Unpredictable and drastic weather is affecting the livelihood of the humble suburban street tree.

The expectation of harsher winters and hotter summers is forcing city planners to ensure tree-lined avenues stay green and resilient.

Researchers from the Australia National University (ANU) say they have witnessed the deaths of 100-year-old trees all around Canberra.

They have now partnered with the ACT Government to look ahead to the next century amid ever-changing weather conditions.

Root of the problem

Associate Professor Cristopher Brack's work with ANU falls under the broad canopy of forestry.

A heatmap shows hotspots in land surface temperature of urban areas around Canberra. ( Supplied: CSIRO )

He said particular streets around Canberra needed urgent attention, with trees having outlived their practical lifespans.

"For avenues to work, they're all the same species, all the same age, all the same size," he said.

"If you look across the whole street, every tree is doing the same thing.

"Gradually, they all die the same way."

The project gathered data from the past 100 years to balance against new climate research.

Middle-aged trees are considered the most productive in terms of pulling carbon out of the atmosphere, but planners have to ensure saplings will grow the distance.

"What we want is a whole forest of trees around 30 to 40-years-old," Dr Brack said.

"They've got big canopies developed, they're pulling all the carbon dioxide out of the atmosphere, they're growing actively.

"But then you have to work out what happens once they reach 50 and 60 years old."

Thinking global, acting local

Even though climate change is considered a global challenge, the street tree project has become intensely local.

Residents have often staunchly defended dying trees or resisted new saplings on the verges.

"People can get quite passionate about their trees," Dr Brack said.

"We start telling people that we should be pre-emptive, we should be planting different species in their street.

"They may not look that bad but we know there are problems dwelling."

Street trees have faced intense competition in city centres with buildings and infrastructure.

Hot roads place a lot of stress on trees and extensive drainage has seen a lot of water sluiced away too swiftly.

But even suburban spaces have become battlegrounds with motorists crushing saplings under their wheels.

"People think that even the verge of the streetscape is theirs; they own the house, so they should own the verge," Dr Brack said.

"They want to use the verge for their own thing, even parking cars."

Street trees are forced to compete in both urban and suburban spaces. ( ABC Canberra: Michael Black )

He said it was easy for residents to take trees for granted, given they generally had longer lifespans.

It has become as basic as explaining to people that trees are, in fact, living things that eventually die.

Rich tapestry of trees

Before the National Arboretum was founded, Canberra's streets served as a de facto tree library.

Tree-lovers and visitors can take a leaf out of this book when touring Canberra. ( Supplied: Street Trees of Canberra )

The urban forest was documented during the 1970s by Audrey H Edwards in her book Street Trees in Canberra.

"The early settlers on the Canberra plain made the first introductions of many exotic trees including elms, oaks, willows, poplars, hawthorns and conifers," she wrote.

"Promising species have been introduced into the street planting program continuously."

Over the decades, planting has fluctuated between colourful streaks of exotics as well as nationalist regimes of native trees.

Dr Brack adopted a flexible definition of what constitutes a native tree versus an exotic.

"A eucalypt that grows in Perth, for example — is that still an appropriate species for here," he asked.

"They have harsher climates there — drier and warmer — so it would probably grow in the modern Canberra.

"If we take a eucalypt from 4,000 kilometres away and plant it in Canberra, is it still native? What if we took one from 10,000 kilometres away from North America?"

Exotic trees typically suffer in harsh winters but are important for diversity in urban forests. ( ABC News: Sonya Gee )

There are over 800 known species of eucalypt in Australia with only about two dozen that have been well-researched but the project has been tipped as an opportunity to stray away from the eucalyptus genus.

Dr Brack said the lessons would be useful for other Australian cities facing the same predicament as Canberra.

"If you want to make an environment robust and strong and able to cope with change, you need diversity," he said.

"We just have to work out how to get the tree in the right spot at the right time.

"My underpinning philosophy is that trees are the answer to any problem that we have."