City Creek Nature Notes – Salt Lake City

May 8, 2017

May 5th

Filed under: Box Elder Tree, Dogwood, Gambel's Oak, Horsechestnut — canopus56 @ 11:24 am

Leaf-Out and Phenology

5:00 p.m. The first day astronomical spring was marked by the first bursting of Woods rose buds (March 20th), and they where followed quickly by buds of the red-osier dogwood and sap rising in the non-native willow tree (March 22nd). This also corresponded with the early leafing-out of young suckers at the base of the larger trees (March 22nd). These can be sacrificed in a harsh spring without endangering the survival of the parent tree, and the understory of the first mile forest quickly filled out. Next, buds of the green apple trees and the native Box Elder trees burst (March 24th). Next came the river birches (March 26th). These were followed by bud busting on cultivar horsechestnut trees at Guardhouse Gate (April 7th). On April 12th, although and early anomaly, the first Gambel’s oak trees budded and leafed (April 12th). On April 22nd, I made rough notes on the percent of leaf-out at mile 0.0, mile 0.5 and mile 1.0 along the road:

• At mile 0.0: Cottonwoods – 0 percent; Horsechestnut – 50 percent with small leaves; Red ozier dogwood – 70 percent with small leaves; River birch – 90 percent with inflorescences; Gambel’s oak – 0 percent to mile 1.5; Box Elder – 50 percent with catkins.

• At mile 0.5: Cottonwoods – buds swelling, 10 percent; Red ozier dogwood – not applicable, none; River birch – 100 percent with inflorescences; Gambel’s oak – 1 plant with leaf blooms.

• At mile 1.0: Cottonwoods – 0 percent; Red ozier dogwood – not applicable, none; River birch – 10 percent with inflorescences; Gambel’s oak – 0 percent.

Next, significant increases in leaf length for the cultivars and Box Elder trees occurred, interrupted by cold weather snaps (April 24th). Leaf-out in the red-osier dogwood and chokeberries paused, but then by May 1st, they, along with Wood’s rose have mostly filled-out with growing leaves. By May 2nd, much of the first mile had the appearance of a partially filled-in (sixty percent) green tube, and today, it is the tops of the larger trees that are bursting with catkins and inflorescences.

* * * *

Phenology is the study of cycles in plants and animals, and for trees, that study focuses on the dates of leaf-out in spring and leaf senescence during fall. Thoreau’s observations of the dates of bud swelling and leaf-out provided the basis for researchers to conclude that leaf-out dates for 43 species near Concord, Massachusetts have advanced by one week since the 1860s (Miller Rushing and Primack 2008). A literature search turns up no data for spring leaf-out of the Gambel’s oak specifically, but since the 1990s, leaf-out has become an area of intensive study as an indicator of climate change (Polgar and Primack, n.d., United States Phenology Network 2017). High quality studies on the autumnal leaf senescence or abscission by tree species and for Gambel’s oak also exist (October 11th).

Leaf-out is being studied by human observation in forest reserves (Polgar and Primack, n.d.), using orbital satellite imagery (Richardson et al 2009), using automated ground-based cameras coupled with image analysis (Richardson et al 2009, Yang et al 2017), and through citizen-science data collection (U.S. National Phenology Network 2017). Partial results include mathematical models of regional forest leaf-out (Schwartz, Ault, and Betancourt 2013).

Tree leaf-out in temperate forests is primarily controlled by a few factors: temperature, photo-period, winter-chilling, and the anatomy of a species (Polgar and Primack 2011). Some, but not all, trees respond primarily to temperature, but others ignore temperature and respond only to the changes in the length of the day and intensity of sunlight. All require some minimal level of winter chilling in order cycle through dormancy and spring rebirth. Trees with smaller diameter vascular systems better survive winter cold, and they can on the earliest rise in temperature being to leaf. This ability provides them with an ecological advantage and niche, but such trees also run the risk of an early frost. In the canyon, the horsechestnut tree is an example that bloomed, but then had its leaves wilted by a cold snap. Conversely, trees with larger diameter vessels are subject to more internal circulatory damage during winter freezing, and such trees, like the Gambel’s oak, need a longer resuscitation period in which to repair that injury before they can swell buds and produce leaves (Polgar and Primack 2011).

* * * *

On May 5th, 1994, the Salt Lake Tribune ran a historical piece by Jack Goodman on the Anderson Tower, a 54 foot tall granite tower that stood at 303 A Street in the Avenues between 1882 and 1932 and that was built by Robert R. Anderson. The tower looked down into City Creek Canyon, at the Temple grounds through its 1894 completion, and later at the State Capitol Building. The tower was featured as a tourist attraction as part of the City’s grand scenic boulevard for horse carriages built up City Creek and around 11th Avenue completed in 1906. Anderson lived at 5th Avenue and A Street. (In the present, the west plaza of the State Capitol serves as a similar scenic viewpoint). On May 6th, 1899, work to replace the City Creek water main with a larger diameter pipe was underway (Salt Lake Herald), although a suit seeking an injunction against the construction had been filed. On May 6th, 1888, Z. Jacobs canvassed citizens for suggestions on how to increase the city’s water supply, including Fire Chief Ottinger (Salt Lake Herald). Jacobs argued against building a dam in City Creek Canyon, since failure of the dam would destroy the downtown (id).

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