The purpose of this chapter is to promote community health, safety, and welfare by protecting the trees in Silverton’s urban forest and setting development standards, for their planting, care, and removal. Together, elements of the natural and built environment contribute to the visual quality, environmental health, and character of the community. Trees provide climate control through shading during summer months and wind screening during winter. The collective aboveground biomass of trees store and isolate carbon allowing removal of pollution. In addition, their leaves and stems help avoid water runoff. Trees and other plants can also buffer pedestrians from traffic. Walls, fences, trees, and other landscape materials also provide vital screening and buffering between land uses. Landscaped areas help to control surface water drainage and can improve water quality, as compared to paved or built surfaces. This chapter regulates the removal, protection, and planting of trees throughout the development process to encourage development to incorporate existing trees, particularly high quality or larger trees and groves, into the site design, to retain sufficient space to plant new trees, and to ensure suitable tree replacement when trees are removed. It is the intent of these provisions to lessen the impact of tree removal and to ensure mitigation when tree preservation standards are not met. (Ord. 25-09 § 7, 2025).

This chapter only applies to development properties within Silverton’s city limits. Trees within public rights-of-way that are managed by the state of Oregon are exempt from the regulations of this chapter. Trees located on lands or within utility corridor easements that are owned by state or federal agencies are also exempt from the regulations in this chapter. However, these trees may be subject to other city regulations or intergovernmental agreements. Furthermore, the city retains summary abatement authority for nuisances posing an immediate threat to public safety. (Ord. 25-09 § 7, 2025).

The following definitions will apply to the terminology used in this chapter. If a definition is not listed in this chapter, the definition in Chapter 1.5 SDC will apply. Where definitions are not provided in this chapter or Chapter 1.5 SDC, their normal dictionary meaning will apply:

“Arboriculture” means the practice and study of the care of trees and other woody plants in the landscape.

Arborist. See “Certified arborist.”

“Caliper” is the standard trunk diameter measurement for trees taken six inches above grade for up to and including four-inch caliper size and 12 inches above grade for a large tree. This may be contrasted with DBH which is always measured at four and one-half feet above grade.

“Canopy tree” is a deciduous tree with a mature height of more than 25 feet. The following sources are approved for determining mature height:

1. Silverton tree and tree crown area reference list (Figure 3.6.170);

2. https://landscapeplants.oregonstate.edu/node/2163 (Oregon State University College of Agricultural Sciences – Department of Horticulture, Landscape Plants);

3. The Tree Book by Michael A. Dirr and Keith S. Warren;

4. Manual of Woody Landscape Plants by Michael A. Dirr;

5. When these sources do not list the species or variety in question other published sources are acceptable.

“Certified arborist” means a person who has a current and valid designation of “ISA Certified Arborist” by the International Society of Arboriculture, demonstrating specialized knowledge, experience, and training relating to arboriculture.

“City” means the city of Silverton.

“City manager” means the city manager or the city manager’s authorized representative or designee.

“City trees” means trees located on property designated as city property, including public parks, and trees located in public right-of-way not defined as street right-of-way.

“Community development director” means the community development director or the director’s designee.

“Conservation” means maintaining significant native trees and vegetation in the landscapes of development and protecting vegetation in sensitive natural areas. The use of mature, native vegetation within developments is a preferred alternative to removal of vegetation followed by replanting. Mature landscaping provides summer shade and wind breaks, controls erosion, and allows for water conservation due to larger plants having established root systems.

“Critical root protection zone” means the distance extending out from and surrounding a tree trunk representing the essential area of the roots that must be maintained for the tree’s survival. The critical root zone distance is calculated by multiplying the diameter of the tree, in inches, measured at four and one-half feet above the mean ground level, DBH, by 12 or the dripline of the tree, whichever is larger. For example, a tree with a diameter of two inches would have a critical root zone of 24 inches, which is two times 12 all around the tree.

“Crown” means area of the tree above the ground, measured in mass, volume, or area extending from the trunk and including the branches, stems, leaves, and reproductive structures.

“Crown area” means the average area in square feet that the tree crown covers (Figure 3.6.120-1).

“Cultivated” means trees and plants grown for their ornamental traits or other ecological and sociological benefits. They may include wild plants and native species.

Figure 3.6.120-01: Measuring Crown Area

“Cutting” means the felling or removal of a tree, or any procedure that results in the death or substantial destruction of a tree. Cutting does not include normal trimming or pruning but does include topping of trees.

“DBH” means the diameter at breast height. See “Diameter at breast height.”

“Dangerous tree” is a tree which in the professional assessment of a certified arborist has a strong likelihood of causing a hazard to life or property.

“Dead tree” means a tree that is dead or has been damaged beyond repair or where not enough live tissue, green leaves, limbs, or branches exist to sustain life.

“Deciduous tree” means trees which shed or lose foliage at the end of the growing season.

“Development” means all improvements on a site, including buildings, other structures, parking and loading areas, landscaping, paved or graveled areas, and areas devoted to exterior display, storage, or activities. Development includes improved open areas such as plazas and walkways but does not include natural geologic forms or unimproved land.

“Development impact area” is the area on a site affected by proposed site improvements, including buildings, structures, parking and loading areas, landscaping, and paved or graveled areas. The “development impact area” also refers to areas devoted to storage of materials, or construction activities such as grading, filling, trenching, or other excavation necessary to install utilities or access.

“Development review” is a generic term meaning any type of review undertaken to ensure compliance with this code.

