(Amended by Ordinance No. 188278, effective April 14, 2017.) The following specifications apply to trees planted to meet a requirement of this Title. These specifications may be combined with other requirements as necessary to ensure trees are properly selected, spaced, and sized.
A. Prohibited Locations.
1. In the South Waterfront Plan district area, planting trees is not allowed between the riverfront trail and the river at major or minor viewpoints as designated in Title 33 Planning and Zoning.
2. In the Columbia South Shore Well Field Wellhead Protection Area as designated in Title 21, planting trees over the top of polyethylene geomembrane liners installed to meet the requirements of the Columbia South Shore Well Field Wellhead Protection Manual is prohibited.
3. Trees may not be planted on or within 25 feet south of the toe of the Marine Drive levee slope.
B. Planting size. In general, the following represent the minimum tree planting size standard; however, the City Forester may allow smaller or require larger trees to suit the site conditions.
1. Broadleaf trees. Broadleaf trees shall meet the minimum caliper size as determined by the development type listed in Table 60-1:
Broadleaf Tree Size Requirements
One and Two Family Residential
Multi Dwelling Residential
2. Coniferous trees. Conifer trees shall be a minimum of 5 feet in height.
3. Native tree exception. The minimum planting size for native broadleaf trees may be reduced to ½" caliper on sites when planted in an environmental (c, p), greenway (n, q, or greenway setback and riverward portion of g, i, and r overlay zones), or Pleasant Valley Natural Resource (v) overlay zone. When planting Garry Oak, Pacific Madrone, or native conifers in these areas, the minimum planting size may be reduced to a 3 to 5-gallon container size. For Street Trees in these areas, the City Forester may approve a smaller planting size for native species.
C. Canopy size category. Tree canopy types are categorized as small, medium, or large based on the estimated canopy size at maturity. The "Portland Tree and Landscaping Manual" suggested plant lists include the size categories recognized for many trees. To determine the size category of a tree not listed in the "Portland Tree and Landscaping Manual", the applicant shall provide an objective source of information about the tree’s mature height, crown spread, and growth rate. This information can come from published sources, internet sources, or nursery information such as cut sheets.
The canopy size category is calculated according to the following formulas, which incorporate the estimated height and crown spread of a mature specimen and the tree species’ growth rate:
1. Small trees have a canopy factor of less than 40, Medium trees have a canopy factor from 40 to 90, and Large trees have a canopy factor greater than 90;
2. Canopy factor = (Mature height of tree) x (Mature canopy spread) x (Growth rate factor) x 0.01;
3. The growth rate factor is 3 for fast-growing trees, 2 for medium-growing trees, and 1 for slow-growing trees.
D. Species requirements.
1. Species diversity. If there are fewer than 8 required trees, they may all be the same species. If there are between 8 and 24 required trees, no more than 40 percent can be of one species. If there are more than 24 required trees, no more than 24 percent can be of one species. This standard applies only to the trees being planted, not to existing trees.
For Street Trees, the City Forester may make an exception to this requirement in order to fulfill or complement an adopted street or landscape plan.
2. Nuisance species. Trees listed in the "Nuisance Plants List" are prohibited for proposed planting or required replacement.
3. Native species. Any trees required to be planted in environmental (c, p), greenway (n, q, or greenway setback and riverward portion of g, i, and r overlay zones), scenic corridors (s), or Pleasant Valley Natural Resource (v) overlay zones shall be native species. Refer to the "Portland Plant List" for information on appropriate native species for the specific site conditions. Planting activities shall be conducted with hand tools, and may not disturb other native vegetation.
In streets, the City Forester may make an exception to allow planting of non-native Street Trees in these areas when the proposed species of tree will not likely displace native species, and the soil conditions, available growing space, or other site constraints make planting a native tree species infeasible.
4. Adopted guidelines. The City Forester will require species that do not conflict with the requirements of this Section and, to the extent practical, are consistent with characteristics set forth in applicable historic design or other adopted guidelines.
5. Street Tree species. Street Tree species shall conform to the City Forester’s "Recommended List of Street Trees". The City Forester may approve or require an alternate or unlisted species when the alternate species is an appropriate and viable selection and is consistent with applicable objectives of an adopted area-specific tree plan or guidelines.
E. Installation and establishment.
1. Installation. All required trees shall be planted in-ground, except when in raised planters that are used to meet Bureau of Environmental Services stormwater management requirements. Plant materials shall be installed to current nursery industry standards and proper arboricultural practices. Plant materials shall be labeled for the inspector and properly supported to ensure 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 by this Title shall be planted or payment in lieu of planting made prior to the expiration of the permit or City’s final acceptance of the project, as applicable. However, it is encouraged that planting occur during the wet months or as per City Forester recommendations. Planting of trees may be deferred between May 1 and September 30 upon filing a performance guarantee as provided in Section 11.10.060 or other assurance deemed acceptable by the City Forester or BDS Director as applicable.
3. Maintenance. Maintenance of required trees including meeting the maintenance specifications in this Chapter is the ongoing responsibility of the property owner. Trees that die shall be replaced in kind. The cost of the tree and maintenance is the responsibility of the property owner.