ACT's Nature Corner: Pine Cones

By Eileen Willard

Unless you climb up thirty or more feet into an eastern white pine tree (Pinus strobus) and take a good look around you might miss seeing a complex reproductive process taking almost two years to complete in this big conifer.

During a recent walk through the Arundel Conservation Trust woods I had the good fortune to see examples of this complex development on downed branches, the result of recent windstorms. We’re all pretty familiar with the 5-6 inch, brown cylindrical woody cones that drop to the forest floor in the fall. We pick them up and look at them with little understanding of their complicated formation process. Rarely do we get to see the immature versions (no larger than an inch) that adorn the treetops in the spring.

Eastern white pines are monecious trees. In other words, they produce both male (pollen cones) and female (seed cones) structures on the same tree. These reproductive structures are commonly called cones and they are very small when they first form in the spring. Tiny green-scaled female cones that turn into those big woody cones we find on the ground are situated in the upper branches while the male cones are found on lower branches--probably nature’s way of discouraging self-fertilization.

The spring pollen grains released from the male cones of another eastern white pine are driven by the wind and settle between the scales on the female cones. Picture each miniature female cone as pointing toward the sky. All the small scales surrounding the outside are ever so slightly opened to allow air to circulate. Tucked between each scale are two ovules that will eventually turn into seeds. The shape of the released pollen grains and the shape of the female cones are actually aerodynamically matched to each other. In this way female eastern white pine cones will only accept the pollen from another eastern white pine. Pollen grains from a different species are excluded. After releasing their pollen, the tiny male cones fall off the tree. Their job is done and we are left sweeping yellow pollen as well as the fallen male cones (they look like “rice-krispies”) off decks and patio furniture.

Once the proper pollen is accepted, the scales on the small female cone compress together sealing in the pollinated ovules. Then the cone starts to curve downward (as though it were bending over) and takes on a more pendant shape. So far the story is a shut-open-shut sequence. In autumn development stops and the undeveloped female cones remain dormant on the branches all winter.

The following spring the small pendant female cones resume growing larger. At maturity (4-6 inches) they take on the more familiar brown woody appearance we are used to seeing in the fall. It might help to think of your grandmother’s Venetian blinds when picturing the arrangement of the developing seeds tucked between the cone’s woody scales. The cone scales are like the slats of the blinds. When the blinds (cone scales) are opened the seeds slide out. Each released seed has a papery wing that allows it to drift down to the soil with the wind. At this point the almost 2-year sequence has been a shut-open-shut-open case.

Having discarded their seeds, the big woody female cones eventually fall off the trees. Perhaps we might pick them up for Christmas decorations. However, the story doesn’t end here. That which began two years earlier may well be just the beginning of the next majestic tall eastern white pine. With any luck, some of the seeds will land in the right place in a field or forest floor and germinate. The result will be a new baby pine tree, the perpetuation through evolutionary wonder of its species.

If you enjoyed reading this blog post and have any interest in contributing as a writer on our non-profit website please reach out at info@arundeltrust.org. We love featuring guest writers and leaning into the expertise of our fellow community members.

Eileen Willard leads nature walks with the Arundel Conservation Trust trails - please check in on our events page to see any upcoming walks!