New Scientist - USA (2021-07-17)

17 July 2021 | New Scientist | 51

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Clare Wilson is a reporter
at New Scientist and
writes about everything
life-science related.
Her favourite place is her
allotment @ClareWilsonMed

These articles are

posted each week at

newscientist.com/maker

What you need
A watering can

BEING called a “tree hugger”

used to be a mild insult, but there

is a growing appreciation for the

benefits of trees. Their best-known

environmental asset is to take in

carbon dioxide from the air, but in

towns and cities they have other

useful qualities too.

In summer, trees cool hot

streets, while in times of high

rainfall, they take up water,

stopping it from running into

drains too quickly and causing

floods. As climate change will lead

most of the UK to have hotter

summers and wetter winters,

trees help on both counts.

Cities and towns are usually

several degrees warmer than the

surrounding countryside, mainly

due to their high proportion of

hard surfaces like pavements and

asphalt, which absorb more heat

from the sun. But streets with

trees can be several degrees cooler

than bare ones thanks to the shade

the plants create and their ability

to take up water, which evaporates

from leaves, cooling the air.

Research carried out in

Manchester in the UK suggests

trees reduce radiant temperatures

of hard surfaces in summer by 4 ̊C

to 7 ̊C. On a large scale, that should

cut deaths caused by heatwaves

and the power used by air-

conditioning units.

Some studies suggest tree-

lined roads are linked with better

mental health and less crime.

While it is hard to show if trees

are really the cause, as more

affluent areas tend to have

more street trees, most would

agree that they make an area feel

With or without a garden, we can all help improve

tree cover in towns and cities, says Clare Wilson

Science of gardening

Urban growth

like a more pleasant place to be.

People with front gardens can

do their bit to help by planting

trees next to pavements where

they add to street shade. When

choosing a tree, “thirsty” varieties

and ones with broader leaf

canopies are best for cooling and

soaking up water, although they

do take more watering during dry

spells, says Elisabeth Larsen at the

UK’s Royal Horticultural Society.

Anyone without a garden can

still help by joining campaigns to

green urban spaces. While many

local authorities let people request

trees for their street, this is a poor

way to allocate planting, says Jon

Burke, a former councillor for the

London borough of Hackney, who

recently began a massive planting

programme there. That is because

better-off households are more

likely to make requests, worsening

inequalities in tree cover.

Instead of asking for a tree on

their road, people should lobby

councils to begin equitable urban

greening programmes, says Burke.

“Street trees are a public necessity

in a warming world.”

There is another way to help.

Local authorities may fail to

water new saplings regularly

and let them die. So people can

join volunteer groups or just

unofficially “adopt” new trees,

whether in their own road or

elsewhere, and regularly water

them during dry weather.

If no one’s looking, you could

even give them a hug. ❚

Feedback

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through your legs;

the week in weird p56

Tom Gauld for 

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puncture? Readers

respond p54

Puzzles

Try our crossword,

quick quiz and

logic puzzle p52

Twisteddoodles

for New Scientist

Picturing the lighter

side of life p56

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