The New Guinea rainforest covers most of New Guinea, the world’s second-largest island (785,753 km²), which lies just north of Australia and is split between Papua New Guinea in the east and six Indonesian provinces in the west. It is the third-largest remaining rainforest on Earth after the Amazon and the Congo, and the island has more vascular plant species than any other: a 2020 study by a team of 99 experts counted 13,634. The forest runs in an unbroken sequence from equatorial glaciers on Puncak Jaya (4,884 m) through moss-hung cloud forest and lowland jungle to some of the largest mangrove stands in the world, and it is home to birds-of-paradise, tree-kangaroos and cassowaries found almost nowhere else. The clearest way to understand it is to follow the water downhill to the sea.
Puncak Jaya, the Tree Line and the Central Range
A spine of mountains, the New Guinea Highlands, runs more than 1,600 km along the island, with many peaks above 4,000 m. The highest is Puncak Jaya, also called Carstensz Pyramid, in the Sudirman Range of Indonesia’s Central Papua province. At 4,884 m (16,024 ft) it is the highest island peak on Earth and the highest point between the Himalayas and the Andes. The Dutch navigator Jan Carstenszoon reported seeing snow on it in 1623 and was ridiculed in Europe for claiming there was ice so close to the equator. The ice is real but shrinking: the summit itself is now bare rock, and the glaciers on its slopes have been retreating since at least 1936.
The tree line sits at about 4,000 m. Above it are alpine grassland and tundra; below it the forest begins, and from there almost every drop of rain that falls on the range feeds one of two great river systems. Northern rivers run to the Pacific, the largest being the Mamberamo, Sepik and Ramu. Southern rivers, among them the Digul, Fly, Kikori and Purari, drain into the Arafura Sea and the Gulf of Papua. The highlands are not empty wilderness, either. When Richard Archbold flew over the Grand Valley of the Baliem River on 4 August 1938, he found about 50,000 farmers living in orderly villages that European maps had shown as uninhabited forest.
In the Indonesian west the range rises out of Lorentz National Park, which covers 25,056 km², is the largest national park in Southeast Asia, and UNESCO inscribed it on the World Heritage List in 1999. It is the only reserve in the Asia-Pacific region that contains the full sequence of ecosystems from marine waters, mangroves and swamp forest through lowland and montane rainforest to alpine tundra and glaciers. Researchers have documented 630 bird species and 123 mammal species there, including the dingiso, a black-and-white tree-kangaroo that science only described in 1995.
Cloud Forest: Moss, Tree Ferns and Tree-Kangaroos
Below the grasslands lies montane rainforest, which the WWF divides into several ecoregions: the Central Range montane rain forests, the Huon Peninsula montane rain forests, the Northern New Guinea montane rain forests and the Vogelkop montane rain forests at the island’s western tip. Tree ferns and mosses are common here, and southern-hemisphere conifers such as Podocarpus, Araucaria and Agathis grow beside tropical hardwoods. Rainfall in parts of the highlands reaches as much as 10,000 mm a year.
This is the realm of the tree-kangaroos, the genus Dendrolagus, marsupials adapted for climbing. They occur in the rainforests of New Guinea and far north-eastern Queensland, and most species are threatened by hunting and forest loss. Matschie’s tree-kangaroo, a chestnut-and-gold species native to the Huon Peninsula of Papua New Guinea, has been listed as endangered since 1996. In 2009 the YUS Conservation Area was established to protect its habitat; YUS covers about 760 km² and takes its name from the Yopno, Uruwa and Som rivers that cross it.
New Guinea’s mammals are overwhelmingly Australian in origin. The island and Australia sit on the same continental shelf and were joined as a single landmass, Sahul, whenever Pleistocene ice ages lowered the sea; today the Torres Strait between them is about 150 km wide. That shared past explains why the island has marsupials and egg-laying echidnas but, apart from bats and rodents, no native placental mammals. Of its 284 mammal species, 195, or 69%, are found nowhere else.
Birds-of-Paradise in the Mid-Mountain Forest
Lower down, in the mid-mountain and hill forests, live the birds-of-paradise. The family Paradisaeidae has 44 species in 17 genera, found mainly in New Guinea with a few in eastern Australia and the Maluku Islands. The males of most species are known for elaborate plumage, which they show off in ritualised courtship, and at least eight species gather to display at leks. Specimens reached Europe in the early 16th century, and plume hunting for European hats was extensive around 1900.
The Raggiana bird-of-paradise, known locally as kumul, is widespread in southern and north-eastern New Guinea and is the national bird of Papua New Guinea. In 1971 it was made the national emblem and placed on the national flag. Across the whole island there are 578 breeding bird species, 324 of them endemic, along with the flightless cassowaries of the lowland forest. Plant life is even richer. The 2020 census of New Guinea’s flora placed the island ahead of every other island on Earth.
