Planting Trees in Urban Areas

Center for Watershed Protection USDA Forest Service, Northeastern Area, State and Private Forestry Center for Watershed Protection USDA Forest Service, Northeastern Area, State and Private Forestry

planting trees in urban areas


Slideshow Content

• Site assessment for urban tree planting

• Basic planting design

• Special considerations for urban tree planting

• Site preparation

• Planting and maintenance techniques


Site Assessment for Urban Tree Planting

• Collect detailed information about conditions at previously identified planting sites

• Use information to: develop planting plan, determine what to plant, where to plant and what special methods are needed to reduce urban impacts on trees


Impacts of Urbanization on Trees

• Air pollution• Poor soils• Exposure to wind• Drought• Flooding/standing

water• Increased

temperature• Competition

• Disease• Damage from humans• Damage from animals• Salt from roads• Inadequate soil

volume• Improper maintenance• Conflicts with

infrastructure


Urban Reforestation Site Assessment (URSA)

Major Sections:• General site information• Climate• Topography• Vegetation• Soils• Hydrology• Potential planting conflicts• Planting and maintenance

logistics• Site sketch


Basic Planting Design

• Plant species – diversity is important, select species that are appropriate for the site and tolerant of urban conditions

• Plant materials – select from balled and burlapped, container grown, bare root

• Plant spacing – based on desired density, should account for plant survival rates

• Planting plan – should include species list, sketch, planting dimensions, instructions, supply list, site preparation, schedule and cost estimate


Urban Tree Selection Guide

• Specific to the mid-Atlantic and Northeastern U.S.• Used to select species that can tolerate the

environmental conditions at the site and perform specific functions

• Chart 1: Environmental Conditions - hardiness zone, soil moisture, sun exposure, soil composition, and tolerance of drought, inundation, pests/disease, soil compaction , salt, and pH

• Chart 2: Tree Characteristics – growth rate, mature height, canopy spread, form/habit, root structure, fruits, flowers

Example Planting Plan Sketch

Source: Omaha Public Power District


Special Considerations for Urban Tree Planting

• Calculate soil volume• Evaluate potential for stormwater

treatment• Recommend setbacks between trees and

infrastructure• Other methods to reduce infrastructure

conflicts• Protect trees from human and animal

impacts


Calculate Soil Volume• Typical tree pit in an

urban area is only 4 feet by 4 feet in area – about 50 ft3 of soil

• Tree roots are typically confined to the pit due to compacted soils

• Use designs that provide as much soil as possible for trees

Calculate Soil Volume

Source: Jim Urban


Evaluate Potential for Stormwater Treatment

• Many urban trees either receive too much stormwater runoff or do not receive enough water because surrounding pipes and pavement direct water away

• Stormwater management and planting strategies should be used to manage runoff at planting sites that receive too much water and to direct runoff to other planting sites to provide treatment and reduce irrigation needs


Evaluating Potential for Stormwater Treatment

Sites should be evaluated to determine if they are:• Under-capacity: currently does not receive

runoff; runoff bypasses the site in pipe/ditch or is infiltrated

• At-capacity: receive sheetflow only• Over-capacity: receive excessive runoff


Recommended Setbacks Between Trees and Infrastructure


Trees vs. Pavement

• Tree roots crack or lift pavement if inadequate setbacks are used

• 10 to 15 foot setbacks are recommended


Trees vs. Utilities• Falling limbs can cause power outages, trees can

grow into wires • Maintenance/repair of utilities can damage tree• Recommended setbacks from overhead wires:

• 10 feet for small trees• 15-20 feet for medium trees• 20 to 40 feet for large trees• Trees planted under overhead wires must be 10 to 15

feet below the height of the wires at maturity

• Recommended setback from underground utilities is 10-15 feet



Trees vs. Sewer and Drainage Pipes

• Tree roots can clog or break sewer and drainage pipes –although most damage occurs with older sewer systems

• Trees that cause damage to sewer pipes are often removed

• Recommended setbacks:• 15-25 feet between trees and perforated

pipes• 10 feet between trees and sewer lines


Trees vs. Buildings

• Tree roots may crack foundations if planted too close to buildings

• Root growth may become one-sided and cause tree to topple from high winds.

