Dean Pryke has cultivated a mini-rainforest, with its own board walk, in the back yard of his Burrawang home during the past two decades.

The 200-year-old Brown Barrel tree on his property, 45 metres high with a circumference of 10 metres, is the largest of its species recorded on the National Register of Big Trees website.

The giant tree stands at the back of Mr Pryke's property in the far corner of his private forest, which covers 70 by 15 metres of his yard.

Brown Barrels are native eucalyptus trees commonly found in south-eastern Australia.

The National Register of Big Trees documents flora from around the nation with the help of South Australian botanical expert Dean Nicolle, who nominates trees for the register.

"That (Brown Barrel tree) can be seen from Kangaloon Road on the side of the valley. You can actually pick it out and say 'that's my tree'," Mr Pryke said. He became interested in rainforest vegetation as a student after school excursions to Minnamurra Rainforest and Sydney's Royal National Park.

His interest grew and he established small rainforest environments at his parents' home in Sylvania before he moved to Yowie Bay and cultivated another.

Mr Pryke said he bought land at Burrawang in 1989 because the geological and environmental conditions were well suited to growing rainforest vegetation.

"I knew a little bit about this area before I bought the land. I wanted an area that was volcanic. This entire area was hell on earth 15 million years ago," he said.

"When I bought the land there was nothing here except long grass all the way to the top."

Mr Pryke said he was interested in preserving rainforest environments because they were quickly disappearing.

"There's so little rainforest left in the whole of Australia because there are too many rednecks that just clear everything."