Emigration Creek Project
Ecology 340
Westminster College, Salt Lake City, Utah

Dianne Boogert
TREES



Index:

What Kinds of Trees Live on Emigration Creek?
What are the c
haracteristics of These Trees?
How Much Organic Material Enters the Stream?
What
Organisms Benefit Most by Tree Leaves?
References

What Kinds of Trees Live on Emigration Creek?

There are at least fourteen common kinds of trees that have been identified on Emigration Creek as it crosses Westminster Campus. This small riparian forest is a mixture of native and introduced species.

The native species in decreasing order of abundance are Box Elder, Lanceleaf Cottonwood, Fremont Cottonwood, Narrowleaf Cottonwood Peachleaf Willow and Gambel Oak. The Lanceleaf Cottonwood clones on our campus are probably F1 and backcross hybrids between the native Narrowleaf and Fremont Cottonwoods and they are found along all reaches of the creek on both sides. The parent cottonwood species are found in only two places on the creek. The Narrowleaf Cottonwood is found only in Reach 2, and three old Fremont Cottonwoods (approximately 60-70 years) are in Reach 6. There are only three Peachleaf Willow trees on campus, one predating the 1983-84 floods at Reach 1 and two others which self-established from seed after the 1983-84 floods in Reach 7. There are only two clones of Gambel Oak on campus, one in Reach 4 on the south side of the creek and one at the extreme end of Reach 7on the north side. These original clones are currently dying of shade supression by the non-native, introduced trees listed below.

The introduced species are Siberian Elm, Norway Maple, Tree of Heaven, and English Walnut. A few individuals of Green Ash, Horsechestnut, Mahaleb Cherry and Honey Locust can be found along various reaches of the creek. They have been carried here by wind and birds from the surrounding landscape.

A more complete listing of trees and shrubs in Westminster Creek Natural Area, with Latin names and notes, can be consulted by clicking on: Checklist of Emigration Creek Trees and Shrubs

What are the Characteristics of These Trees?

Box Elder: Acer negundo. This native tree can reach a height of 75 feet. Its leaves are compound with three leaflets that are coarsely toothed along the edges. The leaves are 3-4 in. long and 1.5-4 in. wide. It prefers moist soil along streams, rivers and lakes.

This is a Box Elder leaf showing its compound nature as well as typical insect damage from native fall cankerworm caterpillars and aphids.

Peachleaf Willow: Salix amygdaloides. It grows to a height of 60-70 feet. It has upright branches and a narrow crown. The leaves are 2-5 in. long and .5-1.25 in. wide. They are often slightly curved to one side of the stem and taper off to a point. The leaf edges are finely saw-toothed and become hairless in age. They are important in protecting riverbanks from erosion.

This is the leaf of the peachleaf willow tree.  All of the leaf structures including the catkins (female, left and male, right) are shown.


Narrowleaf Cottonwood: Populus angustifolia. It is a medium-sized tree that reaches 50-70 feet in height. The crown is pyramidal with slender, erect branches. The leaves are 2-4 in. long and up to 1 in. wide. They are slightly rounded at the tip, and slightly tapered or flattened near the base. They are bright yellow-green on top and paler on the bottom. The trees are an important riparian species generally found from approximately 5,000 feet up to 8,000 feet in the Wasatch Mountain canyons. They are rarely found along the low elevation streams of Salt Lake County but do extend downward in elevation along the streams to approximately 4400 foot elevations. There is only one, old, Narrowleaf Cottonwood clone on Westminster campus and it is found in Reach 2 of the creek, high on the south side, with reproducing clonal roots extending down to the creek on the 1983-84 flood terrace.

