Tree Protection and Placement

What is Tree Protection and Placement?

Trees play an essential role in the overall environmental quality of a property. Protecting existing trees and properly siting new trees can increase the energy efficiency of a building design before considering mechanical enhancements or upgrades. Trees protect buildings by reducing energy loads, reducing interior glare, and blocking potentially harsh winds (see Glare and Heat Gain Reduction). Trees also add aesthetic appeal, reduce stormwater runoff and soil erosion, and can improve air quality. It is essential to locate trees strategically. Trees can take 10-15 years to mature to a size that provides significant shade and protection, therefore protecting existing trees during construction is very important.

Before construction begins, consult with an International Society for Arboriculture (ISA) certified arborist who can work with the project team to formulate a plan to protect existing trees. Symptoms of tree damage from construction may not be visible immediately but may appear years later. In planning for tree protection and determining necessary tree removals, consider the species, size, maturity, location, and condition of each tree.[1] Sometimes saving a younger tree is more beneficial than saving a mature tree because they are better able to adapt to the disturbances of construction. It is essential to maintain a diversity of species and age of trees on the site.

How to Implement Tree Protection and Placement

 A tree protection plan should be created during design and enforced during construction. The plan should define parameters such as materials and dimensions of tree protection fencing required for all trees in the site protection plan. Fencing helps protect trees by keeping construction vehicles, equipment, and materials away from the tree. Penalties, such as a fine proportional to damages accrued, help construction workers adhere to the tree protection plan.

When developing a strategy to preserve existing trees during site construction, it is essential to consider both the aboveground and belowground components of the trees. Machinery can damage the trunk and crown of a tree by breaking branches and gashing the trunk. When digging to install a foundation and utilities, roots are susceptible to being severed.  The majority of the roots of a tree are no more than a foot deep in the soil. However, in a mature tree, the root system can extend as far as 1 to 3 times the height of the tree.[2] As Figure 1 illustrates, the drip line, a vertical plane extending from the perimeter of the crown to the ground, is the minimum area that should be left undisturbed when preserving a tree. Extending that boundary increases the likelihood of the tree’s survival. The closer the cut is made to the tree, the more damage the tree suffers.[3] Removing roots also makes the tree more prone to falling over as they stabilize the tree in the ground.  If a utility line must run through the area of a tree, the International Society of Arboriculture recommends tunneling under the tree’s roots as opposed to running through them if possible.

Although equipment may not always actually cut or physically damage a tree, it should never go within the drip line of a tree because the weight can cause the soil above the roots to compact and impair root development.  Adding or removing soil above the root system should be avoided to prevent smothering or rotting. When making changes to the grade of the soil, stay as far away from the trunk as possible. Exposing trees to the elements by removing nearby trees makes them vulnerable to damage from the sun and to breaking from wind and ice. All of these factors are important as trees require years to adjust to stresses caused by construction.  Continue to monitor and maintain trees and look out for any signs of poor health or safety hazards.  An arborist can provide guidance on how to properly maintain and treat any trees that have suffered damage.

 Select trees carefully and maintain them as necessary to achieve maximum benefits.  To maximize energy savings associated with trees, plant deciduous trees on the south and west sides of the building to lower air-conditioning costs in the summer.[4] Locate trees so that they shade as much hardscape as possible. A commitment to the long-term care of trees is essential to maintaining their health. Consult an ISA-certified arborist for consultation and care.[5]

Example

Washington’s Headquarters at Valley Forge

A reconstruction project at Washington’s Headquarters included taking an inventory of existing trees, protecting historic trees, removing invasive species, and pruning and fertilizing remaining trees on the property.

Benefits

Trees are essential to healthy, livable communities as they provide beauty, shade, and enhance a community’s quality of life. As described in further detail below, trees provide numerous benefits such as cleaning our air, reducing stormwater runoff, cooling buildings, and can even stimulate business in downtown areas by creating a more inviting and comfortable environment.

