Flowering birches

Springtime, and the birch tree at our back door is laden with blossoms.

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This year I took a really close look at these, and then looked up more about them.

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Birches are pollinated by the wind, like corn, but a different design: the male pollen-bearing parts are the pendulous ones in this photo (right), while the much smaller female “catkins” appear from between a pair of leaves and curve upward. On our trees (Betula populifolia, I believe) the female catkins begin to droop downward with age, like all of us––the object intruding into the upper left of the picture is an older female catkin, nearly horizontal. In Britain the long male catkins are also called “lamb’s tails.” They bear a lot of pollen; a week ago when they were new my dark blue vest showed long golden streaks after brushing against them.

After pollination the female flowers will get larger, droop down, and gradually fall apart, loosing the scale-like seeds. Other species have winged seeds but not this one. Some of the male and female catkins survive into the next year. Below are some from last spring, still on the tree among the new ones. The old female catkins are shorter, thicker, & shaggy looking; rub one between your fingers and it easily comes apart into minuscule seeds and scales. The male catkins change with age too, becoming smaller, and hard to break up, almost feeling varnished on the outside.

Birches produce seeds abundantly and in our yard a couple of seedlings spring up each year in places that get water during the dry summers. It’s easy to see why they are known as early colonizers both after fires (secondary succession), and simply moving into wetlands or heath areas (primary succession).

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This tree also bears horizontal rows of holes, at which we have seen woodpeckers, either downy (Picoides pubescens) or hairy (Picoides villosus), probably drinking the birch’s sweet sap. The woodpeckers make the holes but others may come to them when they are exuding sap, and once I did see a hummingbird drinking there. Now that would be a great photo!

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