83.2 meters! What kind of tree grows so high? How does it deliver water to that height?

Expert of this article: Shi Jun, researcher of botany, member of the Science Communication Working Committee of the Chinese Society of Botany

"76.8 meters!"

"83.2 meters!"

Recently, two records about trees were broken! In Green Village, Beibeng Township, Medog County, a 76.8-meter-tall Bhutan pine was recorded, which is currently the tallest tree known in mainland China.

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Recently, the scientific expedition team discovered large tracts of primitive forests of Abies yunnanensis. After multiple measurements using drone ropes, it was found that the tallest tree among them was 83.2 meters tall and had a breast diameter of 207 centimeters, setting a new record for the tallest tree in China.

Weibo screenshot

What kind of pine is Bhutan pine? What kind of tree is Yunnan fir? How do scientists determine its height? What is the significance and value of studying these tall trees? Let's walk into the world of big trees together today.

Bhutan pine

Unlike most pine trees that prefer cool, dry environments, Bhutan pine is a species of Pinus genus that prefers humid environments. They are only distributed in the Himalayas, Yunnan and Tibet in our country, as well as in neighboring Bhutan and India. They often form mixed coniferous and broad-leaved forests in this area together with the closely related pine.

Bhutan pine is a tall tree. In its natural environment, the average height of a Bhutan pine is 25 meters. The tree discovered this time is also a giant among the Bhutan pine group.

Source: @People's Daily

Abies yunnanensis

Yunnan yellow fruit fir is a variant of yellow fruit fir. The main difference from the original species is that the needles are slightly thicker and usually longer. Although it is called fir, Yunnan yellow fruit fir is not a true fir tree. It is a member of the genus Abies in the Pinaceae family.

Abies yunnanensis grows in areas with a mild climate and an altitude of 2,600-3,600 meters. The mountains and valleys with brown forest soil are their favorite living environment. Abies yunnanensis usually forms a mixed coniferous and broad-leaved forest with conifers and broad-leaved trees such as Pinus armandii, Taxus chinensis, Fraxinus chinensis, and Populus chinensis. In the forest, Abies yunnanensis, which is an average of 60 meters tall, is usually a top-story tree species, towering over other plants.

Source: @CCTV News

How to measure the height of a tree?

How do scientists get the height of a tree? I believe that the first method that comes to everyone's mind is to measure it with a ruler. However, this method is not practical for measuring the height of a tree. Not to mention that climbing a tall tree is a difficult task in itself, just how to ensure that the tape measure is vertical from the top of the tree to the ground is a very difficult task.

In this measurement of the height of the Bhutan pine, a backpack laser radar was used. This tool sounds mysterious, but its working principle is very simple, that is, it uses laser to measure the distance between two points. The distance data between the earth and the moon is also measured by laser.

By measuring the position and distance of multiple points in space and processing these data with a computer, we can eventually build a 3D mapping data model of the area where the tree is located. In this way, it becomes very easy to accurately calculate the height of the tree.

Source: @People's Daily

When measuring the Yunnan Huangguo Fir, the drone was used to carry out multiple measurements. The drone was flown to the top of the tree crown, the rope was lowered, and the length of the rope was measured. The use of drones can ensure that the rope is vertically taut, which more accurately reflects the true height of the tree.

Why can't plants grow infinitely taller?

Most plants have a lifespan, and even many tall trees have a fixed life cycle. The most typical example should be the palm tree of the palm family. This tree can be more than 30 meters tall, but they have a fixed reproduction cycle. Once 60 years have passed, the palm tree will bloom and bear fruit, and the life of this tree will come to an end.

Many plants can bloom, bear fruit and reproduce many times in their lifetime, just like the Bhutan pine. Theoretically, plant cells in different tissues retain a certain degree of omnipotence. Because of this, plants have a strong ability to repair themselves. Even if a branch is cut off, or even the entire crown is cut off, new branches and leaves will still grow. As long as the conducting tissues in the roots, stems and leaves of the plant are not damaged and the leaves can photosynthesize normally, the tree will survive. So in this sense, if the conditions are right, these stem cells exist, and different tissues can be constantly renewed, the plant will not die.

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However, in nature, it is difficult for plants to live forever. Because as long as time is long enough, all regions will encounter unexpected events. Even if it is not disasters such as mudslides, hurricanes, earthquakes, and pests and diseases, there will be ice ages and long droughts. Even if you are lucky enough to avoid all natural disasters, you still have to face competition from new species. Therefore, it is impossible for big trees to live forever, and no big tree can grow indefinitely.

What is the significance of studying big trees?

Studying these giant trees is of inestimable value to our study of the evolution of a region's biological community and ecological adaptation. Of course, studying giant trees can also help us solve a scientific mystery, that is, how to transport water and mineral nutrients from the roots to the branches high above?

For example, the Bhutan pine discovered this time is 76.8 meters high, which is equivalent to a 25-story residential building. If there is no water pump to provide pressure, we can't enjoy tap water services at such a height. So how do trees without water pumps send water from the roots to the branches?

Initially, people believed that trees draw water through capillary action. The so-called capillary action means that water will "climb" upward along very thin pipes. The thinner the pipes, the higher the climbing height. However, after calculation, it was found that the capillary action generated by the size of the transport pipes (vascular bundles) of large trees is simply unable to deliver water to a height of dozens of meters.

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In fact, big trees really have a "water pump" - the leaves at the top of the branches. The leaves continuously release water vapor into the air, so that the water in the vascular bundle of the trunk is replenished. Through this transfer, the water absorbed by the roots is "pumped up". Because it is related to transpiration, this special lifting force is called transpiration pull. However, how this water supply system operates all year round and why it produces such a huge pull is still a mystery.

The two record-breaking trees discovered this time are of great value and significance for our study of plant physiology, especially the physiology of water and nutrient transport.

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