Our urban forests are some of the strongest defenses we have against many psychological, sociological, economic and climatic issues we face today.
- “Annual Benefits of Tropical Urban Trees” Infographic (Download PDF)
- “Why We Need Our Urban Trees” Infographic (Download PDF)
- Tropical Community Tree Guide: Benefits, Costs and Strategic Planning (Download PDF)
Trees Improve Property Values
People show a willingness to pay more for the benefits and costs associated with having trees on the property. National studies have shown properties along tree-lined streets may be up to 6% higher value than without. (1 – see numbered citations below) Developers in Hawaii claim to receive higher prices for property with trees.2
Total annual benefit of trees on property values in Honolulu: $3.16 Mil*
Trees Are Good for Business
People across the country have shown higher affinity towards retail locations with trees and they will spend more time and more money (9-12% more) while shopping there. (3)
Trees Save Electricity
Trees reduce ambient temperatures and transpiration uses solar energy that would otherwise heat the air.
Total annual energy savings in Honolulu: $621,760 (based on 2013 rates of $.32/kwh)*
Trees provide many environmental services that improve the quality of life for people and other inhabitants of our planet.
Trees Reduce Atmospheric CO2 by reducing need for air conditioning, which contributes to atmospheric CO2 levels.
Trees Sequester and Store CO2 in woody biomass and leaves thereby removing it from the atmosphere (although some is released during decomposition when trees die.)
Net annual CO2 reduction (includes emissions reduction & stored CO2): 28,859 tons = $22,311*
*This number is a conservative calculation based on $6.68/ton.
Trees Provide Wildlife Habitat
- Trees provide nesting sites for birds and habitat for insects, which are an important food source for birds and other wildlife. Tree berries and nuts are also food for wildlife. (6)
- In urban Honolulu, large trees provide essential nesting habitat for the threatened fairy tern (manu o kŪ), the official bird of Honolulu . (7)
Trees Improve Air Quality by:
- Absorbing gaseous pollutants (via leaves)
- Intercepting particulates (dust, smoke, dirt)
- Releasing Oxygen (photosynthesis)
- Reducing ozone levels (through transpiration)
Honolulu Trees absorb/intercept 7.9 tons annually of (nitrogen dioxide, ozone, sulfur dioxide and small particulate matter.) A benefit valued at $47,365/yr (3)
Interesting Note: BVOCs (biogenic volatile organic compounds released by most trees actually contribute to ozone formation thereby reducing the overall air quality contribution. The amount of BVOC’s emitted is highly variable – Ironwoods contribute nearly half of the total BVOCs in Honolulu.)
Trees Improve Watersheds and Reduce Stormwater Runoff by
- intercepting rainfall and slowing down runoff
- increasing infiltration capacity of soil
- They also improve water quality by reducing soil erosion and removing pollutants (5)
Trees in Honolulu intercept 35 mil. gal of stormwater/ year. This contribution is valued at $350,104/yr (this is a conservative estimate) (3)
Tree provide Social Benefits
Trees improve quality of life in many psychological and social ways. Trees play an important role in reducing stress, promoting physical and mental well-being and in general contribute to healthier communities.
Trees Help Reduce Stress and Improve Overall Well-being
Studies have found that nature viewing after stressful situations results in reduced physiological stress response and more positive emotional responses. In addition, walking in nature or viewing pictures of nature can improve directed-attention abilities.
Trees Reduce Driver Stress
Placing trees next to freeways and roads, and having roads pass through and by green areas, reduces driver stress as measured by blood pressure, heart rate and sympathetic nervous system changes.(8)
Trees Improve Learning & Concentration in Schools
Although not specifically referencing trees, a study at the University of Hawaii showed:
- Students scored higher on standardized testing, and had less disciplinary problems when plants were present in classrooms.
- Students reported that they had lower levels of stress, felt more comfortable, felt the air was fresher, and were able to concentrate for longer periods. (9)
Girls with greener views from home were shown to have greater self- discipline, were less impulsive and had better concentration. This in turn led to better life decisions and better school performance. (These findings applied only to girls; boys are apparently farther ranging, spending more time farther from home than girls.) (11)
Children who played in more natural play areas displayed substantially fewer problems of attention. (12)
Trees Make Communities More Livable
Trees encourage people to spend more time outside interacting with other people in their communities. Trees that provide shade are gathering places and increase the use of outdoor common spaces.(13)
Trees Lead to Reduced Crime
All other factors being similar, areas with more landscaping and trees show less crime. It is thought this is due to the increased surveillance from people being drawn outside and the calming effects of trees.
