Serotinous Cones

The more I learn about lodgepole pines (Pinus contorta), a Western species, the more I realize how complex and diverse this widespread conifer is. At least three, perhaps more, subspecies exist. Each of these subspecies vary depending on their environment.

Lodgepole pines along the coast are short, have heavy limbs and a twisted appearance. In the High Sierras the lodgepole pine can achieve an impressive girth and live for hundreds of years. The most common and best know subspecies is the inland, mountain form – small, straight and short lived. Forest fires help regenerate the inland variety.

Lodgepole pines, particularly the inland subspecies, have serotinous cones. Serotinus cones cling to the tree in a closed condition for several years. They do not open at maturity because of a resinous bond between the cone scales. In a forest fire, although the lodgepole pines may be totally destroyed the seeds in their protective cones remain protected. The resinous bonds are broken by temperatures of 113° F to 140 °F and the cone scales can open hygroscopically (take up moisture from the air). Lodgepole pine seeds remain viable for years within the sealed cone until released  by a forest fire.

Inland lodgepole pines produce and retain large numbers of both serotinous and open cones. Each year the open cones rain down thousands of small, winged seeds, while the closed or serotinous cones protect viable seeds until released by a forest fire. After a forest fire lodgepole pines can compete with more effective, shade-tolerant competitors because large numbers of their seeds germinate quickly and the trees grow rapidly. Sierra and coastal subspecies are less dependent on serotinous cones for their survival. Open lodgepole pine cones remain in the trees for many years after opening making it possible to see many seasons’ cones on the same branch.

Recently at both Medicine Lake (Siskiyou County CA) and Manzanita Lake (Lassen Volcanic National Park, Lassen County CA) I found lodgepole pines with open cones, closed cones and light-colored male strobili (male reproductive structures that produce pollen) growing next to each other.

Also see “Lodgepole Pine” 11-09-2011.

 

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2 Responses to Serotinous Cones

  1. Rockie says:

    I just thought a Pine cone was a pine cone….who knew.

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