“Diameter at breast height” or “DBH” means the measurement of trees as measured at a height four and one-half feet above the mean ground level at the base of the tree (Figure 3.6.120-02). The DBH may be determined by measuring the circumference of the tree trunk four and one-half feet above the mean ground level at the base of the tree and dividing by 3.14. Trees existing on slopes are measured at the mean ground level at the base of the tree (Figure 3.6.120-02). When the trunk branches or splits less than four and one-half feet from the ground, measure the smallest circumference below the lowest branch and divide by 3.14 (Figure 3.6.120-02). For multi-stemmed trees, the size is determined by measuring all the trunks, and then adding the total diameter of the largest trunk to one-half the diameter of each additional trunk. A multi-stemmed tree has trunks that are connected above the ground and does not include individual trees growing close together or from a common root stock that do not have trunks connected above the ground (Figure 3.6.120-02).

Figure 3.6.120-02: Measuring Diameter at Breast Height

Figure 3.6.120-03: Distinguishing Circumference and Diameter

“Dripline” means an imaginary line around a tree or shrub at a distance from the trunk equivalent to the canopy (leaf and branch) spread.

“Dying tree” means a tree that is diseased, infested by insects, deteriorating, or rotting, as determined by a certified arborist, and that cannot be saved by standard horticultural or arboricultural practices, or a tree that must be removed to prevent the spread of infestation or disease to other trees.

“Evergreen” means trees and plants that retain their foliage throughout the year.

“Fee schedule” is the schedule of city fees and charges adopted by city council.

“Grove” means a contiguous and clearly demarcated group of eight or more trees (or three or more Oregon white oaks) growing closely together in a manner that creates a distinct and contiguous canopy. All trees in the grove must be greater than significant size DBH for their species as listed in this chapter. They may belong to the same species or a mixture of species covering an area of less than one-eighth of an acre, or 5,445 square feet.

“Heritage grove” is a grove that has been formally recognized by the historic landmarks commission and the city for its size, age, species, and/or historical, habitat, or horticultural significance.

“Heritage tree” is a tree designated as a historic landmark tree, a historic tree, or a heritage tree by the historic landmarks commission and the city for its size, age, species, and/or historical, habitat, or horticultural significance.

“Infected” means any appearance of a disease on trees or plants that may be a menace to horticultural or farm crops.

“Infested” means when the adult, egg, larvae or pupae of an insect or other plant pest is found in such numbers as, in the opinion of the city, to be a menace to horticultural or farm crops.

“Invasive species” means nonnative organisms that cause economic or environmental harm and can spread to new areas of the city. “Invasive species” does not include humans, domestic livestock, or non-harmful exotic organisms.

“ISA” means the International Society of Arboriculture.

“ISA best management practices” means the guidelines established by ISA for arboricultural practices for use by arborists, tree workers, and the people who employ their services.

“Large tree” is a tree of a species which normally reaches a height of 40 feet or more upon maturity.

“Major pruning” means removal of 20 percent or more of the live crown or pruning cuts removing branches with diameter greater than 40 percent of tree DBH at the point one inch above where the branch attaches to the trunk, or six inches, whichever is greater, or removal of or injury to 15 percent or more of the root system during any 12-month period.

“Mature trees” are trees that are close to their full height and crown size, these dimensions being determined by species and site factors.

“Multi-stemmed tree” is a tree having two or more main trunks arising from the root collar or from the main trunk. Their size is determined by measuring all the trunks, and then adding the total diameter of the largest trunk to one-half the diameter of each additional trunk if the tree is classified as significant.

“Owner” means any person who owns land, or a lessee, agent, employee, or other person acting on behalf of the owner with the owner’s written consent.

“Person” means any individual, partnership, co-partnership, firm, company, corporation, association, joint stock company, trust, estate, governmental entity, or any other legal entity, or their legal representatives, agents, or assigns.

“Pest” means a disease, microscopic organism, insect, nematode, arthropod, parasite, or a noxious weed as defined in ORS 569.175 (definitions for ORS 569.175 to 569.195), capable of having a significant adverse effect on the environmental quality of this state or of causing a significant level of economic damage in this state, including but not limited to damage to agricultural, horticultural or forest plants, crops, commodities or products.

“Plant” means to plant, to put or set a growing plant, whether with roots or a piece of a plant that has the capacity to grow roots, into the ground so that it can grow.

“Planter strip” means a landscaped area for city-approved street trees and other plantings within the public right-of-way, usually a continuous planter area between the street and a sidewalk. See also “Tree well.”

“Public agency” means any public agency or public utility as defined in ORS 757.005, or a drainage district organized under ORS Chapter 547.

“Public right-of-way” means land dedication or easement conveyance to the city or other public entity for public use; typically for streets, utilities, parkland and/or similar facilities. Permanent structures, objects and buildings are not allowed to project over or encroach into public rights-of-way, except as allowed by the city for landscaping and trees.

“Public tree” means a tree on land owned or maintained by the city.

“Public works director” means the public works director or the director’s designee.

“Remove or removal” means to fell or sever a tree or the intentional use of any procedure, the natural result of which is to cause the death or substantial destruction of the tree. Removal does not in any context include normal trimming of trees.

“Significant tree” means:

1. Any tree meeting the threshold size standards in SDC 3.6.150(A).

“Small tree” is a tree species which normally does not reach a height that exceeds 25 feet upon reaching maturity.

“Staging” means a designated area for the storage of equipment and vehicles, stockpiles, waste bins, and other construction-related materials during a construction project. Any construction trailers are to be included in the construction staging area. In some cases, more than one staging area may be established on site.

“Stormwater runoff” is any surface water runoff or runoff in channels which results directly either from a rainstorm or from the melting of snow. The U.S. EPA has declared pollution from stormwater runoff to be the nation’s largest source of water quality problems.

