There are four main tree functions in urban areas these include engineering, architectural, environmental and aesthetic. These can all be broken down further.
Engineering – acoustical, traffic, and erosion control, glare / reflection
Acoustical Control or Noise Reduction
– A screen of trees 30m wide will absorb about 6-8 decibels of sound.
– conifers are year round.
– help direct pedestrian and vehicular traffic.
– screen glare form headlights and other buildings.
– provides a stream for pedestrians to follow.
– both wind and water erosion can be reduced by plantings trees and shrubs on bare soil.
Glare and Reflection Reduction
– careful placement of trees helps reduce glare and reflection from sun, artificial lights and other buildings.
Architectural Benefits – privacy control, defines and/or encloses
architectural spaces, screens objectionable views, softens harsh appearances of buildings.
– examples of these include: trees and shrubs are used to screen parking lots or building structures, as well as soften the view of building surfaces and edges.
Environmental Benefits – trees have numerous influences on urban
microclimates including wind, sun, precipitation and humidity control, and air purification.
– obstructs, guides, deflects and filters airflow
– reduces radiant heat loss from buildings by reducing wind speed
– provides and insulation layer of calm air beside buildings
– to a great extent urban surfaces either absorb heat light and heat up, (black surfaces) or absorb heat and energy (compacted and dry surfaces). Trees and shrubs can reduce this by absorbing heat as they transpire which provides cooling shade that reduces solar radiation and reflection.
Precipitation and Humidity Control
– provides a screening from rain
– reduces fog density by condensing moisture on leaves and twigs.
– provides snow control
– excrete water vapour into the air
– by absorbing CO2 and releasing O2
– absorbing some airborne pollutants (valuable)
– trap particulate air pollutants
– carbon sequestering which all trees do and urban trees are 5-15 times more beneficial than forested trees for reducing air pollution.
Aesthetic Function – trees give character to nieghbourhoods
– this can all be done by variety of form, colour, textures, and patterns in urban landscapes.
– form vistas, frame views, provide focal points, and define spaces.
– trees provide pleasing floral displays or leaf colours, fragrances, sounds and serene settings.
– trees emphasize seasons.
– provide habitat for urban wildlife, especially birds.