A. Purpose: the purpose of these street tree guidelines and standards is to encourage tree diversity and promote strong, healthy trees that are not limited by environmental conditions from achieving a long life and mature size.
B. Applicability: These standards are applicable exclusively to street trees within the Hailey City rights of way.
C. Definitions:
CALIPER: Diameter measurement of nursery stock trees at six (6) inch above the root flare.
DBH (DIAMETER BREAST HEIGHT): On large trees, diameter is measured at four and a half (4 ½) feet above the ground.
PLANTING STRIP: Trees planted in a linear strip along sidewalks and streets.
STRUCTURAL SOIL: A planting medium designed so that when mixed and placed properly any compactive load is born by the stone matrix leaving the soil between the stone matrix uncompacted. The planting medium components should be approximately eighty percent (80%) one (1) inch size crushed stone (no fine particles) and twenty percent (20%) soil by weight, with a small amount of binder such as hydrogel to aid in the uniform blending of the two materials. The soil should range from "loam" to "clay loam" and contain at least twenty percent (20%) clay to maximize water and nutrient holding capacity. Only structural soil shall be allowed underneath hardscape or sidewalk features.
SUITABLE SOIL: Soil should be a “sandy loam” soil with fifty to eighty percent (50 - 80%) medium and coarse sand (less than twenty-five percent (25%) fine sand), five to twenty percent (5 - 20%) clay, five to thirty-five percent (5-35%) silt, contain a minimum of one to three percent (1 - 3%) organic matter by weight (four to six percent (4 - 6%) for the top twelve (12) inches), be free draining at one to two (1-2) inches per hour, contain no more than one thousand two hundred and eighty (1,280) ppm soluble salt, and have a pH appropriate to the planted species. Soil should have a density of sixty-two to eighty-eight (62 - 88) pounds per cubic foot and contain no herbicides, heavy metals, or hydrocarbons that will impact growth.
TREE WELL: Generally located in a hardscape area, a tree well is a three-dimensional space dedicated to usable root area for the tree. Tree wells must contain a minimum amount of suitable soil as herein established for root development, and must be free from compaction.
D. Guidelines and Standards:
1. Tree placement should be a function of expected mature size, with consideration for crown size and height spacing conflicts to existing plantings and utilities. A site assessment shall be performed by an arborist or landscape architect prior to project design to minimize conflicts with retained existing trees and utilities.
a. Existing trees: All existing public trees within the project area shall be identified for species, condition, diameter or caliper, approximate age, heritage, and historical value. Before a project is approved and initiated the city shall identify trees that require preservation or that have specific monetary value and the city shall be compensated for those trees if damaged or removed. Said compensation may include, at the city's discretion, replacement of equal value or greater at locations deemed acceptable to the city, and said compensation shall also include planting expenses and initial maintenance. Appraised value of the tree shall be established by the city or a certified arborist acceptable to the city.
b. New Plantings: New plantings shall be planned with consideration for the mature crown size and necessary clearance to other conflicts.
Linear plantings shall be spaced a maximum of 40 feet on center unless otherwise approved. Alternative designs or clustering for Residential developments may be allowed in lieu of linear plantings at the discretion of the city but are generally discouraged. If allowed, tree clusters should be spaced a maximum of one hundred and twenty feet (120') on center and should consist of between three and seven trees. Individual trees within a cluster shall be spaced in accordance with the needs of the fully developed canopy. The minimum number of trees in an alternative or clustering design shall be no less than the theoretical number of trees in a linear planting design for the same area.
Additional tree placement criteria are as follows:
(1) Trees shall be no closer to the face of curb than shown in the standard drawings.
(2) No Class I trees are allowed within five (5) feet of an improved travel way, (sidewalks, pathways, pedestrian or vehicular lanes, etc.)
(3) Class I trees shall have a minimum planting strip width of ten (10) feet.
(4) Class II and III trees shall have a minimum planting strip width of three (3) feet but wider is preferred.
(5) Trees shall not be located within any designated snow storage area unless specifically approved by the Public Works Department.
2. Infrastructure Requirements:
a. Tree wells: The top 4 inches of a tree well shall consist of organic mulch except within 6" of the trunk. The remainder of the tree well shall be filled with suitable soil not susceptible to compaction and which drains well. Tree wells may have non-invasive grasses, ground cover, bulbs & perennials, annuals or other low maintenance plantings located a minimum of two feet from trunk or as shown on the standard drawings. Any portion of a tree well located under sidewalk or hardscape areas shall be capable of supporting said structures.
b. Root barriers are encouraged as needed to prevent damage to hardscape.
c. Projects subject to the City of Hailey Design Review or Subdivision process shall have plantings as follows (Minor exceptions may be allowed if deemed appropriate by the city):
(1) Tree plantings within new sidewalk or hardscape areas: To create the best environment for trees and guard against compaction, hard surface areas should be supported with suspended pavement systems whenever it is economically feasible. If these systems are not used, other beneficial treatments could be used including structural soils or greater volumes of suitable soil.
No dimension (width, length, or depth) of the tree well should be less than three feet (3’). A minimum of twenty (20) square feet must be open to the air (some hardscape removal may be required) and the tree well must contain a minimum of three hundred (300) cubic feet of suitable soil which may include structural soil or suspended pavement systems beneath hardscape features.
(2) Tree plantings within existing hardscape areas: No dimension (width, length, or depth) of the tree well should be less than three feet (3'). A minimum of twenty (20) square feet must be open to the air (some hardscape removal may be required) and the tree well must contain a minimum of one hundred and twenty (120) cubic feet of suitable soil which may include structural soil or suspended pavement systems beneath hardscape features.
(3) Tree plantings adjacent to any sidewalk or hardscape areas: An uncompacted area of suitable soil at least five feet (5') wide with a length that is equivalent to the diameter of the mature canopy, or an equivalently sized uncompacted area, shall be provided.
(4) Tree plantings greater than five feet (5') from any sidewalk or hardscape areas: In open planting areas trees should be protected from compaction that may occur as a result of parking, movement of automobiles, or heavy equipment.
d. Projects exempt from the City of Hailey Design Review or Subdivision process shall provide a minimum of fifty percent (50%) of the tree well volume described in 18.06.026.D.2.c.
3. Species Selection and Planting Stock:
a. Species Selection shall be in accordance with the approved list (see Hailey Street tree list for approved Class I, II and III trees). Species selection shall maintain consistency within the block but avoid monoculture.
b. Planting Tree Stock: trees shall be no less than two and half (2.5) inches and no greater than four (4) inches caliper size as tagged by a local nursery. Only trees with one dominant stem and no visible fungal or insect damage evident will be allowed. Balled and burlapped stock is generally preferred over containerized stock which often have encircling roots.
4. Establishment and Maintenance of New Trees:
a. Trees should be planted in spring or fall when possible, using proper tree planting methods (see Wood River Valley Tree Guide). Encircling roots in container stock should be cut to a straight root or removed before planting. Permanent irrigation is required with higher application rates provided during the first season. Protection from traffic, compaction, and equipment, including snow removal equipment, must be provided. Electrical and soil standards must be met.
b. Planting areas should connect, either on the surface or within the subsurface space to allow for continuous root development and increase usable soil volumes. Preferred hardscaped surfaces include pavers that allow the penetration of water and air, or permeable asphalt.
(Ord. 1262, 2020; Ord. 1116, 2012)