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By Charli Shield
Not too long ago, many people weren't sure if trees had a place in cities. People, cars, houses and buildings made up urban areas — there wasn't much room for nature.
Trees now have a fundamental place in many big cities around the world, says Sonja Dümpelmann, landscape historian at the University of Pennsylvania — though in most of them, they are still vying for space.
If we want to reap the benefits of urban treescapes, ecologists say it's vital trees are seen as more than just an aesthetic addition to cities. That's especially true now that half the world's population live in cities and a further 2.5 billion are projected to live in them by 2050.
As Cities Evolve, Trees Keep Us Grounded.
Trees are powerhouses when it comes to regulating city microclimates — filtering air pollution, providing shade, absorbing CO2, helping prevent flash flooding, as well as acting as an important antidote to the urban heat island effect that makes cities far hotter than surrounding rural areas.
"Trees can make a huge difference to a city's temperature," says Tobi Morakinyo, an urban climatologist whose research into the cooling effect of trees in Akure, southwest Nigeria, showed using trees to shade buildings could cool them down by up to five degrees Celsius.
In hot sub Saharan African cities like Akure — where average maximum summer temperatures can reach 38 degrees (100 degrees F) — Morakinyo says trees' cooling effect is an important tool councils can wield against both heat stress and cooling costs.
Alongside the eco-services urban trees provide, there are also the qualities "that we can't put monetary value on," adds Cris Brack, a forest ecologist from the Australian National University and director of the National Arboretum in Canberra.
Those are "biodiversity, aesthetics and our visceral, gut-need to experience nature," Brack told DW, referring to the concept of 'biophilia' — the idea that humans have an innate desire to connect with nature. Mounting evidence shows that people who live in places with more trees experience lower levels of stress and mental illness, even when controlling for socio-economic factors.
Trees Make Us Feel Good — Do We Return the Favor?
Though our need for trees in cities appears to only be becoming greater, they often battle oppressive urban environments. Street trees are "in a constant struggle" for space in cities, says Brack, where below ground their root systems can be choked by water pipes, roads and underground car parks, and above ground by pollution, power lines and traffic.
They also face mechanical damage from cars, battering from increasingly extreme weather conditions and regular uprootings to make way for construction sites.
Perhaps the most damaging modern challenge for city trees, though, says Somidh Saha, urban forest ecologist at the Karlsruhe Institute of Technology in Germany, is drought. Following Europe's unprecedented heatwave in 2018, a study co-authored by Saha found 30% of the trees planted in Karlsruhe in southwestern Germany over the previous four years had died — both directly and indirectly because of a lack of water.
"Without enough water, trees become weak and that makes them vulnerable to disease," Saha told DW. At the same time, declining city populations of birds and arboreal mammals, such as bats, leaves insect populations unchecked, and local trees susceptible to their growing numbers.
Seeing the Forest for the Trees
Ambitious greening projects have cropped up in several megacities around the globe in recent years. New York City planted a million trees between 2007 and 2015, London mayor Sadiq Khan hopes to green more than half the capital by 2050 to make the world's first "National Park City," while Paris announced it would build four inner-city urban forests throughout 2020.
But outside the Global North, in places such as Saha's native India and Morakinyo's native Nigeria, where they cite a lack of resources and political will as big barriers to making urban greenery a priority, trees in cities are much scarcer.
As climate change brings hotter temperatures and unpredictable downpours, cities are demanding a new kind of resilience from urban trees. For many cities in the world, ecologists say that means planting more exotic species of trees.
While many people are opposed to the idea of planting non-native species, ecologists Brack and Saha say alternative species are usually better adapted to the artificial environment of a city — especially in the face of increasing heatwaves.
The three-toothed Maple, native to China, Korea and Japan, is one species that could appear in greater numbers in other parts of the world as temperatures rise.
There's also an important distinction to be made between "exotic" trees, which just means they aren't local, and "invasive" trees, which are harmful — spreading very quickly and dominating the environment. As for local wildlife, while ongoing studies are being carried out in places like Germany by Saha's team, Brack says in his local Canberra, where almost all tree species in the city are exotic, birds happily eat fruit from non-natives and mammals alike find homes wherever there is an appropriate hollow.
Citizens Pitch In
One solution to preserving city trees that's grown in popularity in recent years is citizen involvement in urban tree caretaking. New York City's citizen pruner program allows city dwellers to take classes to become official city tree carers, and Berlin — a place that has typically excluded citizens from looking after urban flora — is now allowing residents to apply for permits to maintain tree pits and has proposed that they water city trees in summer.
Involving citizens has its pros and cons, Dümpelmann says, and these kinds of programs may or may not be effective depending on the culture of the city – but even watering trees alone "has been shown to be a really relevant maintenance effort."
