Pine Cones Are Like Hangars for Pine Tree Seeds

Over the past year I’ve written about the making of pine tar and the drinking of pine needle tea. But why stop there? Pines are a fascinating group of plants, worthy of myriad more posts, and so my exploration into the genus continues with pine cones and the seeds they bear.

Pines are conifers and, more broadly, gymnosperms. They are distinct from angiosperms (i.e. flowering plants), with the most obvious distinction being that they don’t make flowers. Since they are flowerless, they are also fruitless, as fruits are seed-bearing structures formed from the ovary or ovaries of flowering plants. Pines do make seeds though, and, as in angiosperms, pollen is transported from a “male” organ to a “female” organ in order for seeds to form. Rather than being housed in a fruit, the seeds are essentially left out in the open, which is why the term “naked seeds” is frequently used in reference to gymnosperms.

seed cone of Scots pine (Pinus sylvestris ‘Glauca Nana’)

In the case of pines and other conifers, the seeds may be naked, but they’re not necessarily homeless. They have the protection of cones, which is where the female reproductive organs are located. Male, pollen cones are separate structures and are smaller and less persistent than the cones that house the seeds. A cone, also known as a strobilus, is a modified branch. A series of scales grow in a spiral formation along the length of the branch, giving the cone its shape. On the inside of these scales is where the seeds form, two per scale. First they are egg cells, and then, after pollination and a period of maturation, they become seeds. The scales protect them throughout the process and then release them when the time is right.

With more than 120 species in the genus Pinus, there is great diversity in the size, shape, and appearance of pine cones. While at first glance they don’t appear all that different from one another, the cones of each species have unique characteristics that can help one identify the pine they fell from without ever having to see the tree. Pine cones are also distinct from the cones of other conifers. For one, pine cones take at least two or, in some cases, three years to reach maturity, whereas the cones of other conifers develop viable seeds in a single year. Pine cones are also known to remain on the tree for several years even after the seeds are mature – in some species up to 10 years or more – and they don’t always part with their seeds easily. Lodgepole pines (Pinus contorta) require high temperatures to melt the resin that holds their scales closed, the cones of jack pine (P. banksiana) generally only open in the presence of fire, and the seeds of whitebark pine (P. albicaulis) are extracted with the aid of birds (like Clark’s nutcracker) and other animals.

immature seed cone of lodgepole pine (Pinus contorta)

Every pine cone is special in its own right, but some stand out in particular. The largest and heaviest pine cones are found on Coulter pine (P. coulteri), measuring up to 15 inches long and weighing as much as 11 pounds with scales that come to a sharp point. It’s understandable why the falling cones of this species are frequently referred to as widowmakers. Longer cones, but perhaps less dangerous, are found on sugar pine (P. lambertiana). The tallest trees in the genus, the cones of sugar pine consistently reach 10 to 20 inches long and sometimes longer.

Pine tree seeds are a food source for numerous animals, including humans. Most are so small they aren’t worth bothering with, however, several species have seeds that are quite large and worth harvesting. Most commercially grown pine nuts come from stone pine (P. pinea) and Korean pine (P. koraiensis). In North America, a wild source for pine nuts is found in the pinyon pines, which have a long history of being harvested and eaten by humans.

immature seed cone of ponderosa pine (Pinus ponderosa)

The seeds of many pines come equipped with little wings called samaras, which aid them in their dispersal. Upon maturity, pine cone scales open and release the seeds. Like little airplanes leaving the hangar, the seeds take flight. Wind dispersal is not an effective means of dispersal for all pines though. A study published in Oikos found that seeds weighing more than 90 milligrams are not dispersed as well by wind as lighter seeds are. When it comes to long distance dispersal, heavier seeds are more dependent on animals like birds and rodents, and some pines rely exclusively on their services. The author of the study, Craig Benkman, notes that “bird-dispersed pines have proportionately thinner seed coats than wind-dispersed pines,” which he points out in reference to Japanese stone pine (P. pumila) and limber pine (P. flexilis), whose seeds weigh around 90 milligrams yet rely mostly on birds for dispersal. Benkman suspects that the seeds of these two species “would probably weigh over 100 milligrams if they had seed coats of comparable thickness as wind-dispersed seeds.”

Whitebark pine, as mentioned above, holds tightly to its seeds. Hungry animals must pry them out, which they do. Pine seeds are highly nutritious and supplement the diets of a wide range of wildlife. Some of the animals that eat the seeds also cache them for later. Clark’s nutcrackers are particularly diligent hoarders, harvesting thousands more seeds than they can possibly consume and depositing them in small numbers in locations suitable for sprouting.

Even large seeds that naturally fall from their cones have a chance to be dispersed further. As the seeds become concentrated at the base of the tree, ground-foraging rodents gather them up and cache them in another location, which Benkman refers to as secondary seed dispersal.

