China Cedar:Specs

From Bwf

Decay resistance of China Cedar (Cunninghamia lanceolata (Lambert) Hooker)

Camille Freitag J.J. Morrell

China Cedar (Cunninghamia lanceolata) grows at higher elevations in many areas of southeast Asia, particularly in southern China, Laos, and Vietnam. This species has a reputation for producing naturally durable heartwood and has been extensively planted in China (Kunshan et al. 2005). Many of these plantations are reaching harvestable ages and a number of importers have begun to bring this material into the United States for use as decking and other exterior decorative applications where durability is desired. While China Cedar has a reputation for durability, there are concerns among potential users that this second-growth material may lack the durability of lumber from old-growth trees since there is evidence of this effect in other wood species (Taylor et al. 2002). In order to assess the potential decay resistance of these materials, the following study was undertaken.

Materials and Methods

China Cedar lumber was evaluated in three separate tests over a three-year period. Boards where randomly selected from shipments into the United States and 19-mm cubes were cut from the heartwood in each board. In all, 15 boards were evaluated in the 3 tests and 12 blocks were cut from each board. In addition, 19-mm cubes were cut from ponderosa pine sapwood (Pinus ponderosa Laws) and western red cedar (Thuja plicata D Donn.) boards. The pine blocks served as decay-susceptible controls, while the western red cedar served as a positive, decay resistant comparator (Scheffer and Morrell 1998). The blocks were oven dried (103 C) and weighed prior to being briefly soaked, and then sterilized by exposure to 2.5 mrad of ionizing radiation from a cobalt 60 source. The blocks were then exposed to either Gloeophyllum trabeum (Pers ex. Fr.) Murr (Isolate Madison 617) or Trametes versicolor (L ex. Fr.) Pilat (Isolate FP 101,664-Sp) in a soil-block test according to procedures described in American Wood Preservers’ Association Standard E10 (AWPA 2004).


Results and Discussion

Weight loss controls for ponderosa pine controls exposed to G. trabeum ranged from 7.2 to 44.5 percent. In several instances, weight losses for the pine blocks were somewhat lower than would normally be found in a decay test, particularly for the G. trabeum exposures; however, weight losses were generally high enough to delineate differences in decay resistance. The lowest weight losses for this fungus were found in Test 2 and appeared to reflect excess moisture in the pine blocks, which may have inhibited fungal attack. Moisture levels in the China-fir blocks were not excessive, leaving us to include these results in our study. Weight losses for western red cedar heartwood averaged –0.35 and 0.32 percent for G. trabeum and T. versicolor, respectively, illustrating the excellent decay resistance of this species. Mean weight losses for China-fir blocks exposed G. trabeum ranged from –1/36 to 1.71 percent and the blocks were largely free of fungal attack at the end of the test period. Weight losses for blocks exposed to T. versicolor varied more widely from a low of –0.49 to 11.49 percent. In general, samples exposed to white-rot fungus experienced low weight losses, but boards from three blocks experienced mean weight losses from 7.28-11.49 percent. It is unclear why these boards were so much more susceptible to fungal attack, especially to a white-rot fungus, although it is possible that some sapwood was inadvertently included in these samples or that these boards were cut from zones of the heartwood that were less durable (blocks were only cut from zones free of visible sapwood). White-rot fungi typically cause lower weight loss on coniferous woods than brown rotters in this test. This variation may reflect the natural range of decay resistance of wood of this species. Based upon the weight losses obtained, the material examined would be classified as highly decay resistant according to the ASTM Standard classification.

The results of this test were then compared with those from pine sapwood and western red cedar hardwood. Decay resistance was classified using the scale described in ASTM Standard D2017 where highly resistant hardwood experiences 0-10 percent weight loss, resistant woods 11-24 percent weight loss, moderately resistant woods 25-44 percent weight loss, and non-resistant woods experience weight losses greater that 45 percent (ASTM 2001). Our method differed slightly because we used an arbitrary 12-week test, while the ASTM method is based upon the weight loss of pine sapwood controls.

Conclusion

Although there was some variation in the durability of the individual boards, the china-fir evaluated in these studies was classified as highly resistant to fungal attack, a classification that is similar to that given to western red cedar.

Literature Cited

American Society for Testing and Materials (ASTM). 2001. Standard 

 method of accelerated laboratory test of natural decay resistance
 of woods. Standard D 2017 In: ASTM Annual Book of Standards, 
 volume 4.10 Wood. ASTM, West Conshohocken, PA. pp. 322-326.

American Wood Preservers’ Association (AWPA). 2004. Standard 

 method of testing wood preservatives by laboratory soil-block cultures.
 Standard E10-01. In: AWPA Book of Standards. AWAP, Selma, AL
 pp. 406-414.

Kunshan, S.L. Zhinyang, L. Fenming, and Z. Rui. 2005. Asia Pacific 

 Forestry sector outlook study. Working Pap. Series. Working Pap. 
 No. APFSOS/WP/14. United Nations, Food and Agriculture 
 Organization, Rome, Italy. 56pp.

Scheffer, T.C. and J.J. Morrell. 1998. Natural durability of wood: A 

  Worldwide checklist of species. Res. Contibution 22, Forest Res.
  Lab., Oregon State Univ., Corvallis, OR. 58pp.

Taylor, A.M. B.L. Gartner and J.J. Morrell. 2002. Heartwood formation 

  and natural durability- a review. Wood and Fiber Sci. 34(4):587-611.
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