To survive in a sea of ​​fire, what tricks do plants have?

Last year, the Amazon rainforest fire burned 500,000 hectares of forest; this year's Australian forest fire killed 500 million animals; on April 5, a forest fire started near the Chernobyl exclusion zone, and on the 13th the fire had spread to about 2 kilometers away from the location where radioactive materials were stored in the exclusion zone.

Fierce Australian bushfires, photo from unimelb.edu

The wilderness ravaged by fire is devastated. Are there no survivors?

Of course not!

The tenacity of life is far beyond our imagination. Many plants have their own unique ways to survive in fire, and they can still survive even if they are unfortunately burned by fire.

Today I will introduce to you some big names in the world of fire and sea survival!

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Fortify the walls and clear the fields: Ponderosa

Plants have very different physiological structures from ours. Even if a large part of their bodies is consumed by fire, they can often repair themselves and continue to survive. Many plants try to improve their defenses and stand firm when a fire comes. This has become a way for them to survive fires. The ponderosa pine (Pinus ponderosa), which is home to western North America, is such a "hero" that can stand firm against wildfires.

The first fire prevention method for yellow pine is "fortification". Their bark, which is like scales, is thick and tough, as if it is a natural fireproof coat for the trunk. Their second fire prevention method is "clearing the field". As they grow taller, the lower branches of yellow pine will fall off one by one, leaving only the green branches and leaves at the highest part of the trunk. Usually, wildfires that only spread in the shrub layer are unlikely to reach the crown of adult yellow pine trees, which are dozens of meters high. Relying on the hardcore trick of "fortification and clearing the field", most yellow pines can be fully recovered after wildfires.

The thick bark is the secret weapon for the yellow pine to survive fires. Image from Wikipedia

Wildfires can’t stop: Beargrass

Every five to seven years, beargrass (Xerophyllum tenax) in western North America produces long spikes of tiny white flowers clustered together. Grizzlies use the long, thin blades of beargrass to bedding their hibernation dens, which is how this beautiful lily-family herb got its name. It is also called Indian basketgrass because Indians used beargrass leaves to weave baskets.

Faced with the raging wildfire, the delicate stems and leaves of bear grass have no power to resist, but fortunately they have long been prepared for rebirth from the fire. Bear grass has short and thick underground rhizomes, which store a lot of nutrients and water, buried deep in the soil where the flames cannot reach. Once the remaining smoke from the fire dissipates, young buds will quietly sprout from the rhizomes, becoming the first new green on the charred wilderness. Regular wildfires not only cannot burn out the bear grass, but also help them clean up dead branches and leaves, making the new bear grass community more vigorous and prosperous.

Bear grass all over the mountains, picture from Wikipedia

Tuber rebirth: King protea

The King Protea (Protea cynaroides) is a national flower that is deeply loved by the people of South Africa. However, the Cape of South Africa where it takes root is not only dry and barren, but also ignites violent fires every ten or twenty years. Countless disasters over thousands of years have forced the King Protea to evolve a complete set of strategies for surviving fires.

They are always careful in their daily lives, transporting water and nutrients to the woody tubers (lignotuber) at the roots. The branches and leaves of the king protea may be completely scorched by the fire, but the woody tubers that are almost completely hidden in the soil can survive the fire. Relying on the large amount of water and starch stored, the many dormant buds on the woody tubers will quickly grow branches and leaves, and the lush king protea shrubs will magically be reborn from the ashes.

For the clever king protea, bushfires are also a good opportunity to spread seeds. Their seeds are wrapped in hard follicles, which often stay patiently on the branches for several years. When the flames burn the king protea, their wooden fruits will crack and fall everywhere due to the heat. When the rain moistens the thirsty wilderness, the moist fruits will gradually push out the seeds, and the seeds that have absorbed the rain water can germinate smoothly.

The beautiful king protea is a master of fire resistance. Photo from South African National Biodiversity Institute

Sowing seeds in the fire scene: Pine

The long-lasting seeds are not exclusive to the king protea. Many plants from fire-prone forests have evolved this trick called serotiny. Year after year, the twisted pine (Pinus contorta) in California, USA, will store pine cones on the top of the tree. Their tower-shaped pine cones secrete thick resin, which firmly wraps each scale, and the plump seeds remain dormant in isolation.

Once a devastating wildfire breaks out, the thin-barked twisted pine tree becomes a giant torch. The flames melt the solidified pine resin, and the scales on the pine cones open up, and countless winged pine nuts float away on the scorching air currents. After a few years, many adult twisted pine trees can no longer recover, but young pine trees have already thrived at their feet. With such a tragic replacement of the old with the new, twisted pine and several other pine trees have overcome wildfires, and even a unique "closed-cone pine forest" has grown in the coastal mountains of California.

