STUDIES IN FOREST PATHOLOGY: IX. FOMES IGNIARIUS DECAY OF POPLAR

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Abstract
Decay of Populus tremuloides and P. grandidentata caused by F. igniarius var. populinus was studied at the Petawawa Forest Expt. Sta., Ont., in stands up to 70 yrs. old. In eight l/10th acre sample plots representing stands 60-70 yrs. old, 28.6-69.2% of the trees were infected; the % of decay in the gross merchantable cubic vol. was 3.2-14.3 in the decayed trees, and 0.9-8.1 in decayed and sound trees considered together. Equally variable results were obtained in younger age classes. No relation between decay and site could be established on the basis of actual cubic volume, but when the trees were measured in board feet a slightly higher % of cull occurred on the poorer sites, owing at least partly to the smaller trees. Net periodic increment continued to increase in the 60-70-yr. age class on favorable sites. Sporophore-bearing trees died in the 2d and 3d yrs. after being girdled, and the original no. of mature living sporophores was reduced to 13% 6 yrs. after girdling. On similar trees that were felled and left intact on the ground during the same period the no. of sporophores increased. Artificial inoculations in both sapwood and heartwood of living trees resulted in the development of typical decay from which the pathogen was re-isolated. Observations on 5 to 18 sporophores from May 4 to June 30 of the following year proved that sporulation of F. igntarius is continuous from early spring to late autumn. There is not necessarily any period of inactivity during which new tube layers are formed, though irregular periods of 1 to several days without sporulation are common. Sporulation is favored by high relative humidity and high temp. The lowest temp. at which sporulation was observed was 40[degree]F.
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