Treatability of Native Softwood Species of the Northeastern United States

Transcription

1 United States Department of Agriculture Forest Service Forest Products Laboratory Research Paper FPL-RP-8 Treatability of Native Softwood Species of the Northeastern United States Lee R. Gjovik David R. Schumann

2 Abstract Several softwood species of the northeastern United States could have greater commercial value if they could be treated with preservatives. Balsam fir, eastern spruce, and eastern hemlock are candidate species. However, these species are susceptible to spruce budworm attack. In this study, we explored whether wood from dead (defoliated) or dying (partially defoliated) trees of these species could be treated successfully with ammoniacal copper arsenate or chromated copper arsenate. We also studied the relationship of treatability to growth rate in three other softwood species (red pine, white pine, and eastern larch), which vary from slow grown (naturally grown) to fast grown (plantation grown). For all species, we studied the effect of incision on penetration and retention of preservative. Our results demonstrate the positive influence of incising to improve preservative penetration of refractory species. Keywords: Waterborne preservatives, wood preservation, ACA, CCA, treatability, northeastern softwood species, refractory species, eastern spruce, eastern hemlock, eastern white pine, eastern larch, red pine, incising, penetration, retention, spruce budworm February 1992 Gjovik, Lee R.; Schumann, David R Treatability of native softwood species of the northeastern United States. Res. Pap. FPL-RP-8. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 20 p. A limited number of free copies of this publication are available to the public from the Forest Products Laboratory, One Gifford Pinchot Drive, Madison, WI Laboratory publications are sent to more than 1,000 libraries in the United States and elsewhere. The Forest Products Laboratory is maintained in cooperation with the University of Wisconsin.

3 Treatability of Native Softwood Species of the Northeastern United States lee R. Gjovik, Research Specialist, Wood Preservation David R. Schumann, Technology Transfer Coordinator, State & Private Forestry Forest Products Laboratory, Madison, Wisconsin Introduction The commercial value of several softwood species of the northeastern United States could be increased if they could be treated to meet existing American Wood- Preservers Association (AWPA) Standards (AWPA 1986). These species include eastern spruce (red, white, and black [Picea rubens Sarg., P. glauca (Moench) Voss, and P. mariana (Mill.) B.S.P.]), balsam fir (Abies balsamea (L.) Mill.), eastern hemlock (Tsuga canadensis (L.) Carr.), red pine (Pinus resinosa Ait.), eastern white pine (Pinus strobus L.), and eastern larch (Larix laricina (Du Roi) K. Koch). Several of these species are susceptible to spruce budworm attack; balsam fir and eastern spruce are the most susceptible and are often killed by the budworm. Smith (1986) studied the treatability of red pine, eastern white pine, eastern hemlock, Norway spruce, (Picea abies [L.] Karst), European larch (Larix decidua Mill.), and bigtooth aspen (Populus grandidentata Michx.) and the effects of incising upon treatability. All specimens were treated with type-c chromated copper arsenate (CCA) via full-cell impregnation. Incising caused significant retention gains in eastern hemlock, Norway spruce, and European larch. Sapwood penetration was good in each species; significant heartwood penetration was found in eastern white pine. Gjovik (1983) compared CCA and ammoniacal copper arsenate (ACA) treatment of Douglas-fir (Pseudotsuga menziessii [Mirb.] Franco) and Engelmann spruce (Picea engelmannii Parry ex Engelm.). We studied the effect of incising on preservative penetration and retention in several softwood species. We also studied whether wood from dead or dying trees could be successfully treated with preservatives. Balsam fir, eastern spruce, and eastern hemlock at varying levels of budworm attack from undefoliated to percent defoliated-were examined for treatability. The wood was visually examined to exclude decayed wood. The treatability of three other softwood species (red pine, white pine, and eastern larch) was examined in relationship to growth rate (slow or fast grown). The question was whether relatively fast-grown wood accepts preservatives any differently than does naturally grown wood. Stake test plots have been established at the Harrison Experimental Forest, Saucier, Mississippi, and in Cumberland Center,. Maine. In addition, exposure decks have been fabricated at the Harrison Experimental Forest and in Amherst, Massachusetts. Replicates of all test species and conditions, including untreated controls, are represented in the test plots and decks. Both the stakes and deck material have been monitored annually, and the results will be reported in the future. Procedure Test Specimens All test material was collected in May 1984 from three sawmills in New England. Eastern spruce and balsam fir were obtained from the Mountain View Lumber Company (West Burke, VT) and P & R Lumber Company (Wolcott, VT). Eastern hemlock, eastern larch, red pine, and eastern white pine were obtained from the R. Leon Williams Lumber Company (East Eddington, ME). All logs were marked on the ends with colored paint in the lumber yard or at the time of logging. Thus, the test material was tracked through the sawmill and into final dimension. The lumber was then shipped to Madison, Wisconsin. If possible, the logs were quarter-sawn. This provided an adequate supply of edge-grain samples and allowed us to select heartwood. Edge-grain samples are desirable because they provide more consistent results by eliminating variation caused by cross grain. Heartwood was selected because the heartwood of most species is difficult to treat. If the heartwood of a species can be treated, the sapwood can most likely be treated as well.

