HomeMy WebLinkAboutBiologist letterCONFLUENCE
ENVIRONMENTAL COMPANY
To: Sean Dugan, Tree Solutions Inc.
From: Kerrie McArthur, PWS Grant Novak
Date: July 11, 2017
Re: 800 SW 27th Street Stream Buffer Functional Assessment
Enclosures: Plantina Plan
Confluence Environmental Company (Confluence) has prepared this assessment on behalf of
Tree Solutions Inc. (Tree Solutions) to define the functions and values provided by the current
vegetation community within the existing stream and wetland buffers and describe how the
proposed project is anticipated to result in no net loss of buffer functions or values.
1.0 PROPOSED PROJECT
The proposed project site is located at 800 SW 27th Street, Renton, Washington. The 13.2 -acre
site includes an industrial warehouse and parking lot adjacent to the Black River. The river is
adjacent to the eastern property line and a wetland is located on the other side of the river (City
of Renton 2017) (Figure 1). Both wetlands and streams are defined as regulated critical areas by
the City of Renton and, as such, have regulatory buffers with associated development
requirements. Both the wetland and stream buffers extend onto the property and include the
proposed planting areas (Figure 1).
On the property, buffer vegetation is limited to non-native vegetation near the entrance, along
the side of the building, and in the parking lot strips. In 2017 Tree Solutions evaluated 14 trees
along the side of the building (Tree Solutions 2017a). Tree Solutions recommended removing
the trees, citing the following issues in their evaluation:
While the trees exhibited good health and structure, they were not ideal for the space.
Since the tree species planted adjacent to the building may grow to over 18 inches in
diameter and over 50 feet tall, it was determined the narrow planting strip is not a
suitable location for the species.
• The trees have outgrown the space, requiring maintenance to prune them away from the
building and provide clearance for vehicles. This maintenance needs to occur on a
regular basis and would likely be required in perpetuity if the trees remain.
146 N Canal St, Suite 111 . Seattle, WA 98103 • www.confenv com
Sean Dugan, Tree Solutions Inc.
July 11, 2017
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Figure 1 Project area with mapped critical areas (Tree Solutions 2017a).
Tree Solutions observed tree roots causing damage to the base of windows and flashing
down the side of the building. The roots were pushing up against the curb and cracks
and were visible in several locations.
Since the trees needing to be removed are within a stream and wetland buffer, the tree removal
necessitates installing new plants and a functional assessment to demonstrate that the proposed
plant installation results in no net loss of functions or values.
2.0 FUNCTIONAL ASSESSMENT
This section describes the existing buffer conditions as well as conditions that would be
anticipated if the proposed planting plan is implemented. Additionally, this section describes
how the proposed planting plan is anticipated to result in the same level of function or value
when compared to existing conditions. Buffers provide numerous functions and the values of
these functions to human society depend on a complex set of relationships between the critical
area (i.e., stream and wetland) and the buffer.
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Figure 1 Project area with mapped critical areas (Tree Solutions 2017a).
Tree Solutions observed tree roots causing damage to the base of windows and flashing
down the side of the building. The roots were pushing up against the curb and cracks
and were visible in several locations.
Since the trees needing to be removed are within a stream and wetland buffer, the tree removal
necessitates installing new plants and a functional assessment to demonstrate that the proposed
plant installation results in no net loss of functions or values.
2.0 FUNCTIONAL ASSESSMENT
This section describes the existing buffer conditions as well as conditions that would be
anticipated if the proposed planting plan is implemented. Additionally, this section describes
how the proposed planting plan is anticipated to result in the same level of function or value
when compared to existing conditions. Buffers provide numerous functions and the values of
these functions to human society depend on a complex set of relationships between the critical
area (i.e., stream and wetland) and the buffer.
www.confenv. com page 2 of 6
Sean Dugan, Tree Solutions Inc.
July 11, 2017
2.1 Methods
lb 1
CONFLUENCE
Buffer functions were evaluated based on existing and proposed conditions to provide a
comparison and to determine if there is or is not a net loss of function. The following four
functions were evaluated under this functional assessment because these functions are directly
affected by the proposed planting plan.
• Vegetative Structure
• Vegetation Species Diversity
• Presence of Native Vegetation
• Water Quality
2.2 Existing Buffer Conditions
As stated above, and described in the arborist's report (Tree Solutions 2017a), vegetation along
the building consists mostly of non-native trees. Some shrubs and ground cover are also
present. The parking lot strip where planting of native trees and shrubs is proposed is
predominantly grassy lawn.
2.2.1 Existing Buffer Functions
The following sections describe the existing buffer functions evaluated for this assessment.
Vegetative Structure
Currently, the vegetated portions of the wetland and stream buffers on the property provide
limited vegetative structure. While the existing vegetated areas are primarily mono -specific
stands of non-native vegetation, the existing mature trees provide perching and some nesting
opportunities for tree -nesting birds, resulting in a moderate function for vegetative structure.
However, the maintained lawn area results in a low -function condition for vegetative structure.
Vegetation Species Diversity
Currently, the vegetated portions of the wetland and stream buffers on the property provide
limited vegetative species diversity. The existing vegetation is a mono -specific stand of non-
native trees or maintained lawn. The lack of species diversity results in a low -functioning
condition.
