The higher the altitude, the taller the tree. Why are the "tallest trees in China" discovered one after another in Tibet?

Audit expert: Shen Tingting

PhD in Botany

Recently, a piece of news about the discovery of the "tallest tree" in mainland China has attracted much attention. The tallest tree is a 76.8-meter-tall Bhutan pine, which grows in Beibeng Township in Medog County. Subsequently, an 83.2-meter-tall fir was discovered in Zayu County, Tibet, snatching the title of "China's tallest tree". However, Medog County is more eye-catching than Zayu County. Medog is known as the "Xishuangbanna" of Tibet. So, what are its unique conditions?

The tallest Bhutan pine Source: Guangming.com

Extending northward, the alternative tropical Medog is a county under the jurisdiction of Linzhi City, Tibet Autonomous Region (the county seat coordinates 29°33'N, 95°33'E), located in the southeastern part of Tibet Autonomous Region, the lower reaches of the Yarlung Zangbo River, and the southern foot of the eastern section of the Himalayas, covering an area of ​​about 34,000 square kilometers. Here the climate is mild, flowers and trees are everywhere, and there are vast forests and rapids everywhere.

The misty Medog is like a fairyland Source: Medog Tourism Bureau

The tropics are the area between the equator and the Tropic of Cancer, and the representative vegetation in the tropics is the tropical rainforest. From the world climate type distribution map, we can find that the global tropical rainforests are mainly distributed in three hot and rainy areas on both sides of the equator: the Amazon River Basin in South America, the Congo Basin in Africa, the Malay Peninsula in Asia, the Indonesian Islands, western India, Sri Lanka, Thailand and the Philippines. The "alternative" of Medog is that it is located at 29 degrees north latitude and belongs to the subtropical area, but it has tropical rainforests.

Global climate type distribution map source: Internet

All of this is closely related to the topography of Medog. Medog is surrounded by mountains on the east, west and north, with high terrain in the north and low terrain in the south. From Mount Namjagbarwa at an altitude of 7,787 meters to Pashika at an altitude of 154 meters, the vertical height difference is more than 7,000 meters. The main part of the world's largest canyon, the Yarlung Zangbo Grand Canyon, is located within the territory.

The lower valley of the Yarlung Zangbo River is the main water vapor channel for the warm and humid air currents from the Indian Ocean to be transported to the Qinghai-Tibet Plateau. The warm and humid air currents are blocked by tall mountains during their advance, resulting in a large amount of precipitation on the windward slope. At the same time, the mountains also intercept a large amount of latent heat released by the condensation of water vapor, thus causing the tropical climate to extend northward along the Yarlung Zangbo River Valley to 29°30′ north latitude, a full 6 degrees of latitude.

It is the special topography of the Yarlung Zangbo River Gorge that makes Medog County the northernmost tropical climate zone on Earth. The average annual temperature in Medog County is 18°C, and the average annual rainfall is more than 2,300 mm. Precipitation is mostly concentrated in June to August, accounting for more than 50% of the annual precipitation.

Medog has abundant water vapor resources | Medog County People's Government Website

Rich vertical zone landscape Warm and humid water vapor makes the tropical climate distributed along the Yarlung Zangbo River Valley, and tropical rain forest landscape can be observed on the mountains on both sides of the valley bottom. As the altitude increases, the ecosystem changes in sequence in the gradual change of water and heat conditions, from the tropical rain forest at the foot of the mountain to the snow on the top of the mountain. This place has the most complete vertical zone spectrum in the world.

The Medog area is based on tropical rainforests, and upwards are tropical low mountain evergreen and semi-evergreen monsoon rainforests, subtropical mountain evergreen and semi-evergreen broad-leaved forests, warm temperate mid-mountain evergreen coniferous forests, cold temperate subalpine evergreen coniferous forests, subarctic alpine shrub meadows, subarctic alpine glaciers and cold extreme mountain ice and snow. Mount Namjagbarwa, which extends from the valley bottom to the 7,782-meter peak, has become the only mountain in China with a complete natural vertical zone spectrum.

According to preliminary statistics, there are more than 1,200 species of vascular plants in Medog, of which about 122 species are endemic to Medog. Medog concentrates almost all vegetation types from tropical to frigid zones, and these different types of vegetation gathered together contain huge ecological value.

