The most intelligent “arsonist” in nature

The Australian fire that had been burning for five months was finally extinguished on February 13, 2020.

In this fire, a kind of magical plant entered the public’s field of vision. It is the familiar and unfamiliar eucalyptus.

Before the fire was completely extinguished, the eucalyptus trees had been “reborn” in the land that was swept by the flames. On the eucalyptus trunk that was burnt to black before, the young shoots “craked out”, full of vitality.

However, many people also read a feeling of “conspiracy theory” from the fast-recovering eucalyptus, and think that eucalyptus is suspected of “deliberate” arson. And when we really understand the relationship between eucalyptus and fire, we will find that this is more like a “gene-level massacre.”

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Eucalyptus is the national tree of Australia. As early as the 16th century, when Europeans landed on the Australian mainland, there were already eucalyptus trees everywhere.

However, there is not only one species of eucalyptus, but a collective term for all plants of the Myrtaceae Eucalyptus genus, with more than 800 species and more than 100 varieties and subspecies.

Eucalyptus almost dominates all of Australia. Australia’s forest coverage is about 20%, but 80% of it is dominated by eucalyptus, reaching 92 million hectares. Although the eucalyptus is a symbol of Australia, some characteristics of the eucalyptus also determine that it needs to be a part of the fire. For example, highly flammable.

We can see the clues from the eucalyptus, especially the nickname “petrol tree” of Eucalyptus blue. Eucalyptus contains volatile aromatic oils (eucalyptus oil) all over the body, especially the leaves of eucalyptus, which are known for their obvious oil gland spots. In hot weather, eucalyptus oil will evaporate at high temperatures, making the entire eucalyptus forest full of this flammable gas.

In addition, when the volatile eucalyptus oil is mixed with dust, water vapor and sunlight, it will also produce a strange blue hue in the air. This phenomenon is very common in Australia, especially in the Blue Mountains of New South Wales. The name “Blue Mountain” is derived from the “blue haze” made by eucalyptus.

But this is not so much a blue haze, as it is a latent “time bomb.” If it happens to be hot, dry and windy, a cigarette butt, a flash of lightning or a bit of sparks can bring a wild forest fire.

In addition, eucalyptus itself also provides a large amount of flammable materials, and the amount of combustibles they accumulate on the ground is far more than other plants. The thick peeling bark and remaining branches and leaves will make the fire develop more rapidly, like adding fuel to the fire.

Coupled with the volatile eucalyptus oil, even if the isolation zone is dug out, strong winds can still spread the fire quickly, which makes common forest fire prevention methods fail. Sometimes, the eucalyptus that is ignited may explode.

According to the global forest fire observation data, more than 70% of fires occur in forest landscapes, and most of them are in different types of eucalyptus woodlands. For example, in 2017, the Portuguese forest fire that killed 66 people, one of the important reasons is the large-scale planting of eucalyptus.

In Australia, where there are eucalyptus trees everywhere, woodland fires have almost become “standard”.

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So the question is, if eucalyptus trees are so flammable and explosive, why can they sit on so much land in Australia?

First of all, the trunks of eucalyptus trees are straight and tall, and their crowns are always too sparse relative to the height of the trunks, which is not too close to the four words “branching and leafy”. When a fire broke out, this high tree canopy prevented the flames from climbing up to a certain extent. Although the peeling bark extending to the ground will also draw the flames up the leaves, the fire on the canopy of this kind often comes and goes quickly, avoiding the prolonged scorching of wild fires.

Secondly, eucalyptus has a thick bark, and its nutrient-transporting conduits located in the center of the trunk are also hidden deep in the xylem, making it difficult to be injured. Compared with other plants, eucalyptus has a higher survival rate after a fire and is less affected.

What is even more surprising is that eucalyptus will use the fire to let its seeds and shoots enter a new round of germination. There are some dormant shoots under the bark of eucalyptus, and its seeds also have hard shells. The high temperature of the fire can just awaken the sleeping dormant buds and burst the seed shells, allowing them to germinate quickly.

In addition, the vegetation ash after the fire nourished the land, and other plants were burned to death. The eucalyptus tree that was the first to come back to life was like a godly help and took the lead. Although fires also harm eucalyptus, they can quickly reverse adversity after the fire and quickly occupy a favorable ecological niche.

Many studies have also shown that after almost every forest fire, the proportion of eucalyptus in Australia will increase, until it becomes the king of Australia. Combined with the previous “time bomb”, the eucalyptus seems to be deliberately set on fire to wipe out competitors, full of evolutionary wisdom.

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However, when it comes to the tenacity and strength of eucalyptus, their use as a kind of artificial economic forest has caused many controversies.

From an economic point of view, eucalyptus can be described as a treasure. They are mixed in various cooling oils, essential oils, mouthwashes, paper, and flower gardening. Of course, the most important thing is that eucalyptus can quickly provide a large amount of high-quality wood. You know, eucalyptus is the fastest growing tree species in the world. In Brazil, the highest annual growth rate of eucalyptus can reach 117m3/hm2. Relying on these advantages, eucalyptus started its “colonization” of the world as early as the 18th century, and became the most widely planted artificial tree species in the world. Together with poplar and pine, it is known as the world’s three major fast-growing afforestation species. Now it can be seen in more than 120 countries and regions ranging from tropical to temperate, and it can also create huge economic value in a short period of time.

However, in recent years, the reputation of eucalyptus in our country has declined severely, and it has become a “demon tree” in the eyes of many people. Eucalyptus is considered to be a “pumping machine”-requiring a lot of water, leading to a drop in groundwater level and land desertification; “fertilizer”-a large demand for fertilizer, leading to soil degradation and poor land; “overlord tree”-for other species It has inhibitory properties, making other plants unable to survive; “poisonous trees”-release toxins, harm the human body, and cause pregnant women to abort.

However, these are old rumors. Regarding the term “pumping machine”, studies have shown that for every kilogram of biomass synthesized, pine trees require 1,000 liters of water, Dalbergia and Acacia trees also require more than 800 liters, while Eucalyptus only requires 510 liters. This shows that it is not true to say that eucalyptus is a “pumping machine”.

The term “fertilizer” is similar. As early as 1959, Liani, a foreign scholar, studied the soil of 25-year-old eucalyptus forests and found that the soil organic matter content was as high as 20.33 grams per square meter, while the pine forest soil organic matter content was only 7.54 grams. Per square meter.

As for the term “overlord tree”, it is also a misunderstanding of the “allelopathy” of plants. The biological world itself has the phenomenon of mutual growth and mutual restraint. Eucalyptus does have a certain inhibitory effect on some plants, but this is also a normal natural law.

The “poisonous tree” is even more nonsense, and there is no scientific evidence to prove it.

However, in China’s eucalyptus plantations, there are problems such as declining land fertility, soil erosion, and decline in biodiversity. But the root cause is not the eucalyptus plant itself, but the wrong planting and management methods.

Therefore, in recent years, the planting of eucalyptus in my country has been continuously optimized and adjusted. And this game between the economy and the ecological environment may continue for a long time.