Author: Lang Lang
In April, when the willows are spitting green, the willow catkins flying in the sky in northern cities have almost become a "seasonal topic" that is hotly discussed in society every year.
According to forecasts, Beijing will have the first high incidence of flying catkins on April 10, and it will last until the 15th.
Some netizens complained that Feixu seemed to be "spring barrage."
There are also people who wonder if there are so many flying catkins, can the willow trees be cut down and replaced with other species?
Pedestrians traveled in flying catkins on the streets of Beijing on April 7.
Photo by China News Agency reporter Yi Haifei
Where do the fluffy cats come from when they enter the high-incidence period?
According to the forecast jointly issued by the Beijing Meteorological Observatory and the Beijing Municipal Bureau of Landscaping and Landscaping, from April 10th to 15th, the first high-incidence period of flying catkins will occur in the inner city of the Fifth Ring Road in Beijing. The main flying catkin tree species will be poplar.
Poplar and willow catkins have obvious periodicity and seasonality. Due to differences in tree species and environmental temperature, the catkin period generally lasts from early April to late April and lasts about 50 days in Beijing.
In a specific area, if there is no obvious precipitation, temperature drop, strong wind, etc., flying flies generally affect about 20 days, and the high incidence period is generally about one week.
The flying catkins in the sky make "everyone has hairs". These "hairs" come from the female plants of the willow tree.
After pollination, the female inflorescence produces small capsules, the bread inside is covered with white flocculent fluff, and some seeds less than the size of a sesame seed are hidden in the fluff.
In order to propagate and multiply the next generation, they "send" these white flocculent fluffs every spring, using wind as the medium to scatter them in the city.
Poplar trees can be seen from 22°N to 70°N, from the plain to 4800 meters above sea level.
In Beijing, the forest accumulation of poplars and willows accounts for 42.2% of the city's total accumulation, making them the veritable "king" among the native trees in Beijing.
Zhang Zhixiang, a professor at Beijing Forestry University, once told the media that poplar trees grow very fast and can play a protective role in two to three years. They can grow into forests in five or six years. They can grow to a maximum of more than 30 meters and have a good shading effect. , Beijing’s "green skyline" will drop 10 meters.
Pedestrians traveled in flying catkins on the streets of Beijing on April 7.
Photo by China News Agency reporter Yi Haifei
The flying "Jiang Yang" has been guarding Beijing
Even if the annoying catkins are scattered like snow, it is undeniable that it is the presence of willow trees that changed the color of Beijing in April and gave it greenery.
Time went back to the 1950s and 1960s. At that time, Beijing was not troubled by flying catkins, but in April Beijing was troubled by wind and sand.
The sand and dust data of Beijing Observatory show that in the 1950s, the average number of dust days in spring in Beijing was as high as 26 days.
In the early days of the founding of New China, there were only 87 kilometers of roadside trees and 476 hectares of public green space in Beijing’s urban area, with only 64,100 trees.
How to make Beijing "green" in the shortest time has become the most urgent reality.
The so-called "ten years of trees" is short of time, and the country at that time did not have much financial resources for landscape greening.
In this tree species selection of "China's Good Vegetation", poplars and willows stand out due to their suitability for Beijing's soil climate, ease of reproduction, fast growth, and low maintenance costs.
They lived up to expectations, and soon settled in Beijing, with luxuriant branches, blocking the wind and sand in spring and winter for Beijing, and becoming a hero in saving Beijing's natural environment.
According to the sand and dust data of Beijing Observatory, the average number of dust days in Beijing was 26 days in the 1950s, fluctuated between 10 and 20 days in the 1960s and 1980s, less than 5 days in the 1990s, and dropped to 3 after 2010. Around days.
However, when the number of windy and sandy days became less and the poplar and willow trees became more and more mature, people's attention gradually shifted to the flying catkins.
"At that time, landscaping workers were more concerned with how to make Beijing green as soon as possible, and did not pay particular attention to the issue of Feixu." State Council counselor Liu Xiuchen told the media.