Tropical monsoon forests are mainly distributed in low-altitude river valleys, where water and heat conditions are the best. Several tall trees have deep roots and lush leaves, and a variety of ferns and epiphytic orchids can be seen on the trunks, such as Dendrobium and Bulbophyllum. Even in winter, it is hot and rainy here, with flowers in full bloom.

Dense forest source | Medog Tourism Bureau

Subtropical evergreen broad-leaved forests are distributed in mountains with an altitude of about 1,100 to 2,600 meters. Common ornamental trees include Magnolia tibetana, Gailia gais, and Medog Jade Leaf Golden Flower. Under the broad-leaved forest, shrubs and herbaceous plants appear in turn. Dendrobium fasciatum, Bamboo-leaved Orchid, Cyperus sedge, and Eupatorium splendidum are famous herbaceous flowers here. On the tree trunks, there are also many epiphytes, such as tree radish (named because the tubers are enlarged like radishes) and chicory.

Source of cracked wood: see watermark

Source of Dendrobium scabra

Tree radish source | Baidu Encyclopedia

The vegetation types at an altitude of 2500-3700m are mixed coniferous and broad-leaved forests and dark coniferous forests. Yunnan hemlock, Cangshan fir and Medog fir are the main tree species in the dark coniferous forest. Under the coniferous forest, there are several species of alpine rhododendrons. Every spring, rhododendrons of various colors bloom, forming a wonderful landscape together with the snow-capped mountains and fir trees.

Source of blooming azaleas丨Medog Tourism Bureau

The area between 3500 and 4000 meters above sea level is a belt of alpine shrubs and meadows. As the altitude increases, the temperature decreases, and the water and heat conditions cannot meet the growth needs of trees, so shrubs become the "protagonists" here. In the mountain pass area, the wind speed is relatively high, and in order to adapt to the environment, the shrubs grow relatively low. When summer comes, the meadows are full of various wild flowers, such as gentian, meconopsis, and pedicularis, which cover the earth with a colorful carpet.

Gentiana flowers on the meadow are located at an altitude of 4000-4300m, which is a high mountain gravel beach. The climate here is cold and the weathering is strong. Large rocks are broken down into many gravels and piled together, making the soil poor. The vegetation coverage here is greatly reduced. In order to adapt to the harsh natural environment, plants have evolved cold-resistant abilities, such as thicker leaves, well-developed root systems, and creeping close to the ground to show their strong life in this bitter and cold place.

Snow lotus on the mountain source丨Baidu Encyclopedia

Due to the special climatic environment of Medog County, and its location at the intersection of the two major geographical units of the Indian subcontinent and the Qinghai-Tibet Plateau, and the steep mountain roads, it has been difficult for humans to reach in history. Many rare animals and plants that are hard to see in other areas have been preserved, such as the Bengal tiger, brown-necked hornbill and other rare animals, as well as the Himalayan yew, long-stamen magnolia and the tree also known as the "living fossil of plants". Therefore, Medog enjoys the reputation of "World Museum of Animals and Plants" and "World Biological Gene Bank".

Medog is changing. Medog has become a dream destination for many people with its unique natural scenery, but in the past, only a few hiking enthusiasts were able to enter Medog. Because the southwest region is located at the junction of the Eurasian Plate and the Indian Plate, the geological activities are active and the terrain is rugged. In addition, the southwest monsoon brings abundant precipitation, making Medog prone to geological disasters such as earthquakes, mudslides and landslides. In winter, the Himalayas are covered with heavy snow, and the mountain roads leading to the outside world in Medog are completely covered with heavy snow for June to August. "The snow-capped mountains lock Medog, and it is difficult to enter and exit. The isolation is accompanied by backwardness, and generations have suffered from poverty." This folk song is a true portrayal of the isolation and backwardness of Medog County in the past.

It was not until October 31, 2013, after more than half a century of construction, that the Medog Highway was finally officially opened to traffic. At this point, the last county in my country without a road can finally have unimpeded access to the outside world.

Medog Highway Source: Sohu

Although it is still far away to get to Medog, with the completion of the Medog Highway, more and more people will have the opportunity to see its mysterious face. The beautiful and unique Medog is waiting for people to explore.