Closed cones of twisted pine, image by Walter Siegmund CC BY-SA 2.5

Giant trees grow towards fire: Giant Sequoia

As an ancient tree with a lifespan of more than 3,000 years, the majestic giant sequoia (Sequoiadendron giganteum) can grow up to 100 meters high, with a circumference of more than 30 meters at the bottom of the trunk, and weighs the same as about 500 African elephants. The bark of the giant sequoia near the roots is 90 centimeters thick, and the bark sap contains rich tannins, which not only give the trunk a unique reddish-brown color, but also serve as a first-class natural flame retardant. For adult giant sequoias with thick skin and flesh, ordinary fires are just a tickle for them.

However, the seeds and seedlings of giant sequoias are quite fragile. In the first few years of their long life, if they do not get enough light and minerals, young giant sequoias will hardly escape the fate of withering and dying. Giant sequoias have to let most of their cones stay on the branches, and these cones will stay in the air for up to 20 years. Only when the airflow generated by the California wildfires reaches the crown of the tree, the cones baked by the heat will dry and open, allowing the giant sequoia seeds weighing only a few milligrams to fall lightly into the soil. At this time, the fire has swept away the shady shrubs, and the new generation of giant sequoias can enjoy the bright sunshine alone. Grow strong enough in the fertile ashes.

Spontaneous combustion helps future generations: Cistus

Cistus ladanifer, a leafy evergreen shrub from the western Mediterranean, bears pretty spotted flowers that resemble wild roses. Its stems and leaves are covered with a sticky, fragrant resin called labdanum, which is collected with a special brush and adds a distinctive amber note to perfumes.

Every year, rock roses produce a large number of fruits with hard wood shells. If the shells are not softened by high temperatures and lack the stimulation of chemicals in smoke, most of the rock rose seeds will remain dormant. Natural wildfires are rare, so rock roses have evolved the strange ability to "play with fire and get burned." In hot and dry summers, the resin on their stems and leaves will evaporate in large quantities, and spontaneous combustion may occur when the temperature exceeds 32 degrees Celsius. As rock roses are reduced to ashes by the raging flames, other shrubs and weeds around them will also be swept away. When the next heavy rain falls, countless rock rose seeds will wake up from their slumber and scramble to sprout new shoots in the empty land.

Rock rose that plays with fire and gets burned, photo by Alvesgaspar CC BY-SA 4.0

The Almighty Arsonist: Eucalyptus

Almost every hot dry season, fires and thick smoke rise from the Australian bush. In order to survive in such a desperate situation, self-pruning of branches and leaves at the bottom of the trunk, as well as woody tubers and crown seed banks are basic operations for many Australian eucalyptus trees. However, the countless dormant epicormic buds hidden deep in the bark are the most popular fire survival trick in the eucalyptus family. Under the tight protection of the outer bark, most epicormic buds will successfully survive the fire. These epicormic buds will be activated in the rainy season, allowing the charred eucalyptus trunks to send out countless new branches from root to tip.

What's even more bizarre is that eucalyptus trees are also a group of silent "arsonists". Whether fresh or withered, eucalyptus branches and leaves contain a large amount of eucalyptus oil with a low ignition point. Therefore, eucalyptus forests are prone to spontaneous combustion and will greatly contribute to the power of fire, thus becoming the culprit for the continuous spread of bushfires. However, often after a tragic fire, the tenacious eucalyptus trees quickly recover their vitality, while other types of tree communities are seriously injured. It is precisely relying on this reckless and fierce competitive strategy that eucalyptus trees eventually became the absolute overlord of the Australian jungle.

New branches sprouting from a burnt tree trunk, image from John O'Neill GFDL 1.2

After seeing so many unique ways of fighting fire by flowers, plants and trees, which one do you think is the most amazing? The survival wisdom evolved from generations allows many plants to escape safely even in a sea of ​​fire, and even use periodic fires to reproduce and grow their families. However, human intervention, intentional or unintentional, is likely to greatly change the rhythm and intensity of fires, putting even the plants that are best at dancing with fire in desperate situations. Is the raging fire in the wilderness a natural rebirth or an ecological disaster? Perhaps everything depends on our thoughts.

References:

[1]Vogts, M. 1982. South African's Proteaceae: know them and grow them. Struik, Cape Town.

[2]Rebelo, T. 1995. Proteas, a field guide to the proteas of southern Africa. Fernwood Press, Cape Town.

[3]Matthews, L. 1993. Protea Growers Handbook. Durban: Trade Winds Press

[4]Rourke, JP1980. The Proteas of Southern Africa by JP Rourke. Purnell. Cape Town

[5] Study on crown seed bank and its ecological significance. Journal of Ecology, 2005, (11)