But the self-described "city girl" did not expect them to talk so much about trees.

When researchers asked what was important to their lives survivors would take them walking around their properties, or down bush tracks.

"They'd talk about beautiful trees that had survived and gave them daily pleasure," Associate Professor Gibbs says.

Or the bare patches where much-loved bushland once stood. The flush of regrowth mirrored their own slow healing, they said. The burnt blackness affected their mood.

The people affected by Black Saturday and related bushfires have progressively recovered but their mental health still suffers, finds a six-year study of 1000 survivors undertaken by Melbourne University and community agencies.

The short-term effect of disaster on mental health is widely known, but there is little data on how an individual's recovery is affected by social and community changes over time.

The most compelling finding was that social ties really matter, and have a 'protective' effect on wellbeing. As a survivor's membership of groups increased, so did their mental health. But there was a point where being signed up to too many groups became detrimental to their psychological state.

Anger could be a barrier to recovery but also motivational. But if regular, explosive bursts of anger were still a regular pattern years after the fires it was associated with poorer mental health.

"If you're sitting on that sort of precipice [with] blank depression on one side and feisty anger on the other, it might be that you need to tip over into anger to prevent yourself going the other way", one interviewee said.

Kinglake resident Lesley Bebbington lost her home in the Black Saturday fires, and her family lived in a caravan for four years.

Before the fires she had worked in the out-of-hours care at Kinglake Primary School and been the school council president, so afterwards she worked to get the school open again.

She noticed that primary-aged kids were being well supported psychologically.

But teens were overlooked. Yet they were exhausted and traumatised from driving past scorched landscapes and the blackened homes of deceased friends every day on their way to school in Diamond Creek, Whittlesea and Yea.

So Lesleystarted a youth group, later known as the Kinglake Wominjeka Youth Group. On the first night 11 young people turned up, a few months later about 60 would come weekly from all over the fire-affected region.

"They took care of each other. If one of them was a bit down in the mouth the other kids would flock around them," she said.

Governments need to acknowledge and support grass roots responses to disaster, Lesley says. She was saddened when the group ran out of the little funding it had, despite the large numbers of young people still on the books.

"During this process I witnessed some of the greatest kindnesses I've ever seen, I saw the best in people."

The majority of those affected by Black Saturday were 'resilient' in the aftermath, but a sizeable minority - about twice the number in a normal population - reported mental health problems severe enough to need professional support, the report found.

It also noted a delayed onset in problems like post-traumatic stress disorder.

Miki Perkins is on Facebook and Twitter