How can we reduce the occurrence of dusty weather?

Dust source control: "cover" is more important than "blocking"

Desertification control is mainly based on soil consolidation. Of course, soil salinization and environmental pollution lead to the decline of plant productivity, which leads to land desertification. We are not worried about the soil "running away", but about the increase of harmful substances in the soil, so other measures need to be taken. Here, we focus on the prevention and control of land desertification in arid and semi-arid areas. Because desertification here directly induces sandstorms, soil erosion and other natural disasters, resulting in a large loss of valuable soil materials. Therefore, very scientific measures must be taken to protect the soil and prevent soil erosion.

The height of sandstorm flying is several kilometers, and the source of sandstorm is above 1000 meters above sea level in Beijing, so the "shelter forest" less than 10 meters on the ground is powerless in front of powerful "invaders". Therefore, it is obvious that the control of dust sources cannot be stopped by forests. In order to show that trees can't stop sandstorms, we made field observations in the spring when sandstorms were most serious, and found that the sand in poplar forests was still flowing when sandstorms came. The visibility outside the forest is less than 5 meters, and the visibility in areas covered by shrubs and grass is more than 200 meters. The role of forests in blocking sandstorms can be seen.

How to cover the source of dust? The following engineering and biological measures are usually adopted.

The first is the mechanical engineering measures to prevent desertification. For example, sand prevention grid, grass grid, plastic grid and dead tree branch grid along railways and highways are all commonly used measures in sandstorm areas. In the Loess Plateau, artificial terraces and fish scale pits are common engineering measures for soil and water conservation. It has also been suggested that fixing quicksand with chemicals such as asphalt or studying sand-fixing agents is another way to prevent desertification from expanding. Of course, some specific engineering measures need to stand the test of biological measures. If the land is fixed, but plants can't grow, it is artificially creating a new desert.

Second, bioengineering measures to prevent desertification. Since the beginning of the new century, six key forestry projects, grassland protection and construction projects, soil and water conservation projects, comprehensive management projects of inland river basins and other projects related to sand prevention and control are typical bioengineering measures. Among biological measures, plants are the most commonly used, but among plants, afforestation and irrigation were emphasized in the past, and grass planting was not paid enough attention. We should correct it in the future practice and fully understand the role of grass. Especially in semi-arid grassland areas and four sandy lands, the role of grass is greater than that of shrubs, and shrubs are greater than forests. In extremely arid areas, even herbs can't grow, but there is a layer of "biological crust" formed by lichens, algae and soil particles in the desert. The role of biological crust in desertification control has not attracted enough attention.

Third, rely on natural forces to restore and curb desertification. This practice is very simple, so simple that humans don't have to do anything, evacuate people and animals, and leave the task of restoring desertified land to nature. From 2000 to 2005, the author conducted an experiment in Bayinhushugacha Village, Zhenglan Banner, Inner Mongolia, which proved that restoring natural forces is the most direct, economical and reasonable way, and should be paid full attention by relevant departments. There are 72 households in Gacha, including 3 herders10, and the land area is126,000 mu. It is a typical Hunshandake sandy land and the largest dust source in Beijing, with both bare sand dunes and seriously degraded grasslands. We enclose 40,000 mu of seriously degraded grassland with purse seine, and organize special people to ride horses and patrol every day to prevent animals from entering and destroying. 200 1, and the restored grass grows to 80-140 cm; The highest grass yield per mu is 5300 kg (fresh weight); In 2002, the total vegetation coverage rate reached 60%. Compared with the control (unprotected), the fixed dune increased by nearly 3.8 times, and the community biomass in the dune lowlands increased by 9 times respectively. In 2003, the highest height of beach grass was 1.85 m, and the biomass exceeded 6500kg/ mu (fresh weight). Herdsmen buy 20,000 Jin of hay every year, and each household gets 70,000 Jin of hay. Since then, the pasture has become rich. In terms of vegetation composition, Artemisia frigida, Cryptomeria asperata and inch grass moss were dominant before restoration, and agropyron cristatum and woody bark were dominant two years later. The dominant vegetation of dune lowland community is Leymus chinensis and Elymus chinensis, which replaced Chenopodium glaucum and Chenopodium acutum. In terms of wildlife, rabbits, foxes, geese, cranes and even wolves have all returned to this long-lost land.

Cover up the source of dust: grassland or forest?

