The park rises from 750 meters at its lowest to 3,064 meters at Mouling Peak, compressing an extraordinary range of ecosystems into a relatively compact area. Tropical forests blanket the lower slopes, thickening into dense canopy fed by 2,343 millimeters of annual rainfall with no defined dry season. As elevation increases, the forest transitions through subtropical and temperate zones until, above 2,800 meters, the vegetation takes on a distinctly temperate character. The Siyom River traces the park's western edge, while smaller rivers - the Siring, Krobong, Semong, and Subong - drain eastward into the Siang. This vertical compression of biomes from steaming lowland to frost-bitten ridge makes Mouling a transition zone between South and Central Asia's ecological worlds, and it has earned the park its reputation as Arunachal Pradesh's cradle of biodiversity.

The species list reads like a catalog of the eastern Himalayas' most compelling fauna. Bengal tigers prowl the lower forests. Indian leopards hunt across multiple elevation bands. The takin, a massive goat-antelope found nowhere outside the eastern Himalayas and adjacent ranges, browses the upper slopes alongside the goral and the serow, two other mountain ungulates adapted to near-vertical terrain. Red pandas occupy the temperate bamboo forests at higher elevations. Barking deer move through the understory. Each species occupies a niche defined by altitude, and the park's extreme elevation range means that an animal walking from the lowest valley to the highest ridge would pass through the territories of predators and prey adapted to entirely different climatic conditions. The park's inaccessibility, which frustrates researchers, also serves as its most effective form of protection.

Mouling's isolation is not an accident of neglect but a fact of geography. The nearest major towns, Along and Pasighat, are 130 and 185 kilometers away respectively. The nearest airfield sits at Along. No road penetrates the park interior, and communication facilities remain poor. The Forest Department manages the park from offices located entirely outside its boundaries, organized into two ranges: the Ramsing range, accessible from Bomdo village, and the Jengging range, accessible from Lissing village. The park's borders were drawn by aerial survey using natural features like the Siyom River and artificial boundaries, but on-ground demarcation remains incomplete. In practical terms, this means that the park exists more as a concept on maps than as a managed space on the ground. Rangers patrol what they can reach, and the forest does the rest.

Mouling does not stand alone. Together with the Dibang Wildlife Sanctuary, it forms part of the Dihang-Dibang Biosphere Reserve, a protected area that encompasses some of the most biodiverse terrain in the eastern Himalayas. The biosphere concept matters here because it acknowledges what the park's inaccessibility makes obvious: protecting this landscape requires thinking beyond administrative lines. The rivers that drain Mouling feed into the Siang, which becomes the Brahmaputra, connecting this remote park to one of Asia's great river systems. At low altitudes, temperatures swing between 15 and 38 degrees Celsius. At the high ridges, winter brings snow and temperatures drop to 4 degrees. Between those extremes lies a living laboratory of species interactions that scientists have barely begun to document, in a park that remains, for now, more wild than known.