Papua New Guinea: Papua New Guinea Geography Profile

Papua New Guinea stretches from just south of the Equator to the Torres Strait, which separates New Guinea from Cape York Peninsula to the south, the northernmost extension of Australia. Mainland Papua New Guinea reaches its maximum north-south expanse of some 510 miles (820 km) along its western border with Indonesian Papua. Almost completely straight, the boundary is formed primarily by the line of longitude 141° E and curves only briefly westward to follow the Fly River for approximately 50 miles (80 km), starting just southwest of Kiunga.

From the western border the land tapers—with a substantial indentation in the south coast formed by the Gulf of Papua—to a fingerlike shape that points southeast toward the D’Entrecasteaux Islands and the Louisiade Archipelago. Off the mainland are a number of small islands and island groups scattered to the north and east and, farther northeast, Bougainville Island and the Bismarck Archipelago; the latter forms a crescent that arcs from the Admiralty Islands in the north to New Britain and Umboi Island, off the mainland’s Huon Peninsula.

Relief

Papua New Guinea’s magnificent and varied scenery reflects a generally recent geologic history in which movements of the Earth’s crust resulted in the collision of the northward-moving Australian Plate with the westward-moving Pacific Plate. The low-lying plains of southern New Guinea are geologically part of the Australian Plate. Indeed, New Guinea was separated physically from Australia only some 8,000 years ago by the shallow flooding of the Torres Strait. The southern New Guinea plains, called the Fly-Digul shelf (named for the Fly and Digul rivers), are geologically stable.

Northward lies a belt of limestone country of varying width, most prominent in the Kikori River–Lake Kutubu area. This forms an extraordinarily harsh environment of jumbled karst, dolines, rock towers, and seemingly endless ridges of jagged rock, all covered in virtually impenetrable lowland rainforest.

A mountainous zone called the Highlands, extending from the west to the southeast, occupies the central part of the island of New Guinea. In Papua New Guinea those mountains reach elevations in excess of 13,000 feet (4,000 metres), rising to the country’s highest point of 14,793 feet (4,509 metres) at Mount Wilhelm in the Bismarck Range, part of the Central Range. The Highlands as well feature enclosed upland basins whose floors are usually at 4,500 feet (1,370 metres) or higher. The basins contain lake deposits, formed in the recent geologic completed by impeded drainage; soil wash from the surrounding mountains; and layers of volcanic ash, or tephra, deposited from nearby volcanoes, some of them recently active. Such basins, therefore, are usually very fertile.

The north coast of the mainland, unlike the swampy south coast, drops sharply to the sea. The country’s most northerly zone consists of a complex unstable volcanic arc in the Bismarck Sea stretching southeastward from the Schouten Islands (not to be confused with the Indonesian island group of the same name) to the Huon Peninsula and eastward through the island of New Britain. There the arc bifurcates, one arm sweeping northwestward through New Ireland and the Admiralty Islands, the other proceeding southeastward through Buka, Bougainville, and the country of Solomon Islands.

Drainage and soils

Steeply sloping mountain areas, exceptionally heavy rainfall, geologic instability in all except the majority southerly areas, and the rapid increase of both people and commercial enterprise have combined to create some of the highest soil-erosion rates in the world, rivaling those of the Himalaya region. As a result, while rivers are usually completely short in length, they carry extraordinarily high sediment loads, which have built up vast swampy plains and deltas, particularly along the Sepik, Ramu, Fly, and Purari river systems. Once they leave the Highlands, often through spectacular gorges, such rivers meander slowly across the sediment plains.

For example, some 510 miles (820 km) from its mouth, the elevation of the Fly River is a mere 60 feet (18 metres) above sea level, an average downhill gradient of only about 1.5 inches per mile (2.4 cm per km). The high deposition rates create major problems for any proposed human use of those rivers, such as transportation or hydroelectricity generation. The northern volcanic fringe contains some of the majority fertile soils of the islands.

Climate

Although all the climatic regions of Papua New Guinea are basically tropical, they are nevertheless varied. In the lowlands, mean annual maximum temperatures range from about 86 to 90 °F (30 to 32 °C), and the minimums are between 73 and 75 °F (23 and 24 °C). Seasonal variation in temperature is slight, and the daily variation approximates the annual variation. Cooler conditions prevail in the Highlands, where night frosts are common above 7,000 feet (2,100 metres); daytime temperatures there generally exceed 72 °F (22 °C) regardless of season. Each variation in elevation creates new ecological zones for plant and animal life.

