© 2000 Heron Publishing—Victoria, Canada
Rapid freezing injury in red spruce: seasonal changes in sensitivity and effects of temperature range
G. R. Strimbeck (1) and D. H. DeHayes (1)
1. School of Natural Resources, University of Vermont, Burlington, VT 05405, USA / Received March 5, 1999
Summary
On calm, cold days in winter, sun-exposed needles of red spruce (Picea rubens Sarg.) may warm 10 to 20 °C above ambient air temperature, and undergo rapid (≥ 1 °C min–1) fluctuations in temperature as light breezes or passing clouds alter the energy balance of the foliage. It has been proposed
that the resulting rapid freeze–thaw cycles (freezing stress) cause a type of winter injury in montane red spruce that is
characterized by necrosis of sun-exposed foliage. In autumn and winter, we monitored rapid freezing stress response of needle
sections from 10 montane red spruce trees by subjecting needles to rapid freezing over the temperature span typically recorded
in the field. In autumn, experimental rapid freezing stress produced severe injury only at temperatures considerably lower
than expected for that time of year. In winter, rapid freezing caused occasional, moderate injury in fully hardened foliage
of trees susceptible to both slow and rapid freezing. Seasonal changes in sensitivity to rapid and slow freezing were correlated,
suggesting that environmental factors that are known to affect sensitivity to slow freezing may also affect sensitivity to
rapid freezing. Experimental manipulation of the start and end temperatures of rapid freezing stress events showed that moderate
to severe needle injury can occur in susceptible trees at temperature spans slightly more extreme than those typically recorded
in the field. The extent of injury was similar at different starting temperatures if rapid freezing occurred over the same
temperature span. Year-old foliage was consistently less sensitive to rapid freezing stress than current-year foliage, but
some year-old foliage was damaged when the rapid freezing stress regime caused severe injury in current-year foliage. We conclude
that rapid freeze–thaw cycles can explain light to moderate injury of current-year foliage, but they do not explain the more
severe and widespread pattern of foliar damage that has occurred intermittently over at least the last 18 years.
Keywords:
forest decline, Picea rubens, solar radiation, temperature fluctuation, winter injury.
