Living root bridges of Meghalaya

Most bridges are made of wood, stone or steel.

But in Meghalaya, some bridges are alive! They are made of tree roots. People walk across them to reach their farms and villages.

Meghalaya is a state in northeast India. Its name means "abode of the clouds." It is a hilly plateau cut by deep, steep valleys, where rivers rush down toward the plains of Bangladesh.

In these valleys, villagers of the Khasi and Jaintia communities have found a way to cross the rivers: they grow bridges from the roots of living trees. In this topic we find out how a root bridge is grown, why it gets stronger with time, and how communities look after them.

Meghalaya, a state of northeastern India since 1972, bordered by Assam and Bangladesh, occupies a mountainous plateau, a detached block of the Deccan plateau, with summits of 1,220 to 1,830 m. Its name combines megha, "of the clouds," and alaya, "abode." Many rivers flow off the plateau through deep, narrow valleys, and the southern faces overlooking the Bangladesh lowlands are particularly steep. Khasi, Garo, Jaintia and English are the official languages; Khasi is a Mon-Khmer language.

In the Khasi and Jaintia Hills, villages have long crossed these valleys on bridges grown from the aerial roots of the India rubber tree, Ficus elastica. Early 19th-century published accounts describe such bridges near Cherrapunji. This topic follows a 2019 survey in Scientific Reports by Ludwig, Middleton and colleagues, India's 2022 UNESCO Tentative List entry and Britannica.

In Meghalaya, the rain can pour down for months.

The rivers fill up and rush very fast. Wooden bridges can rot or wash away. A bridge made of living roots can last much longer.

Meghalaya is home to some of the rainiest places on Earth. Cherrapunji gets about 11,430 mm of rain in an average year, mostly between May and September. That is about five times as much as Shillong, the state capital, only 80 km away.

In the monsoon, rivers swell and rush through the valleys. Bridges of bamboo or wood rot and can be swept away, and steel or concrete ones are expensive to build and keep up. Living roots offered villagers another way across.

Britannica gives Cherrapunji an average annual precipitation of about 11,430 mm, falling mostly in the May to September monsoon, and notes that Mawsynram, directly to the west, has recorded totals of some 17,800 mm in a year; Shillong, about 80 km away, receives about 2,290 mm. Winters, December to February, are relatively dry.

Ludwig and colleagues describe the problem the bridges solve: isolated villages must cross rivers swollen by the monsoon, where bamboo or wooden bridges rot and are easily swept away, and steel or concrete structures are expensive, need outside investment and maintenance, and rust quickly. India's Tentative List entry describes the bridges as connectivity and disaster-resilience structures in more than 75 villages in and near the wettest region on Earth, letting people reach farms and markets through the rainy season.

First, someone plants a young rubber fig tree by the stream.

When it is big, roots hang down from its branches. People wind the roots along a bamboo frame. Slowly the roots reach the other side.

Growing a root bridge starts with a young rubber fig tree planted on one bank of a stream. When the tree is grown, it sends out aerial roots, roots that grow down through the air from its branches.

Villagers wind these roots onto a frame of bamboo stretched across the stream and guide them toward the far bank. There the roots are planted in the soil. They tighten, thicken and send out new roots, which are trained in the same way. Bit by bit, over many years, a bridge forms.

Ludwig and colleagues describe the usual method. A cutting of Ficus elastica is planted on one bank. Once the tree is mature, its aerial roots, which normally hang vertically from the branches, are wound onto a deadwood framework, mainly bamboo, and directed horizontally across the river. When they reach the far bank they are implanted in the soil, after which they shorten, thicken and produce daughter roots, which are trained the same way.

The Tentative List entry divides the community process into four interconnected stages: visioning, siting, planting and nurturing. Handrails, a second deck or supporting struts can be added. Because the work continues for decades, generations of builders contribute, rarely to a single consistent plan, and the time to full use depends on span, sunlight, nutrients and water: one bridge surveyed was still not fully functional after 66 years of growth.

A wooden bridge gets weaker as it gets old.

A root bridge gets stronger! Its roots keep growing thicker. Where two roots touch, they grow together into one.

Living roots behave very differently from dead wood. Once the roots are anchored on both banks, they pull tight and keep thickening as the tree grows.

Where roots are twisted or knotted together, they press against each other and slowly fuse, growing into one. This joining is called inosculation. It turns a loose net of roots into a strong, connected structure. Some bridges are thought to be several hundred years old, and people in Nongriat village estimate that their bridge is about 200 years old.

Ludwig and colleagues point to two processes. Roots may respond to load with adaptive secondary growth: horizontally trained roots differ significantly in shape and cross-sectional area from vertical ones of about the same age, and inverted-T cross-sections were found only in horizontal roots. After anchoring, aerial roots of strangler figs are known to produce tension wood for a time, which contracts them; in the bridges, neighboring roots come under tension, are pressed together at knots and crossings and begin to inosculate, forming natural grafts until the joints become a smooth, unified whole.

The 2015 to 2017 survey documented inosculations in 48 bridges, both nodal joints where roots cross or are knotted and linear joints where roots are twisted together along their length. The paper reports that some bridges are several hundred years old; residents who maintain the Nongriat bridge estimate it at about 200 years. Ludwig and colleagues call the bridges the only known example of repeated, predictable use of tree growth for structural purposes.

People also grow ladders and steps from roots.

Some root structures hold up the soil on steep hills. Families and neighbors work together to look after them.

Not every living root structure is a bridge. People in Meghalaya have also grown ladders, steps, platforms and towers, and root structures that hold steep slopes in place to stop landslides.

The rubber fig tree was useful in other ways too. Its sticky latex, a milky sap, was used to make things waterproof. Bridges in clusters around villages are mostly well looked after, while many lone bridges scattered through the hills have been left untended.

Recent studies cited in the Tentative List entry have found a range of living structures beyond bridges: ladders, platforms, towers, steps, and erosion and landslide prevention structures. Bridges, ladders and steps provide reliable transport, especially in the monsoon; platforms and towers serve recreation and security; slope structures stabilize soil. The trees were also tapped for latex (caoutchouc), used for waterproofing and hunting.

Maintenance is social. The survey found that nearly all the bridges it mapped lie in rainforest valleys, most between 250 and 900 m above sea level, some in clusters around villages and others dispersed through the region; most clustered bridges are well maintained, while many dispersed ones are untended. The entry places the practice within Khasi systems of village governance, land and forest classification and collective cooperation.

People around the world admire these bridges.

India wants them to become World Heritage. That would help protect the bridges and the skills to grow them.

In 2022, India added the living root bridge landscapes of Meghalaya to its Tentative List for UNESCO World Heritage, a first step toward asking for them to be named World Heritage.

The request says many bridges are healthy and still used, but some are at risk as roads and ways of life change. Plans include a conservation cooperative that involves the villages, so communities keep growing, using and caring for their bridges.

The Permanent Delegation of India submitted "Jingkieng jri: Living Root Bridge Cultural Landscapes" to UNESCO's Tentative List on 17 February 2022, under cultural criteria (i), (iii) and (vi), listing sites across dozens of villages. It proposes a phase-wise serial nomination in which each Ficus structure forms a core zone, with its village and catchment as the buffer.

The entry notes that a significant number of bridges remain healthy and in traditional use, but that recent infrastructure development and socio-economic change threaten some sites, to be addressed through zone-based conservation rules and a nature-based conservation cooperative for the villages. A Tentative List entry is an inventory of possible future nominations, not an inscription; the sources opened for this topic do not report a nomination or inscription.