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.
Wandering at Large 
Very interesting Mike….thank you for the time lapse of the cone opening! This is one new thing I learned today!
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Very good article and excellent demonstration….thank you
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Love the demonstration! I’m glad you are there to do things like that as it had never occurred to me.
It’s interesting that the lodgepole in the Sierras aren’t serotinous. I wonder how that will effect regeneration in Yosemite as compared with Yellowstone. When we were in Yellowstone in 2012, i was concerned by the amount of fallen dead wood on the ground. It seemed like a scary amount of fuel for future fires. It also seemed to be breaking down very slowly.
We were driving through Kootenay National Park in 2007 and stopped to talk with a ranger at one of the pullouts. We were on a ridge overlooking a forest of struggling pine trees (I did not note the species in my journal) and she explained that the lifespan of the trees is 80 – 120 years and they were reaching the end of their lifespan so pine beetles were, in some sense, taking the place of fire in the ecosystem. Hopefully, those pines did not have serotinous cones!
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The info on serotiny in the Sierra Nevada came from the U.S. Forest Service Silvics Manual. I was surprised to read that too. Next time I visit that area, I’ll be looking for lodgepoles to confirm the info.
In forests that don’t experience frequent fire serotinous cones are often absent. If the habitat you visited in Kootenay doesn’t burn often, then I’d be willing to bet the trees’ cones were not serotinous. In Katmai, where natural wildfires are extremely rare, insect outbreaks are one of the major agents of forest change.
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Tangential to lodgepole pines, but really fascinating, I was remembering an article I read in Bay Nature magazine about the recovery of Mt. Diablo from the Morgan Fire. I went to look for the article and there is an entire webpage on different aspects of fire recovery. This will probably keep me busy through December and it seems like something you might enjoy as well.
https://baynature.org/diablo/
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Ty Mike for this experiment and your blog!
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Thanks for another great article. Nature will heal itself if we will only allow it to do so.
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Mike, Was interesting to see the cone expand. Do the Sierra Redwoods also have serotiny cones? Really surprised the serotiny cones were rare in Eastern Oregon. We frequently camp there and I cannot remember one summer without forest fire. I do not know if this is a factor but after large forest fires in Eastern Oregon we have seen gov’t workers actually cleaning up all the debri off of the forest floor, almost looks swept clean. Not the same policies obviously as the Nat’l. Parks. As always your blogs are thought provoking – good to always keep learning. Thanks. 🙂
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Giant sequoias do have some serotinous cones, but not all trees produce them. I have a giant sequoia cone from a tree planted in Seattle that opened as it dried out on a bookshelf.
Like the reference for a lack of serotinous cones in Sierra lodgepole pines, that info came from the U.S. Forest Service Silvics Manual. I was surprised to read that too, especially since it is also a fire prone area.
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