Cities may become unlivable as climate change puts many types of urban trees at risk

With easy access to industry, transportation links, and recreational activities, the functions of cities are what make them a popular place to live.

However, a new study led by Western Sydney University in Australia predicts that climate change could threaten their ability to live by 2050.

That’s because more than 1,000 species of trees — including oaks, maples and pines — are at risk of exceeding their natural climate tolerance, according to the researchers.

Healthy trees absorb carbon dioxide and produce the oxygen we breathe, but they also provide shade and cool the atmosphere by releasing water through their leaves.

However, these vital properties are compromised if air temperatures rise too high or precipitation decreases.

Lead author Dr Manuel Esperon Rodriguez said: “The surprising discovery was that about half of the tree species in each city examined were already experiencing climate changes that put them at risk.

By 2050, an average of 65 percent of the species in each city will be at risk.

The news comes as a tree-planting initiative to celebrate the Queen’s Platinum Jubilee has been expanded to allow people to plant trees as a memorial to the king.

Researchers have identified more than 1,000 species of urban trees – including oak, maple and pine – as being at risk of exceeding their tolerance for the natural climate (stored image)

164 cities display projected changes in mean annual temperature in 2050 relative to mean annual core temperature between 1979 and 2013

164 cities display projected changes in mean annual temperature in 2050 relative to mean annual core temperature between 1979 and 2013

Percentage of species that currently exceed their climate safety margin for MAT in 164 cities

Percentage of species that currently exceed their climate safety margin for MAT in 164 cities

Proportion of species that currently exceed their AP climate safety margin in 164 cities

Proportion of species that currently exceed their AP climate safety margin in 164 cities

Tree species at risk of exceeding their climate tolerance

  • silver birch
  • ox
  • Maple
  • poplar
  • elm
  • Pine
  • linden
  • battle
  • eucalyptus
  • chestnut
  • Plum and cherry
  • Jacaranda

The authors claim that the trees and shrubs in our cities provide important benefits to 4.2 billion people – more than half of the world’s population.

Dr Esperon Rodriguez added: ‘Trees and shrubs absorb carbon dioxide and also cool their surroundings by providing shade and by pumping water from their roots and releasing it through their leaves.

This cooling effect makes people more comfortable and reduces the energy used for cooling.

They also purify air and water, provide a habitat for native animals, and improve people’s mental health and well-being through a connection with nature.

“With all of these benefits, increasing urban forest cover is a major climate action and livelihood strategy for many governments and societies around the world.”

In the study, published in Nature Climate Change, the team assessed climate risks on 3,129 species of trees and shrubs in 164 cities across 78 countries, all of which were recorded by the Global Urban Tree Inventory.

They conducted impact analyzes using current and projected temperatures and precipitation, to make predictions for 2050 and 2070.

They identified a “climate safety margin” for each species, demonstrating its ability to withstand changes in mean annual temperature (MAT) and annual precipitation (AP) in its city.

Exceeding a margin does not necessarily mean that the tree will die, but climatic conditions will affect its health and performance.

This includes its ability to store carbon, produce fruit, reduce air pollution, and resist shocks such as drought.

The proportion of species expected to be endangered from projected changes in average annual temperature by 2050 in 164 cities.  Each point represents the proportion of endangered species in a particular city

The proportion of species expected to be endangered from projected changes in average annual temperature by 2050 in 164 cities. Each point represents the proportion of endangered species in a particular city

Proportion of species expected to be endangered from projected changes in annual precipitation by 2050 in 164 cities. Each point represents the proportion of endangered species in a particular city

It was found that 56 percent of the species actually experienced climatic conditions that exceed their safety margin for MAT, and 65 percent for AP.

All tree species found in Barcelona, ​​Niger and Singapore have already outgrown climate safety margins.

The researchers also looked at effects under medium emissions scenarios – where emissions decline after their peak around 2080, and global temperatures rise by 3°C to 4°C by 2100.

Thus the MAT and AP numbers are expected to increase to 76 percent and 68 percent of species, respectively.

Reported species include silver birch, oak, maple, poplar, elm, pine, linden, linden, eucalyptus, and chestnut—all of which are commonly found in cities around the world.

Climate risks for urban types are likely to be higher for cities in low-latitude countries that are highly vulnerable to climate change, such as India, Niger, Nigeria and Togo.

In addition, the plant families with the greatest number of species at risk are Myrtaceae, Fabaceae, and Rosaceae, with a number of fruit trees.

Oak trees – the queen’s favorite species

One tree that has been identified as being at risk of exceeding climate tolerance is the oak tree.

