Effect of Felling Time and Kiln-Drying on Color and Susceptibility of Wood to Mold and Fungal Stain During an Above-Ground Field Test

Nasko Terziev, Julius Boutelje

Abstract


The study shows how the content of low-molecular-weight (LMW) sugars, sugar alcohols, starch, and nitrogenous compounds in Scots pine trees in winter and spring and their subsequent redistribution during drying of timber affect color and susceptibility to fungi during above-ground exposure.

One tree from pairs of Scots pine was felled, sawn, and dried in winter, whereas the other was processed in spring. The content of soluble carbohydrates and nitrogen and also the color of timber surface were measured before and after drying. An above-ground test was carried out to show differences in susceptibility of winter- and spring-felled and dried timber to fungi.

The total content of LMW sugars was 1.59 times higher in winter than in spring. Sucrose was the most common sugar in the living tree at both sampling occasions. The content of oligosaccharides was higher in winter; in spring they were hydrolyzed to monosaccharides. The content of two sugar alcohols was negligible. Starch content rose significantly in spring. Nitrogen content in winter and spring was not significantly different.

Drying enriched the timber surface (0-3-mm zone) with LMW sugars and nitrogen, whereas the deeper zones had an almost constant content of soluble substances. The content of accumulated soluble substances in the 0-3-mm zone after drying was approximately proportional to their content in similarly located wood at the time of felling.

An important practical consequence of the redistribution of LMW sugars and nitrogen is the increased susceptibility to mold. The surfaces of winter-felled and dried timber were more susceptible to mold growth than those of spring-felled and dried timber.

The measured colors on the surfaces of winter- and spring-felled and dried pine timber were not significantly different. At the same time, distinct color differences between regions beside and within sticker marks were observed. It is concluded that the accumulation of water-soluble substances influences the surface color, but a certain difference in concentration has to be exceeded to obtain significant differences in color.


Keywords


above-ground test;color;drying;felling time;fructose;glucose;mold;nitrogen;<i>Pinus sylvestris</i> L;starch;sucrose

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