Site and soil characteristics related to the incidence and spread of Inonotus tomentosus

Inonotus tomentosus (Fr.) Teng causes tomentosus root disease in spruce trees throughout the boreal and sub-boreal forests of central and northern British Columbia. Site and soil characteristics are related to the incidence and spread of this fungus in the Sub-Boreal Spruce, wet-cool subzone (wkl) located near Prince George, British Columbia. Two-hundred and ninety-six plots, 25.2 meters in diameter, were examined to determine the incidence of I. tomentosus, and several ecosystem variables were measured. These included site series, soil moisture regime, soil nutrient regime, mesoslope position, soil texture, soil coarseness, humus form, spruce density, tree species composition and soil pH. The incidence of I. tomentosus infection ranged from none to 31% of spruce trees per plot. Significant differences (p<0.05) in percent infection were found between site series, soil moisture regimes, edatopic grid cell and mesoslope positions. Non-significant trends were observed between infection incidence, and soil nutrient regimes and humus form. The soil pH did not influence the incidence of infection. However, when the pH of soil samples adjacent to uninfected and infected roots were compared, it was determined that I. tomentosus may effect adjacent soil pH, possibly changing it to a more optimal growth level. The interactions between ecosystem variables are discussed as they relate to the incidence and spread of tomentosus root disease. The most important variables influencing the distribution of I. tomentosus are suggested to be: 1) the availability of oxygen in the soils as regulated by the moisture regime and mesoslope position; 2) the rooting depth of spruce trees, which is related to the soil nutrient regime and humus form; 3) the number of root contacts that occur between susceptible roots. Evidence is also presented that indicates .r. tomentosus is a disturbance agent which may be capable of altering the site series of an area.