City Creek Nature Notes – Salt Lake City

October 26, 2016

October 26th

Filed under: Dogwood, Gambel's Oak, Horsetail, Light, People, Sea gull, Watercress, Woods Rose — canopus56 @ 4:04 pm

A Horse’s Tale

1:00 p.m. In the spring and summer, foliage obscures the stream and its banks, but now, with the leaves stripped away, the stream is visible. Low-angle shafts of late afternoon light strike into its depths and illuminate individual pools and rocks. The scouring rush horsetail dominates these dappled stream banks for the first five miles of the canyon. It shares the banks with western poison ivy, occasionally with wild watercress (Nasturtium officinale) and, further from the bank, with Wood’s Rose (Rosa woodsii) and the red-osier dogwood bush. These are surrounded and overshadowed by a variety of trees, some of which like the cottonwood reach 100 feet in height.

Horsetails are the sole survivor of Paleozoic forests that covered the Earth until the rise of flowering plants 250 million years ago. But how did the eighteen inch horsetail evolve into a 100 foot tall cottonwood tree? Here again, another “just-so” evolutionary story will have to suffice. In the canyon, the horsetails occupy the banks at the stream’s spring water line. In the spring, they are flooded, which is consistent with their evolutionary roots as a marsh plant. Thus, they do not need and do not issue deep roots. In the summer, their roots are just sufficient to reach the stream’s water table, but in years of drought, they must grow deeper. Drought fosters evolutionary selection that makes them grow larger and deeper. The larger they grow, the further their seed can spread away from water, and then their descendants must grow even larger to reach down to water. In years of extreme drought, the smaller predecessors may die off all together, leaving only their taller progeny. Over a hundred million years, one can see how this self re-enforcing loop can transform the horsetail into a giant narrowleaf Mountain cottonwood next to the stream or into a Gambel’s oak that drives deep roots and that survives on little water far from the stream.

It is an unusually warm day in the seventies. The leaves of the Wood’s Rose bushes near picnic site 1 have turned a brilliant red. Four sea gulls soar 800 feet above the canyon floor, and they are followed by a distant raptor. There are about twenty walkers and runners, some of who have taken their shirts off, and a group of about 40 first or second graders. To prevent the prisoners (I mean students) from escaping (I mean wandering off), each child is dressed in a bright red T-shirt. Their voices are loud and boisterous until I out-run and leave them behind on the road. But there is only one hunter car on this Wednesday, which is expected. Insects are present, and an array of six types spanning about 30 individuals is found in the first mile. Four blue dragonflies, probably Blue-eyed Darners, fly by at mile 0.6. Several injured grasshoppers are on the road, and they provide a meal for a flock of six Mexican scrub jays.


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