Effects of ectomycorrhizal inoculants on survival and growth of interior Douglas-fir seedlings on reforestation sites and partially rehabilitated landings

We studied the effects of commercially available (Laccaria laccata (Scop.:Fr.) Berk. & Br. and Rhizopogon parksii Smith (Oregon source)) and native (R. parksii (British Columbia source)) ectomycorrhizal (EM) inoculants on the survival and growth of commercially grown interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) seedlings outplanted on reforestation sites (burned piles and clearcuts) and partially rehabilitated (shallow- and deep-tilled to a depth of 15 and 50 cm, respectively) landings. We also examined the physical and chemical properties of the soil and the EM status and foliar element levels of noninoculated Douglas-fir seedlings to provide information on the growing conditions found on these types of sites. Inoculation treatments did not significantly increase survival and growth of Douglas-fir seedlings 2 years after outplanting. However, because the average percent EM colonization of inoculated seedlings at time of outplanting was low (36%), the beneficial effects of these inoculants may not have been attained. It is possible that nursery conditions partially account for the low EM colonization of inoculated seedlings. We therefore suggest that nurseries try to modify growing conditions to favor good EM formation before outplanting interior Douglas-fir. Benefits of inoculations on landings may have been restricted by the poor soil conditions, potentially toxic levels of Fe and Al, and competition from well-adapted native EM fungi.