“Street tree” means a city-approved tree planted in a planter strip or tree well in a city street right-of-way. When any portion of the trunk of a tree crosses a public right-of-way line at ground level, it is considered a street tree.

“Street tree and tree crown area reference list” includes tree species approved by the city for planting within the right-of-way and tree crown calculations for residential development.

“Sustainable and urban tree advisory board” advises the city council and/or the planning commission on programs, practices and decision-making involving all aspects of urban forestry.

“Topping” means the cutting back of limbs or trunks within the tree’s crown to buds, stubs, or lateral branches not large enough to assume the terminal role. It is an inappropriate pruning practice used to reduce tree height by cutting to a predetermined crown limit without regard to tree health or structural integrity. Topping does not include acceptable pruning practices as described in the American National Standards Institute (ANSI) “A300 Pruning Standards” and companion “Best Management Practices for Tree Pruning” published by the International Society of Arboriculture, such as crown reduction, utility pruning, or crown cleaning to remove a safety hazard, dead or diseased material. Topping is considered “removal.”

“Tree” means a self-supporting, perennial woody plant characterized by one main trunk or in some cases multiple trunks, and one main canopy of leaves, usually growing to a height of 15 feet or higher.

“Tree canopy” means the ground area that, when viewed from above the crown of one or more trees, is mostly covered by the tree(s). For deciduous trees, canopy area is based on the time of year when foliage is present.

“Tree circumference” (see DBH) means the distance measured around the trunk of a tree at four and one-half feet above the mean ground level from the base of the trunk. For multi-stemmed trees, the size is determined by measuring all the trunks, and then adding the total diameter of the largest trunk to one-half the diameter of each additional trunk.

“Tree contractor” means a person licensed to complete tree servicing work by the state of Oregon Construction Contractors Board (CCB).

“Tree fund” means the tree fund as created by this chapter.

“Tree well” means a planter area cut out of a sidewalk within the street furnishing zone, planted with a street tree and including ground cover or a grate cover; typically used in commercial districts where on-street parking or pedestrian traffic makes the use of a planter strip impracticable.

“Trimming” is the selective removal of plant parts to meet specific goals and objectives, using best practices as set forth by American National Standards Institute (ANSI) A300 Standards.

“Urban forest” means the trees and vegetation that exist within the city.

“Urban heat islands” are metropolitan places where buildings and pavement cause the area to be hotter than outlying areas, with impacts felt most during summer months. Paved roads, parking lots, and buildings absorb and retain heat during the day and radiate that heat back into the surrounding air.

“Utility” is a public utility, business, or organization that supplies energy, gas, heat, steam, water, communications, or other services through or associated with telephone lines, cable service, and other telecommunication technologies, sewage disposal and treatment, and other operations for public service.

“Wild” is an endemic species, or species native to the Silverton area of the Willamette Valley ecoregion. It is a self-sown (grown from a non-human-planted seed) or self-cloning (by root pieces, suckers, branch layer, or sprout) plant.

“Woodland” is an area of contiguous wooded vegetation where trees are at a density of at least one significant DBH tree per 325 square feet of land where the branches and leaves form a continuous canopy. A woodland shall include areas with continuous canopy of trees over an area of at least 20,000 square feet and with any dimension being not less than 35 feet. A woodland may be delineated through an aerial photograph or a ground survey. A woodland shall include both understory and protected trees. (Ord. 25-09 § 7, 2025).

A. Authority. The city of Silverton shall have control of all street trees, shrubs, and other plantings now or hereafter in any street, park, public right-of-way or easement, or other public place within the city, and shall have the power to plant, care for, maintain, remove, replace, and require the care of, maintenance of, removal, and replacement of such trees, shrubs and other plantings.

B. Public Trees. The public works director is responsible for the implementation and enforcement of public trees and shall have jurisdiction over all street trees and city trees, including the planting, removal, care, maintenance, and protection thereof.

C. Private Trees. The community development director is responsible for the implementation and enforcement of the provisions in this chapter.

D. Advising Body. The sustainable and urban tree advisory board advises the city council and/or the planning commission on programs, practices and decision-making involving all aspects of urban forestry. Duties and responsibilities include the following:

1. Study, investigate and provide advice to the city council and/or the planning commission on the preservation, pruning, planting, replanting, removal, or disposition of the urban forest.

2. Provide advice to the city council and/or the planning commission on policy and regulatory issues involving trees, including climate adaptation and mitigation efforts.

3. Provide outreach and education to the community on tree-related issues and concerns.

4. Provide recommendations to the city council on the allocation of funds from the tree fund.

5. The sustainable and urban tree advisory board, when requested by the city council, will consider, investigate, make findings, report, and make recommendations on any special matter or question coming within the scope of its work. (Ord. 25-09 § 7, 2025).

A. Establishment. A city tree fund is hereby established for the collection of any funds used for the purpose and intent set forth by this chapter.

B. Funding Sources. The following funding sources may be allocated to the tree fund:

1. Tree permit revenue.

2. Payments received in lieu of required and/or supplemental plantings.

3. Civil penalties collected pursuant to this chapter.

4. Agreed-upon restoration payments or settlements in lieu of penalties.

5. Sale of trees or wood from city property.

6. Donations and grants for tree purposes.

7. Other monies allocated by the city council.

C. Funding Purposes. The city will use the tree fund for the following purposes:

1. Expanding, maintaining, and preserving the urban forest within the city;

2. Planting and maintaining trees within the city;

3. Supporting public education related to urban forestry;

4. Assessing urban forest canopy coverage; or

5. Any other purpose related to trees, woodland protection, and enhancement as determined by the city council. (Ord. 25-09 § 7, 2025).

