Role of Winter Water Relations in Determining the Upper Elevational Limits of Three New England Conifers

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9603860 Boyce Evergreen conifers, unlike diciduous trees, must keep their foliage alive during the winter. In addition to freezing stress, they must deal with drought, or desiccation. A lot of water is found in the winter environment, but it is usually locked up as snow and ice and is unavailable to plants. Conifer foliage is adapted to minimize water loss during the winter; losses are replaced during above-freezing periods, when water stored in the wood melts and can flow into the foliage. Shorter growing seasons at high elevations decrease foliar resistance to winter water loss, while the frequency and duration of warm periods in the winter also decreases. Thus, the amount of water lost increases, while the ability to replace it decreases. Winter desiccation appears to cause alpine treeline in some places. However, its role in setting the upper elevational limits of conifers that do not extend all the way to treeline is poorly known. This study will examine the foliar winter water relations, or water balance, of three important New England conifers that differ in location preferences and growth strategies: white pine, eastern hemlock and red pine. Our preliminary data suggest that the older foliage in these species may experience damaging water levels during the winter. We will use physiological measurements of trees collected near their upper elevational limit to determine desiccation stress. These data will be coupled with climatic data collected at the research sites to predict water relations. This approach may be extended to other species and under conditions imposed by a changing climate.