Effects of high drying temperatures and restraint on twist of larch (Larix)

Abstract

During drying, timber changes its shape, mainly as a result of specific properties such as shrinkage anisotropy, radial differences in longitudinal shrinkage and spiral grain. The distortion, causing severe downgrading, can be reduced by restraining the timber and by using special drying schemes. The research described here is related to a project on the improvement of shape stability of Norway spruce. In the present part, different larch species from three stands were dried at high temperatures (80, 120 and 170°C). The effects of restraint during presteaming, drying and steaming on short-term twist reduction were investigated. The permanency of drying distortions was investigated in subsequent moisture cycling. Results showed a clear dependency of twist on the distance to pith. Restrained specimens sawn close to pith experienced reduced twist. This twist reduction was permanent during subsequent moisture variations. Drying temperature did not significantly influence twist and twist amplitude in moisture cycling.     

Effects of high drying temperatures and restraint on twist of larch (Larix)

During drying, timber changes its shape, mainly as a result of specific properties such as shrinkage anisotropy, radial differences in longitudinal shrinkage and spiral grain. The distortion, causing severe downgrading, can be reduced by restraining the timber and by using special drying schemes. The research described here is related to a project on the improvement of shape stability of Norway spruce. In the present part, different larch species from three stands were dried at high temperatures (80, 120 and 170°C). The effects of restraint during presteaming, drying and steaming on short-term twist reduction were investigated. The permanency of drying distortions was investigated in subsequent moisture cycling. Results showed a clear dependency of twist on the distance to pith. Restrained specimens sawn close to pith experienced reduced twist. This twist reduction was permanent during subsequent moisture variations. Drying temperature did not significantly influence twist and twist amplitude in moisture cycling.     

Effects of deforestation on microbial diversity in a Siberian larch(Larix sibirica) stand in Mongolia

For evaluating microbial community changes in a Siberian larch stand disturbed by forest fire or clearcutting,357 clones were randomly selected and sequenced using a culture-independent approach and 16S rRNA sequencing to characterize the bacterial composition and diversity from the different disturbed Siberian larch stands.Interestingly,the burned larch stand had an increase in the relative amounts of b-proteobacteria and Firmicutes and a decrease in Acidobacteria,while Gemmatimonadetes increased Verrucomicrobia decreased in the harvested larch stand.Microbial diversity and richness were higher in the undisturbed larch stand than the disturbed(burned or clear-cut)larch stands,and the influence of clear-cutting was more negative than that of the forest fire.This study indicates that evaluating the microbial diversity of undisturbed,burned,and clear-cutting Siberian larch stands provides information about the impact of forest disturbances on soil microbial communities,which may be helpful for understanding and evaluating soil health and devising reafforestation strategies for larch.     

Effect of growth on wood properties for Japanese larch (Larix kaempferi): Differences of annual ring structure between corewood and outerwood

To investigate the relations between growth and the wood properties of Japanese larch (Larix kaempferi), six sample trees of varied ages and radial growth were felled and the ring width, ring density, percentage of latewood, and some other factors were determined. There were significant differences in ring density and percentage of latewood between sample trees with vigorous growth and those with poor growth. In corewood the ring density decreased with increasing ring width for all sample trees, whereas in outerwood this trend did not appear. Moreover, the latewood width increased with the increment of ring width only in outerwood, whereas there was almost no change in the corewood. The variation in patterns of ring width, ring density, and percentage of latewood in the radial direction and the relation with height was also studied.Part of this report was presented at the 47th annual meeting of the Japan Wood Research Society, Kochi, April 1997