摘要：Winter desiccation and mortality of coniferous foliage are important determinants of carbon balance in trees and thus can influence the location of the subarctic treeline ecotone. The purpose of this study was (i) to assess variation in winter desiccation and viability of first-year conifer needles at several heights and orientations along tree boles across the forest-tundra ecotone near Churchill, Manitoba, from 2008 to 2010, and (ii) determine if there is a noticeable influence of needle health on ongoing treeline advance in the area. Growing season air temperatures around Churchill were significantly cooler in 2009, resulting in the development of significantly shorter needles during 2010. Minimum epidermal conductance ( g min ) varied little with height on the tree or orientation to the prevailing wind direction. The highest values of g min occurred in 2010, when temperatures during the previous June ( t — 1) were 2.9 °C cooler than normal, and the lowest g min occurred during 2009 when June ( t — 1) was 1.2 °C warmer than normal. There were few correlations between needle viability and water content, and little consistency among years. However, significant correlations occurred during all 3 yr in northwest-facing needles at treeline, which suggests that treeline trees could be the most susceptible to water loss and dieback, relative to forest and tundra stems. Despite the occurrence of some winter desiccation, death of coniferous foliage (<10%) and sapling mortality (4–17%) was low, and rapid height growth of live saplings suggests passage through the wind-blown snow abrasion zone does not significantly impede wood production. Ostensibly winter desiccation and foliage mortality does not significantly influence sapling height growth and treeline dynamics around Churchill.