Intent. Trees provide important ecological and social services to the residents of Silverton, but it takes years and sometimes decades to reach a size that makes a substantial contribution. Each tree species varies in the size it may reach at maturity. The size of a tree is not the only measure of its contribution to society or its ecological impact.

A. Significant Trees. The significant tree designations set forth in this subsection establish a threshold trunk size, measured in DBH, for various tree species. A significant tree is defined by the DBH as set forth below.

1. Significant DBH. Figure 3.6.150-01 gives the DBH at which the city considers each tree species significant. Trees with DBH at or greater than that listed DBH are significant and must be treated as such when establishing their status and protection according to this chapter.

2. In order to establish the significance of a tree within city limits, an applicant shall complete the following, in the order listed below:

a. Identify trees four inches or greater in DBH that are located on the development property.

b. Determine the species identity of such trees.

c. Measure the circumference of such trees at DBH. Divide the circumference in inches by 3.14 to determine the product, inches DBH.

3. Mature Crown Area. To calculate mature crown area square half of the mature width then multiply by 3.14. For instance a Grand Fir has a width at maturity of 30 feet, therefore 15 feet times 15 feet times 3.14 equals 706.5 square feet.

4. Minimum Landscape Standards. Significant trees are protected as set forth in subsections below. An applicant may credit significant trees protected in accordance with this chapter toward meeting the minimum landscape area standards in Chapter 3.2 SDC.

* The following sources are approved to establish generally accepted mature height, width, and crown area in the order below:

1.    Silverton Tree and Tree Crown Area Reference List (Figure 3.6.170)

2.    https://landscapeplants.oregonstate.edu/node/2163 (Oregon State University College of Agricultural Sciences – Department of Horticulture – Landscape Plants)

3.    The Tree Book by Michael A. Dirr and Keith S. Warren

4.    Manual of Woody Landscape Plants by Michael A. Dirr

5.    When these sources do not list the species or variety in question other published sources are acceptable.

B. Heritage Trees. The historic landmarks commission may designate certain trees or groups of trees as “heritage trees” within the city; provided, that the landowner(s) of record upon which the tree or grove is located consents. The consent of a property owner will bind all successors, heirs, and assigns. The purpose of the heritage tree or heritage grove designation is to recognize, foster appreciation of, and protect trees and groves having special importance to the community. The historic landmarks commission shall have the authority to determine whether a tree or grove recommended for consideration qualifies as a heritage tree or grove. Any member of the public, whether a historic landmarks commission member, property owner, or third-party citizen, may nominate trees or groves to the historic landmarks commission. Once a tree or grove is designated as a heritage tree or heritage grove, it will remain so unless it becomes necessary to classify it as a dangerous tree and be removed as such. Except as otherwise expressly provided in this chapter, heritage trees and groups of heritage trees may not be removed without the express consent of the historic landmarks commission.

C. Tree Conservation.

1. Applicability. The purpose of this section is to incorporate trees into the landscapes of development and to protect significant trees and trees in sensitive natural areas. The use of mature, native trees within developments is a preferred alternative to removal of trees and replanting. Mature landscaping provides summer shade and wind breaks, controls erosion, and allows for water conservation due to larger trees having established root systems.

The tree preservation requirements in this subsection apply to the following types of development:

a. Land divisions;

b. Design reviews/conditional uses;

c. Expansion of existing parking lots that results in an increase in paved surfaces;

d. Conversion of gravel parking lots to paved parking lots.

2. Protection and Planting Standards.

a. Tree Canopy Preservation and Planting Standards for Private Property. There is a target tree canopy standard for all land use categories on private property. The target tree canopy shall be met either through preservation of existing trees, replanting of removed trees, or planting new trees where a site did not meet the standard prior to development, as provided in this chapter. Public right-of-way and proposed public right-of-way are not considered part of the development site for the purposes of the canopy coverage calculations. When calculating canopy threshold percentages, all percentage numbers shall be rounded to the nearest whole number. See Chapter 3.2 SDC for street tree planting requirements.

b. Tree Preservation on Public Lands. Trees on public lands shall not be damaged or destroyed, except as approved by the city to address an immediate hazard to public safety, and except as otherwise exempted in subsection (C)(8) of this section.

c. Tree Preservation on Private Property. Tree protection on private property shall follow subsections (C)(2)(c)(i) through (C)(2)(c)(ii) of this section during the development process, as applicable.

i. Target Tree Canopy. If a development site has a tree canopy coverage of significant trees greater than the standard, trees may be removed provided the standard is still met after removal. The developer may request on-site existing tree removal up to 30 percent below the target tree canopy standard percentage for its use category identified in subsection (C)(2)(a) of this section with mitigation provided per subsection (C)(4) of this section. The developer may request tree removal in excess of the 30 percent below the target tree canopy standard which is a discretionary review by the planning commission following SDC 4.2.510 and with mitigation provided per subsection (C)(4) of this section.

ii. If a site does not have a tree canopy coverage of significant trees greater than the standard, the developer may request on-site existing tree removal up to 30 percent of the existing tree canopy with mitigation provided per subsection (C)(4) of this section. The developer may request tree removal in excess of the 30 percent existing tree canopy which is a discretionary review by the planning commission following SDC 4.2.510 and with mitigation provided per subsection (C)(4) of this section.

