Last week, images from Assam dominated headlines. Floodwaters swept through Sivasagar, Jorhat and Charaideo, forcing thousands of families from their homes, swallowing farmland, damaging roads and bridges.
Not every flood has the same cause. Some are driven by intense rainfall, others by overflowing rivers, or upstream discharge.
But for centuries, the state’s tropical forests have evolved alongside these monsoon calamities, helping the landscape respond to some of the heaviest rainfall in the state by absorbing, slowing and redistributing water.
At the heart of this living system stands Hollong (Dipterocarpus macrocarpus), Assam’s state tree and one of India’s tallest native rainforest species. Hollong is also Assam’s oldest natural ally.
Over centuries of logging and habitat degradation, its population is estimated to have declined by 50 to 70%, leading the International Union for Conservation of Nature (IUCN) to classify it as Endangered. Photograph: (newsclick)
Even if no tree can stop a flood, forests dominated by native species such as Hollong perform functions that engineered structures cannot replicate. They can intercept rain before it reaches the ground, and improve the landscape’s ability to cope with extreme rainfall.
Growing up to 50 metres, it has evolved in one of the wettest regions in the country.
A tree built for rain
Hollong belongs to the Dipterocarpaceae family, the group of giant rainforest trees that dominates forests across Southeast Asia.
In India, it is native to the northeastern states, occurring naturally across Upper Assam, Arunachal Pradesh and parts of Nagaland.
The species thrives between 100 and 1,300 metres above sea level, where temperatures range between 22°C and 30°C and annual rainfall averages nearly 3,000 mm. These are landscapes shaped by long monsoon seasons, humid tropical conditions and flood-influenced ecosystems.
Its structure reflects that history.
Its immense height helps shape forest microclimates, creating cooler, more stable conditions beneath its canopy. Photograph: (Macaca77-Wikimedia Commons)
Deep root systems anchor the towering trunk in waterlogged soils during heavy storms. Large, leathery leaves rapidly shed sheets of rainwater, preventing fungal damage and reducing the weight that accumulates on branches during prolonged downpours.
After the monsoon, its winged seeds spin through seasonal winds, dispersing away from saturated ground to establish new seedlings.
A forest giant with many roles
Hollong is one of the dominant species in many of Assam’s remaining tropical evergreen forests, including Hollongapar Gibbon Sanctuary, Dehing Patkai, Nameri and parts of Kaziranga’s forested landscapes.
Beyond water regulation, Hollong supports an entire rainforest community.
Its immense height helps shape forest microclimates, creating cooler, more stable conditions beneath its canopy.
Even if no tree can stop a flood, forests dominated by native species such as Hollong perform functions that engineered structures cannot replicate. Photograph: (Facebook/Sanctuary Nature Foundation-Udayan Borthakur/ Debuapriyo- Wikimedia Commons)
The species also plays an important role in climate regulation. Dipterocarp-dominated forests are recognised globally for storing significant amounts of terrestrial carbon, making them important natural carbon sinks.
Why protecting Hollong matters
Despite its ecological importance, Hollong is under pressure.
Over centuries of logging and habitat degradation, its population is estimated to have declined by 50 to 70%, leading the International Union for Conservation of Nature (IUCN) to classify it as Endangered.
The threats are varied. Illegal felling, habitat fragmentation and the expansion of monoculture plantations continue to reduce native forest cover.
In Dehing Patkai and surrounding landscapes, conservationists have repeatedly raised concerns over habitat disturbance. In February this year, residents in Tinsukia alleged that nearly 95% of Hollong saplings planted under an afforestation project in Nalani Reserved Forest had been destroyed, renewing concerns over the long-term future of the species.
Hollong is not a solution to floods, but its future is inseparable from the forests that continue to intercept rain, anchor soil and sustain life across the Brahmaputra valley. It is a species that is rooted in flood-influenced landscapes and central to forests that have evolved over centuries to respond to the monsoon.
