This thing is not only not afraid of fire, it can also help people put out fires!

Plants occupy a very important position in human life. They have many functions. In addition to providing oxygen, plants can be eaten, used for medicinal purposes, and be ornamental. They can also provide humans with clothing, fabrics, wood, etc.

However, some plants can actually prevent fires. They are Schima superba, a plant of the Theaceae family. It is named after its lotus-like flower. It is also called Schima superba, which sounds like "harmony". Schima superba has a beautiful shape and is evergreen all year round. It is not only often used as a landscape plant because of its high appearance, but also a star species for forest fire prevention.

Yes, you read that right, plants can also be used to prevent fire!

Flowers of Schima superba (Photo source: Flora of China)

Part 1

Special plant firefighter - Schima superba

In recent years, due to extremely high temperatures, spontaneous forest combustion and wildfires have occurred frequently, which not only caused serious losses to forest resources, but also caused serious damage to the local ecological environment. In 2019, wildfires in New South Wales, Australia, burned for nearly 7 months, killing about 1 billion wild animals, and burning more than 2,500 houses and 11.7 million hectares of land.

Creating biological fire-proof isolation zones is an effective way to prevent wildfires that can save a lot of manpower and money. Schima superba is an excellent tree species that can be used to create biological fire-proof isolation zones. When facing a blazing fire, rows of Schima superba face the sea of ​​fire and use their trunks that reach the sky to block the spreading flames, just like a tall firewall.

Schima superba (Photo source: Flora of China)

Part 2

What is so special about Schima superba?

The main factors that affect the ignition temperature of plants are the water content and oil content in the plant. The fresh leaves of Schima superba have a high water content (close to 50%). The higher water content requires more heat when the water evaporates, which can reduce its own combustion temperature. At the same time, the oil components in Schima superba, such as crude fat and other combustion-supporting components, are low in content, which makes their combustion heat relatively low and not easy to burn . Therefore, compared with other plants, Schima superba is more likely to avoid fire and can also slow the spread of forest fires.

The low flammability of Schima superba is also due to the fact that it is a plant that is full of "sense of crisis". A study on the changes in water storage in the trunk of Schima superba in different seasons found that Schima superba would store more water in the dry season, which is exactly the case of "having food in hand and no panic in the heart".

In addition, the surface fire resistance of Schima superba is good. The soil moisture content is usually high in the places where Schima superba grows. This high moisture content will also increase the speed of leaf decay and reduce the accumulation of combustibles such as dead branches and leaves. And as it ages, the fire resistance of Schima superba becomes stronger and stronger. It is true that "old ginger is still spicy"!

Therefore, constructing a Schima superba fire-prevention isolation zone can effectively prevent the spread of forest fires, and Schima superba has also earned the title of plant "fire extinguisher"!

Schima superba (Photo source: Flora of China)

In addition to Schima superba, another commonly used plant "fire extinguisher" is larch . Larch has thick bark that is difficult to be burned through by fire. Even if the trunk is burned, larch can prevent the invasion of pathogens, pests, etc. by secreting brown transparent resin. The water content of its leaves is as high as 60%, and the heat of combustion is as low as that of Schima superba, making larch also non-flammable. At the same time, larch has rapid root growth and strong tillering ability, which can hinder the growth of weeds and other shrubs under the forest and reduce the appearance of combustibles under the forest. At present, larch has been used as a low-flammability plant in biological fire prevention in most forest areas in Northeast China.

Larch (Image source: Wikipedia)

In addition, studies have shown that the aloe vera plant that is common in our lives is not afraid of fire. Researchers have found that the dead leaves of aloe vera are extremely difficult to burn, and the dead leaves do not fall off. When a fire occurs, the aloe vera covered with dead leaves can often successfully survive.

Part 3

Are there “arsonists of the heart” in the plant kingdom?

There are plant "fire extinguishers", so there are plant "arsonists". Eucalyptus, Australia's "king tree", is closely related to the frequent wildfires in Australia. Eucalyptus is a general term for plants of the genus Eucalyptus under the Myrtaceae family . 80% of Australia's forests are eucalyptus, and because the bark contains a lot of oil, eucalyptus is highly flammable .

