Benefit of Trees
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Ecosystem benefits
Absorbing carbon, releasing oxygen, regulating the climate
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Hong Kong's annual greenhouse gas emission is 42,700 thousand tonnes
(approximately to 17 Olympic-sized swimming pools); while the emission per capita is 6
tonnes. 1
1 acre (equivalent to 75% of the area of a standard football pitch for 11 people) of new
forest can sequester about 2.5 tonnes of carbon annually. If the annual greenhouse gas
emission in Hong Kong has to be absorbed, we need 17 million acres (6.88million
hectares) of forest land (equivalent to 360,000 Victoria Parks). 2
A young tree absorbs carbon dioxide at a rate of 13 lbs/year, while the trees aged
above 10 years can absorb 48 pounds. 2
1 acre of trees annually consumes the amount of carbon dioxide which is equivalent to
that produced by driving an average car for 26,000 miles ( equal to walking from Hung
Hom Railway Station to the Lo Wu Station for 626 times). 2
On average, one tree produces nearly 260 lbs of oxygen each year. Two mature trees
can provide enough oxygen for a family of four. 3,4
Forest can make the surroundings warm, humid and cool, and absorb carbon dioxide,
thus easing the greenhouse effect.
Preserving water and soil
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The absorbed water moves along the trunk, branches and leaves, with part of the water
being used for food manufacturing, and over 95% of the water returns to the
atmosphere through transpiration. The water vapour condenses and forms clouds, the
water returns to the ground as rain. It is re-absorbed by the trees, thus forming a
continuous water cycle. Layers of plantation help reduce the chance of soil erosion
1
Environmental Protection Department, HKSAR Government (2011)
McAliney, Mike. Arguments for Land Conservation: Documentation and Information Sources for Land Resources
Protection, Trust for Public Land, Sacramento, CA, December, 1993
3
New York Times
4
An average person consumes 250 ml oxygen per minute
2
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resulted from heavy rain.
The fallen and dead leaves absorb and store water ; they help preserve the source of
groundwater
The thick plantation can help prevent soil loss and keep the organic matters and water
in soil
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Filtering air
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Trees can absorb carbon dioxide, and also air pollutants such as SO 2 and dust. They act
as natural barrier to reduce ozone emissions from vehicles.5
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Mature trees absorb 120 to 240 lbs of particulate pollution each year.6
A big tree removes 60 to 70 times more pollution than a small tree.7
Reducing heat island effect
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Tree planting is one of the most cost-effective means to mitigate urban heat islands. Air
temperature differences of approximately 2 to 4°C have been observed across urban areas
having variable tree cover, with 1°C of temperature difference being associated with
approximately 10% canopy cover difference.8
Mature tree canopy reduces air temperature by about 2.75 to 5.5°C.9
Reducing noise
Trees reduce noise pollution by absorbing sounds. A belt of trees (98 feet wide and 49 feet
tall) can reduce highway noise by 6 to 10 decibels.10
5
McPherson, Gregory, James Simpson, Paula Peper, Shelley Gardner, Kelaine Vargas, Scott Maco, and Qingfu Xiao.
“Coastal Plain Community Tree Guide: Benefits, Costs, and Strategic Planting”. USDA, Forest Service, Pacific Southwest
Research Station. (2006). Web.
6
University of Washington, College of Forest Resources. Urban Forest Values: Economic Benefits of Trees in Cities. Rep.
Center for Human Horticulture, 1998.
7
Cray, Dan. “Why Cities are Uprooting Trees.” Time Magazine. (2007). Web.
8
Dixon, Karin K., and Kathleen L. Wolf. "Benefits and Risks of Urban Roadside Landscape:
Finding a Livable, Balanced Response." 3rd Urban Street Symposium, Seattle, Washington. 2007.
9
University of Washington, College of Forest Resources. Urban Forest Values: Economic
Benefits of Trees in Cities. Rep. Center for Human Horticulture, 1998.
10
NJ Forest Service. “Benefits of trees: trees enrich the health and quality of our environment”. NJ Department of
Environmental Protection. Web
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Community Impact
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It helps protect the public source of water and improve the livelihood of villagers, as well
as promote urban-rural interactions.
Villagers can improve his/her livelihood by engaging in reforestation to earn extra
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income.
With more green common spaces, the sense of unity and belonging among residents
within their local neighborhood can be strengthened.11
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Engaging people in reforestation promotes awareness and understanding of the source of
water, and rally public support to conserve water. More than 70% of Hong Kong’s drinking
water comes from Dongjiang. We believe in equity, the rights and responsibilities of the
river should be shared by all.
Public Health Benefits
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Greenery helps people to concentrate.
Trees filter air-borne pollutants and reduce the conditions that cause asthma and other
respiratory problems. The rate of asthma fell by 25% for every extra 340 trees per
square kilometre.12
Neighborhood parks promote exercise, thus reducing obesity.13
Exercising in natural environment is associated with greater feelings of revitalization,
positive engagement, decreases in tension, confusion, anger, depression and increased
energy.14
Visual exposure to settings with trees helps recovery from stress within five minutes, as
indicated by changes in blood pressure and muscle tension.15
Tree shades can protect people from sunburn by UV rays.
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Patients who stayed in ward with a tree-view tend to be discharged sooner and less
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11
Kweon, BS, WC Sullivan, and R Angel. 1998. Green Common Spaces and the Social Integration of Inner-City Older
Adults. Environment and Behavior 30, 6:832-858.
12
American Lung Association (ALA). 1997. Childhood Asthma: A Matter of Control. Pamphlet.
13
Bell, Janice, Jeffrey Wilson, and Gilbert Liu. “Neighborhood Greenness and 2-Year Changes in Body Mass Index of
Children
14
Ulrich, Roger S. "The Value of Trees to a Community” Arbor Day Foundation. Web. 27 June 2011.
15
Ulrich, R. S. "View through a Window May Influence Recovery from Surgery." Science 224.4647 (1984): 420-21.
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reliant on pain-killers.16
Children with ADHD (Attention Deficit Hyperactivity Disorder) benefit from walking in
the park with effects similar to drug treatment.
University student with windows facing natural scenery scores higher marks in
examinations.
Green environment improves work efficiency and decreases sick leave rate by 23%.
Energy Use Benefits
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The net cooling effect of a healthy tree is equivalent to 10 room-size air conditioners
operating 20 hours a day.17
Planting trees can reduce refrigeration costs by 30%. Shading an air conditioning unit can
increase its efficiency by 10%.18
16
Purdue University. "Trees Could Affect Land Use, Reduce Skin Cancer." San Diego Earth Times.Mar. 2003.
University of Washington, College of Forest Resources. Urban Forest Values: Economic Benefits of Trees in Cities.
Rep. Center for Human Horticulture, 1998.
18
Nebraska Forest Service. “Simply trees: tress for energy conservation”. Journal Star. March 2011
17
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