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Growth increment, chemical composition and cellulose ultrastructure of Douglas-Fir stem wood formed under artificial longitudinal compressive loading Kim, Chung Tae

Abstract

A Douglas-fir stem was artificially subjected to longitudinal compressive load equivalent to an estimated green weight of its crown. The wood subsequently formed under the load was compared with that produced before treatment and above the point of loading after seven growing seasons following treatment. The rate of incremental growth was considerably reduced in both volume and weight, while wood density somewhat increased. Holocellulose and alpha-cellulose yields increased and lignin content decreased. A higher holocellulose crystallinity and a smaller cellulose microfibril angle were observed. These changes were immediate and more apparent in the first 2 years after treatment, then there was a recovery to seemingly normal growth increments. The recovery was confounded with possible effects of the changed wood distribution during the 2 consecutive years immediately following treatment. There were marked differences in the responses of incremental growth zones and also at different heights in the loaded stem with respect to the point of loading. The differences could be explained by the expected magnitude of applied stress and resultant strain. It was concluded that the longitudinal compressive stress due to tree weight, to a large extent, influences wood formation and plays a role limiting stem growth, especially its volume. Stem form and the distributional patterns for wood characteristics within a stem are basically shaped by the stress.

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