• Recommended setbacks:• 15 feet for small trees• 20-25 feet for large trees


Other Recommended Setbacks

• 10 foot setback between trees and lighting

• 10 foot setbacks between trees/shrubs and the centerline of trails (for safety)


Other Methods to Reduce Infrastructure Conflicts

• Species selection

• Alternative sidewalk design

• Alternative sidewalk materials

• Root guidance systems

• Structural soils

• Maintenance strategies


Species Selection

• “The right tree in the right place”• Selecting species with specific characteristics

can reduce infrastructure conflicts:• Choose shallow-rooted species when planting

near sewer or drainage pipes• When planting near overhead wires, choose

species with columnar form• Species with a small trunk flare or root buttress

characteristics are ideal for planting next to pavement


Alternative Sidewalk Design


Alternative Sidewalk Materials

• Reinforced or thicker concrete slabs• Asphalt• Pervious concrete• Decomposed granite and compacted

gravel• Permeable pavers• Recycled rubber• Mulch


Root Guidance Systems

• Direct root growth away from infrastructure by restricting root growth laterally or radially, or by directing roots to appropriate areas

• Examples: root barriers, root paths, steel plates, root channels, continuous soil trench


Structural Soils

Graphic by Matt Arnn


Maintenance Strategies

• Use directional pruning instead of topping when pruning trees near overhead wires

• Use tunneling as an alternative to trenching when installing or repairing underground utilities near trees

• Use alternatives to root pruning to minimize damage to trees


Protect Trees from Human and Animal Impacts

• Beaver

• Deer

• Human Impacts• Lawnmowers• Damage from vehicles• Vandalism• Foot traffic


Protect Trees from Deer


Site Preparation Methods

• Trash and debris cleanup

• Invasive plant control

• Soil amendments


Trash and Debris Cleanup

• May be done with volunteers

• Evaluate the site to determine the type and volume of trash

• Implement measures to prevent future dumping


Invasive Plant Control Methods

• Hand removal• Mowing• Heavy equipment

removal• Solarization• Girdling• Burning• Chemical• Cultural • Biological


Soil Amendments

• Compost: improves water and nutrient-holding capacity, increases nutrients, reduces compaction

• Gypsum: decreases soil salinity, increases calcium and sulfur without affecting pH, enhances structure of clay soils

• Limestone: decreases soil acidity• Peat: increases organic matter, acidity, and water

and nutrient-holding capacity without increasing nutrient content

• Sulphur: increases soil acidity

Source: Cornell Urban Horticulture Institute

Typical Characteristics of Urban Soils

• Severe compaction• Elevated pH• Low organic matter

• Low nutrients• Poor drainage• Pollutants may be present

Healthy soil

Compacted urban soil


Planting and Maintenance Techniques

• Tree planting techniques

• Encourage natural regeneration

• Maintenance techniques


Tree Planting Techniques• Planting hole must be 2 to 3 times wider than

the root ball because roots spread out laterally rather than going deep

• Do not plant tree too deep• Technique varies with plant materials and

when planting on slopes• Use tree shelters and mulch to protect tree if

necessary• Stake only on very windy sites or with top-

heavy trees

Tree Planting Specification

Copyright International Society of Arboriculture. Used with permission.


Mulching Trees


Natural Regeneration

• Natural regeneration is the simplest and cheapest way to reforest: simply stop mowing

• In urban areas, poor soils and lots of invasive species and deer can make regeneration difficult

• Good candidate sites have: desirable tree seed sources nearby, adequate seed dispersal methods, bare mineral soils with good seed/soil contact, few invasive plants, controlled deer populations, and no sod-forming grasses (e.g., fescue)


Encourage Natural Regeneration

To encourage natural regeneration:

• Amend soils problems• Control deer• Control invasive species• Disc soils if sod is present• Install perches to encourage

seed dispersal by birds• Supplement with plantings if

necessary


Tree Inspection and Maintenance

• Post planting and long-term inspection

• Watering

• Pruning

• Weed control

• Integrated Pest Management

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Planting Trees in Urban Areas