About seven million hectares of land has already burnt across Australia, with lives lost and homes destroyed.

The time needed for vegetation to recover is unknown and will also depend on the severity of the fires in different areas, CSIRO principal research scientist Andrew Sullivan says.

"Within 12 months you will find most areas covered in a green sheen, in new spouts and coverage," Dr Sullivan told AAP on Monday.

"If you continue to go into drought, the response of the trees is going to be affected. If you get some good rain ... the response from the native vegetation is that much better."

Vegetation at the front of bushfires is likely to be burnt through, while vegetation burnt by a fire's flank should bounce back fairly quickly, he said.

Trees may be killed if the flames scorch the crown - the top of the tree - but new shoots may grow at their base almost immediately. Partly-burnt trees may start to regrow about midway up the trunk.

Monash University senior lecturer Christoph Rudiger, whose research involves using satellites to model the spread of bushfires, agrees the time frame for recovery is still unknown.

"You should see some sprouting in a few months if it is the usual (type of fire). The recovery depends on what the weather and climate does," Dr Rudiger said.

Burnt vegetation may take three to five years to recover properly if other fires across the country in the past five years are a guide, Dr Rudiger said.

"If it continues to be dry like it is now, the remaining vegetation will burn as well and the recovery to that burnt vegetation now will take much longer," he said.

Dr Rudiger is pushing for a dedicated research centre for bushfire recovery, rather than the Bushfire and Natural Hazard Cooperative Research Centre, to better utilise expert knowledge.

Prime Minister Scott Morrison flagged the need for more hazard reduction across the country while announcing the National Bushfire Recovery Agency on Sunday.

Victorian Premier Daniel Andrews was asked on Melbourne radio about backburning in bushland before the fires, after a royal commission proposed a minimum annual burn of public land.

"You can only put fire into the landscape when it is safe to do so. You have to the hectares the climate allows you to do," Premier Daniel Andrews told 3AW radio.

"Not just some broad hectare count to make you feel good, you have to be really careful."

Australian Associated Press