Tree lovers know more than you think


The trees are hot. By that I mean trees are cool. More precisely, the trees are getting colder. Tree planting is all the rage, with tree planting projects involving billions and even billions of trees growing across the planet.

Science supports such initiatives, but a seed of doubt belongs to every sapling. Green thumbs do not replace red lines in emissions. Shade is good, but it should not obscure the hard work of reducing greenhouse gases.

Planting trees is good for the environment and good for the species that work, play, reproduce or take up space on them. The first and most immediate benefit – and the focal point of much of the fascination – is their ability to remove particulates and other forms of air pollution.

Much of the current popularity stems from their ability to purify carbon dioxide: a mature tree absorbs around 22 kg of carbon dioxide from the air per year. Scientists estimate that there is room for an additional 0.9 billion hectares of forest cover in the world, which would store 205 gigatons of carbon, meaning that “global tree restoration is the one of the most effective carbon reduction solutions to date “.

These figures have inspired a number of tree planting projects, the most ambitious of which is the World Economic Forum’s 1,000 billion tree initiative (1t.org). Launched last year, it aims to plant 1,000 billion trees by 2030, which WEF predicts would remove two-thirds of the carbon emissions created by human behavior and reduce carbon in the world. 25% atmosphere.

The EU entered the game in 2018. The Green New Deal aims to expand the EU’s carbon sequestration to 310 million tonnes against a current target of 265 million tonnes, and a key part of that is planting. 3 billion new trees by 2030.

At first glance, it’s a lot of wood. It is estimated that the EU planted almost 300 million additional trees between 2010 and 2015, so this target would roughly double its current rate of forest expansion. The EU published its new forestry strategy last week, which explains how it will achieve this feat. According to EU calculators, the plan would potentially remove 4 million tonnes of carbon dioxide from the atmosphere by 2030 and 15 million tonnes by 2050.

This is just the start, in every sense of the word. According to EU calculations, this would give an additional 2-3 million hectares of tree cover, but this is only about 2% of the 10 million hectares of forest lost each year globally. Worse yet, 3 billion sounds like a big number, but it’s a tiny fraction of 1 trillion – 0.3% to be exact. It’s a seed in a (very big) bucket.

Most projects focus on large plantations – forest-sized growths. Scientists are increasingly paying attention to small efforts and touting their benefits. So-called “mini-forests,” or small pieces of land – a tennis court may suffice – with their density far greater than that of ordinary forests, can absorb 30 times more carbon than a traditional forest. They are based on a style of planting developed by Japanese botanist Akira Miyawaki, and scientists are excited about the prospects. These mini-forests can be placed anywhere – when conditions are right – even in cities.

As Tokyo‘s summer heat intensifies, the appeal of urban trees makes more sense to me. Today, just over half of the world’s population lives in cities; this figure is expected to reach 66% by 2050, more than double the 30% of city dwellers in 1950. In Japan, more than 92% of the population lives in cities. Trees can help transform this experience.

Every time I climb a few floors above street level, the Tokyo cityscape looks very green. But appearances can be deceptive and Tokyo is not what it seems. The Japanese capital has a low percentage of park space (6.2%), especially compared to other big cities like Moscow (54%), Singapore (47%), Sydney (46%), Washington (24%) , 08%) and New York City (21.33%).

But the population density inside the Yamanote Line, a train service that circles the city center, is not that high. Tokyo does not have the urban canyons of cities like New York. This leaves more space and light for the trees, which is why the city looks so green when viewed from above. And green is good.

An analysis by Jessica Turner-Skoff and Nicole Cavender of the Morton Arboretum in Illinois offers an impressive list of (documented) benefits of trees, ranging from emotional to environmental to economical. They note that the presence of trees is “strongly linked to reduced negative thinking, reduced symptoms of depression, improved mood, and increased satisfaction with life.”

Being able to see trees helps patients recover in hospitals, lowers diastolic blood pressure, and reduces stress. People who live on tree-lined streets feel healthier and have fewer cardio-metabolic problems. There is some evidence of improvement in the condition of people with neurodegenerative disease. Planting and caring for trees can improve physical and mental health.

Trees reduce noise and they are positively correlated with reduced crime. Trees increase the safety of cars and pedestrians by making it easier to assess distances and introduce barriers. (Most studies have conceded that the effects are difficult to quantify and that multiple factors contribute to the results, but they still give trees some credit.)

The trees lower the temperature of the street. In Hong Kong, tall trees with short trunks and dense canopy reduced average daytime radiation temperatures to 5.1 ° C at pedestrian level. They store water, reducing runoff and urban flooding. In his study of urban forests in Tokyo, researcher Satoshi Hirabayashi found that trees reduce flooding that costs the city billions of yen each year, and improve outdoor comfort, which could prevent heatstroke.

And trees make economic sense – in most cases. In the United States, a mature tree increases the average value of a home by 20%. The annual profit of a tree is between $ 21 and $ 159, depending on the cost of caring for the tree. In Lisbon, every dollar invested in urban tree management produced a profit of $ 4.48 per capita; in New York and Indianapolis, the figures are $ 5.6 and $ 6.09, respectively.

Interestingly, a study from Kyoto, the hottest city in Japan (we are talking about temperature, not culture), concluded that “the value of the annual benefits generated by street trees in the city of Kyoto did not outweigh. not on tree expenses ”. This does not mean that the trees have not generated a profit. On the contrary, the most common trees in the city had a smaller canopy, and Kyoto’s maintenance procedures were some of the most expensive in the world.

While much relies on the details of one study, the evidence seems to support Polish research which concluded that “the presence of trees alleviates almost all stressors generated by the urban environment”.

Some climatologists are worried about this new penchant for foliage, arguing that it may undermine other efforts to reduce emissions – planting trees does not replace the hard work of reducing greenhouse gases – or undermine biodiversity if it is badly done. (They also note that climate change makes it more difficult for trees to make positive contributions when they too are threatened by its impacts.)

I remain a fan. So in these COVID-19 infected times, when you can’t kiss someone who really matters, go and kiss a tree. Or better yet, plant one.

Brad Glosserman is Associate Director and Visiting Professor at the Center for Rule-Making Strategies at Tama University as well as Senior Advisor (non-resident) at the Pacific Forum. He is the author of “Peak Japan: The End of Great Ambitions” (Georgetown University Press, 2019).

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