City Creek Nature Notes – Salt Lake City

December 6, 2016

December 6th

Filed under: Bald-Faced Hornets, Gambel's Oak, Nests, Starthistle, Weather — canopus56 @ 8:07 pm

Orange Lichens

1:30 p.m. The cold pocket of arctic air has dropped temperatures into the low twenties and with canyon winds down into the teens. The flood retention pond at Bonneville Drive has started to freeze over, and the effect on the cattail patch that grows in the pond is immediate. Previously, the dried cattails stood erect, and now they have fallen over.

As I jog up canyon, the sky is overcast with the cloud bottoms only a few hundred feet overhead, there is a wind driving light snow out of the north. By the time I reach milepost 1.0, this changes and the snow drops vertically. This kind of overcast with falling snow and cold changes perception of the canyon; it makes the canyon seem more dramatic. A buttress that sticks out on the north-west canyon wall at mile 1.1 normally looks insignificant. In the diffuse overcast light, falling snow and severe cold, it looks like a grand mountain. Four mule deer are seen on the high on the south canyon wall; three more are seen back at mile 0.2.

Between mile 1.2 and mile 1.6, lichens (Xanthomendozaon species.) growing on the Gambel’s oaks have turned from green to a dull and bright orange. With the falling snow and overcast light, this orange contrasts greatly with their host tree trunks. This color change can occur when lichens are exposed to nitrogen rich, polluted air, and such changes are used to track air pollution over time in over cities. Salt Lake City has some of the worst air quality in the nation, and the U.S. Forest Service surveys lichens at 128 plots throughout Utah, including one plot in upper City Creek Canyon. But Werstack et al (2016, pp. 43-44), researchers with the U.S. Forest Service Rocky Mountain Research Station, conclude that Utah’s lichens probably overstate air pollution. This is because orange-turning lichens are also correlated with drought tolerance (id). The lichens may be turning orange because they are in a drier climate and not because the air contains more nitrogen dioxide. The Rocky Mountain Research Station is currently conducting studies to calibrate the density of orange lichens by precipitation, thus allowing western researchers to use these epiphytes to monitor air pollution.

At mile 1.6, the snow on the north-west hillside emphasizes yellow star-thistles. Dried tall grasses and the star-thistles have the same hue, and I do not ordinarily perceive them in the meadows. But the ground snow makes for a differing background that allows one to distinguish between hills that are covered in grass and those that are covered in these invasive thistles. It was undesirable plants that the Utah Conservation Corps are trying to eradicate from the meadow one-quarter mile down canyon from here (October 16th).

I take my time jogging back down the canyon. I have been inventorying bird and insect nests in the canyon since December 2nd, and today I am marking each nest’s location using the global positioning system. Hornet’s nests are temporary constructions meant to last a single season. On December 2nd, I find and photograph the largest in the lower canyon between picnic sites 4 and 5. It is twice the size of a basketball, and it precariously sits intertwined with the smallest upper branches at the top of a 100 foot tall Rocky Mountain cottonwood. After three days of snow, rain, and freezing temperatures, I cannot find it again. Apparently, winds have blown it out of the tree or ice formed on it, and the weight of the ice pulled the nest from the heights.


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