The Potential Role of Rime Ice Defoliation in Tree Mortality of Wave- Regenerated Balsam Fir Forests

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Abstract
(1) Overstorey mortality occurs rapidly and synchronously within the dieback zones of subalpine, wave-regenerated balsam fir (Abies balsamea (L.)Mill.) forests (fir waves) of the north-eastern United States. (2) Reductions in leaf area associated with dieback zone formation may cause increases in within-canopy windspeeds and rime ice deposition rates during winter storms, resulting in further foliage loss. (3) Field measurements in a fir wave on Mt. Moosilauke, New Hampshire, U.S.A., showed that rime ice deposition during winter storms and cumulative winter needle litterfall were greatest in the dieback zone. (4) One-year-old foliage had 56% lower photosynthetic capacity than current-year foliage. (5) Using reasonable assumptions, it was estimated that during the course of a single winter, the loss of stand-level potential photosynthetic capacity increased from 2.1% in a 13-year-old sapling stand to 7.5% in a 75-year-old dieback zone stand. (6) Repeated defoliation each winter may contribute to tree death by reducing whole-tree photosynthetic capacity.