d. Parking Lot Standards. Shade trees shall be evenly distributed and conform to the criteria in Chapter 3.2 SDC, SDC 3.2.300(E)(1)(a) through (E)(1)(h) and (E)(3). “Evenly distributed” means that the trees are distributed around the parking lot perimeter and between parking bays to provide a partial canopy. At a minimum, one canopy tree per 10 contiguous (side-by-side) parking spaces shall be provided. All parking area planters with trees shall have dimensions of not less than 48 square feet of area, or not less than six feet in width by eight feet in length, to ensure adequate soil, water, and space for healthy plant growth. Such areas shall have irrigation or temporary irrigation to ensure plant survival and success. Parking lot trees may count toward minimum canopy coverage requirements per Figure 3.6.150-02.

e. Oregon White Oak. Notwithstanding anything to the contrary in this section, it is unlawful to remove any significant Quercus garryana (Oregon white oak) tree within the city limits without first making application to the city and obtaining a permit – except as otherwise exempted in subsection (C)(8) of this section.

f. Any significant Oregon white oak which is removed shall be replaced in accordance with subsection (C)(4)(a) of this section, and an additional Oregon white oak removal fee per SDC 3.6.190 shall also apply to the required mitigation.

g. When the trunk of a tree crosses a property line at ground level it is considered an on-site tree except when the trunk crosses a public right-of-way line at ground level, it is considered a street tree. Public right-of-way will be considered off-site for the purpose of this section.

h. Any tree saved and protected through a land division application must be identified and labeled on the site plan. Prior to the final plat being signed, a sign shall be posted at each tree or grove stating the trees are required to remain and be protected through development and include penalty fees for violation. See requirements for tree protection during construction in this chapter, SDC 3.6.200. Signs shall be weatherproof and installation shall not cause any damage to the tree.

3. Credits.

a. Significant Trees. Significant healthy trees with DBH of more than 25 percent greater than significant for their species shall receive additional canopy credits over their existing tree crown area which shall be factored into the target tree canopy percentage calculations as defined in Figure 3.6.150-03 below.

b. The following table shall be used when calculating the target tree canopy percentage for significant trees with 25 percent or less than DBH than significant for their species and for trees that are to be planted to meet the target tree canopy:

c. In cases where a portion of the crown area of on-site trees extends off site, the entire crown area is eligible for credit towards the tree canopy requirements. In cases where a portion of the crown area of off-site trees on private property extends on site, the crown area is not eligible for credit towards the tree canopy requirements.

d. If trees die or are removed within three years for which credits were issued, those trees must be replaced or mitigated per this chapter.

4. Mitigation Required.

a. Tree Replacement. Where removal of significant trees is approved below the target tree canopy, and such removal or damage is not otherwise exempted in subsection (C)(8) of this section, the city shall require mitigation and the applicant shall submit a tree planting plan that demonstrates the target tree canopy will be met utilizing the tree planting standards in Figure 2.6.150-4. Where mitigation is approved in excess of the 30 percent below the target canopy, in addition to the plan that demonstrates meeting the target tree canopy, above, the canopy removal in excess of the 30 percent shall be mitigated at double the amount in canopy square feet.

i. Mitigation and canopy replacement shall be proportionate to the loss of significant trees as described above. Where complete mitigation on site is not practical due to the amount of trees required for mitigation resulting in a target tree canopy of more than 50 percent above the target, the city shall accept an in-lieu fee for mitigation (see SDC 3.6.190).

5. Application Requirements. For applications listed in subsection (C)(1) of this section an analysis must demonstrate compliance with the applicable provisions of this chapter. Professionals such as ISA certified arborists, engineers, landscape architects, soil scientists, and surveyors may assist as needed in preparing the required information. The minimum submittal requirements include an inventory of existing trees on site, a tree preservation plan, and a tree planting plan. If multiple construction applications are required for a development proposal, including demolitions and subsequent construction, the same plans shall be included with each application.

a. Existing Tree Inventory Requirements.

i. Survey the locations of all trees at least four-inch DBH that are on site, within abutting public rights-of-way, and on abutting sites with root protection zones that extend into the site. The locations and information for trees on abutting sites may be estimated. All invasive trees, regardless of size, are to be located.

ii. Number each tree for identification on the plans.

iii. Identify the common name and scientific name of each tree.

iv. Measure and provide the DBH of each tree in inches according to accepted ISA standards.

v. Measure the approximate average crown radius of each tree in feet.

vi. Provide the crown area of each tree using the formula: (crown radius)2 x π.

vii. Identify if the tree is significant per Figure 3.6.150-01.

viii. Identify if the tree is invasive per the Oregon Noxious Weed List or Silverton Invasive and Potential Nuisance Tree list, Figure 3.6.150-06.

ix. Identify if the tree is a heritage tree as defined in subsection (B) of this section.

x. Identify trees that are dead or in severe decline.

xi. Identify whether the tree is proposed for removal or retained.

xii. Organize the tree inventory information in a table.

b. Tree Preservation Plan Requirements.

i. Provide a site plan drawn to scale.

ii. Include the existing tree locations and corresponding tree numbers from the tree inventory.

iii. Clearly differentiate between significant, invasive and heritage trees through symbols or other methods.

iv. Identify the following site disturbances:

(A) Demolition;

(B) Tree removal;

(C) Staging, storage, and construction access;

(D) Grading and filling;

(E) Paving;

(F) Construction of structures, foundations, and walls;

(G) Utility construction;

(H) Trenching and boring;

(I) Excavation;

(J) Any other demolition or construction activities that could result in ground disturbances and/or tree damage.

v. Locate tree and soil protection fencing to scale.

vi. Locate soil compaction prevention methods to scale.

vii. Include tree protection specifications from the arborist report on the plans including a detail and description of tree protection fencing and signage.

viii. The elements of the tree preservation plan may be included on multiple plan sheets for clarity.

ix. The final approved set of construction drawings must include the tree preservation plan to ensure contractors, inspectors, and other professionals have access to the information.

