He was speaking (sermonising, really) at a tree symposium as part of Canberra Tree Week. I have known sincere clergymen give less impassioned sermons about the glory of God than Dr Brack's impassioned talk – Trees Do Impossible Things – about the glory of trees.

Dr Brack, of the ANU's Fenner School of Environment and Society, spoke of the seemingly impossible heights trees grow to, of the seemingly impossible depths their roots can burrow down to, and of the seemingly impossible abundance of living things a single mature English oak tree can harbour in its leafy bosom.

Trees can be impossibly tall, he told us, and with a clever use of film projected on to a screen took us up and up and up above the Arboretum until we were, in our imaginations, butterflies on the topmost twig of the tallest known tree, a Californian Sequoia. The view was astonishing and the little cars beetling along the road beneath the Arboretum looked like, well, little beetles.

"One hundred and sixteen metres tall, almost 400 feet!" Dr Brack enthused.

He went on to say that Australians could take pride in the thought that it was possible "the tallest tree ever" had been a towering Australian eucalypt.

He said that we know for a fact it had grown to be 497 feet (151 metres) tall (audience gasps) because when impressed colonists came across it in the late 1800s they promptly chopped it down so as to be able to measure it precisely (audience groans).

"The cement tower of Black Mountain Tower is only slightly taller [than the tallest Sequoias]," he told us in a talk in which he used lots of analogies and props to illustrate things.

"But height is only half the story, of course, because not only do trees go up, they go down. So the biggest, deepest root system we have measurements of is about 400 feet."

Of course, there are scientific explanations (involving capillary action and other wonders) for how trees manage to draw water up to their loftiest extremities. But even though Dr Brack knows, in a sense, what those explanations are, he still thinks that "magic" must play a part. After all "you can push water up, but we know trees don't push water up so they must pull it".

Taking out and flourishing a five-litre bucket, he compared the feat of a very tall tree drawing up sufficient water for its daily needs to our carrying "two of these [buckets of water] up Black Mountain Tower, one in each hand, 15 to 20 times".

Then, he marvelled, there is the way in which trees acts as hosts for other living things. He showed us a picture of a burly English oak (there is a forest of infant English oaks at the Arboretum) and said a fully grown oak might have 280 different species of insects and animals in and around it. Some rainforest species in steamy climes may host over 2000 species.

This reporter had to hurry away before the end of Dr Brack's impassioned and entertaining talk but such was the semi-religious fervour of the occasion it will not surprise if it ended with an appropriate hymn; perhaps Hymn 121, Tree of Life and Awesome Mystery.

But, clever as they are, trees can't knit and so humans have knitted the colourful woollens that have been wrapped around some Arboretum trees as part of the Warm Trees project.