HomeMy WebLinkAboutTHE DISTRICT @ CAMPUS WEST - PDP - PDP120003 - CORRESPONDENCE - LANDSCAPE PLAN• Local observations of Swedish Columnar aspens growing along north facing walls
were provided in the photographs. Again it is assumed they are growing
significantly below photosynthetic maximum.
• Species vary greatly in shoot growth response to light intensity.
• In a study of 4 broadleaf species of trees (two birch and two maples) shoot growth
was not adversely affected by reducing light intensity to 45% of maximum.
However, further reduction in light intensity caused decreases in various aspects
of shoot growth. One very shade tolerant species of maple had maximum height
growth between 45%-13% of maximum. All Species had more height growth at
45% of maximum compared to 100% of maximum.
• In another study light intensity had only limited effect on shoot elongation of
American Linden seedlings, which is considered to be a shade tolerant species.
• Local observations of broadleaf trees growing in shade to varying degrees are that
they may be as tall, have thinner crowns and twigs and in some cases orient
growth to a zone of higher light that makes them appear to lean toward the light.
In very dense shade height growth can be slowed considerably and crowns are
thin.
• Trees use carbohydrates produced in photosynthesis for physiological processes
of growth, reproduction, storage and defense. As less and less carbohydrates are
produced the tree makes adjustments to the allocation within its genetic limits.
Low light stress can be tolerated by shade tolerant species. At the extreme limit
that a species can tolerate, growth may be very slow and energy reserves may not
be adequate. This would be at or below the compensation point. The most shade
tolerant trees have the best adaptability to grow and function in low light
environment's
• When trying to determine the degree of impact from long term exposure to lower
light levels on different species in urban plantings, most often shade tolerance
ratings and empirical observations are used to infer results. The best observations
are those that most closely replicate the site being evaluated.
The trees selected for planting have the primary tree selection characteristic identified
for this site to varying degrees so do have potential to grow and function at this location.
Performance is stated as potential because there are not locations to evaluate that
replicate what is being proposed for 3 of the 4 species being used, and in the case of
Swedish columnar aspen two sites were evaluated with different wall heights. With
littleleaf linden one shade site with over topping trees was evaluated and one close
planting to a east facing wall was identified. The lindens were a different cultivar of
littleleaf linden than used on the project. Potential tree performance and function is
inferred from species tolerance ratings, literature reports and a some field
evaluations. There could be variance.
This is a standard requirement that is typically addressed in a note of the plans.
How will initially having no light (direct light) on trees at first affect photosynthesis
and growth rate.
I provide the following information taken from these and other sources and a few of my
empirical observations.
Physiology of trees by Kramer and Kozlowski, 1960
Growth and Development of Trees by Kozlowski Volume 1, 1971
• In the dark there is no photosynthesis
• With added light increments a compensation point is reached at which
photosynthesis and respiration are equal and there is no net carbon dioxide
exchange.
• With additional light above the compensation point, photosynthesis is
proportional to light intensity until light saturation occurs, and the ascending part
of a photosynthesis curve then becomes horizontal
• Three broadleaf trees in one study achieved maximum photosynthesis at one-third
or less of full light and any further increase in light intensity produced no further
increase in photosynthesis. Other broadleaf trees reach maximum rates of
photosynthesis at relatively low light intensities
• Three species considered to be shade tolerant to varying degrees are shown to be
at around 40% of observed maximum photosynthesis at 300 foot candles. One
species was at 100% observed maximum photosynthesis at 1000 foot candles
while two others were at around 70%-85% of observed maximum at this level of
light.
• Shade -tolerant trees make better use of light of low intensity than did trees
described as sun trees.
• In one accepted usage, of the term shade tolerance, it is defined as capacity to
endure shade; a tree which reaches maximum photosynthesis at relatively low
light intensity is tolerant while one whose rate of photosynthesis continues to
increase with each added increment of light up to full sun is considered intolerant.
• Shade is considered a stress just as drought is, and trees that have adaptations can
better deal with it.
• Shade tolerant trees can grow in light levels below photosynthetic maximum.
Some shade tolerant trees can grow under a forest canopy.
• The Delaware Plant partnership provides this information on Norway maple,
"Today Norway maple is a frequent invader of the urban and suburban forests. Its
extreme shade tolerance especially when young, has allowed it to penetrate
beneath an intact forest canopy".
