EXCLUSIVE

BUILDING underground at Sydney's Royal Botanic Gardens is being considered as part of changes to the historic site.

Unveiling a master plan for the gardens, the new executive director, David Mabberley, said any changes would need to make the gardens more financially independent.

''If we do anything it will probably be underground. The point being we shouldn't be alienating green space with permanent buildings,'' he said. ''If we wished to expand the herbarium on this site, we have gone up as far as we can, we would have to go down in future.''

The sensitive site will undergo changes before its bicentenary in 2016, but Professor Mabberley said that he would not countenance ''concreting the place over''.

While there are no plans to introduce an entry fee, the Royal Botanic Gardens & Domain Trust is considering charges for events such as the Autumn of the Arts in the gardens.

An eminent botanical author and previously the director of the herbarium, library, arts and archives (what he describes as ''the dead stuff'') at Kew Gardens in London, Professor Mabberley is eight months into his new role in Sydney.

He said the majesty of the site presented an ''enormous opportunity'' to create the world's best botanic gardens organisation.

''What is astonishing to me is that the people of this state have, in 200 years, kept it free of development - that I think shows an enormous foresight on behalf of governments and the people of NSW,'' he said. ''You think what this would be worth in terms of real estate. If we want to do any developments in here it has to be done in the context of an overall picture and that will involve the other two gardens … We have to ensure that we don't go in and do a backyard blitz.''

But Professor Mabberley conceded the trust needed to maximise its assets. The trust will implement the recommendations of a 22-page peer review of the gardens, conducted by a team of international experts and approved by the Environment Minister, Robyn Parker.

The proposals will force the gardens to become more reliant on generating its own funding and include redeveloping the tropical centre pyramid and arc glasshouses into a multi-functional exhibition, education and function centre.

There will be a drive to attract more children to the gardens.

Kew Gardens in London has been accused of over commercialisation with treetop rope walks, carousels and a children's playground, but Professor Mabberley said he would resist such changes. ''This place offers a tranquillity and an educational opportunity, it is far too precious to trivialise and fritter away.''