Plants find creative ways to travel
At this time of year in the Yukon, you can spend as much time combing the dog as walking him. Every excursion results in a dogload of burrs, foxtails, and seed fluff, some of it virtually knitted into his coat -- and your socks.
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The seeds of this sedge are equipped with tiny air bubbles to help them float down the river to a new home.
(photo: Bruce Bennett)
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Yukon plants are on the move.
Despite the fact that they are firmly attached to one place, plants are very good at traveling.
The burrs that seem to come out of nowhere at the end of summer are just one example of traveling seeds.
The little round burrs that cling to socks and dogs have hidden virtues, says Bruce Bennett, wildlife viewing biologist with Yukon Environment.
"They come from a plant in the coffee family. If you collect them and roast them, they'll work as a coffee substitute."
Since it would take a lot of tiny burrs to produce one cup of coffee equivalent, most people just pick them off and drop them on the ground -- where they have a good chance of growing into Northern Bedstraw, a tall leafy perennial with clouds of tiny, white, fragrant flowers.
Another common Yukon burr belongs to Stickseed, a small upright plant with tiny blue flowers.
"The burr looks like a little starfish," says Bennett.
Stickseed does well in disturbed ground, he says. It often takes root near ground squirrel burrows, and in places where mountain sheep lie down. The single row of prickles running around the edge of the burr attaches it to the sheep's hair. The burr falls off when the sheep settles into the hollow of its favourite resting place.
"It attaches very well to your dog's coat too," Bennett adds.
Burrs work well, but some of the best travelers among Yukon plants use an entirely different approach to dispersing their seeds. They're the sedges.
Sedges are grassy-looking plants that grow in shallow water or very wet soil along the edges of rivers, Bennett explains. They have tall, strong stems topped with spiky-looking flowers and seed clusters.
Some sedges have seeds designed to drop into the river and float downstream until they wash up in a suitable place. The seeds are covered with a Styrofoam-like coating, pocketed with air bubbles to keep them afloat.
Others hold onto their seeds so tightly that they don't drop until winter. The seeds land on the river ice, and in the spring they raft down the river on the ice flows, traveling far from their starting point before the ice melts enough to deposit them along the shore.
The only sedge used as food by humans is the water chestnut, and it's the root we eat, not the tough-coated seeds.
"We haven't learned a way to take that hard coating off the seed to get at the meat in the centre, as we have with grasses," says Bennett.
Neither have water birds like swans. They swallow the seeds in the process of pulling up and eating stalks and roots of aquatic plants, but the seeds are too tough to digest and pass undamaged through the swans' digestive tract.
When the swans settle at their next rest stop, possibly hundreds of kilometres away, the seeds pass out of the birds in their droppings, ready to grow into a new patch of sedge.
"Aquatic plants are one of the best examples of dispersal by birds," says Bennett.
Sedges need help in flying, but other plants fly on their own. Willows are among the plants that send their tiny seeds out attached to bits of fluff that blow about in the wind.
It's a chancy way to travel, and willows have an extra challenge, Bennett says. The seeds survive only a day or so once they're released, not long to find the kind of mineral soil that will allow them to root and grow.
"Willows make up for it by producing millions of seeds, kind of like fireweed," he says.
- For more information about how plants travel, contact the Yukon Department of Environment at (867) 667-8291.