Data map: The landscaping workers are using a fog cannon car to humidify the flying catkins.
Photo by He Jianyong
Spraying, changing sex, injecting... multi-dimensional control of flying flies
Gradually, the fact that the female poplar tree matures will produce a large number of poplar flocks, which has become the "elephant in the room" and can no longer be ignored.
Since 1994, Beijing has implemented the "Millions of Young Poplars Entering Beijing" project, hoping to eliminate the poplar species of flying catkins, but judging from the huge base of the original poplars, it is not so easy to be replaced.
In order to control the flying catkins, Beijing has tried many ways, and the life of Yang Shu has not been easy.
The staff of Beijing Municipal Bureau of Landscaping and Landscaping once introduced to the media that source control is one aspect. During the "13th Five-Year Plan" period, the construction of new urban greening projects, urban leisure parks, Tongzhou administrative sub-center construction, new airport construction, etc. The female poplar and willow trees are no longer used in the landscaping construction project.
For existing trees, we will find ways to "denature", grafting the male scion on the female plant that produces the flies, and transforming the female flies into the superior male plants.
At the same time, during the peak period of flying flies in April each year, high-pressure water spraying is performed on female poplars and willows in combination with pest control and other work to reduce the impact of flies.
When necessary, the willow tree has to be given "injections."
The "Yihua No. 1" flower bud inhibitor is used to control poplar and willow flies, which can reduce 90% of flies.
Data map: The landscaping staff is giving a "sterilization shot" to a tall poplar tree.
Photo by Yu Ying Image source: Visual China
Can you cut it down and replace it with another tree?
Although enhanced cleaning can effectively reduce the amount of catkins during peak periods, it cannot completely eliminate willow catkins.
Therefore, some citizens suggested that all the female poplars and willows that produce flying catkins should be cut down and replaced with other tree species such as phoenix tree, locust tree, and ginkgo. Is this feasible?
Zhang Zhixiang clearly expressed his opposition, "You can't deny their ecological contribution just because of flying catkins. Poplars and willows are great contributors to increasing the amount of green in Beijing's city and improving the ecological environment. Once they are cut down, they are absolutely not!"
Moreover, other tree species also have their own shortcomings. Ginkgo grows slowly and the fruit is unpleasant. The platanus flies all over the sky every spring. Not only is the tree not as tall as the poplar, but also the hanging "hanging ghost (inchworm)" and the sprinkling of gum. It's annoying.
What's more, poplars and willows have significant resistance to air pollution, which is mainly manifested in various aspects such as oxygen release and carbon fixation, cooling and humidification, bacteria reduction and sterilization, and absorption of toxic and harmful substances.
It has strong resistance to harmful gases such as SO2, Cl2, HF, particulate matter, and heavy metals. It is an excellent anti-pollution tree species for urban landscaping, and its resistance to air pollution is better than that of Chinese Sophora japonica and Platycladus orientalis.
Data shows that a poplar with a diameter of 20 cm can absorb 172 kg of carbon dioxide, release 125 kg of oxygen, and hold 16 kg of dust a year.
A willow tree with a diameter of 20 cm can absorb 281 kg of carbon dioxide, release 204 kg of oxygen, and hold 36 kg of dust a year.
Bai Jin, an expert from the Forestry Resource Breeding Research Office of the Beijing Academy of Forestry and Fruit Science, told the media that in Beijing, Populus tomentosa has the largest amount of fly flocs among all poplar and willow species, but no tree species in Beijing can achieve the ecological effects of Populus tomentosa.
"The poplar and willow trees planted in Beijing in the 1960s and 1970s have grown into big trees. If a large number of them are cut down, it will cause a decline in the quality of the urban environment and the green landscape, causing more serious ecological losses." Zhang Zhixiang said.
Source: China Popular Science Net, China Weather Net, Beijing Municipal Bureau of Landscaping, Xinhua Net