4 Table 1 Alphanumeric designation of test specimens Position of character Identification Code Figure 1 Incising pattern. Eastern spruce and balsam fir trees were selected on the basis of budworm attack: (1) undefoliated (healthy), (2) approximately percent defoliated, and (3) percent defoliated (dead, but not decayed). Eastern hemlock trees were selected on the basis of only two conditions: undefoliated and percent defoliated. The extent of defoliation was determined by a subjective visual evaluation of the crown of the standing tree. Red pine, white pine, and eastern larch were selected from natural stands and plantations. Growth rate was determined by comparing annual growth rings per inch (25.4 mm). When the material arrived at the Forest Products Laboratory, it was kiln dried to a moisture content of 10 to 12 percent and then surfaced on four sides into nominal 2- by 4-in. (standard 38- by 89-mm) test specimens. Portions of each test specimen were incised with 60 oyster-shaped incisions per square foot (0.09 m 2 ). The incising pattern is shown in Figure 1. Each specimen was marked with a 6-part alphanumeric designation, as described in Table 1. An example of marked test specimens is shown in Figure 2. Preservatives The preservatives selected for this study were ammoniacal copper arsenate (ACA) and chromated copper arsenate (CCA). Water-borne salt preservatives were used because refractory species are more difficult to treat with water-borne preservatives than with oil-borne preservatives. This is particularly true of CCA. All specimens were treated by the full-cell process, using the schedules shown in Table 2. The lower pressure (125 lb/in 2 (861 kpa) was used for the treatment of eastern spruce and balsam fir to avoid cell-wall collapse. The other species (red pine, eastern white pine, First Second a Third Fourth Fifth Sixth Species Extent of budworm attack Growth rate Log series Sequence of pieces cut from log End-match as related to incising Location of final specimen F balsam fir A eastern hemlock L eastern larch R red pine S eastern spruce W eastern white pine 1 undefoliated 2 approximately -percent defoliated 3 -percent defoliated 1 fast grown 2 slow grown 1 (butt log), 2, 3,... A, B, C,... 1 unincised 2 unincised 3 incised 4 incised 1 1st piece from log center 2 2d piece... a The treatability of balsam fir, eastern spruce, and eastern hemlock was evaluated on the basis of extent of budworm attack. Bed pine, white pine, and eastern larch were evaluated on the basis of growth rate. eastern hemlock, and eastern larch) were treated using the higher pressure (1 lb/in 2 (1,034 kpa)). All wood specimens were precisely molded to 1.44 by 3.44 in. (36.58 by mm) and precision endtrimmed to in. (457 mm). This procedure allowed a single volume for each and every specimen. Thus, the preservative retentions obtained during weighing of the specimens were very accurate. Each specimen was weighed before and after treatment to determine the preservative or chemical oxide retention in pounds per cubic foot (16 kg/m 3 ). The treating solution concentrations were analyzed and calculated in accordance with the AWPA Standards (1986) and held constant at 2.5 percent oxide basis. 2

