Observations on the Temperatures of Arctic Plants and Their Environment

Abstract

Thermocouple measurements on Salix arctica leaves at Resolute, North West Territroy (75[degree]N) show that they are warmed by sunlight to an extent which varies[long dash]depending primarily on the height of the sun in the sky [long dash], but which commonly amounts to several degrees Centigrade and is significant even at midnight during the "midnight sun" period. The maximum difference between leaf and air temperatures (at midday) is, however, less than that reached in temperate and tropical regions. During the nights which occur later in the season, leaf temperatures fall slightly below air temperatures. The warming effect of sunlight is reduced by wind; crude sheltering of an insolated leaf may increase its temperature by several degrees Centigrade. Diurnal fluctuations in soil and air temperatures occur even during the "midnight sun" period (contrary to statements in the literature); the fluctuations are, however, of smaller amplitude than those of lower latitudes, and the minimum occurs at an especially early hour. Some observations on the effect of soil type and aspect on soil temperatures in arctic regions are recorded. In the region within a few centimeters of the soil surface [long dash]where plants grow in arctic lands[long dash]relatively high temperatures occur on clear days; at "night", this layer is slightly cooled. Gradients established by day in the soil and air near ground level become inverted at "night", as in temperate regions. Because of this special temperature microclimate near the ground surface, and because of the direct effect of radiation on plant temperatures (especially in clear weather) meteorological screen records give an unsatisfactory estimate of the temperatures of arctic plants.