The iconic eucalyptus

Depending on which reference you use, there are between 700 and 900 species of Australia’s iconic eucalyptus tree. Something like 75% of our forests are made up of eucalyptus species, (next is the acacias and then the melaleucas). Eucalypts grow on tops of mountains, on the coast, in high rainfall gullies and on dry mallee and mulga plains.

Although considered to be endemic to Australia, naturally occurring eucalypts are found in New Guinea, Timor and parts of the Philippines. The genus is cultivated world-wide now, and in some places has become naturalized.

In 1777, a botanist sailing with Captain James Cook collected samples from Tasmania’s Bruny Island. In 1788, a French botanist identified and named the first species, Eucalyptus obliqua, more commonly known now as Messmate.

Proper identification of eucalypts is not easy at times and requires a certain amount of botanical knowledge about the bark, the fruit, the flowers and the leaves. Matters are made more complicated when it is accepted that some species are known to hybridize. Many factors come into play for the proper identification of eucalypts:

          Geographical location – elevation or depression, coastal, alpine, etc.

          Habit – tall and straight, small, spreading, single or multi-trunked, etc.

          Bark – colour, form and consistency.

          Flower and fruit – colour, size, shape and arrangement.

Leaf – colour, lustre, size, shape, arrangement, juvenile/adult and even the arrangement of the veins and oil glands.

(The glossary for one common text on eucalypts contains definitions of over 250 botanical terms!) 

Many of our eucalypts have learned to deal with fire by re-sprouting from buds under the bark or from tubers at the base of the tree.

Eucalypts are a valuable and important species for many reasons. Like all trees, they provide shade, lower the water table, purify the air and sequester carbon. Eucalypts are notable for their oils, fibre and timber and of course, many native birds and animals are entirely dependent on eucalypt habitat.

Not only iconic, but invaluable!

Trees are cool

With the heat of summer well and truly upon us, it is worth noting that researchers point out that ground temperatures on a hot day can be as different as 10⁰C in some localities due to the presence or lack of tree cover (ABC News link).

Credit: US.Forest Service

Trees are natural air conditioners that help keep us cooler and healthier.

When the sun’s rays reach a hard surface such as a building, a bitumen road or concrete footpath, heat is absorbed into the object and radiated into the surrounding air. This is one of the reasons that overnight temperatures in cities are always higher than the countryside – the heat collected through the day is being radiated back into the air.

Not only do they provide shade from the sun’s direct radiation on a hot day, trees can also actually cool the air by transpiration. Moisture in the ground is absorbed by the roots and transported throughout the tree and out into the air through pores in the leaves.

Transpiration at the surface of the leaves occurs when the moisture in the leaves changes to water vapour by absorbing heat from the air, thus cooling the air around the tree – pretty much like the evaporative coolers on the roofs of houses.

A large gum tree on a hot summer’s day can transpire as much as 200L of moisture into the air, taking around 118,000 calories of energy from the air to do so.

Provided there is enough moisture in the soil, the amount of transpiration is directly proportional to the leaf area, hence leafy tree and understorey plus mulched ground surface to retain soil moisture are important factors that make trees nature’s air conditioners.

For our own health and wellbeing as our climate warms up, well-designed streetscapes and developments that include trees, should be an important consideration of urban planning.

Integrating nature into the urban environment

The benefits to physical and mental health obtained from relating with nature are well documented and yet large proportions of urbanised populations are unable to access green spaces in their daily lives.

For the first time in history, more than half the world’s population lives in cities. 87% of Australians live in cities. Globally, cities occupy 2% of the world’s land mass and consume 75% of the world’s resources. Currently, we in Drouin are fully aware of the effects of urban expansion.

Not much room to plant a native!

Just by occupying land, urbanisation can have a detrimental effect on biodiversity. New developments often require dramatic modification of the natural environment. As we move into these developments, bringing our cars, pets and exotic plants, we are negatively impacting on biodiversity. 

Corymbia ficifolia – Not just a symbol of our town, perhaps the last chance for some nectarivores.

Many researchers now believe that by concentrating human populations into urban areas there is an opportunity to preserve biodiversity. People in urban communities often prefer to live in green and leafy areas. Many native wildlife species are adapting to urban environments. The recent catastrophic fire events in Queensland and New South Wales have resulted in vast losses of habitat. The urban environment might be the last chance of survival for some species.

Southern Brown Bandicoot – just clinging on in West Gippsland, in a few remaining patches of roadside habitat.

Biodiversity is our own life support system. It provides us with food, clean air and water and it keeps us healthy.

Golden-headed Cisticola - missing from Gum Scrub Creek wetlands in the October bird surveys. Nearby development?

Integrating nature into an urban environment has so many benefits and surely it isn’t difficult to increase tree canopy, preserve remnant vegetation, protect wetlands, add understorey, encourage native gardens, etc, it simply requires some wise and careful planning.