[Ko Gyu-hong's Trees and People] What Am I Supposed to Do with This Heart That Cannot Live Apart

<14> The Tree's Special Survival Method - Yeonri (連理)

Goh Kyuhong, Tree Columnist.

Earth was formed 4.5 billion years ago, and after a billion years of silence, life was born on Earth. Over a period too long for humans to perceive, life evolved into various forms. While new forms of life emerged, some once active life forms quietly disappeared. We call this entire process of change and diversification of life ‘evolution.’

In evolutionary biology, seven principles govern the process of life’s evolution: variation within populations, persistence, reinforcement, competition, cooperation, combinatorial richness, and repetition. These principles interact harmoniously, resulting in the biodiversity we see before us today.

Trees That Cannot Choose Their Own Place to Live
Cooperation as Important as Competition in Evolution

The intertwined branches of the Zelkova tree and pine tree standing at the entrance of Gyesiri Village, Yeongdeok.

In the harsh reality of human life, the most prominent principle of evolution is ‘competition.’ This applies to our livelihoods, and trees also survive through fierce competition with other living beings around them. Living beings are often considered ‘selfish’ because they strive to survive within the principle of ‘competition.’ However, cooperation is an equally important principle of evolution. Nature always rewards cooperative organisms.

Trees are wise organisms that, when faced with extreme competition threatening their survival, abandon competition and switch to cooperation, gaining remarkable rewards. Observing the living space of trees, which require a certain distance from each other, reveals their meticulous and clever survival strategies.

Trees need a certain distance between each other. Not only trees but all living beings require a space suited to themselves. We have painfully realized through the COVID-19 pandemic how harsh the consequences of losing ‘social distancing’ can be. However, in human society, we currently believe that social distancing is not as urgent as other factors. But this applies to humans who are less than 2 meters tall and live less than a century at most. For trees that can grow over 30 meters tall?more than fifteen times a human’s height?and live for a thousand years, the situation is entirely different.

Trees need space to spread their branches and open areas that do not block sunlight. The distance between trees is far more critical than social distancing among animals because trees cannot move to find their own space. Trees that fail to secure a certain distance cannot properly enjoy even minimal life and inevitably perish. For example, a ginkgo or zelkova tree standing alone in a wide field can live for over a thousand years, whereas trees densely packed in a forest typically live only about 200 to 300 years for this reason.

Trees that cannot choose their own place must remain fixed in the spot assigned by nature for their entire lives. Sometimes, they encounter competitors they did not anticipate at first. While young, neighboring trees do not interfere with each other’s survival, over time, nearby trees become obstacles that block branch expansion and cast shadows over leaves, hindering photosynthesis.

If trees do not harmonize with their neighbors in some way, disaster is inevitable. If they persist in selfish competition, their survival itself may be threatened. Trees seek ways to live together with neighboring trees they once competed with. This is a survival strategy to gain rewards by shifting from a competitive system to a cooperative one.

Intertwined Branches Known as Yeonri
Yeonrimok and Yeonrigeun with Joined Trunks and Roots
Different Species of Trees Sometimes Join

The Yeongju Eumnaeri Yeolliji Pine is correctly called Yeollimok because its trunks are grafted from the lower part, but it has long been referred to as Yeolliji.

Trees have a very special way of cooperating called Yeonri (連理). Yeonri is a unique form of cooperation where neighboring trees become one body. It is not a common phenomenon, but neither is it extremely rare. Yeonri is generally divided into three types: Yeonri-ji, Yeonrimok, and Yeonrigeun. All refer to trees growing close together and physically joined. Yeonrigeun refers to roots joined underground, Yeonrimok to trunks joined from the root upward, and Yeonri-ji to branches fused together.

The most visually astonishing phenomenon is Yeonri-ji, where branches of separate trees meet and perfectly merge, making it impossible to distinguish their origins. It is truly mysterious. Yeonrimok refers to trunks joined together, where the trunks rising from the roots are completely fused from the bottom up. This is not just a visual connection but a complete merging of tissues, requiring detailed examination to confirm. Yeonrigeun, where roots intertwine underground, is difficult to verify without expert knowledge.

The cedar inosculation at Yakushima Temple in Japan, where the stem part rising from the root forms one body.

Yeonrimok and Yeonri-ji often come with various legends and stories due to their mysterious appearance. Especially since two trees become one body, many stories relate to the process of two lovers becoming one, symbolizing love. Sometimes, Yeonri-ji is used as a metaphor for love. For example, the Tang Dynasty poet Bai Juyi (Baekgeo-i) in his poem "Changhen Ge" (The Song of Everlasting Sorrow), which satirizes the love between Emperor Xuanzong and Yang Guifei, compares their love to Yeonri-ji: "On the seventh day of the seventh month at Changsheng Palace / A secret promise made in the deep night / In heaven, they wish to become a pair of flying birds / On earth, they wish to become Yeonri-ji."

It is common to find stories that making a wish near Yeonrimok or Yeonri-ji, or circling them several times like a Buddhist pilgrimage, will make love come true. Regardless of whether wishes are fulfilled, slowly circling around Yeonri-ji and observing the mysterious phenomenon of cooperative trees is a delightful experience in itself.

The Spectacular Bija Tree in Pyeongdae-ri, Jeju
The Twisting Pine Tree in Eumnae-ri, Yeongju, Gyeongbuk
Expressed as Symbols of Love Since Ancient Times
A Beautiful Lesson for a Society of Infinite Competition

The trunk part of the connected trunks of the nutmeg trees standing in the 800-year-old natural primeval forest, Bijanamu Forest in Pyeongdae-ri, Jeju.

In the mountains and fields of Korea, trees forming Yeonri can be found not infrequently. Among the well-known Yeonri-ji and Yeonrimok, the most spectacular is the Bija tree Yeonrimok in the Bija tree forest of Pyeongdae-ri, Jeju. This enormous Bija tree, whose age is difficult to estimate, is nicknamed the ‘Love Tree,’ and like other Yeonri-ji, there is a story that circling the tree with a loved one will make love come true.

The Yeonri-ji pine tree standing on the grounds of the Sunheung-myeon office in Eumnae-ri, Yeongju, Gyeongbuk, is also a magnificent tree not to be missed. This pine tree, over 200 years old, has two trunks twisting upward like dragons, meeting in midair to become one body, creating a mysterious spectacle.

Most Yeonri phenomena occur between trees of the same species, but sometimes different species form Yeonri-ji. For example, in Gyesi-ri, Yeongdeok-gun, Gyeongbuk, there is a Yeonri-ji formed by a hackberry tree and a pine tree. However, when different species form Yeonri-ji, detailed observation is necessary to determine whether the tissues are truly joined or if the connection is only external.

Whatever the form, trees must live for long years continuously spreading their branches, making them wise organisms that harmonize the two opposing life principles of competition and cooperation. This is the life principle that has allowed trees to survive peacefully on this land for a long time.

In a society of infinite competition, especially when selfish competition that bites and ultimately kills the opponent seems to be the only way to survive, looking at the cooperative lifestyle of trees encourages us to live more beautifully through cooperation strategies.

Ko Gyu-hong, Tree Columnist.