Warmer weather ironically helping city trees flourish

Urban trees in the Marina Bay area in Singapore

Although the globe is warming and climate change is a cause of concern for many, trees across the world are growing instead, relishing in the warmth – but the trees in the centre of urban heat islands are not only thriving, they’re growing faster, according to the Climate News Network.

Root space may be premium and cramped, and their leaves forced to deal with more pollution than their brethren in the countryside, but they are nonetheless growing, offering pedestrians more shade.

“We can show that urban trees of the same age are larger on average than rural trees because urban trees grow faster,” Hans Pretzsch, a forester from the Technical University of Munich, Germany, who spearheaded the research study published in the journal, Scientific Reports, that exposed the trees’ behaviour. “While the difference amounts to about a quarter at the age of 50, it is still just under 20 per cent at a hundred years of age.”

The study had research scientists hailing from nations such as Australia, Chile, and Vietnam, among others, sampling and gathering data from more than 1,300 trees including the English oak, white spruce, and black locust trees from 10 cities – Houston, Texas, United States (U.S.); Munich, Germany, and Hanoi, Vietnam, among others – boasting a wide spectrum of climate zones, from temperate to subtropical, and subartic to Mediterranean.

Altogether, over a period of several decades, the researchers worked with some 73,600 observations of stem diameter growth, and discovered that trees in urban areas were positively responding to the urban heat island (UHI) effect – inner cities tend to be between three and ten degrees Celsius warmer than the countryside – benefitting from more active photosynthesis, a longer growing season attributed to the higher atmospheric levels of carbon dioxide, driven by climate change.

With more than half of mankind now city dwellers, the urban population is slated to grow to two-thirds of the global population by 2050. Trees, able to offer residents of the cities some measure of relief from extreme heat, are capable of helping cut costs for air-conditioning and heating, and improve health of the people so effectively that a research team even estimated that a single square kilometre of urban trees is worth US$1.2 million to citizens. Another research study found that in California, U.S., avenues of city trees added US$1 billion to property values.

While scientists have cautioned that this more robust growth could lead to a shorter life cycle, the growth may not be completely negative for the soil upon which new factories, houses, and roads may be built on in the future. As a group of scientists from Italy, the Netherlands, and Russia reported in the Journal of Cleaner Production, as cities grow, so do urban green areas.

And though carbon in soil is lost in paving streets, the urban soil that remains would instead be enriched by a combination of compost, peat, and new plants.

“The results of our study show the potential of urbanisation for the increase of soil organic carbon stocks. This process, in turn, would probably mitigate the effects of climate change,” Vyacheslav Vasenev, from the agro-biotechnology department of the People’s Friendship University of Moscow, Russia, said. “The optimistic conclusion of our study should be further explored by land-use planners and scholars worldwide, since urbanisation will be progressively more important in the future.”


Source: Climate News Network