Trees planted by the ACT's first afforestation officer that will be felled for the second stage of light rail stage two will live for at least 15 years, instead of the five years territory officials told a federal parliamentary inquiry they would.
Himalayan and Atlas cedars planted on the Commonwealth Avenue median will have to be pulled out when construction on the second stage of the network begins.
The cedars were planted in the 1920s by Charles Weston, Canberra's first afforestation officer, who helped to transform the infertile, windy and rabbit-infested rural outpost into a city fit to be Australia's capital.
The ACT government told the federal parliament's Joint Standing Committee on the National Capital and External Territories the cedars had a life expectancy ranging from only five to 40 years, as assessed in 2013.
The government also quoted the National Capital Authority in saying the trees were in a poor condition and "starting to fail" and "it's really just an old age thing".
But a confidential report prepared for the project in late 2017 said the cedars would live for between 15 and 40 years.
The arboricultural report also said the cedars were of high value and pointed to problems with only three of the trees.
A spokeswoman said the ACT government provided correct information to the committee as the lifespan of 15 years was within the range quoted in its submission to the Commonwealth inquiry.
The report was obtained under freedom of information.
The Canberra Times requested technical documents related to stage two last April to help inform public debate about the benefits and challenges of the routes being considered by the territory government.
But after 14 months, the Transport Directorate chose to deny the bulk of the request, claiming the reports were cabinet in confidence.
The tree report was the only one they would release as the information was "purely factual" and "will not involve the disclosure of a deliberation or decision of cabinet".
The removal of the trees is shaping up to be a controversial issue for the second stage of the project.
Former National Capital Development Commission landscape architecture director Dr John Gray, who wrote the book on Charles Weston and his transformation of Canberra, said last year the trees should be saved if possible.
""In all of my work in Canberra I always tried to retain trees that had been planted by others before me. They take a long time to grow. They're an important part of our heritage. I think our landscape is too precious to be chopping away at it the way it's been done in Northbourne Avenue," Dr Gray said.
The National Arboretum has said the lifespan of a Himalayan cedar is 600 years and 300 years for an Atlas cedar.
However the ACT government has pointed out trees are an exotic species in Australia and it is unclear how the Canberra's environment would affect that lifespan.
The Atlas cedar is native to the Atlas Mountains of Morocco while the Himalayan cedar native to western Himalayas in Eastern Afghanistan, Northern Pakistan and India.
Despite this, the government has said that any proposal to change the landscape of Commonwealth Avenue would be accompanied by a detailed landscape and reafforestation strategy.
The strategy would be "conditioned" by the federal environment minister through the environmental impact statement process, well ahead of the works approval.
The government has also said it is unlikely the Weston cedars could be removed and relocated elsewhere, although there was potential to recycle and reuse the material.
If possible, the government would also seek to propagate those trees in other suitable locations agreed with the National Capital Authority.
The ACT is losing 3000 trees per year, however the ACT government committed to plant 17,000 trees over the next four years.