A Defence spokesperson said the Pialligo Redwood Forest was on Commonwealth land, managed by Defence. Plant Health Australia had negotiated with Defence to place and maintain a hive on the site as part of the National Bee Pest Surveillance Program, the spokesperson said.

The program places sentinel beehives near airports and sea ports as an early warning system of the entry of varroa mite, other bee pests and exotic bees into the country.

Authorities have confirmed the fire on Wednesday January 22 began at the beehive, which is maintained by local volunteer beekeepers. It is believed a smoking operation went wrong, sparking the fire which spread rapidly southwest and was upgraded quickly to emergency.

Separately, a Defence helicopter has been blamed for the massive fire in Namadgi National Park, sparked five days later. The landing light of the helicopter is believed to have sparked the light when soldiers were clearing landing zones for aircraft.

The fire grew to threaten Tharwa and southern Canberra and crossed into NSW. On Saturday, February 1, the fire flared around Bredbo and Michelago, destroying 12 homes.

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The Pialligo Redwood Forest is a small patch of forest near the airport runway. Covering about 12 hectares, the plantation is heritage listed.

It is the remnant of a plantation established by Charles Weston in 1918, at the request of Walter Burley Griffin - mainly giant sequoias and coastal redwoods.

The trees were planted, despite advice that the Canberra climate was too dry for these species, according to the group Friends of the ACT Trees.

Most had succumbed to lack of water, with only 3000 of the original 120,000 trees remaining.

A number of trees had been removed for the airport extension in the 1960s, and the friends group said the remaining trees were showing signs of stress and some were dying. More trees were planted in the 1980s but most had failed.

Fire has hit the area before, according to the heritage citation, with trees in the southeastern corner burned in late 2001.