A living carpet of moss
The Phou Dendin summit peatland is an ecosystem built by generations of Sphagnum moss. This genus of bryophytes, with around 300 species worldwide, is the principal architect of peat bogs. Sphagnum thrives in wet, nutrient-poor conditions. The moss itself creates these conditions. Its leaves have large, dead hyaline cells that absorb and hold vast amounts of water, making the ground permanently saturated.
This waterlogged environment is low in oxygen, which slows decomposition to an extremely low rate. As new moss grows on top and older layers die, they do not fully decay. Instead, they become compacted over centuries, forming dense layers of peat. Sphagnum also acidifies its surroundings by releasing hydrogen ions, further inhibiting the bacteria and fungi responsible for decomposition. This process of accumulation allows the peatland to grow, preserving organic matter like pollen and spores within its layers. In Southeast Asia, most peatlands began forming after the last glacial period, which ended around 11,000 years ago.
A remote montane island
The peatland sits within the Phou Dendin National Protected Area, a remote, 2,200-square-kilometer reserve in Laos's northernmost province, established in 1993. The park's terrain is rugged, with elevations ranging from under 500 meters in the river valleys to peaks exceeding 1,800 meters. The summit peatland exists in this high-elevation zone, a cool, moist island with temperate flora like rhododendrons, oaks, and magnolias, unlike the subtropical forests below.
This area is one of the least explored protected regions in Laos. Its unique position at the junction of the Indo-Burmese and Sino-Himalayan biogeographic zones contributes to its distinct biodiversity. While specific bryophyte surveys of the peatland are limited, the park hosts a wide array of wildlife. Mammals include the critically endangered northern white-cheeked gibbon (Nomascus leucogenys), Asiatic black bears, and gaurs. The forest also supports over 200 bird species. The peatland's isolation and the park's general inaccessibility have helped preserve its condition, though the broader area faces threats from illegal logging and poaching.