c. Tree Planting Plan.

i. Provide a site plan drawn to scale.

ii. Include the existing trees to be retained and their crown areas to scale.

iii. Include the trees to be planted and their mature crown areas to scale based on the street tree and tree crown area reference list. Any trees not listed shall use the following approved sources to establish mature crown in the order listed below:

(A) https://landscapeplants.oregonstate.edu/node/2163 (Oregon State University College of Agricultural Sciences – Department of Horticulture – Landscape Plants);

(B) The Tree Book by Michael A. Dirr and Keith S. Warren;

(C) Manual of Woody Landscape Plants by Michael A. Dirr;

(D) When these sources do not list the species or variety in question other published sources are acceptable.

iv. Include a diagram depicting the tree planting that is consistent with ISA best management practices.

v. The minimum size of planted trees is one-and-one-half-inch caliper for deciduous trees, five feet tall for evergreens, three feet tall for Quercus garryana, and Arbutus menziesii. Nursery stock must be in good health with the size and quality consistent with ISA best management practices and ANSI Z60.1 standards.

vi. The species selection and spacing of trees to be planted must be such that it provides for the eventual mature size of the trees. Soil type, soil conditions and other site constraints shall be considered when selecting species for planting.

vii. Root barriers must be installed according to the manufacturer’s specifications when a tree is planted within five feet of pavement or an underground utility box.

viii. Where there are overhead high voltage utility lines, the tree species must be from the city approved street tree list with a designation allowing planting under high voltage lines.

ix. The elements of the tree planting plan may be included on multiple plan sheets for clarity.

x. The final approved set of construction drawings must include the tree planting plan to ensure contractors, inspectors, and other professionals have access to the information.

xi. Include a planting timeline for when the trees are to be installed, who will install the trees, and how the planting will be assured if deferred to after the construction phase of the project.

d. Report.

i. Provide a written narrative that summarizes the information from the tree inventory, tree preservation plan, and tree planting plan.

ii. Provide findings and calculations that demonstrate whether the tree preservation and planting standards in subsection (C)(2) of this section have been met.

iii. If the tree preservation and/or tree planting standards have not been met, provide calculations for the applicable tree mitigation fees as required by subsection (C)(4) of this section.

iv. If the applicant is seeking a variance to the tree preservation and/or tree planting standards in place of providing mitigation planting or fees, provide findings that demonstrate the proposal provides equivalent or greater environmental benefits as preserving or planting the required tree canopy as required by subsection (C)(9) of this section.

v. Provide findings that demonstrate compliance with the tree protection standards in SDC 3.6.200(A).

6. Construction. All trees on a site that are not otherwise designated and approved by the city for removal shall be protected prior to, during, and after construction in accordance with SDC 3.6.200(A).

7. Additional Approval Criteria. When an application is submitted the city may approve the request when the following additional review criteria is met:

a. Wooded areas along ridges and hilltops will be retained for their scenic and wildlife value in addition to preventing erosion.

b. Wooded areas along property lines shall be retained at a minimum width of 10 feet to provide buffers from adjacent properties.

8. Exemptions. The protection standards in this section do not apply to:

a. Dead or diseased trees. Dead or diseased trees meeting the criteria for “significant trees” may be removed after approval of a Type I land use review.

b. The removal is necessary to alleviate a dangerous tree posing an imminent threat to the public health or safety or posing an imminent threat to public or private property or prevent an imminent threat of serious environmental degradation.

c. Tree removal as required by the city or public utility for the installation or maintenance or repair of roads, utilities, or other structure.

9. Tree Variances. The applicant may seek an adjustment or variance at no cost to the applicant for smaller lot sizes, sidewalk deviations, on-street parking reduction, frontage improvements, reduced setbacks or a reduction in the number of parking spaces to avoid removal of significant trees, provided the applicant also takes measures to preserve the health of the trees.

a. Review Criteria. The city shall consider the following review criteria and may approve, approve with conditions, or deny a design review adjustment based on the following; the applicant shall bear the burden of proof:

i. Adjusting the subject code standard(s), i.e., decreasing, increasing, waiving, or making a material substitution, will result in a design that is as good or better than what would likely result under the base standard;

ii. The adjustment is consistent with the code’s stated intent and is in the public interest.

10. Invasive and Nuisance Trees. Trees on the Silverton invasive and potential nuisance tree list shall be removed during site development regardless of their size. The planting of species on the Silverton invasive and potential nuisance tree list is prohibited.

11. Trees Requiring Approval. It is unlawful to plant native or nonnative willow, cottonwood, or poplar trees outside of riparian restoration projects anywhere in the city unless the public works director approves the site as one where the tree roots will not likely interfere with public sewers.

12. Wild growing, naturally sown or distributed (through normal asexual spread such as stollens or rooted branches) Willamette Valley native Salix and Populus species may persist within city limits. This allowance does not extend to non-native, ornamental, or exotic species.

13. Prohibited in Right-of-Way. It is unlawful to plant fruit trees (other than ornamental fruit trees) or nut trees (other than ornamental nut trees) in or on a public right-of-way.

D. Wetlands and Riparian Overlay District. Trees play a critical role in the ecological function of riparian corridors. The city and residents have strong interest in ensuring the ongoing function of these areas and vested interests in the existing and future trees growing there.

1. Applicability. The wetland area regulations apply to those areas meeting Division of State Lands criteria for wetland classification. Precise wetland boundaries may vary from those shown on the comprehensive plan map exhibit if on-site inspection and delineation by a recognized authority and/or other city-approved documentation indicate more accurate boundaries. Those more precise boundaries can be identified, mapped, and used for review and development without a change in the comprehensive plan wetlands map exhibit. All developments proposed within a designated wetland area shall be subject to the provisions of conditional use review and the wetland area regulations (per Chapter 2.7 SDC).

