Winter and early spring microclimate of a subalpine spruce-fir forest canopy in central New Hampshire

Abstract

Recent evidence suggests that the decline of red spruce in the northeastern United States is directly related to freezing injury during winter. As part of a study on the relationship between red spruce decline and winter conditions, within-canopy micrometeorological measurements were taken in a subalpine red spruce ( Picea rubens Sarg.)-balsam fir ( Abies balsamea (L.) Mill.) forest on Mt Moosilauke in central New Hampshire during the winter and early spring of 1990 and during the late fall, winter and early spring of 1991. At 880- and 1010-m elevation in 1990 and at 880-m elevation in 1990–1991, solar radiation and relative humidity were recorded at one height within the canopy, and air temperature and wind speed were recorded at two heights within the canopy. Hourly mean and maximum temperatures were slightly greater in the upper canopy than in the lower canopy. Both the maximum (26.1°C) and minimum (−27.6°C) temperatures of the study were recorded in the upper canopy at the 1010-m elevation study site. The maximum temperature drop that occurred within one hour and also spanned freezing was 9°C. Temperature minima below −35°C and much greaer rapid temperature drops are believed to be necessary to cause or induced red spruce freezing injury. It appears that conditions during the study period were not severe enough to cause freezing injury; this conclusion was supported by the relatively small amount of visible injury observed in the periods following the study. These data on winter microclimate in a spruce-fir forest should be of value to investigators studying freezing injury and to other forest scientists.