UBC Theses and Dissertations

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UBC Theses and Dissertations

Western hemlock regeneration on coarse woody debris is facilitated by linkage into a mycorrhizal network in an old-growth forest Orrego, Gabriel


Western hemlock (Tsuga heterophylla (Raf.) Sarg.) is the climax tree species in most of the low elevation Pacific northwest coastal forests. Regeneration of western hemlock under a closed canopy it is tightly associated with coarse woody debris (CWD). Nurse-logs contain physical, chemical and biological features that make them the most suitable seedbed for hemlock in old-growth forests. However, the preference of western hemlock for CWD is still not completely understood. Few studies have investigated belowground dynamics related to western hemlock growing on decayed wood, specifically ectomycorrhizal (EM) associations and the potential access to a mycorrhizal network (MN). My research addressed two objectives: 1) To compare establishment and survival of western hemlock germinants among different microsites (CWD with different wood breakdown levels and forest floor) in the forest understory; and 2) To investigate whether carbon is transferred through mycorrhizal networks from mature trees to seedlings established on CWD. To accomplish this, I pulse-labeled ¹³C-glucose solution into the phloem of mature trees. I found that western hemlock successful recruitment was associated with the presence of medium to advanced decay classes of CWD. I also found the first evidence that there is carbon transfer from mature trees to regenerating seedlings established on CWD. I conclude that western hemlock regeneration on nurse-logs is facilitated by mycorrhizal networks of canopy trees in an old-growth forest of coastal British Columbia.

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