2. Canopy Protection Thresholds. The minimum threshold canopy percentage for each use area is doubled in the riparian overlay district.

3. Tree Removal and Mitigation. Removal of significant trees in the wetland and riparian overlay district is allowed pursuant to the other sections of this chapter. Tree removals must be mitigated on site whenever possible to maintain tree cover in the corridor pursuant to the other sections of this chapter.

E. Invasive and Potential Nuisance Trees. The preservation and removal of trees on the Silverton invasive and potential nuisance trees list is governed by the following provisions:

1. Planting. Planting of any tree on the invasive and potential nuisance trees list is prohibited

2. Reproduction. It is prohibited to let any plant with a noxious weed designation on the invasive and potential nuisance trees list produce seed, disseminate fruit, or reproduce sexually (via flowers) within the city.

(Ord. 25-09 § 7, 2025).

A. Mature Crown Area. To calculate mature crown area square half of the mature width then multiply by 3.14. For instance a Grand Fir has a width at maturity of 30 feet, therefore 15 feet times 15 feet times 3.14 equals 707 square feet.

(Ord. 25-09 § 7, 2025).

(Ord. 25-09 § 7, 2025).

A. Tree Protection Specifications.

1. Intent. Tree protection during development helps to reduce the negative impacts of construction. The tree protection regulations keep the foliage crown, branch structure and trunk clear from direct contact and injury by equipment, materials, or disturbances; preserve roots and soil in an intact and noncompacted state; and visibly identify the root protection zone in which no soil disturbance is permitted, and other activities are restricted. The protection of roots and soil where roots dwell is of critical importance during construction activities. Maintaining these protections through development will lessen undesirable consequences that may result from uninformed or careless acts, preserve both trees and property values, and reduce risks associated with damaged or destabilized trees.

2. Applicability. These standards apply to any tree that is required to be retained on site or in the street during a development activity. Proposed tree protection shall meet the requirements below, except that the city may approve or require alternate protection methods for street or city trees.

3. Protection Methods. The tree preservation plan shall show that trees retained are adequately protected during construction using the method described below:

a. Establish a critical root protection zone by using one of the two following methods:

i. Calculate by multiplying the diameter of the tree, in inches, measured at DBH, four and one-half feet above the mean ground level, by 12. For example, a tree with a diameter of four inches would have a critical root zone of 48 (four times 12 equals 48) inches all around the tree.

ii. Determine the tree dripline which is an imaginary line around a tree at a distance from the trunk equivalent to the canopy (leaf and branch) spread as illustrated in Figure 3.6.200-01;

b. Install protection fencing at the critical root zone perimeter before physical development starts and remain in place until final inspection. The fence shall meet one of the following:

i. A minimum four-foot-high metal chain link or no-climb horse fence.

ii. Four-foot-high orange construction fence.

iii. Existing structures and/or existing secured fencing at least three and one-half feet tall can serve as the required protective fencing with city approval;

Figure 3.6.200-01: Tree Dripline Location

c. Signage designating the protection zone and penalties for violations shall be secured in a prominent location on each protection fence and shall remain until construction is complete;

d. Installation of landscaping is allowed within the root protection zone and is not an encroachment. Any in-ground irrigation systems are considered encroachments;

e. The following is prohibited within the root protection zone of each tree or outside the limits of the development impact area: ground disturbance or construction activity including vehicle maneuvering or parking, storage of equipment or materials including soil, temporary or permanent stockpiling, proposed buildings, impervious surfaces, underground utilities, excavation, or fill, trenching or other work activities; and

f. Hand excavation in the root zone will be allowed if approved through the application process with the submittal of an arborist’s report.

4. Changes to Tree Protection. Changes to tree protection measures during the development may be approved as a revision to a permit provided that the change is not the result of an unauthorized encroachment into a root protection zone, and the applicant demonstrates that the tree protection standards of this section continue to be met. When an unauthorized encroachment has occurred, the city may pursue an enforcement action or other remedy.

5. Tree Protection Inspections. The city may conduct inspections during project activity to determine compliance with this chapter and confirm that tree protection zones are being maintained and root protection methods are effective. No person may refuse entry or access to a permitted development site to any authorized representative of the city who provides proper credentials and requests entry for the purpose of conducting a tree protection inspection. In addition, no person may obstruct, hamper, or interfere with any such representative while in the process of carrying out their official duties.

6. Performance Bond. To ensure that the significant trees identified through the development review process will be retained and protected, the review authority may require the developer to post a performance bond in an amount determined by the size of the trees being preserved as shown in the fee schedule (SDC 3.6.190). The amount of the required performance bond shall be determined by totaling the number of trees being preserved based on size and bonding value in the fee schedule.

B. Tree Installation and Ongoing Tree Maintenance.

1. Installation. Plant materials shall be installed to current nursery industry standards and proper arboricultural practices ANZI Z60, and ISA best practices. Plant materials shall be labeled for the inspector and properly supported to ensure long-term survival. Support devices such as guy wires or stakes shall not interfere with vehicular or pedestrian movement.

2. Timing. All trees required or approved to be planted shall be planted or payment in lieu of planting made prior to the certificate of occupancy, as applicable. However, it is encouraged that planting occurs during the wet months, October through April. Planting of trees may be deferred between May 1st and September 30th upon filing a performance guarantee or other assurance deemed acceptable by the city.

