The effect of soil disturbance on growth and ectomycorrhizae of Douglas-fir and western hemlock seedlings: a greenhouse bioassay

In a greenhouse bioassay of soils from the central Oregon Cascades, Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)seedlings had the most total and ectomycorrhizal root tips when grown in soil from an unburned clear-cut and the least whencrown in soil from (i) a 20-year-old plantation that had been clear-cut and burned in the late 1950's and (ii) one old-growthsorest. Tip formation was intermediate in soil from a second old-growth forest, a recently burned clear-cut, and a 40-year-old-..rural burn. Root weights followed the same trend, but top weights did not differ among the various soils. Ectomycorrhizal..nd total root tips of western hemlock (Tsuga heterophvlla (Raf.) Sarg.) were lowest in soils from the plantation and recently:-arned clear-cut. Unlike Douglas-fir, western hemlock's tip production was not greater in the unburned clear-cut than in theAd-orowth forest soils. In this species. both top and root weights varied according to soil, with the largest seedlings produced:n soil from the unburned clear-cut. With both species, there was a significant interaction between ectomycorrhizal type andoil type. Cenoco•cum geophilum Fr. predominated on western hemlock and was reduced in soils from the burned clear-cutand plantation. In comparison with the mean for all soils, ectomycorrhizal types that predominated on Douglas-fir wereenhanced in the unburned clear-cut soil and reduced in one old-growth soil, an effect apparently related to litter leachate.