Naturespeak A naturalist's view of the world

December 29, 2008

Basswood A-Go-Go

Filed under: Uncategorized — wykes @ 9:56 pm

While in the midst of a windy and bitter Alberta clipper cold snap, I am usually less than tempted to go outside. My only excuse for this lack of fortitude is that most sensible animals sit tight during such periods.  “Holing up” is a natural and safe thing to do. I am a sensible animal. I will, however, spend an inordinate amount of time standing by the window during such weather and mumble to myself – saying middle-aged things like “Geeze, it’s really blowing out there” or “It looks like there’s no letting up.”

During one of my window expeditions, I spotted a basswood seed bract swirling around just outside the back door (see above). It was riding on an endless wind-go-round on top of the snow crust along with a variety of vegetative riff-raff.  The closest Basswood tree was, as far as I knew, nearly a quarter mile away.  So the sight was a slightly unusual one around my place. It prompted me to crack open the door, venture a few feet out into the bitter cold, and snap a few pictures. I used a zoom setting so I didn’t have to go too far out. “Geeze,” I mumbled upon returning, “it’s really blowing out there.”

Being that nature came to me this time, I felt it only right to spend some time contemplating the fine details of Basswood seed distribution. Basswoods are common mid-western trees known for producing fine carving wood and “bast” – or twine – rendered from the bark. They are also known as “honey trees” for the honey produced by bees feeding on their nectar-rich flowers. These flowers bloom in June and eventually turn into the unique seed structures shown above.

The flower/seed unit consists of a woody stem suspended from the center line of a modified leaf called a bract. Like the winged seeds of the maples and ashes, the Basswood cluster is made to take flight upon being released. The structure (see below) bears an uncanny resemblance to one of those old-fashioned whirligig flying toys – you know, the kind that inspired the Wright Brothers to break the bonds of gravity. Unfortunately, this uni-wing only propels the falling seed bunch a few tree lengths away under the best of fall wind conditions and straight down when no wind is present. Ahh, but the Basswood has another trick under its woody sleeve to overcome this fault.

They don’t release most of their seed structures until winter arrives. They wait until winter levels everything first. Tiny, but tenacious, tendrils hold the stem onto the branch until winter gales force them to finally relent. Taking advantage of crusted snow and high velocity winds, the structure sails along over the open surface like an ice boat over a glassy frozen lake.  In other words, the initial flight sends the seeds a short distance from the tree and the skidding experience keeps it going, and going, and going like the Energizer Bunny. One by one, the tough encapsulated seeds fall off and settle down through the melting snow to the spot they will call home for the next 100 years if they are lucky enough to sprout.

This snow sliding technique is all but ignored in modern literature – the wing function rather than the sail function, is emphasized. I consulted one of the old texts to find a description which adequately explained this winter dispersal method.

Towards that end, I quote Dr. W.J. Beal, professor of botany at the Michigan Agricultural College (now Michigan State University) from his 1898 book called Seed Dispersal. He observed that “before snow had fallen in 1896, by repeated moves on a well-mown lawn, fruits and bracts (of the Basswood) were carried about 200 feet, while with snow on the ground the distance was almost unlimited. With a crust on the snow and a good wind the conditions are almost perfect…to propel it much a sail propels a boat.”

Some 110 years after Dr. Beal revealed it, this unique little piece of natural history news announced itself at my own back door. “It looks like there’s no letting up” when it comes to uncovering nature’s wonders.

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