Urban Forest Facts

·       In summer, on average cities are 5 degrees warmer than the surrounding countryside

·       Properly placed trees & shrubs reduce energy use by lowering temperatures and shading buildings and blocking winds during winter

·       Although trees & shrubs are a useful carbon sink (approx 27t stored carbon /hectare of canopy – US figures), their greatest benefit is in reducing energy consumption (net reduction in carbon at the power station) . 

·       Energy savings stats (US Forestry Service study across 13 states showed:  One correctly sighted 8m tree shading a single story 139m² produced average annual energy savings (cooling) 218KWh and 0.5MBtu. (about $A70/yr), however it reduced carbon emissions at the power station by 27kg Carbon/yr.

·       Multiple properly placed trees produced up to 20 -25% energy savings.

·       Average energy savings with properly placed trees were about 4% more than with no trees and 13% more than improperly placed trees ( negative effects – shading during winter)

·       Large healthy trees of >77cm diameter remove 70 times more pollution than small healthy trees <8cm diameter

·       Trees & shrubs alter windspeed and direction. US data: In a Pennsylvania suburb with 67% tree cover, windspeeds were reduced by 60% in winter & 67% in summer (reduces energy consumption)

·       Along with transpirational cooling, trees & shrubs helps cool the local environment by reducing the solar heating of some below canopy structures (buildings, carparks etc) by as much as 5deg C.

·       US Data: 16% of the annual irrigation requirement for trees & shrubs in Tuscon (arid city) was offset by the annual water savings at power plants through energy savings from trees.

·       Reducing urban noise on motorways:  wide belts (30m) of tall trees reduced urban noise levels by 50% (6-10 decibels)

·       Extensive research in inner Chicago have shown urban forests to alleviate some of the hardships of inner city living:  contribute to stronger ties among neighbours, greater sense of safety and adjustment, more supervision for children in outdoor places, healthier patterns of outdoor play, more use of common outdoor spaces, fewer incivilities, fewer  property crimes and fewer violent crimes.

·       Treed thoroughfares reduce driver aggression and stress recovery.

Urban forest design and management strategies that help improve air quality & reduce carbon emissions:

·       Increase the number of healthy trees (increase pollution removal)

·       During drought, sustain existing tree cover (maintains pollution removal levels)

·       Sustain large healthy trees (large trees have greatest per tree effects)

·       Use long lived and low maintenance trees & shrubs (reduces the maintenance effects)

·       Plant trees & shrubs in energy conserving locations (reduces polluting emissions from power plants)

·       Plant trees to shade parked cars (reduces pollution from cars)

·       Supply ample water for vegetation ( enhances pollution removal &temperature reduction)

·       Plant trees & shrubs in heavily populated or heavily polluted areas ( maximises tree & shrub air quality benefits)

·       Avoid pollutant sensitive species (increases tree health)

·       Consider the potential of vegetation to improve local site conditions or alleviate local problems (eg , poor air quality, neighbourhood revitalization)