Buildings with high levels of greenery had 52% fewer total crimes: 48% fewer property crimes and 56% fewer violent crimes. (14, 15)
Trees Lead to Improved Health and Productivity
- Views of nature have led to 23% fewer sick days among workers and overall improved well-being. It also results in higher productivity and satisfaction for workers. (16, 17)
- Research has shown, exposure to nature and gardens speeds recovery of hospital patients and results in fewer complications and a more positive outlook among patients post-surgery. Most (80% as evaluated by a Johns Hopkins Medical School evaluation) rigorous studies found positive links between environmental characteristics and patient health outcomes. (18, 19, 20)
*applies to the 43,817 inventoried trees in urban Honolulu
Download the Honolulu Municipal Forest Resource Analysis
(1) Wolf, K, 1998. Urban Forest Values: Economic Benefits of Trees in Cities, University of Washington College of Forest Resources, Factsheet #29.(2) Alan Arakawa, Castle and Cook, “Design, Construction and Maintenance with Trees in Mind” conference, Honolulu, October 2005.(3) STRATUM: Vargas, K. E., McPherson, G. E., Simpson, J. R., P. J. Peper, Gardner, S.L., Xiao, Q. City of Honolulu, Hawaii Municipal Forest Resource Analysis. Center for Urban Forest Research, USDA Forest Service, Pacific Southwest Research Station. November, 2007. Note about data and methodology: “The estimates in the Stratum provide first-order approximations of tree value. … This estimate of benefits applies only to the 43,817 trees in the inventory. Unfortunately, because the inventory does not represent a statistically random sample of the population, it is not possible to extrapolate directly from the values given here for the inventoried trees to the urban forest as a whole. It is clear, however, that the total benefits are at least several times those given here.” For Complete description of methodology and procedures see Appendix D, p.51(4) Wolf, Kathleen L. “More In Store: Research on City Trees and Retail.” Arborist News, Vol. 18, No. 2, April 2009, 22-27.(5) Fazio, J.R., Ed. “How Trees Can Retain Stormwater Runoff” Tree City USA Bulletin No 55. Arbor Day Foundation:http://www.fs.fed.us/psw/programs/uesd/uep/products/11/800TreeCityUSABulletin_55.pdf(6) Hastie, C. 2003. “The Benefits of Urban Trees”(7) Bornhorst, Heidi. “Threatened tern an appropriate choice as city bird,” Honolulu Advertiser. April 20, 2007.
(8) Parsons, R., Tassinary, L. G., Ulrich, R. S., Hebl, M. R. and Grossman-Alexander, M. (1998) The view from the road: implications for stress recovery and immunisation. Journal of Environmental Psychology, 18, 113
(9) Poster: Kaufman, A. J., Kawabata, A. F., Cox, L. J. & Miura, T. “Beyond Abc’s: Can Plants In A Classroom Have An Impact On High School Math Student Behavior And Academics?”
(10) Taylor, AF, Kuo, FE, Sullivan, WC, 2001. “Coping With Add – The Surprising Connection to Green Play Settings” Environment and Behavior 33(1), pp 54 – 77.
(11) Taylor AF, Kuo FE & Sullivan WC (2002) “Views of nature and self-discipline: Evidence from inner city children.” Journal of Environmental Psychology. 22:49-63.
(12) Grahn P, Mårtensson F, Lindblad B, Nilsson P & Ekman A (1997) Ute på dagis. Stad and Land Nr. 145.
(13) Kuo, FE, 2003. The role of Arboriculture in a Healthy Social Ecology. Journal of Arboriculture 29(3), pp148 – 155
(14) Kuo, FE and Sullivan, WC, 2001. Environment and Crime in the Inner City. Does Vegetation Reduce Crime. Environment and Behavior. 33(3), pp 343 – 367 (15) Kuo, FE and Sullivan, WC, 2001. Aggression and Violence in the Inner City – Effects of Environment via Mental Fatigue. Environment and Behavior 33(4), pp 543 – 571 (16) Wolf, K, 1998. Urban Nature Benefits: Psycho-Social Dimensions of People and Plants, University of Washington College of Forest Resources, Factsheet #1. (17) Kaplan, R. 1992. Urban Forestry and the Workplace. In P. H. Gobster (editor), Managing Urban and High-Use Recreation Settings. USDA Forest Service, General Technical Report NC-163. Chicago, IL: North Central Forest Experiment Station. (18) Ulrich, R. S. (1984) View through a window may influence recovery from surgery. Science, 224, 420–421. (19) Ulrich, R. et al. 1991. Stress Recovery During Exposure to Natural and Urban Environments. Journal of Environmental Psychology, 11, 201-230. (20) Ulrich, R. “Effects of Healthcare Environmental Design on Medical Outcomes” International Academy for Design and Health.