Mr Tonkin, a director at Sydney-based architecture firm Tonkin Zulaikha Greer, had seen a design competition for the National Arboretum Canberra advertised in early 2004.

Interested, he met with landscape architects Taylor Cullity Lethlean in Canberra, and took a walk around the proposed site.

''I remember trudging out to the cork oaks and it was sitting there that we really got the idea to plant forests of one type of tree,'' he said.

''When you go to the cork oaks, all you can see is one species of tree all around you and it's just extraordinary the power one species of tree can have.''

The two firms won the contract in 2005 with their 100 forests and 100 gardens design. On Saturday, Mr Tonkin saw the realisation of that initial vision finally embraced by Canberrans.

Thousands of visitors poured through the Arboretum's central building, the spectacular village centre. The building's centrepiece is its enormous vaulted roof, crafted from Tasmanian oak. No two pieces of timber in the roof are the same size, and each piece was digitally designed before being cut in Hobart and shipped to Canberra.

''It all just went together with millimetre accuracy,'' Mr Tonkin said.

''The inspiration was the shape of the hills and some of the trees.

''You can see palm fronds in it,'' he added.

''Some of the ginkgo leaves have some of the shapes used in the roof.''

Another worker on the project returned to see the finished product.

Warren Saunders worked as a landscaper for one of the contractors employed to plant some of the thousands of trees across the site.

''We planted about 8000 plants all up - sugar maples persian silk trees, fig trees,'' Mr Saunders said.

''During the drought, it was just a dust bowl, the whole place was just brown.

''But everyone likes it now,'' he said.