Calculation of heat storage in stems

A method for calculating heat storage in tree stems from measured ambient air temperatures is described. The method is easy to use also for sites where the variation in the stem radii is large. The results are exact provided the thermal properties of the stems are constant, the temperature field within the stems has radial symmetry, and the stems are in radiative equilibrium with their surroundings. Either the stem surface temperature or the temperature of the surrounding air can be used as input. For the latter case, an exact solution involving a surface resistance is derived. The method has been applied to a pine plantation in Fiji, where the calculated heat storage was compared to the storage inferred from the measured stem temperatures. Despite non-ideal conditions, the overall correspondence is good.