by Carla Caruso

Many enjoy the purple ‘reign’ jacaranda trees have over our city in November and early December.

Parkgoers love getting social media snaps of the mauvest displays around town, sometimes even colour-coordinating their outfits with the blooms.

The arrival of the flowers is up there with the Christmas pageant in heralding the start of the festive season locally.

But not all are so enamoured with the trees, which are actually native to South America, rather than here.

In fact, local pollination ecologist and educator Bianca Amato – behind the Adelaide Pollination Project – thinks the species, well, “sucks”.

As Bianca wrote online:

“There can be a happy medium between natives and exotic plants. However, I think councils have gone a bit jacaranda-mad.

It’s important that we plant a diversity of trees, ensuring our streets aren’t lined with the same species – that goes for all trees.”

According to Bianca, jacarandas are particularly bad news for native bees and hollow-dependent wildlife.

“Jacaranda trees provide floral resources for only a brief period of one to two weeks annually, with each flower lasting for just one to three days.

In contrast, native eucalyptus trees in Australia have extended flowering periods, frequently blooming for months.

Each eucalyptus flower can secrete nectar for weeks, providing a huge supply of floral resources for pollinators over an extended period.

Native pollinators are never seen foraging on jacaranda flowers. Instead, European honeybees cover the trees.

Jacarandas increase honeybee abundance, which leads to an increase in competition for resources and the displacement of native pollinators.

Lastly, Australia has the most hollow-dependent wildlife in the world. Jacaranda trees do not make good hollows.

We plant too many jacaranda trees. They are pretty for two weeks of the years, but at what cost? Essentially our jacaranda-lined streets are ecological dead zones.

Native trees support urban biodiversity more than exotic species.”

The prettiness of the trees aside, would you agree with her?

Plane trees also under ‘attack’

Jacarandas aren’t the only trees to have been put in the spotlight of late, albeit interstate. In October, the City of Sydney announced that it would largely phase out the use of plane trees across its streets and parks.

Environmentalist Tim Flannery once called plane trees “foreign weeds … about as much use to our wildlife as concrete posts”. Others to criticise them include asthma and hay fever sufferers.

But the Sydney city council’s decision to wind back the use of the trees is based instead on the changing climate. In most cases, the plane trees will be replaced, once they reach the end of their lives, by more drought-tolerant plants.

This includes native species – like bloodwoods, tulipwoods, and ivory curls – and introduced deciduous species that’ll still allow light to shine through in winter, while being more resilient to heat and drought.

Adelaide’s own most iconic plane trees line the aptly-named Plane Tree Drive in Park 11.

A local parliamentary inquiry, though — rather than maligning just one tree variety — has highlighted the need to mix up the number and types of species in our city, echoing Bianca’s sentiment.

Parliament’s Environment, Resources and Development Committee tabled an interim report on its inquiry into Adelaide’s urban forest in October.

(The inquiry began in late 2022, prompted by concerns about trees being felled for new housing developments and the impact of urban infill on the city’s liveability.)

Within the report, University of Adelaide researcher Dr Stefan Caddy-Retalic, pictured, was quoted as saying:

“We need to rapidly diversify our urban forest. This is not just a question of planting native species – that is often put forward as a bit of a silver bullet.

We are not going to be able to regain our pre-European plantings, and nor should we try.

The requirements of our city today are very different from a native ecosystem. We have huge demands on our urban forest that aren’t present in a woodland environment.

And so, we need to make sure that we are planting trees that perform well under the conditions that we have and provide the ecosystem services that we need – things like shade and hydrological control and health benefits.

We shouldn’t necessarily use pre-European vegetation as our guide; our needs are different.

It’s far harder for disease to establish and spread if a target has a low diversity and can’t spread from one tree to its neighbour as well.”

Spokespeople at the City of Adelaide and Green Adelaide were contacted on the issue but didn’t provide any comments.