Feral animals will take advantage of the open, fire-ravaged landscape and pick off injured and recovering small native mammals unless a stepped-up control program is part of the recovery effort.
Invasive Species Council chief executive officer Andrew Cox said that the weeks and months following the fires would be a critical time to "get on top" of the feral pest problem through baiting and trapping because it was when native animals were in greater danger of attack.
"While the feral animals like foxes and cats living in our state forests are not impervious to the fires, they recover faster, they will be hungry and they are fierce predators," Mr Cox said.
"They will roam further for prey and with the passing of the fires, have the added advantage of more open woodland in which to hunt.
"This leaves our small natives even more vulnerable than before."
He said endangered animals like the mountain pygmy possum in the Snowy Mountains and various species of endangered bandicoots were at significant risk.
"There is a massive food shortage for those native animals which have survived the fires. This is on a scale we've never seen before."
He said a previous examples of a feral species that proliferated after a fire was in 1994, when bushfires around Sydney burnt about 800,000 hectares and into such areas as the Ku-ring-gai, Chase and Royal national parks.
"There was a program proposed after those 1994 fires to control the feral deer population but the government baulked, and the deer population grew and spread exponentially," he said.
He said the months after a bushfire were among the best times to control pests and feral animals, which congregated in areas where scant feed was available.
"Australians and the world have been quick to respond to the bushfire wildlife disaster, with generous donations being sent to help rescue and care for injured animals," Mr Cox said.
"But unless we get on top of the feral and pest issue early, it will be too late."
The contentious feral horse issue was certain to be rekindled across the fire-damaged alpine landscape to Canberra's west and south-west.
"As a result of the fires, the horses in the affected alpine areas will roam further for feed. This will send them into areas of the Kosciuszko and the Namadgi [national parks] they haven't been before," he said.
The latest Australian Alps Feral Horse Aerial Survey published in December estimated the feral horse population in the Kosciuszko National Park at 25,318 animals, which is more than double the number from 2014.
Horses pose a significant threat by over-grazing and trampling in Canberra's fragile water catchment areas and alpine eco-systems high in the Namadgi National Park, bordering NSW.
ACT Parks and Conservation believes the ecosystem already has been damaged.
"There was a summer trapping program initiated in September but that would have barely started before the fires hit and resources had to be diverted," Mr Cox said.
"The stakes are even higher now."
He said major weeds such as Coolatai grass and lantana were known to benefit from fires by spreading into burnt areas.
"If we fail, we will inherit a landscape full of feral animals and weeds and a hostile environment for Australia's native plants and animals," Mr Cox said.
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