Heat Accumulation: An Easy Way To Anticipate the Flowering of Southern Pines

Abstract

Abstract Accumulation of degree-day heat sums accounts for most of the year-to-year variation in dates of peak pollen shed by slash (Pinus elliottii Engelm.), longleaf (P. palustris Mill.), loblolly (P. taeda L.), and shortleaf (P. echinata Mill.) pines. During 19 years of observation for longleaf and 6 years for each of the other species, the average deviation of observed from predicted peak date was four days or less. Slash pine had the greatest range among years in date of peak flowering (45 days), followed by longleaf (40 days), loblolly (23 days), and shortleaf (20 days). Male strobili of slash pine developed without pause. except on cold days, after their emergence in late November or early December. Longleaf, however, had a period of winter dormancy that averaged about one month, and loblolly and shortleaf were dormant about two months during winter. Only the pollen shed periods of longleaf and loblolly pines overlapped during this study. Differences in heat and dormancy requirements apparently preclude overlap between longleaf and slush pines, or between shortleaf and any of the others.