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Pine cones

Photo: Vines Arboretum

Pines Producing Bumper Cone Crop

By Kevin McKeon, Director, Mousam Way Land Trust

Have you noticed all the pinecones on the forest floor this winter? This has been an uncommonly abundant year. Only once every three to five years do white pine trees produce abundant seeds. These seeds are a mainstay in the diets of birds such as red crossbills, chickadees, nuthatches, pine siskin, and grosbeaks, and mammals such as snowshoe hares, porcupines, deer, red and gray squirrels, and cottontails.

Today, we’re going to be talking about female cones, male cones, female eggs, male pollen, and finally seeds – here we go!

The familiar pinecones we see at the tops of pine trees are the reproductive structures of these trees. But pine trees actually produce two kinds of cones – female cones and male cones – which are both modified branch stems that have been adapted for reproduction. The female cones, which are larger than the male cones and grow high up on the trees, have a thick, inner stem from which radiates a cluster of scales. These pinecone scales remain closed as the eggs inside mature.

The smaller male cones grow on the lower part of the tree and produce tiny pollen grains that have microscopic winglike structures that allow the wind to carry them up the tree to the eggs inside the female cones. The eggs are inside protective cases located at the juncture of the scales and the stem inside the cone.

When the eggs have matured, the female cone opens her scales to receive the male pollen. The wind-blown male pollen grains enter the female cone between the scales and attach themselves to an opening in the egg cases. The female cone then closes her scales to protect the soon-to-be fertilized eggs as they grow into seeds.

Within this closed pinecone, the male pollen germinates and grows a special pollen tube, eventually reaching and attaching to the egg. This tube then carries the male fertilization material to the female egg. The embryo thus produced is protected by both the closed scales of the cone and a tough seed coat. The seed is also encased in a papery winged case that sits on the scale inside the protective pinecone.

The female cone remains closed from 8 to 24 months, depending on tree species, as the egg matures into a seed. When ready, the female cone opens her scales to release her seeds, but she only does this when the weather is optimal for seed dispersal. During wet weather, the scales of the cone close to protect the fertile seed. During dry, warm weather, the scales open up to allow the wind to disperse the seed far from the tree and its shade, where it grows into a new pine tree. Watch a short video here.

The opening and closing cycles of pinecones happen often during their lifetime, persisting after seed dispersal and even after dropping to the forest floor. Thus, cones can be useful in gauging the dampness of the forest floor to help indicate fire danger levels. Closed cones indicate wetter conditions and a lower level of fire danger. Try hanging a cone from a string to estimate upcoming rain and humidity levels.

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