City Creek Nature Notes – Salt Lake City

July 18, 2017

July 17th

Seed Dispersal, Porcupine and First Trout

2:00 p.m. Although the canyon is still in the estival and not the serotinal season, I have inadvertently stepped into a patch of common Foxtail barley (Hordeum jubatum L.), and my shoes are covered its spikelets. I pause to remove about twenty out. The serotinal season, which begins on August 15th, is the time of maximum seed production and dispersal. Although a native plant, Foxtail and like the invasive Cheat grass disperse by animals. Dispersal by animals is particularly effective, which explains why many invasive and weeds move their seeds by spikes and velcro-like surfaces that grab onto mammal fur and bird feathers. Others use animals. Along the road today around the cultivar crabapple trees (genus Malus) in the first mile, there are half-eaten rotting fruits. Birds have been pecking at them and consuming both the sweet pulp and seeds. Mule deer have already consumed the fruit on the lower branches. I have often wondered at the inefficiency of other plants like Gambel’s oak and Box Elder trees. Both produce large prodigious amounts of seeds at a great expense of energy, but only an infinitesimal portion of the seeds can ever be reasonably expected to reach maturity. The oak drops its seeds vertically by gravity, where they cannot do not sprout in the shade. Presumably the oaks are helped by Rock squirrels (Spermophilus variegatus) that move and store the acorns in their burrows. The Box Elder is covered in is catkins of helicopter seeds that by its aerodynamics float a short distance from its parent. Cottonwoods, Western salisfy (Giant dandelion), and Fireweed, respectively, produce pollens and seeds that parachute away from their parent suspended below a feathery pappus. Watercress (Nasturtium officinale) fruits and floats down the stream to establish new colonies. How watercress moves upstream is unclear. Perhaps small crushed leaves fall off the lips of deer that browse on it. Dandelions, who favor the stream’s banks, moves its seeds upstream on the wind and downstream by floating on the water. Other plants like the Gambel’s oaks and aspen trees increase their range asexually by extending tubers underground.

6:00 p.m. The heat of the Sun bakes the water out of the land, and afternoon thunder clouds, born from the Great Salt Lake and reservoirs covers the valley. The great cloud tops are only threats, and pass with leaving any life-giving water to the city or to the canyon. It has been several weeks since I last remember any rain falling in the canyon. Checking weather records, the last rainfall above a trace amount was about one-tenth of an inch on June 13th.

8:45 p.m. I take a second late-evening run thorough the cool air and fading light. In the pond at picnic site 5, the first Brown trout (Salmo trutta) of this season has returned to the lower-canyon stream. A brushy tree limb has been removed, so the trout does not have the same cover as last year (Oct. 21st), but there is a bare six inch diameter tree trunk in the pond’s bottom. The trout uses this scant cover and goes for a hiding place in between the bottom of the log and the stream bed. The presence of the trout is related to shade provided by 100 foot canopy trees like Box Elder and Narrowleaf cottonwoods (Lanner 1984). Trout prefer cool water and the exposed stream, the flood retention ponds both below Guardhouse Gate and above at mile 3.0 may have become too warm for them. Now they seek cool pools shaded by the forest and where the stream has deep, vertical banks.

As I pass the watercress field in the tunnel seep below picnic site 6, I notice two eyes starring back from the darkness. A small North American porcupine (Erethizon dorsatum) is sitting at the edge of the seep, contentedly grazing on the watercress. I have not seen a porcupine in the lower canyon for about two decades, and I had thought most of them to be driven out of the upper canyon above mile 4.0 by the increasing drought (Nov. 2nd). This porcupine, like its species, is docile and unafraid. Because of it quills it has few serious natural enemies, although quills have been found in mountain lions, coyotes and bears. Eventually, it becomes wary of me and effortlessly climbs a nearby forty feet tree. They eat green plants, like clover, leaves, and the bark of trees (Hayward 1948 at 494, Spencer 1964). Such discoveries of old animal friends raise my spirits. They have not been driven from Salt Lake canyons. In the fading twilight, bicyclists streak out of the canyon illuminating their way with blinding LED lanterns.

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There are four primary methods of seed dispersal: by wind, by water, by gravity, and by animals. Animals move seeds by several methods. Epizoochory is the movement of seeds, like the Foxtail, by attaching to the outside of an animal. Endozoochory is the movement of seeds by animals internally, i.e. – eating of seeds by birds and mammals followed by the seed’s excretion distant from the parent. More recently anthropochory, the movement of seeds by humans, has radically changed the canyon and western habitats, by moving seeds across oceans and continents.

In 1993, now Utah State University of Utah botanist Eugene Schupp noted that the benefit to a plant that an animal disperser provides is a probability function of the quantity of seeds dispersed and the quality of the seeds produced (Schupp, Jordano, and Gómez 2010, Schupp 1993). Quantity of dispersal depends on the number of disperser visits and the number of seeds dispersed on each visit. The quality of seeds produced depends on either its treatment in an animal’s digestive tract or quality of seed deposition, i.e. – some animals are sloppy eaters and drop seeds close to the parent and others efficiently eat all seeds and move them a significant distance from the parent. Combining these factors gives a seed dispersement effectiveness index, and that single dimensional index can be used to relatively rate the importance that the many animals that consume a plant’s seeds contribute to the plant’s reproduction. For example, any single tree species many have five or ten bird species that eat and disperse its seeds.

Seed dispersal matters to the recuperation of forests. Where forests, like the canyon’s Gambel’s oak chaparral or stream-side association, are long-lived and mature, bird dispersers have little effect on a forest’s health. But when a forest is disturbed, for example by fire or clear-cutting, a forest cannot re-colonize unless it also supports a healthy bird population that can distribute its seeds (Howe and Miriti 2004, Martínez and García 2017). This process works in reverse. Bird dispersers can be lost, and eventually this may lead to the loss forests that they visit (Howe and Miriti). This underscores the need to preserve bird habitats on a continental scale, since the avian distributors of seeds that will help City Creek Canyon’s oak and montane forests recover from a future fire, may overwinter in Central American forests (May 22nd, May 23rd and May 24th).

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On July 17th, 1915, the U.S. Weather Bureau installed an advanced stream flow measuring gauge at the High Line Water Tanks in Pleasant Valley (Salt Lake Herald). On July 17th, 1908, the Salt Lake Telegram reported that the city prison road work gang had labored for 18 months to improve City Creek Canyon Road. On July 17th, 1888, ten families had set up tents for cool summer camping in City Creek Canyon (Salt Lake Herald). On July 17th, 1887, the Salt Lake Herald reports that several families have moved into tents in and for the cooler air of City Creek.


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