Presence of Native Vegetation
The vegetation proposed for removal is non-native. Vegetative communities with little to no
native vegetation are considered to be low functioning.
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Sean Dugan, Tree Solutions Inc.
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July 11, 2017 CONFLUENCE
Water Quality
Additionally, the existing vegetation provides little water quality function. The bare ground
and maintained lawn do not contain the vegetative structure needed to slow water velocities or
provide filtration. The lack of vegetative structure and maintained lawn are considered to
provide low water quality functions.
2.2.2 Values
The City of Renton Municipal Code (RMC) 4-3-050 requires that planting plans located within
stream and wetland buffer must use native vegetation.
Native vegetation is considered to have a higher ecological value than non-native vegetation.
Since the vegetation proposed for replacement in the planting plan is non-native, the value of
these plants is considered to be low.
2.3 Proposed Planting Plan
Implementation of the proposed planting plan would result in the removal of 14 trees along the
east side of the building. The trees would be replaced with a mix of 19 native shrubs and trees
(Tree Solutions 2017b). The proposed planting plan replaces the trees removed at a ratio greater
than 1:1. The proposed planting plan is attached.
2.3.1 Proposed Buffer Functions
The following sections describe the buffer functions evaluated for this assessment once the
proposed planting plan is implemented.
Vegetative Structure
The proposed planting plan would decrease the vegetative structure adjacent to the building by
removing the trees. However, the proposed planting plan would also increase the vegetative
structure in the lawn area. Thus, there would be no change in this function's condition.
It is important to note that most of the trees and shrubs would be planted within a parking lot
strip located along the eastern portion of the property, which is closer to the stream and
wetland edge. Wildlife are likely to benefit more from increased vegetative structure and a
native plant community closer to the stream and wetland than if these plants were installed
along the building. In addition, by installing most of the plants, and all the trees, within the
parking lot strip, damage to the building will not occur.
Vegetation Species Diversity
As shown on the proposed planting plan, a mix of five different species of native trees and
shrubs is proposed. One species of non-native tree will be removed. Implementing the
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Sean Dugan, Tree Solutions Inc.
July 11, 2017
CONFLUENCE
111 K11..,1 V I it ( 11101111
proposed planting plan will increase species diversity. Thus, implementing planting plan
would increase this function from a low to moderate condition.
Presence of Native Vegetation
As stated above and shown on the proposed planting plan, all species proposed for planting are
native. Thus, implementing the planting plan would increase this function from a low to
moderate condition.
Water Quality
Planting a mixture of trees and shrubs in the parking lot strip will also increase the vegetative
structure needed to slow runoff velocities and increase filtration. Thus, implementing the
planting plan would increase this function from a low condition to a moderate condition.
Table 1 summarizes the functions of the existing and proposed buffers.
Table 1 Buffer Assessment Summary
2.3.1 Values
By replacing non-native species with native species, values are improved, as native vegetation
has been deemed to have a higher ecological value than non-native vegetation (City of Renton
Municipal Code 4-3-050).
In summary, the proposed tree removal and planting of native vegetation would result in no
net loss of function or value of the on-site buffer. In fact, replacing non-native plants with native
plants is expected to increase functions and value.
www.confenv. com page 5 of 6
Existing
ProposedFunction
Bu ffer Quality
Buffer Quality
Functional
While the project would remove existing mature trees, the proposed
planting plan will increase the vegetative structure by planting a
Vegetative Structure
Low/Moderate
Low/Moderate
mixture of trees and shrubs on site compared to current conditions.
Once planted trees mature, vegetative structure is expected to be
nater than current conditions.
Vegetation Species
The proposed planting plan will increase the number of species on
Diversity
Low
Moderate
site compared to current conditions by removing t species of tree
and re lantin w th 5 species of trees and shrubs.
Presence of Native
Low
Moderate
The proposed planting plan will increase the number of native
Vegetation
species on site compared to current conditions.
Water Quality
Low
Moderate
The proposed plan will increase the structure needed to slow runoff
velocities and increase filtration.
2.3.1 Values
By replacing non-native species with native species, values are improved, as native vegetation
has been deemed to have a higher ecological value than non-native vegetation (City of Renton
Municipal Code 4-3-050).
In summary, the proposed tree removal and planting of native vegetation would result in no
net loss of function or value of the on-site buffer. In fact, replacing non-native plants with native
plants is expected to increase functions and value.
www.confenv. com page 5 of 6
Sean Dugan, Tree Solutions Inc.
July 11, 2017 CONFLUENCE
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3.0 REFERENCES
Tree Solutions (Tree Solutions Inc.). 2017a. Arborist Report for 800 SW 2711 Street, Renton,
Washington. Prepared for TrojanLitho, Renton, Washington, by Tree Solutions Inc., Seattle,
Washington.
Tree Solutions (Tree Solutions Inc.). 2017b. Planting Plan for 800 SW 2711 Street, Renton,
Washington. Prepared for TrojanLitho, Renton, Washington, by Tree Solutions Inc., Seattle,
Washington.
1175.0011800 SW 27m Fund Assessment.doc
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