First-year survival of Tsuga heterophylla without mycorrhizae and subsequent ectomycorrhizal development on decaying logs and mineral soil

Roots of western hemlock (Tsuga heterophylla) seedlings 1-5+ years old that had established naturally on logs in threestates of decay or on mineral soil were compared for numbers and kinds of ectomycorrhizae. Mycobionts colonizing root systemsincluded Cenococcum geophilum Fr., Piloderma croceum (Bres.) Erikss. & Hjorts. , and four unidentified fungi distinguished bycolor and morphology. About half the seedlings surviving the first growing season (2-7 months) were nonmycorrhizal.Nonmycorrhizal seedlings were most frequent on the least decayed logs. However, mycotrophy appeared to be advantageous tohemlock; 1st-year mycorrhizal seedlings had shoots 60% longer and roots 47% longer than 1st-year nonmycorrhizal seedlings.All 2nd-year and older seedlings were mycorrhizal. The ability of western hemlock to survive the first growing season withoutmycorrhizae may contribute to its success in colonizing decaying logs, which may contain microsites devoid of effectiveectomycorrhizal inocula.