Environment

Absorption of Air Pollutants – Preserving and increasing trees on site is a simple strategy for improving local air quality. Trees remove pollutants from the air by absorbing airborne particles and gaseous pollution. According to the US Forestry Service, 100 trees remove 53 tons of carbon dioxide and 430 pounds of other air pollutants per year.[6]

Carbon Sequestration – Trees reduce greenhouse gases by storing carbon dioxide in their leaves, branches, trunks, and roots. They use carbon dioxide to form carbohydrates and cellulose for plant structure and function and release oxygen back into the atmosphere.[7]^,[8]

Reducing the Urban Heat Island Effect – The high percentage of impervious surfaces in urban areas absorb heat and create what is known as the urban heat island effect; this causes the annual, mean air temperature of cities to be 5.4°F warmer than surrounding areas.[9] Trees help cool urban areas by shading pavement and absorbing excess urban heat, reducing the urban heat island effect. This same strategy can be applied in less densely built areas by shading hardscaped areas.

Energy Conservation – Trees strategically placed on-site can reduce the energy needed to cool and heat buildings. In the summertime, large trees on the west and east side of a building can save up to 30% of air-conditioning costs and allow units to operate more efficiently (see Energy-Efficient Landscaping).[10]

Capturing Storm Water Runoff and Preventing Erosion – Trees capture and absorb rainwater, reducing stormwater runoff. Tree roots also hold soil in place, preventing erosion (see Rain Gardens).[11]

People

Biophilia – The presence of trees nurtures the inherent affinity that humans are believed to have with nature known as biophilia (see Biophilic Design). Well-treed environments have also been shown to reduce stressors in urban environments due to the beauty and serenity they convey. For instance, a study in a Chicago public housing development showed reduced crime levels in apartment buildings that were surrounded by greenery compared to the same buildings in barren landscapes.[12] Another study showed that exposure to greener play environments reduced ADHD symptoms in children in the United States.[13] Also, studies find a connection between the presence of trees and lower levels of violence.[14]

Noise Reduction, Traffic Calming, and Pedestrian Safety – Trees can serve as useful sound buffers. For example, a 98-foot-wide by 49-foot-tall tree belt can reduce highway noise pollution by 6 to 10 decibels.[15] Trees also serve as physical barriers which protect pedestrians in high traffic areas. Since the presence of trees often indicates the presence of pedestrians, trees near roads help suppress the notion of a transportation corridor meant only for vehicles and can help calm traffic.[16]

Economy

Increased property values – Property values have been found to increase by as much as 10%, according to the U.S. Forest Service, while the International Society of Arboriculture estimates a 5-20% increase in property value due to street trees.

Increased Business in Shopping Districts – A study conducted by University of Washington’s Center for Urban Horticulture found that the presence of trees and other vegetation positively influenced consumers’ perception of retail districts. Furthermore, shoppers spent more time shopping in downtown business districts that were well landscaped compared to those areas with little vegetation. Shoppers were also willing to pay more for parking and spend up to 11% more for goods and services in highly treed retail areas.[17]

Costs

On average, caring for a large tree costs $13/year but returns about $65 in energy savings, improved stormwater management, and higher property values.[18]

The cost benefits of large, medium and small trees are as follows:[19]

Large Tree                                                         Medium Tree

Total benefits/year = $55                                   Total benefits/year = $33

Total costs/year = $18                                       Total costs/year = $17

Net benefits/year = $37                                     Net benefits/year = $16

Life expectancy = 120 years                              Life expectancy = 60 years

Lifetime benefits = $6,600                               Lifetime benefits = $1,980

Lifetime costs = $2,160                                     Lifetime costs = $1,020

Value to community = $4,440                         Value to community = $960

 

Small Tree

Total benefits/year = $23

Total costs/year = $14

Net benefits/year = $9

Life expectancy = 30 years

Lifetime benefits = $690

Lifetime costs = $420

Value to community = $270

Resiliency

Trees provide multiple resiliency benefits. During severe storms, tree roots help to manage flooding and coastal/riparian erosion by soaking up water and stabilizing soil. Trees help reduce strain on local sewer systems, especially combined sewer systems where flooding events can negatively affect water quality and lead to public health concerns.  By infiltrating water where it falls, trees help replenish groundwater reserves, relieving stress on local water supplies and reducing the need to import potable water.[20] Consequently, trees can lessen the impact of droughts.

