This sobering thought sobered your columnist while attending Tuesday's opening of the intoxicating Freefall Experience Design Ideas Competition display at the Gallery Of Australian Design.

The competition asked engineers to design a feature installation for the Engineers Australia Freefall Pin Oak Forest at the National Arboretum. The pin oak (Quercus palustris), much used in Canberra streetscapes, is a deciduous tree with leaves that go all colours (including 50 shades of tangerine) before they fall in Autumn. A whole lurid forest of them (it is the Arboretum's forest number 41) must in Autumn surely be visible from outer space.

All 33 submitted designs are gathered together in one place for the first time in the GAD show. The exquisite but big (35 metres long) sculpture/installation imagined in the winning design, Rod Bligh's Freefall, (of which more in a moment), really will be installed. Engineers Australia's Helen Leayr told us that it's hoped it will be there, nestled in the ever-maturing, brilliantly-coloured-in-Autumn pin oak forest, in 2019. That is the year of the 100th anniversary of the founding of what is today Engineers Australia. She tantalised with the tease that "some exciting sponsors" are being approached to help pay for this Arboretum-adorning structure imagined to cost at least $800,000.

A high-standard design competition like this always comes with the collateral melancholy of the sadness one feels for the runners-up. Eliel Saarinen's running-up design for our federal capital city imagined a metropolis that would have been quite marvellous here or anywhere on earth, but the Griffins pipped him at the post. Great runners-up in the Freefall Experience competition include Egg Sanctum (pictured). The entry, by a team of five including engineer Vesna Spasovski, comes with this delightful and plausible-sounding saga.

"Five hundred million years ago, when dinosaurs flew in the sky above where Canberra is now, a healthy and happy dinosaur we will call Shiro was among their number. Shiro was a Hatzegopteryx belonging to a species known as Azhdarchid pterosaur, a winged reptile known for its light and hollow bones and large brain. They were winged reptiles - the first vertebrates to evolve to have winged flight.

"Shori may have been unaware, but she was one of the largest flying creatures of all time with an extremely long wingspan of 12m.

"One day all those millions of years ago Shiro, as she flew low over trees, in mid flight dropped an egg. The egg landed and became half buried in the steep gradient of the pin oak forest. This baby version of Shori was fortunate enough to survive the crash, and emerge unscathed, but the surviving structure of its shell remained embedded in the ground for hundreds of millions of years. As no one ever cleared it away over time it became the pin oak forest egg sanctum, and became a place recognised by its local indigenous population. For them it was a calming amphitheatre from which they could sit to enjoy the night sky, its stars and darkness, its tranquility, and the rustle of leaves blowing in the breeze.

"Scientifically, all the birds that inhabit the Arboretum are Shiro's ancestors, feathered dinosaurs; meaning dinosaurs aren't really extinct at all."

So the envisaged space, the entrants trill, "is a sanctum in which to contemplate the surrounding trees, and at night a sanctuary from which to appreciate the night forest, the stars and moonlight".

His winning Freefall, Rod Bligh explained to us from Brisbane, is inspired by and refers to the shell shape of the famous cochlear implant, of course an engineering innovation and triumph.

He thinks of Freefall as both a journey and a destination. A longish walkway leads walkers up on a sweep through the forest, and delivers them to the centre of the shell's whorl.

There are more things about Freefall than we have room to mention, but it was part of his concept, Bligh explains, to echo the ways in which the cochlear implants almost magically transform their wearers' relationships with the world around them. He hopes Freefall, by its design and by employing some clever technologies devised by engineers, "will explore the sensory experience of [being in] the forest". There may be artful inbuilt things (all of them celebrations of engineering) to use your iPhone for while you're visiting. And he even imagines somehow having the sculpture/installation tremble a little "with low-level vibrations" when there is thunder about.

And the structure is designed so that in Autumn some of the falling leaves will lodge in its bare steel ribs and become, in their vivid, decomposing tangerinery, a part of the artwork of the sculpture-structure.

One shy and quiet guest at Tuesday morning's launch (shy and quiet myself we established an immediate rapport) was an actual Quercus palustris sapling in a very big container.

"Do you know," I confided in the sapling as we stood together in our own little sanctum of shyness, "that in his classic Trees in Canberra (1962) Professor Pryor rhapsodises about your species?"

"He carries on about your amazing ability to thrive in Canberra, about your 'full crown with dark green foliage in summer and brilliant shades of scarlet and crimson in Autumn'."

The exhibition continues at the Gallery of Australian Design, at 47 Jardine Street Kingston, until 20 March.