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

Abstract

Decay of Populus tremuloides Michx. and P. grandidentala Michx. caused by Fomes igniarius var. populinus (Neuman) Campbell was studied at the Petawawa Forest Experiment Station, Ont., in stands up to 70 years of age. In eight [Formula: see text] acre sample plots representing stands 60 to 70 years old, 28.6 to 69.2% of the trees were infected; the percentage of decay in the gross merchantable cubic volume was 3.2 to 14.3 in the decayed trees, and 0.9 to 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 percentage 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-year age class on favorable sites. Sporophore-bearing trees died in the second and third years after being girdled, and the original number of mature living sporophores was reduced to 13% six years after girdling. On similar trees which were felled and left intact on the ground during the same period the number 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. igniarius 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 one to several days without sporulation are common. Sporulation is favored by high relative humidity and high temperature. The lowest temperature at which sporulation was observed was 40° F.