Trees matter

By Huang Yiran Source:Global Times Published: 2019/4/9 19:09:54

Foreigners, expert discuss Chinese landscape protection methods


Cherry trees with white-painted trunks blossom in the street in Jinan, Shandong Province. Photo: VCG





Why are the bottom halves of tree trunks in China painted white?

You may not expect this to be a question that puzzles a lot of foreigners when they first come to China, but it is. Someone even raised this question on the knowledge-sharing platform Quora.

"Why do trees in China have white trunks? Are they born this way?" A netizen asked on Quora.

Every year before winter comes, usually in October, Chinese people begin to paint tree trunks white. It's common to see people carrying a bucket, a brush or spray bottle, to paint the bottom halves of tree trunks white. But why do they do this?

Global Times reporters hit the streets of Sanlitun, Beijing to see if foreigners share this same curiosity. It turned out that many of them have noticed this phenomenon, but most of them don't know the exact reason behind it.

"To me, I think they just want to make everything look white," said Saif Arshad from India. "I mean during winter, there is snow. So white ground, white trees, maybe."

"I think it's a sign to show people a message that these trees are newly planted and [that] we should encourage this kind of behavior," said Jason Lee, a Chinese-Canadian man.

People's answers varied, but the curiosity is real. Why are tree trunks painted white especially in winter? Is it a kind of decoration or custom only found in China? 

Not an exception



If you think only trees in China have this "special treatment," you're wrong. Actually some European countries, such as Germany, Greece, and even tropical countries like Panama, do this. 

How about people from these countries? Do they know the answer?

"In Germany, we paint trees white to make them visible at night when they are close to the streets," said Jonas from Germany. "But I think it's different in China."

"We don't have winter in my country, but we also paint trees white," said Ruben from Panama. "I think they put it on to confuse insects that may eat wood."

Similarly, many Chinese people share the same idea that the white paint is used as an insect repellent.

Is it the whole truth?

"In fact, people paint the tree trunk white for three basic reasons," said Cai Ming, a professor at Beijing Forestry University who is a professional in the field of landscape architecture. "One is to repel pests. The second reason is to reflect sunlight and reduce the damage that can be caused by diurnal temperature range. The last reason is for decoration and traffic safety."

According to Cai, the main ingredient of the "white paint" is quick lime and lime sulfur, which are effective for preventing pests from overwintering and oviposition inside the old tree bark. What's more, white color can reflect most of the sunlight in winter. So it can prevent the tree bark from getting too hot due to the sunshine during the day and help protect trees during cold nights. In addition, the white color makes the tree more visible at night. It's not only a decoration, but also a sign to warn people of the street curb.

Improvement expected

"Isn't it harmful to the tree or the soil?" some interviewees asked.

According to a 2014 report from yuanlin.com, a Chinese website for sharing landscape and forestry information, in some developed countries, people prefer natural methods of pests and disease control. Once a tree is infected by pests or a disease, it will be cut down to prevent the disease from spreading.

"It is what we do in Germany," Jonas said. "If the situation is really bad and may threaten the whole forest, for example, they cut down trees to prevent [insects from] moving on."

"In fact, painting tree trunks white to repel pests was first introduced in Europe," Cai said. "Previously, European countries applied this technique to fruit trees. But today, most Western European countries stopped using this method while only a few Eastern European countries keep doing this."

According to Cai, the reason why these countries stopped painting tree trunks is because the main ingredient in the "white paint" -  quick lime, is alkaline. If washed off of the tree by rain, it can harm the soil.

As society develops, people's awareness of environment protection also increases. "Because of this controversy, you can see more and more trees, especially in gardens, parks and campuses, without "white paint" and other methods are being used to prevent these trees from being harmed by pests and disease," Cai told us. "Today, you can only see these 'white-trunk trees' in city streets and country roads, and the function is mainly for decoration and warning the pedestrians and cars at night."

Posted in: METRO BEIJING

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