5 Table 2 Preservative treatments Solution Vacuum Time Pressure temperature Final Preservative a (inhg) (kpa) (min) (lb/in 2 ) (kpa) ( F) ( C) vacuum ACA None 1 1,034 CCA Amb. Amb. None 1 1,034 a ACA is ammoniacal copper arsenate; CCA is chromated copper arsenate. purple-blue when copper is present and a salmon color when copper is absent. The preservative penetration patterns for all the test species are shown in the figures in Appendix A. Figure 2 Alphanumeric designation of test specimens. Figure shows designation of two nominal 2- by 4-in. (standard.8- by mm) specimens cut from third log of undefoliated hemlock tree. The compositions of the preservatives were as follows: ACA 49.2 percent copper oxide.8 percent arsenic pentoxide CCA 47 percent chromium trioxide 19 percent copper oxide 34 percent arsenic pentoxide Analysis of Treatability After preservative treatment, the specimens were dried before being examined for preservative penetration. To prepare the specimens for analysis, a 0.5-in. (12.7-mm) cross-section was removed from the center of each 18-in. (457-mm) length. One 9-in. (229-mm) end-piece was cut lengthwise to show penetration of the preservative along the grain. Figure 3 illustrates how the test specimens were prepared for analysis. Specimens were then placed on a rack and sprayed with a solution of 0.5 percent chrome azurol S, an indicator stain for copper (AWPA 1986); this indicator turns The percentage of preservative penetration in each specimen was determined by subjective visual evaluation of the cross-sectional area. The tables in Appendix A show values for individual specimens. These values can be compared to the penetration patterns illustrated in the figures. Statistical Analysis Because the variables of preservative penetration and retention were not normally distributed, nonparametric tests were used in the analysis. Two tests were conducted. The first test was designed as a factorial: two preservatives (ACA and CCA), two incising conditions (incised and unincised), three species (eastern spruce, balsam fir, and eastern hemlock), and three foliation conditions (undefoliated, -percent defoliated, and -percent defoliated). (Note: For the remainder of this report, the term partially defoliated refers to -percent defoliated and the term totally defoliated to -percent defoliated.) The second test was a factorial with the same preservatives and conditions as in the first analysis, three different species (red pine, eastern white pine, and eastern larch), and two growth rate conditions (fast-grown and slow-grown). Levels of significance for the tests are shown in Appendix B. Heartwood was also considered in the testing even though we attempted to obtain all the samples from heartwood. Some specimens of undefoliated eastern spruce, undefoliated and partially defoliated red pine, and partially defoliated eastern larch contained sapwood (Appendix A; Tables A1, A9, A10, A14). However, the analysis showed that the small amount of sap wood did not have a significant effect on the penetration and retention of the preservatives. 3

