This afternoon I just couldn’t decide what to write about, and then in flew inspiration: an e-mail from PBSC Interim VP for Academic Affairs Dr. Ginger Pedersen about a state champion challenger slash pine near PBIA , and an old stand of uncut pines in Dade County. So I’m now in a pine kinda mood, and that’s a nice way to be. Long ago in this blog we looked at slash pine, the turpentine industry, and the nasty toxaphene insecticide spin-from that. Today it’ll just be pretty pine trees.
Two native pines grace our immediate area, Sand Pine in scrub habitats, and Slash Pine all over the county. Divided into two varieties, the latter species is native throughout Florida and across much of the southeastern U.S., and cultivated worldwide in warm climates for turpentine, pulp, and wood. Variety elliottii is in North and Central Florida and in nearby states. Variety densa, with heavier wood and a fire-resistant grassy stage, is mostly in southern Florida, and their natural ranges don’t overlap much.
Pines are tough and diverse, a hundred species resisting drought, poor soils, and extreme weather from the far north to the equator. Very few true pines occur naturally in the southern hemisphere (although the name “pine” gets applied to many posers).
Pines have weird wind-dispersed pollen grains with two airbags suggesting Mickey Mouse ears. The pollen ears possibly help orient the grain for its job of fertilizing the egg in the young cones, which take 3 years to mature. Anyone who has parked under a pine in the spring has brushed the yellow pollen off the windshield. It comes from small papery male cones that bust apart and evaporate. The female cones are big and woody, and release wafer-thin windblown seeds from between the scales if squirrels don’t chew the cones up.
Slash Pines maintain fungal root associates. Perhaps sometimes in relation to those symbiotic fungi, the trees often don’t like certain suburban yards, altered water regimes, ozone, over-fertilized soil, alkaline soil, irrigation that renders the soil alkaline, and a number of insect pests.
Many types of trees to varying degrees shed lower branches from the trunk. Some snap off cleanly, others break irregularly and decay. Slash Pine is a leader in branch shedding, although the anatomical-physiological mechanisms are unstudied. Most observers interpret the self-pruning as an adaptation to keep the upper canopy safely above ground fires. Whether fire induces branch loss directly is unclear. Pines have unusual growth responses to stresses, making stress a suspect in forcing branches to fall. As another possibility, aging pine needles lose function, so that old ones may fail to keep their branches alive.
Slash pines have additional fire adaptations, such as young variety densa with grassy needles wrapped protectively around the bud, and when older by having fire-resistant bark. Back in the Cretaceous Period when dinosaurs ruled, conifers helped rule, and forest fires became common. Botanist Tianhua He and collaborators have shown fire adaptations in pines to date back into dinosaur days eons before Florida was here to have pine woods.