For a long time, the management idea is still based on afforestation. The "Three-North Shelterbelt Project", which began in the late 1970s, is positioned as afforestation. In order to welcome the 2008 Olympic Games, the "Beijing-Tianjin sandstorm source control project" was launched urgently, with forests as the "boss"; Returning farmland to forest (grass) has always been "shy" hiding in brackets, but only after repeated appeals from experts, grass is sometimes "released" from brackets. Even the burden of controlling sandstorms falls on the State Forestry Administration. For example, the office for combating desertification specially established by the state is located in the State Forestry Administration. It can be seen that in people's subconscious, sand control belongs to the forest.

With such a guiding ideology, it is not surprising to see the following scenes: many tree pits are dug rigidly on the well-growing grassland for afforestation, and the forests cannot survive and form artificial wind erosion pits; On the arid grassland, the dead trees are in sharp contrast with the tenacious desertification grassland; On sandy land such as Hunshandake, evergreen roebuck pine has been planted on the restored grassland; It is often seen that people use cars, tractors or people to carry water to ensure that the planted trees can "drink water". Because once you leave people's care, those trees are doomed to death. Still because of the above guiding ideology, Toyama Jingwei volunteered to plant trees in the arid areas of China; American companies come to promote their "solid water" (water retaining agent); A non-governmental organization started a "Wan Li Afforestation", trying to cover Xinjiang in China with forest. Coincidentally, the goal of "Three-North Shelterbelt" is to cover grassland with 15% forest!

However, have we succeeded? The sandstorm that has been raging for several years is self-evident. It has been nearly ten years since I visited the grassland from 1997. The poplars on both sides of the road are still standing there unwillingly, with thick fingers. In fact, the "owner" has changed several times, because the trees on the grassland are "planted every year and die every year". We can't help asking, have we fallen into the paranoia of "blind afforestation"?

Most arid and semi-arid areas in China are the source of sandstorms. From the perspective of ecological function, the role of grass is greater than that of shrubs, and shrubs are greater than forests. The current practice is that if there is a problem with grass, take the forest to treat it; The cost is used for forests, followed by shrubs and grasslands. Returning farmland to forests on grasslands means "returning" forests with money, and returning grasslands without money or with less money, so that ordinary people can go to afforestation regardless of whether the trees can survive or not. The money went out, but the forest didn't survive, which helped the sandstorm-the tree pits in those arid and semi-arid areas became man-made "wind erosion pits"

What is the relationship among grass, shrub and forest? In ecology, we use biomass to reflect their ecological functions. The commonly used value is annual net primary productivity, which refers to the amount of carbon that plants can fix in the air every year in all seasons of photosynthetic production. In Hunshandake sandy land, we spent two years dissecting this value, and found that the average productivity of sandy land last year (actually only three and a half months) was 0.67 tons per hectare/kloc-0 (including roots), of which the contribution of grass was 93.3%, shrub was 6.4%, and forest was only 1.3%. This was measured in a healthy sandy land where Sanguisorba officinalis (trees) can be distributed. If it is on the pure grassland, the contribution rate of forest is almost zero. This result is also consistent with the calculation result of coverage rate. On Xilin Gol grassland, we count the sparse forest in Hunshandake, and the forest coverage rate is only 0.87%. It can be seen that it is unrealistic for the "Three-North Shelterbelt" to achieve the goal of forest coverage rate 15% in grassland areas.

The above natural laws show that in arid and semi-arid areas where dust comes from, grass can not only be ignored, but also must be highly valued. Planting trees on grasslands can no longer be advocated, but it should be stopped decisively and a lot of money should be saved to protect or restore grasslands.

Or ask, in the sand or desert, the sand has flowed away, can the grass still work? Of course, fixing quicksand in such areas requires shrubs with strong roots or a small number of trees (such as sand). However, the mobile dunes were formed after the destruction of grassland vegetation. Before 1950s, the area of mobile dunes in Hunshandake sandy land was only about 2%. Grass is still very important after being fixed with artificial sand barriers or shrubs. Shrubs such as Haloxylon ammodendron, Nitraria tangutorum and pearls are very important in severe drought areas in the west. However, it is difficult to fix loose soil only by adding shrubs and grass. Shrubbery (trees naturally distributed in the sand also have this function) is used to nail the soil like nails, and grass is used for covering, because the roots of grass are closely connected. It is not feasible to plant trees in severely arid areas, because trees can't grow at all.