6 in undefoliated eastern hemlock and eastern larch, totally defoliated eastern spruce, and undefoliated and partially defoliated red pine. Figure 3 Preparation of test specimen for analysis of treatability. Results and Discussion Our results demonstrate the positive effect of incising on preservative penetration of refractory species. For the 20 replicate samples, incising also reduced the variation in retention in most cases. Both ACA and CCA penetrated more deeply into incised wood compared to unincised wood under most conditions, Undefoliated eastern larch, eastern hemlock, and red pine, and undefoliated and partially defoliated white pine had highly significant incisingpreservative interactions for penetration. Likewise, preservative retentions were significantly greater in incised wood than in unincised wood. Highly significant incising-preservative interactions for retention occurred in undefoliated eastern larch and eastern hemlock, totally defoliated eastern spruce, and undefoliated and partially defoliated red pine. When the effect of the preservative type was significant, ACA penetrated the wood deeper than did CCA, with the exception of partially defoliated red pine. The effect of preservative was insignificant for partially defoliated balsam fir and totally defoliated eastern hemlock. Highly significant incising-preservative interactions occurred in undefoliated eastern hemlock, eastern larch, and red pine, and undefoliated and partially defoliated white pine. An anomaly exists with regard to red and white pine. In both species, CCA penetrated better than ACA. To our knowledge, this is contrary to general opinion. The effect of ACA retentions was also significantly greater than that of CCA retentions with two exceptions: undefoliated and partially defoliated white pine. The effect of preservative was insignificant for partially and totally defoliated balsam fir, totally defoliated eastern hemlock, and undefoliated eastern spruce. Highly significant incising preservative interactions occurred The analysis of the incising-preservative interactions indicated that in undefoliated eastern hemlock and eastern larch, the preservatives had a highly significant effect on penetration of the incised specimens. Ammoniacal copper arsenate penetrated the deepest. On the other hand, in undefoliated red pine and undefoliated and partially defoliated eastern white pine, the preservative effect was highly significant in the unincised specimens. In these specimens, CCA penetrated deeper than ACA. The effect of the incising-preservative interaction on retention was significant in undefoliated eastern hemlock, undefoliated and partially defoliated eastern larch, and totally defoliated eastern spruce, regardless of whether the trees were incised. The ACA retentions had a greater effect than the CCA retentions, except for undefoliated eastern hemlock. For red pine, the preservative effect was highly significant for only unincised specimens, and CCA retentions had a greater effect than ACA retentions. The data indicate that ACA penetrated eastern spruce, balsam fir, eastern hemlock, and eastern larch better than did CCA (see Appendix A; Tables A1-8 A13, A14). Retentions of both CCA and ACA were consistently higher in white pine than in red pine. It is noteworthy that white pine heartwood was quite treatable. Smith (1986) reported similar results. This would indicate that incising of white pine, as currently recommended by AWPA standards (1986), may not be necessary. Most red pine lumber, like Southern Pine, contains predominantly sapwood and is relatively easy to treat. As the data indicate, the heartwood of red pine was more difficult to treat than that of white pine. Retentions of CCA and ACA were the lowest in eastern larch. Even though the analysis showed no significant effect of defoliation, retention of both CCA and ACA in eastern hemlock was substantially better in the test material taken from the totally defoliated trees. This same trend was true for the balsam fir, but not as pronounced. However, the reverse was true for eastern spruce. Retention levels were consistently higher for both CCA and ACA in material taken from undefoliated, healthy eastern spruce. The growth rate of the material (fast or slow) apparently had no appreciable, consistent, or significant effect on either preservative retention or penetration in any of the three species tested: red pine, white pine, and eastern larch. 4

