Neville Passmore: Why trees are good for suburban gardens (Part 1)

Positive impacts on the built environment

Cooling effects are at the top of my list because we are facing an urgent problem called the ‘urban heat island effect’.  Cities and suburban areas are characterised by hard heat retaining surfaces including asphalt roads and parking areas, concrete buildings, brick homes, and stone walls.  All of these materials absorb heat during the day and radiate it back into the air at night.  The result is that the areas where we live and work are gradually heating up. Humans have limits as regards the heat in our immediate environment.

The Black Saturday fires in Victoria took the lives of 190 people as a direct result of the flames.  Same weekend, same city – Melbourne, just under 400 people died from the result of the build up of heat in and around the city.  This dramatically underscores our fragility and the damage that can occur when it gets, in the words of the song “Too darn hot”.  Seventy five percent of the victims were over 60 years old.

Shade from trees is a counter to the heat island effect.  Perth City Council research has demonstrated a difference of as much as 6 to 7 degrees Celsius on a hot day, between streets that get shade and those that don’t.

Bitumen preservation seems like an unusual thing to talk about in a story about trees; but the cost to our local councils of replacing bitumen is a major recurring expense.  Bitumen roads and carparks situated under tree shade fare much better than those in full all day sun.  Trees save dollars!

Reverse cycle air conditioning is one of the lovely attributes of deciduous trees which shade homes and buildings.  Shade in summer cools the building and, by the way makes the air conditioning unit more effective and efficient, and then bare branches in winter allow the sun’s warming rays in to lessen the need for energy hungry heating.

Privacy screening is another benefit particularly when neighbours get approval to develop a second story.  Evergreen trees can block the vision into your home if appropriately placed.  One of the big drivers of advanced tree planting in suburbia is for privacy.

Transpirational cooling might sound like a religious experience, however all plants pass moisture from their tissues as an everyday part of growing. This also reduces the temperature of the air around a tree.

Creating amenity is another way of saying that trees can bring beauty, colour and form and a ‘sense of place’ to our homes, our suburbs and our workplaces.

Picture a red flowering gum (Corymbia ficifolia) in full flower, a mango tree (Mangifera indica) heavy with golden fruit and the autumn foliage of a Chinese tallow tree (Triadica sebifera) or a liquidambar (Liquidambar styraciflua); the beauty of trees can really light up our day.