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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

December 1996

Pine cone. © Scott Nielsen.

The nature of cones

Pick up a pine cone and let the mysteries hidden by the shingle-like scales unfold.

Anita Carpenter

Pine cones enter our lives in many ways – as decorated wreaths, in floral displays and crafted into holiday ornaments. We suspend them as bird feeders packed with peanut butter or suet coated with seeds. We kick them along forest paths and cuss when they litter our lawn or get chewed up in the mower. We watch red squirrels shred them and crossbills meticulously extract seeds with surgical precision.

We've all picked up cones of various sizes and shapes, casually looked at them and then unceremoniously tossed them aside, but do we really know what they are?

We use the term "pine cone" to describe any cone from any conifer, but that's not right. Evergreens come in many types: spruce, fir, pine, hemlock, cedar. They are all called conifers because they all bear cones. We should name the cones for the parent trees – spruce cones, balsam fir cones and so on.

Each evergreen has two distinct cone types: female and male

The hardened, dark brown cones are the females. These cones consist of a woody stalk surrounded by overlapping, stiff, shingle-like scales. Behind each scale is a bract, a small, flat modified leaf. Depending on the tree species, the bract may be hidden within the cone or extend well beyond each scale, like the western Douglas fir cones.

The smaller, inconspicuous male cone (or pollen cone) grows either singly or in clusters, depending on the species. They are usually found on the lower branches. The male cones wither and die shortly after releasing their pollen in the spring, though dried remnants of pollen may remain stuck to the tree for months.

Each evergreen species has its own timetable for flower development, pollination and cone maturation. Only true pine cones take two years to mature. All other evergreen cones mature in the same year they are fertilized.

In spring, pine buds begin to grow producing male cones in clusters at the base of new twigs. The female cones appear much later as the twigs grow. Each small gumdrop-sized female cone is soft and green tinged with a purplish red. Its tiny scales are slightly separated.

When the tree is ready to be pollinated, it secretes a small amount of fluid that collects in the narrow crevices between the scales. At the same time, the mature male pine cone releases a heavy dusting of yellow pollen. These primitive plants rely on wind pollination. Enormous quantities of pollen are released on breezes to drift onto roads, ponds, cars, sensitive noses and the waiting female cones.

Each evergreen species produces a uniquely shaped pollen grain that will only reach female cones of its own species. The wind-borne pollen settles on the fluid within the female cone. It gets trapped and drawn into the crevices to rest on the two ovules at the base of each cone scale. Fertilization is usually immediate, but not always. Jack pines are not fertilized until 13 months after the pollen is trapped.

After pollination, the cone scales thicken until they are tightly pressed together. As the cone grows, it darkens, hardens and encloses the developing seeds. When the cone is mature and the timing is right, the cone dries out, pops open and releases two seeds per scale, each with a tiny wing to guide its flight.

Each species disperses seeds in a different way

White pines open and drop their seeds late in their second summer, then the cone drops off the tree. Some jack pine cones open naturally, others may wait 10-20 years and only open when exposed to intense fire. White spruce cones open and fall their first winter. Black spruce cones mature in one year, but can remain on the tree for several years releasing a few seeds each year. When balsam fir cones mature the scales and a few seeds flake off over a period of several days to weeks, leaving a bare core on the tree. This particular dispersal method is a welcome invitation to red-breasted nuthatches which can easily extract the balsam fir seeds.

When you are hanging up the holiday lights or looking for a holiday tree, take a good look at the cones. Examine the trees in your yard. Are the female buds patiently waiting for spring? Can you can find the bracts or a few seeds still stuck inside? Can you guess how each cone will disperse its seeds?

An entire textbook of the evergreen classroom may be as near as your front door or back yard. Don't be in such a hurry! Take your time and take a closer look.

Anita Carpenter checks out each tree in the stands near her Oshkosh home.