This was a favorite of the late Queen Elizabeth II, who made a stop at a particular tree in Helmingham Park, Suffolk while hunting.

Every November, she would take refuge in a hollowed-out oak tree with a drop of whiskey.

Co-author Dr Jonathan Lenoir of the French National Center for Scientific Research said that when climatic conditions exceed the trees’ natural tolerance, they can not only lead to poor tree health, but can also reduce the cooling effect.

“During drought or heat stress, trees can stop transpiration to reduce tissue damage,” he said.

This means that at a time when we most need natural air conditioning, it can be turned off.

“Selecting species that are able to adapt to future climatic conditions is important to the health and survival of our urban forests, ensuring that these trees and shrubs continue to work to keep our bodies cool.”

The authors state that their predictions are likely conservative, as they do not take into account the potential effects of increased population, urbanization, and the spread of diseases and pests.

They hope that the study’s findings will help prioritize efforts to protect urban plants and secure their associated ecosystem services to make cities livable.

“This study is important globally because it identifies species that are at risk and also indicates species that are likely to be climate-resistant,” said Dr. Esperon Rodriguez.

Relationship between the proportion of species at risk by 2050 under the medium-emissions and city-latitude scenario.  Point size refers to the size of the human population

Relationship between the proportion of species at risk by 2050 under the average emissions scenario and city latitudes. Point size refers to the size of the human population

The researchers studied the UK cities of Belfast, Bristol, Birmingham, London and York and found that the driest weather is expected to have the greatest impact on the latter three.  Pictured: Trees shed their leaves in London's Brunswick Park in 'False Autumn' to withstand drought during summer

The researchers studied the UK cities of Belfast, Bristol, Birmingham, London and York and found that the driest weather is expected to have the greatest impact on the latter three. Pictured: Trees shed their leaves in London’s Brunswick Park in ‘False Autumn’ to withstand drought during summer

The authors conclude that immediate action is needed to protect global urban forests and prolong the benefits offered by these social ecosystems.

This includes selecting and planting varieties that are more climate-resistant as well as those that provide a great deal of cover.

Dr. Esperon Rodriguez said: ‘Trees at risk of lower rainfall can be helped by a water-sensitive urban design, which allows precipitation to absorb into the ground and reach the root zones, instead of going down the drain.

The urban heat island effect will exacerbate increased temperatures, but more cover for trees and shrubs in urban areas helps reduce this effect, so leaving large trees and shrubs in place to fulfill these roles is really important.

Before her death on September 8, Her Majesty Queen Elizabeth II regularly planted memorial trees throughout her 70-year reign.  Pictured: Queen Elizabeth planting a eucalyptus tree

Before her death on September 8, Her Majesty Queen Elizabeth II regularly planted memorial trees throughout her 70-year reign. Pictured: Queen Elizabeth plants a ‘Black Sally’ eucalyptus tree in the grounds of Government House, Canberra, Australia

The researchers studied the UK cities of Belfast, Bristol, Birmingham, London and York and found that the driest weather is expected to have the greatest impact on the latter three.

Before her death on September 8, Her Majesty Queen Elizabeth II regularly planted memorial trees throughout her 70-year reign.

Expressing her ambition to create a global network of trees, she told Sir David Attenborough of this desire in a 2018 nature documentary called The Queen’s Green Planet.

“It may change the climate again,” she told the naturalist sarcastically.

To celebrate her platinum jubilee in 2022, the Queen launched this unique tree-planting initiative, called The Queen’s Green Canopy.

The initiative invites everyone from individuals to Scouts and Guides groups, villages, cities, counties, schools and businesses to play their part in improving our environment by planting trees.

The website says the project will “create a material and lasting legacy of the Queen’s leadership in the Commonwealth”.

It has been extended until the end of March 2023 to give people the opportunity to plant trees as a memorial to the Queen.

A study finds that the ability of forests to recycle carbon will be affected by climate change

A study finds that the ability of forests to withdraw carbon dioxide from the atmosphere will be affected as the planet warms due to climate change.

Photosynthesis is the process in which leaves convert sunlight and carbon dioxide into oxygen and energy in the form of sugar, which occurs best between 59°F and 86°F (15°C and 30°C).

Canopy leaves are widely accepted to be able to maintain an ideal temperature for photosynthesis, even as the air around them warms.

However, researchers at Oregon State University have found that leaves actually struggle to regulate their temperature when they get too hot.

They speculate that global warming could impair the ability of leaves to stay cool and thus conduct photosynthesis, particularly in warm climates.

Read more here

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