Sydney's avenues of plane trees have their new leaves for spring and will provide much-needed shade in the city's concrete jungle for an expected hot El Niño-charged summer.
But the London plane trees also draw the ire of hayfever sufferers as their trichomes grow and take flight, setting off allergy-related symptoms.
The trees are the second most common species (after brush box) across the City of Sydney but under a new plan they will eventually become a thing of the past.
Why does Sydney have so many plane trees?
There are about 4,000 plane trees in the City of Sydney, making up 8.5 per cent of the city's street and park trees.
Their popularity stems from a failed experiment in the 1850s with blue gums and pine trees in Victoria, according to landscape architecture academic Helen Armstrong.
A combination of the two evergreen trees meant the roads, which were not sealed, never dried out.
According to Professor Armstrong, in 1889 the Victorian Department of Agriculture spelled out why street trees should be deciduous trees instead:
"They give shade from heat in summer, and they let the light in in the winter.
"When there's most rain, the drip from them is little, and at the moistest season the roads beneath them soon dry up and keep in good preservation."
Professor Armstrong said this reasoning underpinned the planting of deciduous trees in cities, including plane trees, from the 1890s onwards.
The trees also were planted because of their widespread use in London, Professor Armstrong said.
"It's always maintained its stateliness as an urban tree," Professor Armstrong said.
"The fact that there are so many is because they've survived so well."
'Great urban trees'
Plane trees are also very well suited to being an urban street tree where they need to thrive underneath concrete, according to City of Sydney urban forest manager Karen Sweeney.
"Plane trees are great urban trees in the sense that they are very tough and hardy," Ms Sweeney said.
"They're often planted covered in asphalt or concrete, they're not watered … they're able to grow up and have quite large canopy."
Ms Sweeney said they were also great city trees because it was easy to predict where they would grow.
"We have to direct the canopy of trees around buildings up above clearances for pedestrians, clearances for vehicles and trucks, around signs, lighting, powerlines," Ms Sweeney said.
"So many cities have planted them because they've just performed so well."
Changing climate forces cutback
As an introduced tree, plane trees draw the ire of some Sydneysiders, especially when tiny hairs from their new leaves become airborne and a source of irritation.
Fortunately for the naysayers, the city has a plan to phase out plane trees from the city's streets.
But it's not for being a non-native tree or producing allergens — it's because of climate change.
Ms Sweeney said the city went through 400 species to find the ideal street tree that could thrive in Sydney with a climate featuring greater periods of drought and warmer conditions, similar to Grafton in northern New South Wales.
To their surprise, the plane tree was one of the least well suited.
"We looked at all of the research and did an extensive amount of work to futureproof our urban forest and our canopy cover," Ms Sweeney said.
"Of the 400 species, the plane tree was found to be ranked the third most vulnerable to drought."
When a plane tree goes, it will not be replaced by another
The city's plan is that when a plane tree needs to be removed, it will be replaced with a species better suited to the changed climate in the long term.
The replacements will be a mix of native and introduced species and have been chosen based on many factors including the side of the street they are on.
Some examples include native eucalyptus, bloodwoods and leopard trees and imported species such as rain trees.
"We really do need to have that balance between summer shade and winter sunlight in some locations," Ms Sweeney said.