The Times Australia
The Times World News

.
The Times Real Estate

.

We need urban trees more than ever – here's how to save them from extreme heat

  • Written by Renée M Prokopavicius, Postdoctoral Researcher in Plant Ecophysiology, Western Sydney University
We need urban trees more than ever – here's how to save them from extreme heat

Australians are bracing for a hot spring and summer. The Bureau of Meteorology has finally declared El Niño is underway[1], making warmer and drier conditions more likely for large parts of the country. And we’ve just watched the Northern Hemisphere swelter through their summer, making July 2023 Earth’s hottest month on record[2].

We studied the effects of extreme heat on urban trees in Western Sydney during Australia’s record-breaking summer of 2019–20. So we hold grave concerns for the survival of both native Australian and exotic species in our urban forest[3]. These stands of trees and shrubs – along streets and in parks, gardens, and yards – play vital roles in our cities. Trees improve people’s mental health and wellbeing, lower energy use, and reduce temperatures through shading and evaporative cooling.

In previous research, we compared the heat tolerance of different species[4]. Our new research, published in the journal Global Change Biology, assessed their water use. Most of the trees we measured lost more water on hot days than models predicted[5].

Much like sweating in humans[6], trees lose water to keep cool[7]. If there’s not enough water, dieback or tree death occurs. This means access to water will be crucial for the survival of our urban forests during the hot summer ahead.

A photo of a city street in western Sydney showing London plane trees with scorched leaves during the 2019-20 summer.
London plane trees in western Sydney lost leaves during the hot, dry 2019-20 summer. Renee Prokopavicius

Read more: Climate change threatens up to 100% of trees in Australian cities, and most urban species worldwide[8]

Trees during heatwaves in Sydney

During December 2019 and January 2020, Western Sydney had 12 days over 40℃. The city’s record maximum temperature of 48.9℃ was set on January 4, 2020.

We measured carbon uptake and water loss[9] from urban tree leaves on these hot summer days.

We found some species had low heat tolerance. Those most vulnerable to heatwaves[10] included both native Australian and exotic species. Some trees died, including red maple (Acer rubrum), tulip poplar (Liriodendron tulipifera), coast banksia (Banksia integrifolia) and water gum (Tristaniopsis laurina). Others did not die but suffered to such an extent they were later removed.

In contrast, Chinese elm (Ulmus parvifolia) and ash (Fraxinus excelsior) avoided excessive dieback or death, as did the native weeping bottlebrush (Callistemon viminalis) and kurrajong (Brachychiton populneus).

Closeup photo showing heat damage in maple leaves, which are especially vulnerable because they are large and thin Large, thin maple leaves are particularly vulnerable to damage from heat. Renee Prokopavicius

Read more: Without urgent action, these are the street trees unlikely to survive climate change[11]

Why are some species more vulnerable?

Some species are inherently less heat and drought tolerant. For example, species with large, thin leaves[12] are particularly vulnerable. Large leaves have thicker insulating boundary layers and so release heat more slowly. Thin leaves are less able to buffer against overheating on hot, sunny days when the wind lulls.

But it can be hard to predict how individual trees will respond to heat stress. That’s because access to water is important, but changes over time.

Trees with enough water can usually tolerate high temperatures. Microscopic pores in the leaves called stomata open up, allowing water vapour to pass through. This cools the plant down.

In drought, trees conserve water by closing these pores. This causes tree leaves to heat up. When hot days occur during drought, tree leaves can reach lethal temperatures above 45℃.

Our research found most urban tree species –- even those under drought stress –- opened their pores to cool leaves[13] on hot summer days. This results in rapid water loss but may help prevent tree leaves from scorching.

Closeup photo showing Renee Prokopavicius using a thermal camera to measure leaf temperature Renee Prokopavicius uses a thermal camera to measure leaf temperature. Laura Dillon

Why is water so important during heatwaves?

As part of the latest research, we grew seedlings in a glasshouse to test how access to water affected heat tolerance. We kept half the plants well watered and exposed the rest to drought conditions.

We found water loss was higher[14] than predicted during heatwaves for all plants.

For well-watered trees and shrubs, water loss was 23% higher than predicted. This kept leaves nearly 1℃ cooler than the air temperature.

Thirsty plant leaves were more than 1℃ hotter than the air temperature.

In urban trees, leaves reached lethal temperatures of 49–50℃ for species with the lowest rates of water loss. But when species with low rates of water loss had access to water, there was little heat damage or scorched leaves. For trees that lost foliage due to overheating, their recovery took multiple years after the end of drought and return of average temperatures.

Photo showing Western Sydney University student Nicholas Spurr collecting leaf temperature data on a hot day in Penrith, taken from behind Western Sydney University student Nicholas Spurr collecting leaf temperature data on a hot day in Penrith. Renee Prokopavicius

Preserving our natural air conditioners

Our research shows access to water is crucial for the survival of urban trees during heatwaves.

That means urban greening programs need to find ways to provide trees with enough water when rainfall is unreliable.