• Local observations of Littleleaf Linden were made growing in a lot of shade from
the over topping canopies of Siberian Elm and have been provided in
photographs. It is assumed they are growing significantly below photosynthetic
maximum for this species.
In your professional opinion, what is the typical maximum radius for the four trees
scheduled for planting on the north face of the building?
Crimson Sentry Norway Maple
Height: 30'-35'
Width: 12%15'
Radius: 6'-7.5'
Source: Fort Collins Wholesale Nursery Descriptive Guide
Corinthian Littleleaf Linden
Height: 45'
Width: 15'
Radius: 7.5'
Source: Manual of Woody Landscape Plants by Michael A. Dirr
The photo I provided of a putative Corinthian Littleleaf Linden appears to be close to
these dimensions.
Swedish Columnar Aspen
Height: 30'-40'
Width: 10'-15'
Radius: 5'-7.5'
Source: Fort Collins Wholesale Nursery Descriptive Guide
My observations are that crown spread is most often narrower than than listed is the
descriptive guide.
Pyramidal Hornbeam
Height 30'-35'
Width: For the cultivar `Columnaris' Dr. Dirr states that it is spire -like but does not give
a width dimension. He goes on to discuss that there is confusion in the nursery trade
between the cultivar `Columnaris' and one called `Fastigiata'. "It is obvious that there is
confusion among upright -growing cultivars or that more than on fastigiated clone is in
the trade". The trees of pyramidal hornbeam that I provided in the photos appear to the
narrow growing cultivar `Fastigiata that I would estimate could have an eventual crown
spread between 10-15 feet.
Source: Manual of Woody Landscape plants by Michael Dir and field observations of
local specimens.
Do you have photos that available that demonstrates successful growth and
maturity of the Maple, Hornbeam, and Linden on the north face of a tall structure?
I have no additional photos available demonstrating the other species. Previously
included is a photo of a Littleleaf Linden growing in shade and another along an east
facing wall.
Given the high tree density and narrow space on the north side of the building, will
an irrigation water delivery system be required to ensure tree survival?
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Subj: FW: Trees at The District
Date: 4/25/2012 11:49:45 A.M. Mountain Daylight Time
From: TSHEPARDafcgov.com
To: Rvlopez(a)aol.com
Hello Rich — I am forwarding this e-mail and attachment from our City Forester, Tim Buchanan to me
dated April 20, 2012 regarding the trees to be planted on the north side of the proposed buildings. Linda
Ripley referred to the information from the City Forester in her presentation as well as in her response to
citizen input. The attachment includes pictures that were presented into the record by one of the citizens,
perhaps Mr. Tim Erickson.
Please let me know if you have any questions.
Thanks,
Ted
From: Tim Buchanan
Sent: Friday, April 20, 2012 2:39 PM
To: Ted Shepard
Cc: Ralph Zentz; 'timaerickson@gmail.com'; 'Linda Ripley'
Subject: Trees at The District
Hi Ted,
As a result of some discussion at the hearing for The District on 4-6-12, Linda Ripley asked me
to provide you some information about the Forestry review of the project, specifically trees
shown to be planted along the north wall. This information is being provided to you, Linda and
Tim Erickson.
The north wall of The District has a narrow planting area in the shade. The applicant desires to
screen the wall with trees. The primary criterion for tree selection at this site includes narrow
crown form, height to screen the wall and shade tolerance.
Forestry staff reviewed and presented tree species to the project landscape architect, which have
the characteristics of a narrower crown form and the height to screen the wall, with adaptability
to shade. The trees selected for planting along the north wall have all these characteristics to
varying degrees, so they do have potential to grow and function on this site. More than one
species needs to be used in this area to meet the minimum species diversity standard of 15%.
Photos are attached of the five species of trees shown to be used along the north wall.
Two site meetings occurred with the project landscape architect and 8 comments were provided
through round one and two. Comments and suggestions were acknowledged or incorporated.
Forestry staff visited the site separately on two other occasions.
A meeting occurred with Mr. Tim Erickson at his request to discuss the trees at The District. Part
of this meeting involved making a site visit to the proposed project.
Tim Buchanan
City Forester
221 6361
Wednesday, April 25, 2012 AOL: Rv lopez