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Head west along National Highway 317 on the Northern Sichuan-Tibet Line into Tibet, where you will see the city of Nagqu, famous for its large size, at the intersection with the Qinghai-Tibet Highway. Nagqu City is the northern gate of Tibet, an important part of the country's five major pastoral areas, and has always had the reputation of the source of China's rivers and the water tower of China. Located between Tanggula Mountain, Nianqing Tanggula Mountain and Ganges Mountain Range, Nagqu covers an area of 430,000 square kilometers and is the largest city in China.
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The city of Nagqu is larger than Gansu Province, and is no weaker than some countries, equivalent to four South Koreas. Originating in the southern foothills of the Tanggula Mountains, nagqu is formed by melting ice and snow, and is the upper reaches of the Nu River, which was called the Black River in ancient times because the river is so deep and black, and naqu means black river in Tibetan.
The average altitude of Nagqu City is more than 4500 meters, the urban area is more than ten square kilometers, the permanent population exceeds 500,000, and after the opening of the nagqu to Yangbajing section of the world's highest highway, the driving time between Lhasa and Nagqu has been shortened from more than six hours to three hours.
Nagqu is strategically located, bordering Qamdo to the south with Lhasa, Xigaze and Nyingchi to the east, Ali to the west, and Qinghai and Xinjiang to the north. Nagqu is one of the most popular tourist destinations in Tibet, and the famous Namtso Sacred Elephant Heavenly Gate is located here, Namtso is one of the three holy lakes in Tibet, and the Sacred Elephant Heavenly Gate is known as the most beautiful ending place in Tibet.
Nagqu is known as the roof of the roof of the world, with unique scenery, many lakes and mountains, in addition to Namtso, there is also Lake Tsuna and Selincuo, the largest lake in Tibet. Every august, the grand Nagqu Horse Racing Festival is held here, and the summer of the Changtang No Man's Land Grassland is the golden season for tourism in northern Tibet, and today Nagqu has become one of the most well-known tourist destinations in Tibet.
However, when people arrive at Nagqu, they will find one thing, except for the snowy mountains and meadows, there is not a single tree in sight, and even in the county town, they cannot see a single green tree.
When you take the train into Tibet and pass through the Nianqing Tanggula Mountain, you can see a large expanse of grassland, herds of cattle and sheep, and majestic snow-capped mountains, but you can't see a single tree until you reach Lhasa.
Because there are no trees in Nagqu City, it has been hotly discussed by many people on the Internet, and after scientists came here to test, they also said that they could not do anything. For thousands of years, the local people have a very persistent spirit of planting trees, and the huge funds that have been invested in the scientific research of tree planting have also been wasted.
However, there are rich winter grasses and summer grasses, precious snow lotuses and nyingchi, why can't a single tree be planted? So much so that even scientists feel helpless?
After expert research, the main reasons why naqu cannot plant trees are as follows:
First, the altitude is too high
The capital of Tibet, Lhasa, is 3650 meters above sea level, ordinary people will feel breathing difficulties here, a little careless will cause high reaction, many people may think that the altitude of Lhasa is high enough, but in fact, the average altitude of Lhasa is far less than the altitude of Nagqu City.
Nagqu City is the highest prefecture-level city in China, the altitude here is above 4500 meters, the high altitude makes the air here thin, the oxygen content is only about 45% of the plain area, the local average annual temperature is only minus 2.2 degrees, the lowest minus 40 degrees, belongs to the cold and hypoxia area.
The cold and hypoxic environment makes it very difficult for the plants here to survive, and this environment is not suitable for the growth of large trees at all.
Second, the frozen soil that does not melt
If it's too cold to survive, some might say that the northeast has cooler temperatures in winter, so why can trees still grow? The minimum temperature in the Nagqu region is not as low as the temperature in the northeast region.
This is related to the geographical location of Nagqu, although the winter in the northeast region is cold, but it belongs to the plain, not to the high altitude area, and nagqu is at an altitude of more than 4500 meters, where the year-round snow makes most of the soil become permafrost. Trees must stand tall in order to grow tall, but most of the area here is tundra, and the soil layer is very shallow, and the trees cannot take root.
Under the frozen soil, basically in addition to the grassland, there is no other plant can grow and reproduce here, there are scientific studies that show that the frozen soil can preserve a certain amount of soil nutrients and water, timely to the trees with water and fertilizer supplementation, so that they can thrive. But in Tibet, frozen soil is not a good thing, and the natural fertility of the underground frozen soil is very small, and even simple crops are difficult to grow.
From November to March of the following year in Tibet, the dry wind season is low, and the climate is mild from May to September, with 80% of the annual rainfall. With the change of seasons, the change of temperature, the frozen soil will freeze and thaw, the weeds that can grow on this soil are already very vigorous, and the trees are difficult to survive here.
Third, the air is thin
At an altitude of 4500 meters above sea level in Nagqu, not only is the temperature low, but the air is thin and oxygen-deficient, and the oxygen content here is only about 45% of the plains, not only ordinary people have become difficult to survive here, but the trees are the same.
Although studies have shown that carbon dioxide is an important factor in restricting plant growth and carrying out integrated effects, the oxygen content in the air is the main factor restricting their growth.
Earth has experienced several mass extinctions, and plants began to grow on Earth about 500 million years ago, when the oxygen content in the Earth's atmosphere reached 10%. About 300 million years ago, the earth's oxygen content increased to 35%, when the trees on the earth became towering trees, up to tens of meters high.
Later, millions of years of forest fires caused most of the life on the earth to go extinct, and only a few creatures survived, and then under the influence of plants, the oxygen content has been maintained at about 21%.
In the Nagqu area, the original thin air is still low and the role of the permafrost layer, it is difficult for oxygen to enter the rhizome part from the branches of the vegetation, so that the vegetation cannot absorb nutrients in the soil layer. We all know that how tall a tree can grow depends entirely on how deep its roots are, and the roots of the tree cannot absorb nutrients, so it is naturally difficult to survive here.
4. High winds of more than 100 days per year
If the climate in the Nagqu area is not suitable for tree growth, then there is an important reason why trees are not suitable for tree growth, there are more than 100 days of windy weather here every year, the trees cannot withstand the baptism of strong winds, they are easily blown down, and the trees that have just been planted are not too late to take root and sprout, and they are blown to pieces in the winds of the second year.
The growth of trees is inseparable from water, although the Nagqu area is not short of water, the local annual precipitation is about 400 mm, although it seems that the precipitation is not much, but because the permeability of the tundra belt is very strong, it is impossible to retain water, and it is difficult for trees to break through the permafrost layer to take root in the ground, which is a huge obstacle to the development of tree roots.
Here under natural conditions, conventional means are very difficult to plant live trees, the solution is to plant trees in the laboratory, but once you leave the laboratory, placed in the natural environment, it is difficult to survive, and soon die.
In short, the growth of any life needs to have certain conditions, and sometimes it is really indispensable. The extremely special environment of Nagqu County is the main reason why there are no trees for thousands of years.
Trees have always been an indispensable part of our lives, and afforestation has always been something that people all over the world are doing, making the earth a little greener and making our lives a little more colorful. Every year on March 12, Arbor Day, the people of the whole country set out to plant trees, plant hope, and plant the future.
With the development of science and technology, the indomitable spirit of the people of Nagqu for thousands of years has broken through the spell of the unliving trees, but it takes more manpower and material resources, although it cannot see the same green eyes as the southern city, but you can also see the tenacious small trees growing on the gray streets.
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