Damage by Tomentosus root rot in white spruce plantations in Ontario, and the effects of thinning on the disease

Abstract

Mortality caused by Inonotus tomentosus (Fr.) Teng (Tomentosus root rot) to dominant and codominant trees was found in all but one of 17 white spruce (Picea glauca [Moench] Voss) plantations 43–58 years old. Even though mortality usually commences at 30–35 years, younger trees can be killed. An average of 0.7% of white spruce were killed annually over the 6-year study period.Average accumulated mortality of dominant and codominant trees was 10.3 % for all plantations. Butt cull in remaining living trees averaged 13.8% of gross merchantable volume in two plots that had been clearcut at Searchmont, Ontario. Observations of the stumps of clearcut trees at Searchmont revealed that 56% of the trees had been infected. At Petawawa, Ontario, significantly higher proportions of trees were killed by I. tomentosus, and there were higher numbers of sporophores of this fungus in unthinned than in heavily thinned plantations. Tomentosus root rot also killed trees in 35- to 60-year-old plantations of black spruce (P. mariana [Mill.] B.S.P.), red spruce (P. rubens Sarg.) and Norway spruce (P. abies [L.] Karst.). Circumstantial evidence is presented that indicates Tomentosus root rot was introduced into plantations as I. tomentosus basidiospores.