The effects of some factors on the natural resistance of pine and spruce sapwood against fungal decay and against attack of house-longhorn beetle larvae have been studied in laboratory tests and the results are evaluated by analysis of variance and regression analysis. Following conclusions were reached: Wood from summer-felled trees did not have a lower inherent natural durability against fungal decay and house-longhorn beetle than wood from winter-felled trees. Storage of pine logs in water had no significant effect on the weight losses obtained in laboratory tests with Gloeophyllum sepiarium and Fomitopsis pinicola but reduced the weight losses obtained with Phlebiopsis gigantea very significantly. In the case of outdoor use of wood, this result implies that the decreased nutritive value of wood from water-stored logs for certain fungi to some extent compensates for the effect of increased permeability. Wet storage also reduced the growth of house-longhorn beetle larvae. The effects of density on weight loss by fungal decay were different for the three test fungi. The growth rate of the house-longhorn beetle larvae in the inner sapwood was much lower than that in the outer sapwood. In comparison with between-trees variation and with differences between outer and inner sapwood the other observed effects, each on its own account, are of minor practical importance for larval growth.

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