GROWTH AND ECTOMYCORRHIZA FORMATION OF DOUGLAS-FIR SEEDLINGS GROWN IN SOILS COLLECTED AT DIFFERENT DISTANCES FROM PIONEERING HARDWOODS IN SOUTHWEST OREGON CLEAR-CUTS

Soil was sampled from sites clear-cut and broadcast burned 5 yr previously, poorly stocked with conifer reproduction, and occupied primarily by grasses, forbs, and scattered individuals of tanoak Lithocarpus densiflora, Pacific madrone Arbutus menziesii and canyon line oak Quercus chrysolepis. Five-month-old Pseudotsuga menziesii seedlings grown in media containing mineral soil collected beneath hardwood crowns had on average 60% greater height, 2.2 times greater weight (roots plus shoots), and almost 2 times more total and ectomycorrhizal short roots than seedlings grown in media containing soil collected >4 m from a hardwood. Rhizopogon sp. and Cenococcum geophilum dominated on seedlings grown in hardwood soils, and an unidentified brown ectomycorrhiza dominated on seedlings grown in open area soils. A study of soils collected at various distances from hardwoods indicated that the effect extended between 2-3 m. Average foliar N was slightly higher for seedlings grown in hardwood area than in open area soils, and rates of mineralizable N (anaerobic) were 2-6 times higher, and soil pH was higher. -from Authors