Not only that, every year the outermost bark of eucalyptus withers and falls off and accumulates at the roots (the fallen leaves and bark contain phenolic compounds, eucalyptol and other substances that inhibit the growth of microorganisms. The accumulated dead branches and leaves are not easy to decompose and are perfect fuel). When the temperature reaches 40℃ in summer, it will spontaneously combust, causing a fire. Among them, Eucalyptus globulus in the genus Eucalyptus is even known as the "gasoline tree".

Is the eucalyptus tree stupid? Why would it add fuel to the fire when others can’t even hide from it?

Blue gum (Image source: Wikipedia)

It turns out that the trunk of the eucalyptus tree is straight and tall, and the crown is sparse, so that when a fire occurs, the high crown can prevent the flames from climbing up. At the same time, the hard and thick bark can also withstand the baking of the fire. Most importantly, under the bark of the eucalyptus tree are seeds with hard shells, and the high temperature brought by the fire can just make the seed shells burst and germinate quickly.

A wildfire is a "reshuffle" of life. Eucalyptus trees have seized this "fire" vehicle for population renewal, and through forest fires, they have achieved the goal of "growing their own flames and destroying the prestige of others." Scientific research has also shown that fire plays an important role in the evolution of plant flammability. Plant species in fire-prone ecosystems are often more flammable than species in non-fire-prone ecosystems.

In addition to eucalyptus, the rock rose , which is afraid of heat but not cold, is also a plant "arsonist". The rock rose, which looks harmless to humans and animals, can secrete a large amount of oil in its branches and leaves. When its seeds are about to mature, the oil reserves in the branches and leaves are close to saturation. Once the external temperature exceeds 32°C, the rock rose will start to self-ignite. While the "scheming" rock rose "commits suicide", it also takes the surrounding plants with it, so that its seeds with a fireproof layer have a wider living space.

Rock rose (Image source: Wikipedia)

From this, we can see that those plant "arsonists" who "commit arson" often have seeds that are not afraid of fire or need the help of fire to germinate. For example, the seeds of Banksia can only open their shells after being baptized by wildfires. This is probably the reason why they can "set fires" without restraint!

Part 4

Conclusion

Whether it is a plant "fire extinguisher" or an "arsonist", these seemingly strange operations are actually the continuous efforts made by plants to better adapt to their living environment!

References:

Cui, X., Alam, MA, Perry, GL, Paterson, AM, Wyse, SV, & Curran, TJ (2019). Green firebreaks as a management tool for wildfires: Lessons from China. Journal of environmental management, 233, 329-336.

Cui, X., Paterson, AM, Wyse, SV, Alam, MA, Maurin, KJ, Pieper, R., ... & Curran, TJ (2020). Shoot flammability of vascular plants is phylogenetically conserved and related to habitat fire-proneness and growth form. Nature Plants, 6(4), 355-359.

Gao, J., Zhao, P., Shen, W., Rao, X., & Hu, Y. (2017). Physiological homeostasis and morphological plasticity of two tree species subjected to precipitation seasonal distribution changes. Perspectives in Plant Ecology, Evolution and Systematics, 25, 1-19.

Bond, W. (1983). Dead leaves and fire survival in southern African tree aloes. Oecologia, 58(1), 110-114.

Wang Hanguang, Zhang Jian, Yang Wanshen, Liao Wei, & Wang Jingang. (2017). Analysis of volatile allelopathic components of Eucalyptus grandis leaves by gas chromatography-mass spectrometry. Journal of Sichuan Agricultural University, 24(01), 51-54.

Zhang Hongwei, & Zhang Wei. (2001). On the fire resistance of larch. Heilongjiang Forestry, (4), 22-22.

Zhang Ping, Zhou Zhichun, Jin Guoqing, Wu Yunsheng, & Fan Huihua. (2005). Differences in the flame retardant and combustion-supporting chemical components of fresh leaves from Schima superba provenances. Journal of Forestry Science, 18(1), 80-83.

Produced by: Science Popularization China

Author: Liu Yang (Wuhan Botanical Garden, Chinese Academy of Sciences)

Editor: Sun Chenyu

Producer: China Science Expo

The article only represents the author's views and does not represent the position of China Science Expo

This article was first published in China Science Expo (kepubolan)

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