Microclimatology of treeline spruce–fir forests in mountains of the northeastern United States

The objective of this study was to characterize the temporal and altitudinal variation in microclimate of high elevation spruce–fir (Picea rubens–Abies balsamea) forests in three major mountain ranges of the northeastern United States. Mean lapse rates of air temperature were comparable to those previously reported for this region, but lapse rates varied considerably in relation to diurnal (and, to a lesser degree, seasonal) effects. Mean annual soil temperatures and soil temperature heat sums did not show a consistent pattern with regard to elevation. Within our study region, it has been suggested that frequent cloud immersion at high elevation results in radiation fluxes at that are dramatically reduced compared to those at mid and low elevation, but results of this study appear not to support this hypothesis. The frequency of very high (≥90%) relative humidities increased with elevation, but although clear-sky fluxes of photosynthetically active radiation increased moderately with increasing elevation, mean mid-day fluxes during the growing season were almost identical between mid and high elevation