Ectomycorrhizal mushroom distribution by stand age in western hemlock – lodgepole pine forests of northwestern British Columbia

Commercial forest rotations are usually shorter than natural disturbance return intervals, which could affect the distribution of ectomycorrhizal fungal (EMF) species dependent on late-seral stands. We examined this potential reduction in species richness by comparing ectomycorrhizal mushroom communities across four age-classes (pole stage, young, mature, and old growth) of western hemlock (Tsuga heterophylla (Raf.) Sarg.) – lodgepole pine (Pinus contorta Dougl. ex Loud.) stands on submesic sites in northwestern British Columbia. Almost 130 species of ectomycorrhizal mushrooms were identified over the 12 sites during the 3-year study period. EMF richness was lowest in pole stands and almost twice as high in the older age-classes. Species composition and abundance were related to stand age, with relatively large differences in communities between the ages of 20 and 120 and relatively smaller differences between 120 and 225 years. Twelve species, including the economically important pine mushroom (Tricholoma magnivelare (Peck) Redhead), were late-seral stand dependent, fruiting in forests that are at least older than 85 years. This distribution of ectomycorrhizal mushrooms across stand ages suggests EMF succession is primarily an accumulation of species and is likely affected by differences in dispersal by ectomycorrhizal fungi, soil properties (increased soil acidity and reduced nitrogen availability), and the rate of stand development. The evidence for EMF species limited to late-seral stands supports the maintenance of some mature forests within these landscapes to conserve EMF richness.