In the event of a significant heat wave, shade-providing trees help to reduce the urban heat island effect, reduce indoor cooling loads, and reduce stress on the power grid. When emergency events disrupt regular supply and delivery networks, fruit producing trees can supplement local food supplies. Furthermore, properly sited and maintained trees can block buildings from severe winds and offer protection from extreme cold.

Note that debris from storm-related tree damage and downed electric lines caused by wind, snow, and ice, flooding and lighting is often one of the most substantial storm-related expenses. Maintaining tree health through proper pruning, watering, and disease control can help prevent tree damage and preserve the many benefits of trees.

[1] International Society of Arboriculture (ISA). Trees Are Good. “Avoiding Tree Damage During Construction.” https://www.treesaregood.org/portals/0/docs/treecare/AvoidingTreeDamage.pdf  (accessed March 21, 2018.)

[2] ISA. Trees Are Good. “Avoiding Tree Damage During Construction.” https://www.treesaregood.org/portals/0/docs/treecare/AvoidingTreeDamage.pdf (accessed March 21, 2018).

[3] Ibid.

[4] ISA. Trees are Good. “Tree Care Information:  Benefits of Trees.” https://www.treesaregood.org/portals/0/docs/treecare/benefits_trees.pdf (accessed March 21, 2018).

[5] Sustainable Urban Forests Coalition. “Urban Forests Curb Greenhouse Gases.” http://www.urbanforestcoalition.org/doc/SUFC_GHG_PolicyPaper.pdf  (accessed March 21, 2018).

[6] US Forestry Service: Benefits of Trees. https://www.fs.fed.us/learn/trees (accessed March 21, 2018).

[7] Colorado Tree Coalition.  “Education: Why Plant a Tree?”  http://coloradotrees.org/education/ (accessed March 21, 2018).

[8] Sustainable Urban Forests Coalition. “Urban Forests Curb Greenhouse Gases.” http://www.urbanforestcoalition.org/doc/SUFC_GHG_PolicyPaper.pdf (accessed March 21, 2018).

[9] US EPA.   “Heat Island Effect.”   http://www.epa.gov/heatisland/ (accessed March 21, 2018).

[10] Arbor Day Foundation.  “Benefits of Trees.” https://www.arborday.org/trees/benefits.cfm (accessed March 21, 2018).

[11] Ibid.

[12] Kuo, F.E., & Sullivan, W.C. (2001). Environment and crime in the inner city: Does vegetation reduce crime? Environment and Behavior, 33(3), 343-367. http://lhhl.illinois.edu/crime.htm (accessed April 10, 2018)

[13] Faber Taylor, A., Kuo, F.E., & Sullivan, W.C. (2001). “Coping with ADD: The surprising connection to green play settings.” Environment and Behavior, 33(1), 54-77. http://lhhl.illinois.edu/crime.htm (accessed April 10, 2018).

[14] Sullivan, W.C. & F. E. Kuo.  Human-Environment Research Laboratory Department of

Natural Resources and the Environmental Sciences University of Illinois at Urbana-

Champaign.  “Do Trees Strengthen Urban Communities, Reduce Domestic Violence?”  January 1996.  http://www.aces.edu/urban/metronews/vol1no4/forestry.html  (accessed April 10, 2018).

[15] National Forest Foundation.  “New Research Proves Just How Green Urban Forests Are.” https://www.nationalforests.org/blog/green-urban-forests  (accessed March 21, 2018).

[16] Jacobs, Allan B.  Great Streets.  Cambridge MA: MIT Press.  1995.

[17] Center for Urban Horticulture, University of Washington, College of Forest Resources.  “Fact Sheet #5: Trees in Business Districts.”  http://www.naturewithin.info/CityBiz/Biz3Ps-FS5.pdf (accessed March 21, 2018).

[18] US Forest Service, Center for Urban Forestry Research and Information.  “The Large Tree Argument.”  https://www.fs.fed.us/psw/topics/urban_forestry/products/cufr_511_large_tree_argument.pdf  (accessed March 21, 2018).

[19] Ibid.

[20] US EPA. Green Infrastructure: Climate Resiliency. https://www.epa.gov/green-infrastructure/green-infrastructure-climate-resiliency (accessed April 25, 2018).