Many seeds in these cones wait to be released.

Fire is a boon to some species and a detriment to others. When fire sweeps across the landscape there are winners and losers.The cones of lodgepole pine (Pinus contorta) demonstrate adaptations that allow the species to survive potentially catastrophic changes.

Serotiny is an adaptation of some plants to release seeds in response to an environmental trigger. Serotiny is expressed in lodgepole pine through its cones. In fire prone habitats, lodgepole pine cones are glued shut by resin. Heat from fires melts the resin allowing the cone scales to separate and release seeds. Since it’s not safe to watch a wildfire burn through lodgepole pines, I placed a tightly sealed serotinous cone from a lodgepole pine in a toaster oven to watch how it responded to temperature changes.

The cone scales began to expand noticeably when the temperature reached about 50˚C (122˚F).  According to the U.S. Forest Service, more precise lab experiments have found the resinous bonds between the cone scales begin to break between 45˚C and 60˚C, so serotinous cones lying at or near the soil surface can also open with these ground temperatures. If this cone was kissed by fire its scales would have expanded and allowed the seed to be slowly released. (I let the temperature in the oven rise to over 200˚C (400˚F) just because I felt like watching the scales fully expand.) Serotinous cones collect on the ground or on tree branches for many years. The seeds under the scales lie in a state of dormancy, waiting for the opportunity to sprout.

Not all stands of lodgepole pines have serotinous cones. Serotinous cones are not common in eastern Oregon, rare in coastal populations, absent in some fire prone habitats like the Sierra Nevada, and “many stands in the Rockies have less than 50 percent serotinous-cone trees.” Wherever it grows through, lodgepole pine thrives in full sun. Its seeds sprout best in or on bare mineral soil and disturbed duff free of competing vegetation—the exact conditions many fires create.

After huge wildfires burned large swaths of Yellowstone National Park in 1988, lodgepole pine sprouted back in earnest. This NPS photo was taken ten years after the ’88 fires. The lodgepole trees are much larger now.

Serotiny in lodgepole pine makes large quantities of seeds available to germinate following a fire. In many cases, especially regarding lodgepole pines, fire may be an enemy to the individual, but not to the species.