   

Fremont Cottonwood: Populus fremontii. This is the largest of our cottonwood trees. They were probably introduced as shade trees to northern Utah from southern Utah or the Uintah Basin during pioneer times. The trees grow 40 to 80 feet in height. The leaves have similar colors on both sides, and the edges have only 5-10, coarse, rounded teeth. They are fairly large and heart-shape to kidney-shape. The leaves are greenish on both sides, and they turn yellow in the autumn. Many Fremont Cottonwoods have pubescent or hairy buds. On Emigration campus there are only 3-4 mature Fremont Cottonwoods which are located in Reach 6 of the creek on the north bank. We think they became established during or slightly after the 1935? construction of the Dane Hansen Althletic Stadium. The trees are located among concrete demolition debris placed there during the contruction of the stadium. The trees were established at the high-water mark of the creek's flood plain, and the creek's bed has significantly entrenched since that year, leaving the large, old trees several feet above the current high flood line. One of the old cottonwood trees spontaneously fell down into the creek of its own weight and imbalance during the spring of 2000. This event was witnessed by several Westminster grounds staff members. The tree created a natural dam in the creek through the Spring and Summer of 2000, but was removed by flood control personnel in the fall of that year.

This is a drawing of a typical Fremont Cottonwood leaf and female catkin showing the unopened cottonwood seed capsules

Lanceleaf Cottonwood: Populus acuminata. This a hybrid tree species created by the natural cross-pollination between the Fremont Cottonwood and the Narrowleaf Cottonwood. The leaf shape is intermediate between the broad, heart or kidney shape leaf of the Fremont Cottonwood and the narrow, pointed shape of the Narrowleaf Cottonwood. Its leaves are 1 to 2.4 times jwider than long. The hybrid clones live along streams and rivers and around ponds and lakes reproducing by underground rhizomes similar to the parental Narrowleaf Cottonwood. In northern Utah they are often found growing at the mouths of canyons at intermediate elevations where the parental types are found together. This elevation is approximately 4500 ft. to 5500 feet.

   

Gambel Oak: Quercus gambelii. This native drought tolerant tree is commonly found at higher elevations in the Wasatch foothills above 5100 ft. elevation but we have discovered two individual clones growing on campus which predate the original farm and subsequent college establishment. Several isolated individual oaks are similarly found along Parley's Creek in Sugarhouse only one-half mile to the south. See the web site Hidden Hollow for additional information on the oak and other associated species.

This is a drawing of the Gambel Oak showing its deeply lobed leaves, acorns, and male flowers (catkins) which bear the pollen in the spring just as the leaves are starting to appear.


Siberian Elm: Ulmus pumila. These introduced trees were planted throughout Utah for shade or ornamental purposes from the 1930's onward. Their leaves are 1-3 in. long and alternate along the stem. They are fast growing and have wide-spreading lateral roots. They are very drought tolerant trees. They are often refered to as trash trees due to their massive production of seeds and seedlings. These trees are no longer planted in urban landscapes but still persist due to older trees shedding seed. Several older trees exist along Emigration Creek and need to be removed in the future.

Norway Maples: Acer platanoides. These trees have a rounded crown with dense foliage. Their leaves are opposite on the stem and are 4-7 in. long as well as wide. They are five-lobed and dull green with sunken veins on top. They are hairless. The leaves turn bright yellow in the autumn. These maples are invading the Emigration Creek natural area from surrounding homes. The seedlings are very shade tolerant and persist under the native trees and eventually can replace them. Many small saplings and established trees exist along the creek and all need to be removed. In Reach 6 of the creek, invading Norway Maples have over-topped and killed the native Gambel's Oak.

Tree of Heaven: Ailanthus altissima. These invading trees grow to 40-60 feet in height. They have loose open crowns with long, pinnately compound leaves. The leaflets are 3-5 in. long and 1-2 in. wide. They are covered with very fine hairs when the tree is young. The trees grow very fast from winged, wind distributed seeds. A number of old, original trees are found west of the Gore Building on Westminster campus which are probably the seed source for the Emigration Creek trees. Like the Norway Maple and Siberian Elm trees, seedling of the Tree of Heaven can become established under native trees and compete with them for light, nutrients and water. All of these trees need to be removed from the natural area. The Tree of Heaven is famous because of the book A Tree Grows in Brooklyn.