7 Acknowledgments Partial funding for this study was provided by the Canadian-United States Spruce Budworm Project. Many people provided help and support. The assistance of Apolonia Bocanegra-Severson in preparing specimens for treatment and importing data and David Gutzmer in treating specimens is deeply appreciated. This project had substantial support from outside the Forest Products Laboratory as well. These individuals and firms include the following: Harold Bumby, Maine Wood Treaters, Inc.; Steve Clark, Northeastern Lumber Manufacturers Association; Robert Doyen, Mt. View Lumber Company; Jack Dwyer, Vermont Department of Forest Parks and Recreation; Barry Goodell, University of Maine College of Forest Resources; William Haynes, Hatheway and Patterson Company, Inc.; Kenneth Kilborn, USDA Forest Service, Northeastern Area State and Private Forestry; Paul O Reilly, Furman Lumber, Inc.; Victor Patoine, P & R Lumber Company; Dr. William Rice, University of Massachusetts, Department of Forestry and Wildlife Management; Dr. James Shottaffer, University of Maine College of Forest Resources; Dr. William Smith, SUNY College of Environmental Science and Forestry; and Melvin Williams, R. Leon Williams Lumber Company. Appendix A. Preservative Penetration Patterns The tables and figures in Appendix A show the penetration patterns for chromated copper arsenate (CCA) and ammoniacal copper arsenate (ACA) for the test species and various growth conditions. The values in the tables can be compared to the penetration patterns in the corresponding figures. Each figure shows 80 test specimens. Specimens are arranged horizontally by preservative (ACA or CCA) and condition (incised or unincised). The vertical columns are arranged such that the four specimens in each column are end-matched in nearly all cases. The figures show the effect of the preservative and incising on treatability. References American Wood-Preservers Association Book of Standards. Standards A-2, A-3, and C-2. Stevensville, MD: American Wood-Preservers Association. 240 p. Gjovik, L.R Treatability of southern pine, Douglas-fir, and Engelmann spruce heartwood with ammonical copper arsenate and chromated copper arsenate. In: Proceedings, American Wood-Preservers Association. Vol. 79. Smith, W.B Treatability of several northeastern species with chromated copper arsenate wood preservative. Forest Products Journal. 36(78):

8 Table A1 Preservative retention and penetration in undefoliated eastern spruce Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetrawood (%) (lb/ft 3 ) a (%) (%) (lb/ft 3 ) a (%) (%) (lb/ft 3 ) a (%) (%) (lb/ft 3 ) a (%) (Mean) 0.97 (SD) b (0.21) 0.63 (0.39) 1.08 (0.15) 0.87 (0.27) a 1 lb/ft3 = 16 kg/m 3. b SD, standard deviation. Table A2 Preservative retention and penetration in partially defoliated eastern spruce Incised Heart- Reten- Penetrawood tion tion (%) (lb/ft 3 ) (%) Unincised Heart- Reten- Penetrawood tion tion (%) (lb/ft 3 ) (%) Incised Unincised Heart- Reten- Penetra- Heart- Reten- Penetrawood tion tion wood tion tion (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (Mean) 0.64 (SD) (0.16) (0.29) (0.16) 0.61 (0.26) 6

9 Table A3 Preservative retention and penetration in totally defoliated eastern spruce Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetrawood (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (Mean) 0. (SD) (0.13) 0.42 (0.19) 0.93 (0.12) 0.63 (0.16) Table A4 Preservative retention and penetration in undefoliated balsam fir Heart- Reten- Penetra- Heart- Reten- Penetra- Heart Reten- Penetra- Heart- Reten- Penetrawood (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (Mean) 0.92 (SD) (0.07) (0.08) (0.07) (0.10) 7

10 Table A5 Preservative retention and penetration in partially defoliated balsam fir Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetrawood (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (Mean) (SD) (0.13) (0.22) (0.21) (0.17) Table A6 Preservative retention and penetration in totally defoliated balsam fir Heart- Retenwood Penetra- Heart- Reten- Penetra- Heart- Reten- Pentra- Heart- Reten- Penetra- (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (Mean) (SD) 1.05 (0.17) 0.79 (0.19) 1.04 (0.11) 0.82 (0.18) 8

11 Table A7 Preservative retention and penetration in undefoliated eastern hemlock Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetrawood (%) (lb/ft 3 ) (%) (%) (lb/ft) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (Mean) (SD) (0.07) (0.08) (0.13) (0.06) Table A8 Preservative retention and penetration in totally defoliated eastern hemlock Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetrawood (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (Mean) (SD) (0.16) (0.25) (0.11) 0.67 (0.20) 9

12 Table A9 Preservative retention and penetration in fast-grown red pine Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetrawood (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (Mean) 0.60 (SD) (0.21) (0.17) (0.11) (0.13) Table A10 Preservative retention and penetration in slow-grown red pine Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Pentra- Heart- Reten- Penetrawood (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (Mean) (SD) (0.13) (0.12) (0.09) (0.04)

