Around the world, since the 1960s, trees in urban areas have been growing faster than in rural areas. This has been confirmed for the first time by a study of how the "heat island" effect (an increase in ambient temperature in places where industrial objects and populations are concentrated) affects tree growth by the Technical University of Munich. An international team's data analysis shows that climate change has long had an impact on tree growth in cities, but that this impact has only just begun to affect trees in rural areas.
“While extensive research has been done on the effects of climate change on tree growth in forests, there has been little information on urban trees,” says University of Munich professor Hans Prezsch. This is the first systematic study in this area, and its results are published in the journal Nature Scientific Reports.
This topic has interested researchers in the context of global urbanization. According to the UN, by 2030, the world's urban population will grow by 60 percent, and will continue to grow. Trees improve the climate of cities and the quality of life of citizens, and this forecast indicates a further increase in their importance in the future.
Samples of trees taken in the agglomerations of Berlin, Brisbane, Cape Town, Hanoi, Houston, Munich, Paris, Prince George (Canada), Santiago, Sapporo were examined. The cities were chosen to include different climatic zones - northern, temperate, Mediterranean, Mediterranean and subtropical. In total, nearly 1,400 predominantly mature trees were treated. For each city, the most characteristic tree species was taken, in the center and in the surrounding countryside.
Trees in the city grow a quarter faster than in the countryside
“We have shown that urban trees of the same age are, on average, larger than those grown outside the city,” says Professor Precz. At the same time, the relative difference in size between urban and rural trees decreases with increasing age, but remains significant. "At age 50, the difference reaches a quarter, but at age 100, it is less than 20 percent."
The researchers believe that the acceleration of tree growth in the city is influenced by the effect of the "heat island" - an increase in temperature in places where the population is concentrated. At the same time, the temperature in the center can be 3 - 10 degrees Celsius higher than outside the city. Higher temperatures can accelerate tree growth in two ways - by stimulating photosynthesis and lengthening the growing season.
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But the positive effect of growth is accompanied by accelerated aging of trees, which means that more frequent replacement of dying trees with new ones is necessary.
Climate change is accelerating growth everywhere
In addition to the benefits for the growth of urban trees, the study by Professor Prezsch's group also shows that the growth of both urban and country trees has accelerated since the 1960s as a result of climate change. This observation for trees in the forest was previously confirmed by similar studies in other countries.
“The 20 percent overall growth acceleration for all trees that we report in this study is consistent with previous work. This effect has also been noted in agricultural production,”explains expert Precz. Obviously, there were and are natural changes that contribute to the accelerated growth of trees in different climatic zones. "In this context, in addition to global warming, fertility effects from rising atmospheric carbon dioxide and increasing nitrogen deposition are discussed as potentially leading topics."
Despite the potentially damaging effects of global climate change on trees - such as droughts that limit growth or even kill trees - the trees in the study performed well. The result is unambiguous: both “urban” and “village” trees in all climatic zones have shown significant growth in the past decades.
Vadim Tarabarko