Utilization of Beetle-Killed Southern Pine
George Woodson – Prepared under contract with the Forest Service, U.S. Dpearment of Agriculture Forestry Associate Professor, Wood Utilization, School of Forestry, Louisiana Tech University, Ruston, LA.
United States Department of Agriculture, Forest Service, General Technical Report WO-47.
Suitability for Various Products
Lumber yield and quality decrease with increasing time after beetle attack. The following measures of mill efficiency have been reported from research studies in three States:4
|Location||Time since beetle attack||Beetle infested logs||Green logs|
|Days||– – – – – – – – – – LRF – – – – – – – – – –|
It has been noted that mill workers change their sawing practices when processing beetle-killed pine. The sawyer intentionally slabs heavier than normal to remove the outer sapwood, and edging methods are altered. Grade recovery and lumber yield are thus substantially reduced. Walters and Weldon (1982a) reported that trees dead for 90 days in east Texas yielded 75 to 79 percent as much lumber as green sawlogs. Trees dead for 180 to 360 days did not appear economical to utilize. The volume of No. 2 and better lumber produces from trees dead for 90 days or longer is much less than that from green trees.
Table 1 illustrates a comparison of rough grades and dry planed (S4S) lumber grades for lumber prodcued from 327 logs taken from trees with crown conditions varying from green to devoid of needles (black). The differences between 1-inch boards and 2-inch dimension were significant. The volume percentages of boards (1-inch) in each grade remained about the same for the rough green and dry planed gradings, indicating that the lumber was properly graded with regard to stain. The grader did not manage as well with the dimension lumber due to the difficulty in distinguishing the difference between heavy stain and the beginning stages of decay. Since stain is not a defect in dimension lumber, the grader was forced to make a judgement as to which condition existed. The lumber apparently looked much worse in the rough green condition. Grades between rough green and final dry planed material differed considerably. Generally, the rough green grading indicated a lower percentage of No. 1 and a higher percentage of No. 2 lumber than the actual dry-planed grade for lumber than the actual dry-planed grade for lumber from all crown conditions. Lumber taken from the trees with red-thin and black crowns had substantial amounts of heavy stain, and the grader downgraded a high percentage of these to No. 4 because of decay. When these pieces were dried and planed, however, the grades were changed from No. 4 to No. 1 in many cases. It must be noted that lumber is normally graded in the dry-planed condition, and this alleviates much of the problem.
Table 1 – Comparison of rough green and dry planed lumber grade by crown color¹
|Crown color||Surface condition||Boards (1-inch)||Dimension (2-inch)|
|– – – – – – – – – – – – Percent – – – – – – – – – – – –|
¹ Values are expressed as percentages of total lumber within a given thickness.
Additional information on dry-planed lumber grade recovery for butt and upper logs from the 327-log sample is given in table 2. As expected, butt logs yielded more No. 2 and better lumber than the upper logs, and the effect of knots in the upper logs contributed to a higher percentage of No. 3 lumber. Butt logs generally yielded the highest percentage No. 4 lumber (indicating presence of decay).
Table 2 – Dry planed lumber grade recovery data or beetle-killed timber by crown condition and location in the tree.
|– – – – – – – – – – – – – – – – – – – – Percent – – – – – – – – – – – – – – – – – – – –|
Utilization of beetle-killed southern pine for veneer and plywood is feasible for several weeks after attack. Walters and Weldon (1982b) reported that green and beetle-killed trees dead for up to 45 days in east Texas were equal in volume, grade, and type of veneer produced. Plywood recovery factor (PRF = square feet of 3/8-inch plywood per cubic foot of wood input) for green and 45-day kill class combined was 15.25. The PRF for 90-and 180-day kill class combined was 13.53 (approximately 11 percent less recovery than for green and 45-day kill class). The lower PRF for SPB-killed trees at 90 and 180 days after kill can be attributed to the lower veneer volume and grade and higher percentage of 4- and 8-foot random width veneer as shown in the tabulation below.
|Kill class||Cubic recovery||Veneer type|
|C & better
|Days||Percent||– – – – – – – – – – Percent of total – – – – – – – – – –|
|0 + 45||47.66||37.14||33.25||4.53|
|90 + 180||42.28||27.12||42.55||8.56|
Reduction in the amount of full-width veneer and increased amounts of random-width veneer translate into higher veneer processing costs for SPB-killed timber in the 90- and 180-day kill classes.