3. Maintenance. If a tree(s) fails to survive three years after planting, the property owner shall replace them with an equivalent specimen (i.e., deciduous tree replaces deciduous tree, etc.) within six months of their dying or removal, whichever comes first.

a. Height Requirements. Trees growing in the right-of-way or on private property must be trimmed to maintain a minimum canopy height of eight feet above sidewalks, or 12 feet above streets or alleys.

b. Trimming – Specifications – Owner Responsibility.

i. Trees, standing in or upon any public street or alley, or on private grounds, and having branches projecting into the public street or sidewalk, shall be kept trimmed by the owner or owners of the property adjacent to or in front of such trees growing so that:

(A) The lowest branches shall not be less than a minimum of 12 feet above any surface of the street pavement and shall not be less than 14 feet above the surface of streets designated as state highways.

(B) The lowest branches shall not be less than a minimum of eight feet above any surface of a sidewalk.

ii. Newly planted trees may remain untrimmed; provided they do not interfere with street traffic or people using the sidewalk or obstruct the light of any street electric lamp.

(A) Trimming – Notice to Comply. Whenever the owner or owners, lessees, occupants or persons in charge of private grounds neglect or refuse to trim any tree as provided in this code, the city shall serve upon such owner or owners, lessees, occupants or persons in charge a written notice to trim such tree or trees within 10 days after giving of such notice; failure to do so will be considered in violation of this chapter and subject to the penalties provided in this code. Such notice shall be served upon the owner or owners, lessees, occupants, person in charge, or occupant of the property by posting the same upon such property or near to the trees, to be trimmed.

(B) Trimming – City to Perform Work When. If the owner or owners, lessees, occupants or persons in charge of the property fail and neglect to trim such trees within 10 days after receiving said notice, the city manager or duly authorized representative may cause any vegetation in or upon any parking strip, street right-of-way or other public place in the city to be trimmed, pruned, or removed.

(C) Topping. Tree topping is prohibited in Silverton. Topping is destructive and creates situations resulting in tree growth that is compromised and ultimately dangerous and that diminishes the ecological and social benefits provided by the urban forest. In lieu of topping use standard ISA pruning practices such as tree reduction.

C. Tree Removal Specifications. Trees shall be removed in a manner that will not jeopardize public safety or damage structures including utility lines or services, or adjacent trees. Trees shall be entirely removed.

1. Completion. A tree will be considered completely removed when reduced to a stump no taller than four and one-half feet. For street tree removals, the city may direct the stump be ground out up to 18 inches below grade.

2. Woody Debris Disposal. Utilizing urban wood is encouraged. Consider rather than burning or hauling to the landfill using cut trees for durable wood products. In all cases disposal, use, or reuse of wood and woody debris from private trees is at the property owner’s discretion, provided storage of wood does not constitute a public health or safety nuisance. If the city determines that the tree is affected by a pathogen or insect infestation that will likely adversely impact surrounding trees, all portions of the tree shall be removed from the site and properly disposed of at the property owner’s expense.

3. Ordered Removals. The city manager may remove or cause or order to be removed any tree or part thereof, planted or growing in or upon any public street or alley which is in unsafe conditions, which by reason of its nature is injurious to sewers or other public improvements, or is affected with an injurious fungal disease, insect, or other pest.

D. Arborist Certification. A tree contractor shall have on staff a certified arborist who is qualified to trim, treat, or remove street or city trees. The certified arborist must oversee all trimming work and certify that all work meets the city’s trimming specifications in subsection (B)(3) of this section. If a certified arborist is not on the staff of the tree contractor, the public works director, applying criteria developed by best practices as set forth by the ISA, must approve the tree contractor before the work begins. In cases where the professional opinion of a certified arborist differs from that of the public works director, the public works director may refer the matter to the sustainable and urban tree advisory board for a decision. Nothing in this section shall prevent the employees of public agencies with property in the city, who are not certified arborists, from trimming trees on the property of those public agencies. (Ord. 25-09 § 7, 2025).

A. Purpose. This section establishes an enforcement system to prohibit illegal tree activity to further the city’s goals for optimizing and enhancing the urban forest.

B. Applicability – Where These Regulations Apply.

1. City of Silverton. This section applies to all trees within the city of Silverton.

C. City Authority. The city has the ultimate authority to:

1. Interpret the provisions of this section and determine whether code criteria have been met.

2. Establish conditions of permit and land use approval to ensure this section is properly implemented.

D. Penalties. The following penalties apply to violations of the provisions of this section:

1. A person who removes a tree regulated by this section without first obtaining the necessary permit from the city, removes a tree in violation of an approved permit, or violates a condition of an approved permit must pay a fine in an amount established in the fee schedule.

2. Topping, pruning, or otherwise inflicting willful and negligent damage to a tree crown or roots in a manner that is inconsistent with ISA best management practices:

a. Up to the amount established in the fee schedule or up to the appraised loss in value of the illegally topped or pruned tree as determined by an ISA certified arborist plus the arborist’s reasonable appraisal fee.

b. Restoration of the tree crown, trunk, or root system as prescribed by an ISA certified arborist and approved by the city.

3. Tree protection zone violations:

a. Up to the amount established in the fee schedule.

b. Restoration of the tree protection zone as prescribed by an ISA certified arborist and approved by the city.

4. Evidence of Violation.

a. If a tree is removed without the necessary permit, a violation will be determined by measuring the stump. A stump that is eight caliper inches or more in diameter will be considered prima facie evidence of a violation of this chapter.

b. Removal of the stump of a tree removed without the necessary permit is a violation of this chapter.

c. Proof of violation of this chapter will be deemed prima facie evidence that such violation is that of the owner of the property upon which the violation was committed. (Ord. 25-09 § 7, 2025).