While planting trees in urban spaces is an effective and fairly efficient way to adapt to climate change, Dümpelmann stresses that it isn't a holistic solution.
"It's something we should work on while at the same time addressing the root causes of climate change," she said.
Beyond using trees as geo-engineering fix, urban ecologists point out that more trees in cities could change perspectives on urban living and give people a greater understanding of how to value nature as part of a sustainable, livable city – not separate from it.
That means seeing trees as living, growing beings, Brack says – not fixed in time, or immune to the stressors of living in harsh urban environments.
Reposted with permission from Deutsche Welle.
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For centuries, the delicate silver dove has been a symbol of love and fidelity.
Biodiversity and Habitat Loss<p>Their near extinction is a symbol of the <a href="https://www.dw.com/en/global-biodiversity-outlook-targets-extinction-summit-new-york-pledge/a-54932895" target="_blank">biodiversity crisis</a> in the UK, largely driven by habitat destruction. Britain is now one of the countries with the most <a href="https://www.wwf.org.uk/future-of-UK-nature#:~:text=The%20UK%20is%20one%20of,than%20half%20are%20in%20decline" target="_blank">depleted nature</a> in the world according to the World Wildlife Fund. Half its plant and animal species are in decline and more than <a href="https://www.rspb.org.uk/about-the-rspb/about-us/media-centre/press-releases/let-nature-sing-wales/#:~:text=a%20natural%20tragedy.-,Over%2040%20million%20birds%20have%20vanished%20from%20UK%20skies%20in,unaware%20of%20the%20impending%20danger" target="_blank">40 million birds</a> have vanished in just half a century.</p><p>"[Turtle doves] are the canary in the [coal] mine because there are all these other species before it and after it," said Tree. "It's an umbrella for all the other species that are heading that way."</p><p>Turtle doves migrate south through Europe to sub-Saharan Africa between July and September, ending up in dry woodland and farmland areas of countries like Mali and Senegal for winter. </p><p>Droughts in West Africa and the Sahel region are believed to have contributed to the fall in turtle dove species recorded in northern Europe, with low rainfall reducing supplies of the seeds and insects the birds rely on for energy for the long journey home.</p>
Conservation and Farming<p><a href="https://www.operationturtledove.org/" target="_blank" rel="noopener noreferrer">Operation Turtle Dove,</a> a partnership project of charities including the Essex Wildlife trust, works with landowners and farmers to actively build turtle dove habitat.</p><p>Outten works with <a href="https://www.ebws.org.uk/birdsites/blue-house-farm-ewt-north-fambridge" target="_blank">Blue House Farm</a>, a 660-acre nature reserve in the UK county of Essex, where they have replicated weedy fallow plots. </p><p>"We work on it every year to make sure it's in the condition it needs to be with plants such as clovers and black medic," Outten said. "These plants are native to the landscape and produce the seed the birds feed on." </p><p>The birds eat a wide range of seeds from various plants that would have been abundant 50 or 100 years ago, added Guy Anderson, program manager for species recovery with The Royal Society for the Protection of Birds (RSPB). </p><p>"But it's simply true that with the gradual process of <a href="https://www.dw.com/en/farming-without-pesticides-how-can-we-make-agriculture-greener/a-52216796" target="_blank" rel="noopener noreferrer">intensifying our agricultural production</a>, the availability of those seeds has dropped and dropped," said Anderson.</p><p>Part of the project includes supplementary feeding — providing sources of food in the form of seed or grain. Under the Countryside Stewardship Scheme in England, farmers can receive financial support to create a turtle dove habitat. </p><p>Though they haven't recorded an increase in doves across the sites in the four years of working on the project, Outten said they are seeing improvements in how landowners and farmers manage habitat for the birds. </p>
A Turtle Dove Haven<p>The 3,500-acre Knepp Estate in West Sussex is another project taking a different approach and one of the few places where turtle dove numbers are increasing.</p><p>Isabella Tree and her husband Charlie Burrell converted their intensively farmed land into a rewilding project almost 20 years ago. They have let the land return to nature.</p><p>Just one year after they'd finished <a href="https://www.dw.com/en/uks-most-talented-architects-are-not-human/a-35952128" target="_blank">rewilding</a> the southern part of their property, they heard turtle doves for the first time. It's now a breeding hotspot for the birds with an estimated 19 pairs. Knepp is also home to <a href="https://www.rewildingbritain.org.uk/rewilding/rewilding-projects/knepp-estate" target="_blank" rel="noopener noreferrer">2% of the UK's population</a> of nightingales. </p><p>Tree is critical of supplementary feeding schemes that, in her view, are short term. She questions the chances of turtle doves getting to feed on scattered seeds before other mammals eat them first.</p>
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