The lower initial moisture content of veneer from beetle-killed timber in combination with the increased permeability (due to effects of blue-stain fungi) results in overdried veneer when dried at normal green veneer schedules. Glue-line quality tests indicate that normal drying schedules, adhesives, and gluing practices may required modification to process beetle-killed timber. As pointed out earlier, best results could be achieved if veneer from SPB-killed timber could be segregated and processed separetly. This special handling would be justified if a sufficient volume of SPB-killed timber were processed.
Studies have shown that pulp yield dropped very little from beetle-killed pines dead up to 12 months in east Texas and up to 24 months in Virginia.5 Under proper processing methods, pulp yield differences between green and beetle-killed timber are minimal. However, special problems are created when processing dry, beetle-killed timber into pulp chips due to greater energy requirements at the chipper and the creation of more fine particles. Nonuniformity of chip sizes means that cooking condition need to be adjusted to produce the right kind of pulp. The low initial moisture content of chips is an obstacle to achieving uniform pulp. Dry chips require higher levels of alkali to reach the same screened yield and reduce the lignin content to the same level as that of pulp from fresh green wood. Achievement of uniform pulp treatment would require a change in operating techniques during digestion such as chip presteaming or a vacuum pretreatment cycle.
Comparisons of handsheet strength properties from Kraft pulp made from Class A and Class B beetle-killed wood indicate poorer burst, tear, and tensile strengths than from healthy woodpulp. Hitchings and Levi (1981) reported losses in tear strength of 30 to 35 percent for Class B chips. Burst and tensile strength levels were reduced by 20 to 25 percent from those with healthy material.
Particleboard – Research by Kelly et al. (1982) has shown that boards prepared from SPB-killed trees dead for 30 months in western North Carolina had bending, internal bond, screw withdrawal, hardness, water absorption, thickness swelling, and linear expansion properties similar to those of boards manufactured from healthy pine trees. All properties except linear expansion met industry specifications. Particleboards made from beetle-killed trees were darker in color than boards made from healthy trees. The difference was attributed to the blue staining of the beetle-killed wood.
Hardboard – Kelly et al. (1982) also reported that hardboard produced from beetle-killed trees was slightly inferior in quality to that from healthy trees. However, as with particleboards, linear expansion was the only property failing to meet industry specifications. When 50 percent of the fiber furnish came from healthy trees, the hardboards met specifications.
Reconstituted panels – Research has shown that composite products with flakeboard core and veneer faces can be made from beetle-killed timber, Koenigshof et al. (1984) reported that the only variables affecting performance of reconstituted panels made with oriented flake board cores were the density of the core and the resin level used in its construction. Panels were made from beetle-killed trees where deterioration class varied from "just attacked" to "having lost all needles and small branches." No mixes of flakes made from the various classes were detrimental to strength, durability, or moisture swelling properties of the panels.
The presence of blue-stained sapwood in beetle-killed trees presents no special technological problems in the manufacture of paneling, and the wide range of "character" marks in heavily deteriorated beetle-killed pine makes it attractive to many users for decorative purposes. Blue-stained paneling made from beetle-killed pine wood is now being manufactured and marketed successfully (Fig. 7). Although SPB-killed timber can be used for paneling, there are certain limitations to such use. First, the wood must be strong enough to survive the handling, sawing, and planing throughout the processing stages. Second, air drying is not sufficient to control woodboring beetles still alive in the tree at the time of harvest. The wood, therefore, must be kiln dried to temperatures higher than 180°F to assure an insect-free paneling product. The finished paneling can be left in its natural state or receive standard stain or varnish treatments.
Figure 7 – Paneling from southern
pine beetle-killed trees.
The demand for wood for use in home fireplaces and woodburning stoves has increased in recent years. It has long been believed that using southern pine as a fuel source for woodburning stoves produces excessive amounts of cresote. It is also commonly believed that the moisture content of the wood contributes to creososte production. Southern pine, therefore, has been generally rejected as a fuelwood for woodburning stoves. Allen and Maxwell (1982) studied the creososte production of beetle-killed pine and compared the results with those for green pine and hardwoods (seasoned and green) in the following tabulation:
|Wood type||Lbs creosote|
Although these results indicate that beetle-killed pine produced the greatest mass of creosote per ton of dry wood, their study concluded that the major factor controlling creosote production was the amount of air provided to the combustion process rather than the type or condition of the wood burned.
Developed by the University of Georgia Bugwood Network in cooperation with USDA Forest Service - Forest Health Protection, USDA APHIS PPQ, Georgia Forestry Commission, Texas Forest Service
and the Pests and Diseases Image Library - Australia
Last updated on Wednesday, August 09, 2006 at 01:35 PM
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