13 Table A11 Preservative retention and penetration in fast-grown eastern white pine Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetrawood (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (Mean) 1.05 (SD) (0.07) (0.07) (0.08) 0.71 (0.10) Table A12 Preservative retention and penetration in slow-grown eastern white pine Chromated copped arsenate Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetrawood (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (Mean) 1.05 (SD) (0.04) 0.96 (0.09) 0.99 (0.07) 0.76 (0.17) 11

14 Table A13 Preservative retention and penetration in fast-grown eastern larch Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetrawood (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (Mean) (SD) 0.38 (0.04) (0.21) (0.05) 0.36 (0.09) Table A14 Preservative retention and penetration in slow-grown eastern larch Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetra- Heart- Reten- Penetrawood (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (%) (lb/ft 3 ) (%) (Mean) (SD) (0.14) (0.07) (0.10) (0.08) 12

15 Figure A1 ACA and CCA preservative penetration patterns for undefoliated eastern spruce. Figure A2 ACA and CCA preservative penetration patterns for -percent defoliated eastern spruce. 13

16 Figure A3 ACA and CCA preservative penetration patterns for -percent defoliated eastern spruce. Figure A4 ACA and CCA preservative penetration patterns for undefoliated balsam fir. 14

17 Figure A5 ACA and CCA preservative penetration patterns for -percent defoliated balsam fir. Figure A6 ACA and CCA preservative penetration patterns for -percent defoliated balsam fir. 15

18 Figure A7 ACA and CCA preservative penetration patterns for undefoliated eastern hemlock. Figure A8 ACA and CCA preservative penetration patterns for -percent defoliated eastern hemlock. 16

19 Figure A9 ACA and CCA preservative penetration patterns for fast-grown red pine. Figure A10 ACA and CCA preservative penetration patterns for slow-grown red pine. 17

20 Figure A11 ACA and CCA preservative penetration patterns for fast-grown white pine. Figure A12 ACA and CCA preservative penetration patterns for slow-grown white pine. 18

21 Figure A13 ACA and CCA preservative penetration patterns for fast-grown eastern larch. Figure A14 ACA and CCA preservative penetration patterns for slow-grown eastern larch. 19

22 Appendix B. Results of Statistical Analysis The tables in Appendix B show the effects of individual test variables on treatability and the effects of interactions between variables. Table B1 Significant effects of variables on treatability a Species Balsam fir Eastern hemlock Eastern larch Eastern spruce Red pine Eastern white pine Condition b Preservative treatment Foliation or Penetration (%) Retention (lb/ft 3 ) c Penetration (%) Retention (lb/ft 3 ) growth rate I U α I U α ACA CCA α ACA CCA α Undefoliated % defoliated NS d NS % defoliated NS Undefoliated Significant interaction for penetration α = Significant interaction for retention α = % defoliated NS NS Fast-grown Significant interaction for penetration α = Significant interaction for retention α = Slow-grown Undefoliated NS % defoliated % defoliated Significant interaction for retention α = Fast-grown Significant interaction for penetration α = Significant interaction for retention α = Slow-grown Significant interaction for retention α = Fast-grown Significant interaction for penetration α = Slow-grown Significant interaction for penetration α = a Results of significant interactions are shown in Table B2. b I is incised, U is unincised. Values are means. c 1 lb/ft 3 = 16 kg/m 3. d Not significant. Table B2--Significant effects of interactions between variables on treatability a Species Foliation or growth rate Penetration (%) Retention (lb/ft 3 ) ACA CCA α ACA CCA α ACA CCA α ACA CCA α Eastern hemlock Undefoliated NS Eastern larch Fast-grown NS Eastern spruce % defoliated Red pine Fast-grown NS NS Slow-grown NS Eastern Fast-grown NS white pine Slow-grown NS a Values are means.