It’s worth exploring new techniques such as passive irrigation storage pits[15] and raingardens[16]. Passive irrigation pits capture and store stormwater in underground trenches. This both decreases runoff during storms and provides water for trees. Raingardens also naturally reduce stormwater runoff and use plants to filter pollutants from rainfall.

Providing trees with the water they need to keep cool on hot summer days will not only improve their chances of survival, but also protect people. Cities need trees now more than ever, as these natural air conditioners take the edge off the extremes.

Read more: The illegal killing of 265 trees on Sydney's North Shore is not just vandalism. It's theft on a grand scale[17]

References

  1. ^ declared El Niño is underway (media.bom.gov.au)
  2. ^ hottest month on record (public.wmo.int)
  3. ^ urban forest (nph.onlinelibrary.wiley.com)
  4. ^ heat tolerance of different species (www.sciencedirect.com)
  5. ^ lost more water on hot days than models predicted (onlinelibrary.wiley.com)
  6. ^ sweating in humans (www.scientificamerican.com)
  7. ^ lose water to keep cool (doi.org)
  8. ^ Climate change threatens up to 100% of trees in Australian cities, and most urban species worldwide (theconversation.com)
  9. ^ measured carbon uptake and water loss (onlinelibrary.wiley.com)
  10. ^ most vulnerable to heatwaves (www.sciencedirect.com)
  11. ^ Without urgent action, these are the street trees unlikely to survive climate change (theconversation.com)
  12. ^ large, thin leaves (www.sciencedirect.com)
  13. ^ opened their pores to cool leaves (onlinelibrary.wiley.com)
  14. ^ water loss was higher (onlinelibrary.wiley.com)
  15. ^ passive irrigation storage pits (wsroc.com.au)
  16. ^ raingardens (www.sydneywater.com.au)
  17. ^ The illegal killing of 265 trees on Sydney's North Shore is not just vandalism. It's theft on a grand scale (theconversation.com)

Read more https://theconversation.com/we-need-urban-trees-more-than-ever-heres-how-to-save-them-from-extreme-heat-211414

The Times Features

Itinerary to Maximize Your Two-Week Adventure in Vietnam and Cambodia

Two weeks may not seem like much, but it’s just the right time for travelers to explore the best of Vietnam and Cambodia. From the bustling streets of Hanoi to the magnificent te...

How to Protect Your Garden Trees from Wind Damage in Australia

In Australia's expansive landscape, garden trees hold noteworthy significance. They not only enhance the aesthetic appeal of our homes but also play an integral role in the local...

Brisbane Homeowners Warned: Non-Compliant Flexible Hoses Pose High Flood Risk

As a homeowner in Brisbane, when you think of the potential for flood damage to your home, you probably think of weather events. But you should know that there may be a tickin...

Argan Oil-Infused Moroccanoil Shampoo: Nourish and Revitalize Your Hair

Are you ready to transform your hair from dull and lifeless to vibrant and full of life? Look no further than the luxurious embrace of Argan Oil-Infused Moroccanoil Shampoo! In a...

Building A Strong Foundation For Any Structure

Building a home or commercial building can be very exciting. The possibilities are endless and the future is interesting. You can always change aspects of the building to meet the ...

The Role of a Family Dentist: Why Every Household Needs One

source A family dentist isn’t like your regular dentist who may specialise in a particular age group and whom you visit only when something goes wrong. A family dentist takes proa...

Times Magazine

"Eternal Nurture" by Cara Barilla: A Timeless Collection of Wisdom and Healing

Renowned Sydney-born author and educator Cara Barilla has released her latest book, Eternal Nurture, a profound collection of inspirational quotes designed to support mindfulness, emotional healing, and personal growth. With a deep commitment to ...

How AI-Driven SEO Enhancements Can Improve Headless CMS Content Visibility

Whereas SEO (search engine optimization) is critical in the digital landscape for making connections to content, much of it is still done manually keyword research, metatags, final tweaks at publication requiring a human element that takes extensiv...

Crypto Expert John Fenga Reveals How Blockchain is Revolutionising Charity

One of the most persistent challenges in the charity sector is trust. Donors often wonder whether their contributions are being used effectively or if overhead costs consume a significant portion. Traditional fundraising methods can be opaque, with...

Navigating Parenting Arrangements in Australia: A Legal Guide for Parents

Understanding Parenting Arrangements in Australia. Child custody disputes are often one of the most emotionally charged aspects of separation or divorce. Parents naturally want what is best for their children, but the legal process of determining ...

Blocky Adventures: A Minecraft Movie Celebration for Your Wrist

The Minecraft movie is almost here—and it’s time to get excited! With the film set to hit theaters on April 4, 2025, fans have a brand-new reason to celebrate. To honor the upcoming blockbuster, watchfaces.co has released a special Minecraft-inspir...

The Ultimate Guide to Apple Watch Faces & Trending Wallpapers

In today’s digital world, personalization is everything. Your smartwatch isn’t just a timepiece—it’s an extension of your style. Thanks to innovative third-party developers, customizing your Apple Watch has reached new heights with stunning designs...

LayBy Shopping