Diversity of ectomycorrhizas in old-growth and mature stands of Douglas-fir (Pseudotsuga menziesii) on southeastern Vancouver Island




Goodman, Douglas Mark

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Concern about potential losses of biological diversity and productivity following clear-cut logging of old-growth forests in British Columbia led me to compare ectomycorrhizas in old-growth and mature stands of Douglas-fir. Two sites were selected, each with an old-growth (288-, 441-yr-old) and a mature stand (87-, 89-yr-old) well-matched in tree species, soil and topography. A total of 120 soil cores ≤15 cm deep by 5 cm diameter were taken at random from four 60 m square plots (one per stand). Samples were taken in spring and fall at each site. All morphological types of ectomycorrhizas in one half of each core were counted and characterized in detail. Ectomycorrhizal abundance and frequency was compared in logs, stumps, the forest floor over bedrock or gravel, the forest floor near the base of trees, the forest floor elsewhere, and mineral soil. Old-growth and mature stands were very similar in richness, diversity and types of ectomycorrhizas. Sixty-nine types of ectomycorrhizas were described. Nineteen types each accounted for more than one percent of the 17,500 ectomycorrhizal root tips examined, and eighteen types were found in five or more of the 120 soil cores. Extrapolation indicates a total richness of roughly 100 types in the four plots. Co-dominant fungi were Cenococcum geophilum Fr. (24% of all ectomycorrhizal root tips), a Rhizopogon Fr. of the section villosuli (10%), Hysterangium vitt. (9%), Lactarius deliciosus (Fr.) S.F.G. (6%), and Piloderma fallax (Libert) Stalpers (4%). Cenococcum geophilum, Rhizopogon Fr. and L. deliciosus were abundant in both mineral soil and organic substrates, Piloderma fallax was associated with decayed wood, and Hysterangium and type 27 were in organic substrates only. A bright greenish-yellow felty type was found in 5 cores in mineral soil only. The similarity of the ectomycorrhizal communities of old-growth and mature stands was probably due to their proximity ($<$200 m apart) and the similarity of their vegetation and soil. Differences may occur at some sites if ectomycorrhizal succession has been delayed or redirected as a result of frequent or severe disturbance, lack of old-growth legacies (logs and stumps), or lack of old-growth stands from which fungi can disperse.



Douglas fir, British Columbia, Vancouver Island, growth, Douglas fir, British Columbia, Vancouver Island, morphology