Particularly in pine species with wind dispersed seeds, what the weather is like helps determine when the hangar door will open to release the flying seeds. When it is wet and rainy, the scales of pine cones close up. The seeds wouldn’t get very far in the rain anyway, so why bother? When warm, dry conditions return, the scales open back up and the seeds are free to fly again. You can even watch this in action in the comfort of your own home by following the instructions layed out in this “seasonal science project.”

immature seed cones of limber pine (Pinus flexilis)

mature seed cones of limber pine (Pinus flexilis)

Further Reading:


Photos of pine cones were taken at Idaho Botanical Garden in Boise, Idaho

Making the Case for Saving Species

It is no question that the human species has had a dramatic impact on the planet. As our population has grown and we have spread ourselves across the globe, our presence has altered every ecosystem we have come into contact with. Our footprints can be detected even in areas of the planet uninhabited by humans. As awareness of our impact has increased, we have made efforts to reduce it. However, much of the damage we have caused is irreversible – we can’t bring species back from extinction and we can’t replace mountaintops. Furthermore, for better or for worse our continued existence – despite efforts to minimize our negative influence – will continue to be impactful. This is the nature of being human. It is the nature of all living things, really. As John Muir said, “when we try to pick out anything by itself, we find it hitched to everything else in the Universe.” That we are cognizant of that fact puts us at a crossroads – do we make a concerted effort to protect and save other species from the negative aspects of our presence or do we simply go on with our lives and let come what may?

The quandary isn’t that black and white, obviously. For one thing, cleaning up polluted air, water, and soil is beneficial to humans and has the side benefit of improving the lives of other species. Protecting biodiversity is also in our best interest, because who knows what medicine, food, fiber, or other resource is out there in some living thing yet to be discovered that might be useful to us. On the other hand, putting our own interests aside, what about protecting other species and habitats just to protect them? Purely altruistically. That seems to be the question at the crux of an article by Emma Marris in the May/June 2015 issue of Orion entitled, “Handle with Care: The Case for Doing All We Can to Save Threatened Species.” [Listen to a brief discussion with Marris about the article here.]

The main character in Marris’ article is the whitebark pine (Pinus albicaulis), a species whose native habitat is high in mountain ranges of western United States and Canada. Whitebark pines thrive in areas few other trees can, living to ages greater than 1,000 years. Here is how Marris describes them:

Whitebark pine’s ecological niche is the edge of existence. The trees are found on the highest, driest, coldest, rockiest, and windiest slopes. While lodgepole and ponderosa pine grow in vast stands of tall, healthy-looking trees, slow-growing whitebarks are tortured by extremes into individualized, flayed forms, swollen with massive boles from frost damage. Their suffering makes them beautiful.

photo credit:

photo credit:

But in recent years they have been suffering more than usual. White pine blister rust, an introduced pathogen, is killing the trees. The native mountain pine beetle is also taking them out. Additional threats include climate change and an increased number, extent, and intensity of wildfires. Combined, these threats have been impactful enough that the species is listed as endangered on the IUCN Red List where it is described as “experiencing serious decline.”

So people are taking action. In Oregon’s Crater Lake National Park, botanist Jen Beck is part of an effort to select blister rust resistant trees and plant them in their native habitats within the park. Hundreds have been planted, and more are on their way. Great effort is taken to minimize human impact and to plant the trees as nature would, with the vision being that blister rust resistant trees will replace those that are dying and that trees with rust resistant genes will dominate the population.

But Beck faces opposition, and not just from challenges like seedlings being trampled by visitors or a warming climate inviting mountain hemlocks and other trees into whitebark pine’s native range, but by people who argue that the trees shouldn’t be planted there in the first place – that what is “wild” should be left alone. Marris specifically calls out a group called Wilderness Watch. They and other groups like them profess a “leave-it alone ethic.” Rather than be arrogant enough to assume that we can “control or fix disrupted nature,” we should respect the “self-willed spirit of the wild world.” Proponents of nonintervention criticize what they call “new environmentalism” and its efforts to engineer or manage landscapes, fearing that these actions are “morally empty” and that “rearranging bits of the natural world” lacks soul and will ultimately serve to benefit humans.

In her article, Marris argues against this approach. First off, the human footprint is too large, and for natural areas to “continue to look and function the way they did hundreds of years ago” will require “lots of human help.” Additionally, nonintervention environmentalism “perpetuates a false premise that humans don’t belong in nature,” and if we decide not to work to protect, save, or restore species and habitats that have been negatively affected by our actions simply because we are “in thrall to wildness”, we will be withdrawing with “blood on our hands.” Marris sums up her position succinctly in the following statement:

We have to do whatever it takes to keep ecosystems robust and species from extinction in the face of things like climate change. And if that means that some ecosystems aren’t going to be as pretty to our eyes, or as wild, or won’t hew to some historical baseline that seems important to us, then so be it. We should put the continued existence of other species before our ideas of where or how they should live.

Marris acknowledges that there are risks to this approach. “Our meddling” may save species, but it could also backfire. But that doesn’t mean the effort wasn’t worth it. We can learn from our mistakes and we can make improvements to our methods. Some sites can even be cordoned off as areas of nonintervention simply so that we can learn from them. The ultimate goal, however, should be to save as many species and to keep as much of their habitat intact as possible. Putting “other species first, and our relationship with them second” is what Marris considers to be a “truly humble” stance in our role as part of nature.

Cones of whitebark pine, Pinus albicaulis (photo credit: wikimedia commons)

Cones of whitebark pine, Pinus albicaulis (photo credit: wikimedia commons)

The dichotomy presented in this article is a tough one, and one that will be debated (in my mind particularly) long into the future. If you would like to share your thoughts with me about this issue, do so in the comment section below or by sending me a private message through the contact page.

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