Can you make a fighter jet out of wood? It's true!

Plants have different choices. Some trees grow 5 or 6 meters a year, while some trees grow 5 or 6 centimeters a year. Why is there such a big difference?

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01

Why do trees grow taller?

Let’s first talk about why trees grow tall - actually it is to compete for sunlight.

In the hot and humid tropical rainforest, there is no shortage of water or temperature, but sunlight has become a precious resource that many plants compete for. As long as you walk into the rainforest, you will find that the light suddenly becomes much darker. Generally speaking, after 4 pm, it is like sunset in the rainforest.

In the Xishuangbanna tropical rain forest, the radiation in the canopy can reach 158.92 watts per square meter, while the intensity of radiation on the ground is only 12 watts per square meter. The sunlight is intercepted by layers of plants before reaching the ground.

In order to get more sunlight, plants have to grow taller as fast as possible, so many plants living here are much taller than we can imagine. For example, teak can reach 40 meters, and parashorea chinensis can reach 60 meters. This is a world of competition for light, so the big trees in the forest basically grow straight up.

Of course, with sufficient light, the plants look completely different.

For example, in the African grasslands, the height of the trees is usually only about 10 meters, and few of them reach the sky. Their shape is more like a big umbrella. In fact, by opening their leaves, they can absorb a lot of sunlight, because there is no strong competition between trees here, and they are all far away, so there is no need to grow very tall to get enough sunlight.

02

Every tree has its own value.

So being tall actually has high rewards, and is growing taller quickly the best option? Not necessarily. What we didn’t expect is that both fast-growing trees and slow-growing trees appear in the rainforest, which is actually a different competitive strategy for different plants.

Some plants choose to accumulate strength and then develop. For example, the familiar Dalbergia odorifera, it doesn’t matter if you are not familiar with this name, we can change its name, its name is Huanghuali.

Hainan Huanghuali Pear Bracelet. Copyrighted pictures in the gallery, reprinting and using may cause copyright disputes

Under good water and fertilizer conditions, Huanghuali grows about 2 cm per year, gradually increasing, that is, the diameter of its trunk closest to the ground increases by 3 cm. It usually takes 6 to 7 years of growth before core wood is produced.

What is the heartwood ? As the name suggests, it is the wood in the center of the tree. In fact, they are the aged xylem, located between the pith and the sapwood. These cells used to be the pipes for transporting water to the tree. During the growth of the tree, the pipes in the center of the tree gradually lost their function. These heartwoods that have lost their function will gradually be filled with oil, gum, tannin and other colored substances, which will make the color of the heartwood in the area darker and darker, making it clearly distinguished from the surrounding sapwood.

As for the surrounding wood that still maintains activity and can transport water to the tree, it is called sapwood. Because they are not filled with secondary metabolites, the color appears lighter and the wood is softer.

Everyone, please note that whether the wood is hard enough is actually directly related to the secondary ecological metabolism and the amount of secondary metabolites filled in to a large extent.

Of course, some plants choose to grow fast. For example, there is a plant called balsa wood in the rainforest. It can grow 5 to 6 meters a year. The growth rate is beyond imagination. But their material is very loose and the wood is very light. How light is it? An adult can hug a 2-meter-long tree trunk and run. Can you imagine how light it is?

But very light wood also has its uses. Before the emergence of synthetic materials, we mainly used this kind of wood to make model airplanes, and this kind of wood can even affect the direction of the war.

During World War II, Britain produced an airplane called the Mosquito bomber, and its main material was balsa wood. The wings were lighter, so the airplane could fly very fast. Under the same engine, a wood-light airplane could fly very fast, which gave it an advantage. Secondly, airplanes made of wood are particularly easy to repair, which is easier than metal repairs. You can find a carpenter to take this wood and patch it up, and it will be repaired quickly, and the damaged airplane can return to the battlefield quickly. So from this perspective, balsa wood made an outstanding contribution to the victory over German fascism. In this regard, every tree has its own value.

I would also like to remind everyone that no matter whether it is a heavy tree or a light tree, everyone thinks that it is a plant that can grow continuously, so we have an illusion that wood can be produced infinitely and seems to be a renewable resource.

Logically, there is nothing wrong with it, but it is wrong to add a limitation - under the limited conditions of human historical development, wood is not a renewable resource.

For example, it takes about 300 years for a red sandalwood tree to grow to the point where it can be used to make furniture, about 500 years for a huanghuali tree to grow to the point where it can be used to make furniture, and more than 800 years for a parashorea chinensis tree to grow to adulthood. So when we were restoring the Forbidden City, it was really difficult to find a golden nanmu tree.

Golden nanmu handicrafts. Copyright image from the gallery. Reprinting and using may cause copyright disputes.

We preserve this big tree, and it preserves not only the material for furniture, but also a living history book.

This article is a work supported by Science Popularization China Starry Sky Project

Author: Shi Jun, PhD in Botany, well-known popular science writer

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.

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