Down the Sepik and Mamberamo to the Pacific
On the north side, the Sepik is the longest river on the island, at about 1,100 km. It rises in the Victor Emanuel Range near Telefomin, leaves the mountains near Yapsei, makes a short loop into Indonesian Papua and then turns north-east along a broad lowland trough called the Central Depression. It meanders through swamp forest and, unusually for a big river, has no delta at all: it flows straight into the Bismarck Sea about 100 km east of Wewak. The Sepik basin is often called perhaps the largest uncontaminated freshwater wetland system in the Asia-Pacific region, and the river is navigable for most of its length.
Further west, in Indonesian Papua, the Mamberamo forms where the Tariku and Taritatu rivers meet in the Lakes Plains, an interior basin of freshwater swamp forest. It then cuts north through gorges between the Van Rees Range and the Foja Mountains. The Foja forest tract covers 9,712 km² and is the largest roadless tropical forest in the Asia-Pacific; the mountains have no recorded visitors before 1979 and rise to 2,193 m. These northern lowlands form another WWF ecoregion, the Northern New Guinea lowland rain and freshwater swamp forests.
The Fly River, Ok Tedi and the Southern Swamps
The southern lowlands are wider and wetter still. The Fly River, 1,060 km long, rises in the Star Mountains near the border and crosses Papua New Guinea’s Western Province to the Gulf of Papua. It carries more water than any other river in Oceania and is the largest river in the world with no dam anywhere in its catchment. With its longest tributary, the 824 km Strickland, the Fly–Strickland system is 1,224 km long. Its funnel-shaped delta is more than 100 km wide at the sea, with sand-and-mud islands held together by mangroves.
The Fly also shows how fragile this system is. In 1984 an earthquake brought down the half-built tailings dam at the Ok Tedi copper and gold mine, near the river’s headwaters, and for decades the operators then dumped mine waste straight into the Ok Tedi River. About two billion tonnes of untreated waste spread along roughly 1,000 km of the Ok Tedi and Fly. Around 1,588 km² of forest has died or is under stress, and the lives of about 50,000 people downstream have been disrupted. BHP Billiton handed its majority share to a Papua New Guinea development fund in 2002 and left the project.
West of the Fly, the Digul, which rises in the Star Mountains, is the largest river of the island’s western half. These southern lowlands of mangrove, tidal and freshwater swamp forest are home to fishing and gathering peoples such as the Asmat. The southern ecoregions, the Southern New Guinea lowland rain forests and freshwater swamp forests, grade into mangroves near the sea and, on both sides of the border in the monsoonal south, into the Trans-Fly savanna, grassland with Eucalyptus and Melaleuca woodland that resembles northern Australia.
Papua New Guinea and Indonesian Papua: One Forest, Two Countries
The island’s border runs mostly along the 141st meridian east, bending briefly where the Fly River forms the boundary. To the east, the mainland of Papua New Guinea, governed from Port Moresby, holds the Sepik, the Fly and the Huon Peninsula. To the west, Western New Guinea is part of Indonesia and is divided into six provinces: Papua, Central Papua, Highland Papua, South Papua, Southwest Papua and West Papua, with Jayapura the largest city. Satellite data for 2020 showed that the Indonesian west held about 54% of the island’s primary forest and about 51% of its total tree cover.
The forest ignores the frontier. The Sepik starts in Papua New Guinea, crosses into Indonesia and comes back; the Fly briefly forms the border, and under the boundary deal Indonesia keeps the right to navigate it to the sea.
Logging and Palm Oil: What the Forest Is Losing
Papua New Guinea lost 1.57 million hectares of tree cover between 2001 and 2020, a 3.7% decline since 2000, according to the figures cited by Wikipedia’s article on deforestation in the country. Western Province, home to the Fly, lost the most of any province, about 205,000 hectares. Illegal logging is the main driver: it has been estimated to account for 70–90% of the country’s timber exports, one of the highest rates in the world. In 2012 less than 6% of the country’s forests were independently verified or certified.
On the Indonesian side, the listed threats are logging, conversion of forest to plantations including oil palm, and smallholder clearing, and the Trans-Papua Highway is expected to open large areas of rainforest to logging. Under a 2010 deal with Norway, Indonesia declared a two-year moratorium on new logging concessions on 20 May 2011 and extended it in 2013. Analysis of 2024 satellite data still reported localised increases in primary forest loss in Papua.
Even so, much of the island remains intact, and much of it is still unexplored. Between 1998 and 2008 scientists described 1,060 new species from New Guinea, and between 2011 and 2017 they added another 465 plants. To see how New Guinea compares with the other great tropical forests, read our guide to the Borneo rainforest, or look at the mountain that sits at the top of this one in our profile of Puncak Jaya. For the eastern half of the island as a nation, our Papua New Guinea country guide covers its people, provinces and capital.