Vietnam is proud to have a 700-year-old "spiritual treasure", the only two countries in the world that possess it.

Known as "Ha Long on land", Ben En National Park, covering 15,000 hectares in the two districts of Nhu Xuan and Nhu Thanh (Thanh Hoa), is considered a fertile land with beautiful landscapes and rivers.

Not only is it home to an extremely diverse and rich flora and fauna ecosystem, it also possesses immense green primeval forests and a lake of nearly 3,000 hectares.

Many people may not know that in Ben En National Park, there is a 'spiritual treasure' that is highly valued and protected by local people. It is an ancient green lim tree, nearly 700 years old. Not only is it a treasure of the great forest, a spiritual treasure of the people of Thanh, the green lim tree is also recognized by the State as a Vietnamese Heritage Tree in 2022.

According to the records of the Vietnam Association for Conservation of Nature and Environment (VACNE), the green lim tree in Ben En National Park is 688 years old this year, nearly 30 meters high, with a canopy diameter of about 20 meters and a circumference of about 6 meters.

After nearly 7 centuries, the green lim tree still stands tall in the forest. This individual is not only rare in Vietnam but also a true treasure in the world. The Red Book of the International Union for Conservation of Nature (IUCN) states that the green lim tree currently only grows in 2 countries, Vietnam and China, in humid tropical rainforests, at an altitude of about 800 meters above sea level.

This partly explains why many people consider this nearly 700-year-old tree a treasure representing freshness, longevity, and prosperity. A recent article in Tien Phong newspaper said that local people consider this green lim tree a spiritual treasure that protects peace, brings happiness, and prosperity to everyone.

Therefore, to protect this ancient tree, Ben En National Park established a control station, sending station staff to regularly patrol to protect this individual in particular from illegal loggers. Not only is this tree species valuable, it is also very rare. According to the IUCN Red List, green lim (scientific name: Erythrophleum fordii) is classified as EN - Feared of extinction.

Because of its many outstanding characteristics in terms of wood and folk medicine, green lim wood has been overexploited in the wild, leading to the risk of complete disappearance in the wild. Currently, the number of mature individuals of green lim is on the decline. However, under the conservation efforts of green lim of Ben En National Park, young individuals are being carefully cultivated.

According to IUCN, green lim is a very valuable timber species. The easily recognizable characteristics of green lim wood are brown, shiny wood, fine and tight grain, and especially very hard, can resist termites, and is very resistant to wood fungus.

A scientific article published in Wood Science Magazine (of the Japan Wood Research Association) in 2018 said that due to its superior wood quality, green lim is classified as the most durable wood in Vietnam, belonging to the Tu Thiet group (4 precious woods), including dinh, lim, sen, tau.

The outstanding feature of green ebony wood comes from its resistance to two famous wood fungi: white rot fungus Phanerochaete sordida and Phanerochaete chrysosporium (which can destroy lignin, cellulose and hemicellulose in wood).

By observing with a microscope, scientists discovered the high structural hardness of green lim wood. Green lim wood fibers include thick-walled fibers that are highly lignified with almost completely closed fiber lumens. When using the Fourier Transform Infrared Spectroscopy (FTIR) method combined with 2D Nuclear Magnetic Resonance (NMR), it was discovered that green lim wood has a highly condensed lignin structure reflected through the durability layers.

These unique parameters play an important role in the high natural disease resistance of green teak, making it a wood of high economic and historical value.

Thanks to its outstanding characteristics, green lim wood was previously often used to produce boats, high-class furniture, floors, sculptures and handicrafts. Not only that, a surprising discovery is that green lim also appears in many historical works in Vietnam.

Wood Science magazine reported that wooden artifacts excavated from archaeological sites in Vietnam such as Thang Long Imperial Citadel (Hanoi capital); or at Bach Dang Stake Site (Quang Yen, Quang Ninh province) have been identified as green lim wood.

At the Bach Dang Stake Site, archaeologists found sharpened wooden stakes, 2.6 to 2.8 m long and 20-30 cm in diameter. Surprisingly, although these wooden artifacts were buried for hundreds, even thousands of years underwater, the level of green lim wood was very limited.

The disappearance of the wood surface layer is limited to the outer 1-2 cm. When scientists observed, chemically analyzed, and mechanically tested these thousand-year-old green ironwood artifacts, they found no significant differences between the excavated wood and modern wood.

Thus, the stake field at Bach Dang River (with most of the stakes made of green ironwood) became an important historical document, a place to preserve the glorious feats of our nation against invaders thousands of years ago.

According to wood scientists, although further testing and research is still needed, the antifungal properties of green ironwood are due to the high concentration of lignin as well as the tightness of the wood fibers inside the tree trunk. This explains why green ironwood can survive underground for centuries, even a millennium.

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