Nature Notes
3:18 pm
Thu July 31, 2014

Cottonwoods And Poplars

Here is another Nature Note inspired by Rupert, Nature Note’s West Highland white terrier. For those of you who don’t know, Westies, as they are called by those in the know, are a very close relative to the Cairn terrier. For those of you who don’t know Cairn terriers, Toto, the small black dog in the Wizard of Oz was one. Both are Scottish breeds designed by farmers to chase to ground small mammals and dig them out. Their stout short tails are the result of being pulled out of the hole when farmers decided they wanted to move on. According to one story, farmers discovered they could spot a white dog on a distant slope more easily than they could a colored dog, hence the development of the white Westie.  

This fluff comes from female cottonwood trees, whose seeds burst into tufts of downy fibers that float aimlessly on the wind.
This fluff comes from female cottonwood trees, whose seeds burst into tufts of downy fibers that float aimlessly on the wind.
Credit Andi Willman

Now Rupert likes things that move. Squirrels, cats, other dogs, or kids on bikes or skateboards. He has mostly gotten over birds. But on our walks this past spring, Rupert  became much enamored of small white tufts blowing this way and that along the street; these fleeting objects of his canine desire were actually the seeds of cottonwoods, after which he dashed with great enthusiasm. The odd spring weather was especially kind to the reproductive potential of local cottonwoods, although research shows cottonwoods pump out the same number of uncountable seeds every year, no matter the weather conditions.

On our walks this past spring, Rupert became much enamored of small white tufts blowing this way and that along the street.

Native cottonwoods and poplars frequent wet places along streams, lake or marsh sides. Our black cottonwood, widely distributed in the west, is an imposing, tall (to over 100 feet), fast growing but relatively short-lived (200 years is old) riparian or streamside tree. Cottonwoods are pioneer and early seral species in plant succession, the first trees to occupy disturbed sites. They do not tolerate shade and do best in open disturbed sites like exposed gravel bars. They are very tolerant of short-duration floods.

Poplars come as boys and girls with male and female flowers on separate trees. Pollination is by wind. The tiny, tufted seeds are widely distributed by wind and water. In spite of enormous, consistent, seed production, most reproduction is asexual. Most seeds are quick to germinate but are also quick to die, if soil moisture conditions are not just right. If the seedlings roots can’t keep up with drying soil, the seedlings die. As a result, seed reproduction is episodic.

Cottonwoods do have amazing asexual reproductive potential. They can reproduce by root and shoot suckering, or by cladoptosis, the physiological dropping of twigs with leaves attached. This method of reproduction is particularly important on gravel bars in relatively moist climates. Broken black cottonwood branches grew when deposited in the fresh mudflows of the Mount St. Helens blowup.

Every time I am around cottonwoods in the early spring, I am reminded of a long ago trip to the flood plain of the Nisqually River in western Washington to collect morel mushrooms with my friend Margaret McKinney, author of The Wild and Savory Mushroom. The perfumed, heady odor of balsam from the trees’ big sticky buds brings on my memory of big fat morels, just like the scent of Douglas fir needle reminds me of Christmas.

Back to Rupert. Maybe those little white fuzzies remind him of baby Westies. Maybe he thinks they are baby Westies. When he is a little older, I’ll tell him all about the dogs and the bees.