Content area
Full Text
Abstract
The decay resistance of China-fir (Cunninghamia lanceolata) was evaluated in several tests using white- and brown-rot fungi in an American Wood Preservers' Association soil-block test. Although there was some variation in weight loss among boards, China-fir heartwood was found to be similar in decay resistance to western redcedar (Thuja plicata) and should be classified as highly decay resistant.
China-fir (Cunninghamia lanceolata (Lambert) Hooker) 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 decorative exterior applications where durability is desired. While China-fir 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-fir lumber was evaluated in three separate tests over a 3-year period. Boards were 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 redcedar heartwood (Thuja plicata D Donn.) boards. The pine blocks served as decay-susceptible controls, while the western redcedar served as a positive, decay-resistant comparator (Scheffer and Morrell 1998).
The blocks were ovendried (103°C) and weighed prior to be being briefly soaked, and then sterilized by exposure to 2.5 mrad of ionizing radiation from...