe Lowe and others in the Walnut Council. In addition to annual crops (e.g. corn) and short-rotation trees (e.g. poplar) already under trial, shade-tolerant, bareroot nursery stock or flower bulbs could be produced between the walnut trees. While cattle are likely to cause damage by rubbing the trees, it may be possible to graze sheep on grass-clover pasture sown in strips between the tree rows.
Nut production is an important source of early returns in many black walnut plantings. However, most of the hybrid walnuts now planted in Oregon are not good edible nut producers because of difficulties with meat extraction, according to Gary Goby. Some thin-shelled varieties, e.g. 'Cooksie,' are grown commercially in the state. Goby believes that the threat of blackline disease, which ruins timber quality, precludes the possibility of high-grafting English walnut varieties to hybrid black walnut rootstock for a combination of nuts and timber.
Seed Source Important
As with any tree crop, careful selection of seed source is a prerequisite to success. A diverse genetic base exists in Oregon, including hybrid crosses and the pure parent species, J. nigra and hindsii. A high degree of variability in both growth and form has been observed among individual trees growing in the Willamette Valley. Goby stresses the need to maintain careful records on the characteristics of parent trees, the soil type and management regime of the plantation, the growth of progeny, and ultimately the quality of the wood they yield.
In a joint effort with Oregon State University cooperative extension, the Oregon Chapter has identified promising individual trees as sources of seed for new plantations. For example, the 'BV' source originates from a 100 ft. tall, approximately 120 year old hybrid tree that is currently growing at a rate of about three-fourths inch in diameter per year and that yields large, heart-shaped nuts. Several test plots have been established since the local chapter was founded three years ago. In order to select the best seed sources for new plantations, there is an on-going need for more nut collections from good local trees, establishment of seedling seed orchards, and progeny trials.
The strategy which Gary Goby recommends to landowners is to plant their walnuts at higher initial stocking and then remove the poorer trees at age five, leaving the best trees to grow at a final thinned spacing. The overall objective is to develop a straight, branchless trunk (bole) 16-20 ft. long with a small "defect core" through timely training and pruning. once a satisfactory trunk is developed, then the only effort required is to maintain diameter growth so the tree will add high value, knot-free "clearwood" until it reaches optimal harvest size.
According to Gary Goby, hybrid black walnut in western Oregon grows best in deep, well drained soils. Its soils requirements are similar to those of commercial fruit trees; the OSU extension service has prepared maps of suitable valley soils as a guide to landowners. Black walnut prefers moister north or east facing slopes, and creek banks. Shallow, dry or poorly drained soils should be avoided for new plantations.
Landowners don't need to plant large acreages of black walnut to make a profitable investment, according to Goby. Farm woodlots as small as 1-2 acres can be sited in odd-shaped areas which are difficult to cultivate for annual crops. Clusters of black walnut trees can also be incorporated into riparian buffer strips.
Planting Black Walnut
Starting with a good seed source, the nuts are first stratified (moist chilling treatment) to increase the rate of germination. Following ground preparation, growers can plant either bareroot seedlings, or one or two pre-germinated (or ungerminated) nuts per planting spot. The initial spacing is usually 10-14 ft. between rows, depending on the size of the implements used for cultivation, and 10 ft. within the row. Although individual tree shelters are optional in the mild Oregon climate, some improvement in growth and protection from deer browse has been observed.
Most of the work required to grow black walnut between planting and harvest occurs during the first 10-12 years. Weed control is perhaps the most important task during this establishment phase, particularly to reduce grass competition prior to canopy closure. Where moisture is not limiting, cover crops could be planted and mown between the rows while maintaining an herbicide cleared strip beneath the trees. Fertilization and irrigation during dry periods will promote faster growth. In Oregon, black walnut encounters no significant disease, insect or deer browse problems.
Early training and pruning are necessary for the production of high-value veneer and sawlogs. Training starts in the second year to eliminate branch crotches and other form defects. The aim of pruning is to remove shoots along the trunk in stages ("lifts") to 16-20 ft. high, yielding two branchless 8-10 ft. logs at harvest. Modified farm equipment such as a tractor-mounted cherry picker can be used for pruning. To minimize knot size, limbs should be removed before they reach an inch in diameter.
Thinning at about age five is also recommended for black walnuts. The best formed, apically dominant trees are selected to grow on after removal of the poorer trees. The Oregon Chapter of the Walnut Council presents special workshops on pruning black walnut.
Taxation and harvest regulation are important considerations for farm woodlots. Black walnut is considered an exotic species in Oregon, and is not recognized as a forestry species in all counties where it is grown. Under state forestry regulations, certain species qualify for special tax consideration, property tax deferral, and severance tax, payable at harvest. Gary Goby suggests there is a need for interested landowners to lobby their local county governments to recognize black walnut as a forest crop.
(This article appeared originally in the Temperate Agroforester, January 1996. Thanks to Gary Goby for his help with the preparation of this article).