Air Temperature, Heat Sums, and Pollen Shedding Phenology of Longleaf Pine
Abstract
Between 1957 and 1966, pollen shedding by longleaf pine (Pinus palustris Mill.) in southwestern Alabama peaked at dates ranging from February 23 to April 3. January 1 and 50°F was the combination of starting date and threshold air temperature that minimized annual variations in heat sums before the trees flowered. The heat sum required for peak pollen shedding declined as the season advanced. The regression Y = 19009 -89.26X, in which Y is the degree-hour heat sum above 50°F and X is days from January 1 through date of peak pollen shedding, accounted for nearly all observed annual variations in peak date. For the data from which the regression was computed, deviation of observed from expected date of peak pollen shed averaged 0.3 day. For eight subsequent observations, including two in North Carolina and one in northern Alabama, the deviation averaged 1.6 days.