Asymmetric diurnal cycles in forests and the calculation of heat sums

Heat sums are frequently used as a scale to measure physiological development or as a parameter to describe a particular environment. Calculation of heat sums frequently assumes a sinusoidal diurnal cycle. Examination of data from forest canopy gaps shows that the diurnal cycle in these areas is highly asymmetric and that this asymmetry affects the accuracy of heat sum calculations. The degree of asymmetry depends on gap size, location in the gap, and time of year. This study presents analysis of heat sums and asymmetry, examining methods to quantify relationships between asymmetry and heat sum errors.