@毛絮絮: Don’t be too “floating”! To reduce flying catkins in cities, these 9 points are the key →

Willow catkins are "floating" again, right? Too many willow catkins are not only annoying, but also pose certain safety and health risks. However, in order to deal with them, we are very entangled, but we have been working hard!

01 Where do willow catkins appear? You really need to "follow the map"!

Where do poplar and willow catkins mainly appear? Wherever poplars and willows grow, poplar and willow catkins are likely to appear. We need to "follow the map" from two angles to find them:

From the perspective of natural selection, this is a place with climatic conditions suitable for the growth of poplars and willows:

Poplar is a sun-loving positive tree species, requiring long days and weather with a certain amount of strong radiation light. Poplar is also a moisture-loving tree species, and is not suitable for planting on hills and slopes. It generally grows more on river beaches, river beaches, valleys and lakesides, and grows better. Poplar is a forest tree species scattered in the temperate and cold temperate zones of the Northern Hemisphere. In my country, it is distributed between 25 degrees and 53 degrees north latitude and 80 degrees and 134 degrees east longitude, that is, it is distributed in vast areas such as Central China, North China, Northwest China, and Northeast China.

Figure 1: Poplar trees in the forest farm of the Sanggan River Poplar High-Yield Forest Experimental Bureau in Shanxi Province (Source: Xinhua News Agency)

Willow is a tree with a wide range of ecological adaptability. It can grow in a variety of different environments and climatic conditions. There are different species of willow. Its growth range is wider than that of poplar. It is light-loving, moisture-loving, cold-resistant, salt-alkali-tolerant, and drought-tolerant. It is mainly distributed in temperate and subtropical regions.

Figure 2: Willow trees on both sides of the river in Lvzhou Street, Minquan County, Henan Province are green (Source: Xinhua News Agency)

From the perspective of artificial selection, humans are willing to plant willow trees in the following places:

As for poplars, they are widely used in intensive cultivation due to their rapid early growth, strong adaptability, wide distribution, many types and varieties, easy hybridization, easy improvement of genetics, and easy asexual reproduction.

Willows have strong germination ability, well-developed root systems, and extremely fast growth, making them the main choice for concentrated cultivation. Therefore, willows are the first choice for planting along roads, river banks, or in many windbreaks.

02 Expansion and contraction: We are facing a dilemma

Poplar and willow catkins bring great trouble to human beings in terms of endangering human health, affecting the urban environment, and posing potential safety hazards. However, people choose poplar and willow trees as the main tree species for afforestation because they have the functions of releasing oxygen and fixing carbon, cooling and increasing humidity, reducing bacteria and inhibiting bacteria, and preventing wind and dust. At the same time, they have low maintenance costs and good landscape effects, making them the main tree species for urban greening. Tall poplars and charming willows bring us infinite vitality in spring, especially in desert areas and river valleys, where the planting of poplar and willow trees has become our first choice for afforestation.

In Fengtai District, Beijing, a worker cleans up newly pruned poplar branches to reduce flying catkins. ( Source: Xinhua News Agency )

On the one hand, people like poplars and willows, which are also suitable for the growing environment in the north, have strong survival ability and the characteristics of rapid growth; on the other hand, people are troubled by the above-mentioned harm caused by poplar and willow catkins, especially poplar and willow trees in big cities, which have become the focus of governance and prevention. For this reason, many cities have invested a lot of costs in the season when poplar and willow catkins are prevalent. For example, in 2020, Beijing dispatched more than 27,000 governance personnel and more than 4,000 water spraying and cleaning vehicles to spray and moisten 357,000 female poplar and willow trees, and shaped and pruned 69,000 trees, reducing the situation of flying catkins during peak hours.

In Beijing's Fengtai District, a worker uses a high-pressure water gun to spray water on female poplar trees to reduce flying catkins. (Source: Xinhua News Agency)

People are facing a dilemma as to whether to expand the planting of willow trees or reduce them, and the control of willow catkins has become a hot topic.

03 All-out prevention and control: Keep the urban landscape as it was and reduce the flying catkins

To this end, what we can do now is to make every effort to prevent and control willow catkins while keeping the original appearance of the urban landscape. There are many methods to prevent and control willow catkins, including biological, physical, and chemical methods. In summary, the main measures for preventing and controlling willow catkins are:

1. In the process of urban greening and tree species renewal, a large number of male poplar and willow trees should be selected and bred by cutting seedlings, and female plants should be gradually eliminated. This is a long-term task that can be gradually promoted without affecting the greening layout as much as possible;

2. Reasonably prune the crown of poplar and willow trees to control branch growth, reduce plant biomass, and reduce the generation and dispersion of fluff;

3. Use high-position grafting technology to cut off the crown of the original female plant and graft young male branches onto its main branches;

4. Plant other tree species around poplar and willow trees to form a barrier belt to reduce the chance of fluff flying, or set up necessary barriers, fences and other physical measures to prevent poplar and willow catkins from flying;

5. Inject plant catkin inhibitors into the trunks of poplar and willow trees to inhibit the formation of catkins by inhibiting the differentiation of flower buds of poplar and willow trees;

A staff member of the Beijing Municipal Bureau of Landscape Architecture injects drugs into a female willow tree to prevent catkins from flying ( Source: Xinhuanet )

6. Choose safe and non-toxic pesticides and spray them on poplar and willow trees to control the number of pests and reduce the production and dispersion of fluff;

7. Implement water spraying, increase the frequency of cleaning, and promptly handle the willow catkins that fall on the ground to prevent them from spreading further and eliminate safety hazards;

8. The meteorological department will issue early warning information on poplar and willow catkins. Citizens should pay attention to the high-incidence periods and areas of poplar and willow catkins, reduce unnecessary outings, and take necessary protective measures such as wearing masks and scarves. People who are prone to allergies should take precautions.

9. When willow catkins are in full bloom, try to close doors and windows to prevent catkins from entering the room. Catkins that do enter the room must be cleaned up promptly.

Author: Wang Yuanhong, Senior Weather and Climate Engineer

Reviewer: Wang Kang, Director of the Science Museum of the National Botanical Garden, Professor-level Senior Engineer

Produced by: Science Popularization China