© 1993 Heron Publishing—Victoria, Canada
Midwinter needle temperature and winter injury of montane red spruce
G. R. Strimbeck (1, 2), A. H. Johnson (1) and D. R. Vann (1)
1. Department of Geology, University of Pennsylvania, Philadelphia, PA 19104, USA / 2. School of Natural Resources, University of Vermont, Burlington, VT 05405, USA / Received June 25, 1992
Summary
To assess the role of solar warming and associated temperature fluctuations in the winter injury of sun-exposed red spruce
foliage, we used fine wire thermocouples to monitor midwinter needle temperature in the upper canopy of mature red spruce
trees over two winters. In 1989–1990, 15-min mean temperatures were recorded for six needles in a single tree. In 1990–1991,
10-min mean temperatures of six needles in one tree, and 1-min mean temperatures of seven needles in a second tree were recorded
during rapid temperature changes. Warming was more frequent and greatest on terminal shoots of branches with a south to southwest
aspect. The maximum rise above ambient air temperature exceeded 20 °C, and the maximum one minute decrease in temperature
was 9 °C, with maximum rates of 0.8 and 0.6 °C min–1 sustained over 10- and 15-min intervals, respectively. These data demonstrate that red spruce is subject to rapid temperature
fluctuations similar to those known to produce visible injury in American aborvitae, a much hardier species. We concluded
that solar warming to temperatures above the freezing point was unlikely to result in dehardening and subsequent freezing
injury, because warming
was infrequent, of short duration, and did not always raise needle temperature above the freezing point. Parts of branches
and some individual shoots were frequently covered by snow or rime that may have prevented injury by reducing the frequency
or intensity of needle temperature fluctuations. Radiation load on exposed shoots may have been increased by reflection of
short wave radiation from snow and rime deposits on surrounding surfaces, which would exacerbate temperature fluctuations.
Keywords:
cold hardiness, foliar temperature, forest decline, needle injury, rapid cooling, solar warming.