English Walnut: Junglans regia. This tree grows to a height of 60 feet and has an open, broad crown. The large, pinnately compound leaves generally have 5-9 large leaflets which are 1.5-2 in. wide. These trees are usually planted in warmer areas, but the young trees growing along Emigration Creek came from an original landscape grove which was removed when the Giovale Library was constructed on the north side of the creek. The original walnut trees produced nuts almost every year and the nuts were gathered and cached by resident rock squirrels. The buried nuts germinated and produced the sapling trees we now see along the creek.


How Much Organic Material Enters the Stream?

An estimation of autumnal leaf drop into Emigration Creek was conducted on October 30, 2000. Fresh leaves which had been accumulating over the past 10 days on flat areas adjacent to Emigration Creek were picked up inside six, one-meter square quadrats and put into brown paper bags. The collection quadrats were located along a the woodchip walking path that lies along the south bank of the creek. See map of Emigration Creek. One quadrat was randomly located along each of the stream's reaches as shown on the map. The leaves were dried for two weeks, separated by species, and weighed on an electronic balance.

An estimate of the amount of dry organic material (leaf biomass) that fell into the creek during October of 2000 is given in the follow table:

Quadrat #

(1.0 m2)

1

2

3

4

5

6

Average

(of six quadrats)

Leaf Biomass

(grams dry wgt.)

81.0 177.0 36.0 33.0 73.9 39.2

73.4

An average of 73 grams of dry leaf material per square meter falls into the creek every autumn. This is an under-estimate since the trees still retained an estimated 10-15 percent of their leaves at the date we made the collections. Also, the amount of biomass which enters the creek ecosystem from twig and tree fall at other periods of the year is not given here. However there is a significant amount of wood lying in the bed of the creek which is often moved by periodic floods and high water. Salt Lake County Flood Control personnel remove tree trunks and large pieces of wood from the creek floodplain every two years even though this source of organic energy may be important to the creek organisms. Nevertheless, the annual input of leaves may be more important to the creek ecosystem due to their higher content of minerals and finer material ready, for detritivore shredding and for rapid decomposition by bacteria and fungi.


What Organisms Benefit Most by Tree Leaves?

The organisms that benefit most by the leaves that enter the creek are the planarians and segmented worms, mayfly and caddisfly larvae, bacteria and fungi. The amount of organic material which enters the creek ecosystem varies seasonally and in amount. Leaves, which contain higher levels of mineral elements such as nitrogen and phosphorus than wood, may be an important source of nutrients which limit the growth of photosynthetic organisms aquatic ecosystem. Leaves enter the creek in a large pulse in the fall while wood and twigs fall into the creek during the winter and other times of the year. Due to the finer texture and larger surface area of leaf material, fungi and bacteria can act more quickly in the aquatic decomposition process, releasing limiting nutrients back into the ecosystem. In this way, fall blooms of photosynthetic diatoms and Cladophora algae can increase productivity for the ecosystem.

The deposition and movement of leaves and wood in the creek channel is affected by physical conditions of flooding during fall storm events on the watershed or spring flooding events during watershed snowpack melt and runoff. The movement of leaf and wood material deposited in the creek is probably affected by urban stormdrains that move floating leaves and wood downstream, not leaving them available as an energy source for the various detritivore organisms in the Emigration Creek foodweb. ;Therefore the biennial removal of any and all logs along and in the creek by Salt Lake County Flood Control personnel probably damages the ecological integrity of the creek, decreasing the water depth in pools and decreasing the buried wood which is available for detritivore insect use. This in turn affects the urban fishery and habitat for trout and other fish and amphibian species.

References:

Brough, Sherman G. and Darrell J. Weber. Trees of Utah, Provo, Utah: Bristlecone Press, 1993.

Collingwood, G.H. and Warren D. Brush. Knowing Your Trees, Washington D.C.: American Forestry Association, 1964.

Preston, Richard J. North American Trees, Ames, Iowa: Iowa State UP, 1961.

Welsh, Stanley R., N. Duane Atwood, Sherel Goodrich and Larry C. Higgins. A Utah Flora, Great Basin Naturalist Memoir No. 9, Brigham Young University, 1987.


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