But the transfer never materialised, and the TLC has confirmed it was not informed of the prison decision until the public announcement was made in June.

Documents released under Right to Information include a 2015 report that showed threatened flora species blue pincushion and chocolate lily were observed, while seven other threatened species were found nearby that could find suitable habitat on the land.

The land was in the line of a sight of an eagle's nest, documented as part of a 2015 DPIPWE report considering a conservation covenant for the property. The report recommended setting aside areas for habitat and species management, and agreed that a covenant would be established once it was transferred to TLC.

The land had been "unmanaged" since the Crown purchased it in 1999, allowing gorse, blackberry and thistle to proliferate, and poor fencing had allowed livestock to enter the area.

But in the 2015 report, it was estimated the weed infestation would take two people two weeks to initially control, and the TLC had agreed to carry out the required ongoing maintenance.

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"Once the property has been transferred to DPIPWE Revolving Fund the TLC will undertake required weed control treatments and also erect those fences necessary to exclude stock access," the report reads.

The Brushy Rivulet land was described as a "nice patch of vegetation alongside Brushy Rivulet which links to a larger patch of native vegetation to the north".

The majority of the property was seen as containing "fair to good" examples of eucalyptus amygdalina forest and woodland on dolerite, with "an open age structure of approximately 15-25 years with the occasional large older tree" with few juveniles present.

Tasmanian devils were sighted in the area multiple times in 2010, green and gold frogs were seen repeatedly between 2000 and 2011 and a masked owl was sighted in 2009.

Government-appointed botanist Fred Duncan recommended examining the inclusion of the area in the CAR Reserve System in 1997, prior to its purchase in 1999.

The documents did not reveal the reason why the agreement to transfer the land to the TLC never eventuated.

Documents detail the arrangement, including that in February 2011 "the government offered the property to the Tasmanian Land Conservancy to sell (with a covenant on title) through its revolving fund with the proceeds to remain with the fund".

IN OTHER NEWS:

"The TLC has accepted the offer from the Crown and this transfer is now being processed," DPIPWE documents state.

TLC chief executive officer James Hattam confirmed that the organisation was unaware of the government's decision to use the land as a prison until the public announcement was made.

"The TLC was informed of the selection of the property for the location of the northern prison by the Department of Primary Industries, Parks, Water and the Environment at the same time as the community," he said.

"As outlined in the Brushy Rivulet - Westbury Conservation Covenant Proposal the property has numerous natural values, including suitable habitat for a range of rare and threatened species and is supportive of the property's conservation (as originally intended) through the revolving fund mechanism.

"The TLC believes the property ... on Birralee Road, Westbury should be conserved as originally intended through the Private Forest Reserve Program, contributing to the National Reserve System."

Field naturalist Sarah Lloyd OAM - who has previously raised concerns about endangered birds on the Brushy Rivulet land - said the documents confirm that the site has strong conservation values.

In addition to the blue pincushion, she said other flora species such as white gum, swamp gum and other eucalpyts had been raised by botanists in reports to the government.

Ms Lloyd said it reinforced her view that the site was inappropriate for the proposed $270 million Northern Regional Prison.

"You couldn't think of a more inappropriate site," she said.

"My main impression from these documents was how keen the botanists were to preserve it. They could see the high conservation values.

"It's an important piece of bush and shouldn't be levelled for a prison."

While the 16-hectare site proposed for the prison was on the southern edge - adjoining Birralee Road - Ms Lloyd said the level of construction work, ongoing lighting and noise would ruin the area for native species.

Prison opposition group Concerned Residents Opposed to the Westbury Prison Site also raised further concern about the bushfire buffer zone, which it claimed was previously an additional 19.5 hectares around the prison site, but they had been told this could now be incorporated into the 16-hectare prison footprint.

The RTI documents' reference to dolerite rock also raised concern about the potential for blasting to level the site, CROWPS said in a statement.

"CROWPS calls on the government to provide transparency on how much more we will all be expected to pay for the laundry list of additional costs, including the blasting and removal of rock next to an eagle's nest, earthworks to flatten the site, road works and providing services to an area without electricity, water or sewerage," the statement reads.

Attorney-General Elise Archer said the TLC had been notified that the land would not be transferred prior to the prison announcement, and the conservation values were no longer current.

"It is important to note that information released under the recent RTI includes information on natural values that is now out of date," she said.

"The vegetation community present on the site was reclassified approximately five years ago when it was determined to be of a different, non-threatened type.

"The site does not contain the values for which it was originally purchased, and indeed for more than a decade, consideration has been given to allowing the land to be sold.

"The Tasmanian Land Conservancy was notified of the decision not to proceed with the transfer of the informal reserve prior to the announcement of the site as the new site for the Northern Regional Prison. This land is not a reserve."

The government announced a 16-hectare section of the land along Birralee Road as its preferred site for the prison, after backing away from a site in the Westbury industrial estate following community backlash.