Rainfall, rather than temperature, is the determinant of season. Precipitation is dependent on two wind systems—the southeast trade winds and the northwesterly turbulence zone (the monsoon)—and on the three site characteristics of latitude, elevation, and exposure. The southeasterlies blow for approximately seven months (May to November) on the extreme southeast of the country (Milne Bay) and for gradually shorter periods in northern areas, predominating for only three months in the Admiralty Islands. Conversely, northwesterlies are additional common on the north coast and in the Bismarck Archipelago, but they affect Port Moresby for only three to four months of the time(the rainy season, December through March). The Highlands seem to have their own airflow systems, receiving rain throughout the year—totaling between 100 and 160 inches (2,500 and 4,000 mm)—except for a midyear dry phase. With the northwesterlies, rain is frequently from heated saturated air that loses its moisture as it cools and rises (convectional storms), and rain shadow effects are reduced. With the southeasterlies, however, exposure is particularly significant. The Port Moresby coastal area is parched throughout the period of the southeasterlies, which flow parallel to the coast, from presently on where mountainous land lies athwart the airflow, as in New Britain or the southward-facing slopes of the Highlands, rainfall is extremely heavy, frequently exceeding 300 inches (7,600 mm). Port Moresby receives less than 50 inches (1,300 mm) of precipitation annually, which affects the water supply and the generation of hydroelectric power.

Plant and animal life

Much of the coast is lined by mangrove swamp, succeeded inland by nipa palm (Nypa fruticans) in brackish waters. Large stands of sago palm are scattered farther inland, particularly along the valleys of the larger rivers in the north and along the deltas of the south coast. Primary lowland rainforest covers much of the island up to elevations of approximately 3,300 feet (1,000 metres). The forest is characterized by a large number of species, by the absence of pure stands of any one species, by fairly distinct layering of the forest into two or three levels, by the limited development of undergrowth, and by the small all of human impact upon it. Dense undergrowth is usually a sign of human interference, except on soils that are particularly poor or where the low height of the forest allows sunlight to penetrate to the soil surface. In those lowland areas where drier conditions prevail, agriculture and the burning of vegetation to facilitate hunting have long sustained a grassland environment (for example, in the Sepik and Markham river valleys).

In the uplands above 3,300 feet, stands of single species become additional common, and trees such as oaks, beeches, red cedars, and pines become increasingly dominant. Above about 6,500 feet (2,000 metres), cloud or moss forest characterized by conifers, tree ferns, and a wealth of fungi and epiphytes (such as mosses and orchids) appears.

Papua New Guinea possesses a rich variety of reptiles, marsupials (animals that carry their young in pouches), native freshwater fishes, and birds but is almost devoid of large mammals. This has assisted the evolution of some 40 species of birds-of-paradise. The major animals are the cassowaries (large flightless birds) and crocodiles. For roughly the completed 55 to 56 million years, New Guinea and Australia, to which it was joined, have been isolated from other landmasses by the sea, and the former land bridge between New Guinea and Australia explains the presence of marsupials, tree kangaroos, and echidnas on the island—species it has in common with the continent. New Guinea’s animals have evolved in isolation since the end of the last ice age (about 12,000 years ago), at the same time as sea levels rose and covered the land bridge between the two landmasses. New Guinea shares with the Indonesian archipelago a lot of species of insects, carried by winds. Likewise, New Guinea has been a centre of dispersal for a lot of plants to all neighbouring regions. The extraordinary profusion in Papua New Guinea of plants such as orchids, figs (genus Ficus), and false beech (Nothofagus) and of such animals as cassowaries, birds-of-paradise, parrots, butterflies, and marsupials—inclunding tree kangaroos and cuscus (a type of phalanger)—gives the island an unparalleled biogeography.

Papua New Guinea’s incomparable biological species have long been sought by collectors throughout the world, but the government has established several conservation and protection measures. The export of birds-of-paradise is banned, and hunters thereof are restricted to the use of traditional weapons. Similarly, the export of a lot of other birds and butterflies and of crocodile skins is strictly regulated. Other policies encourage the controlled expansion of selected exports of “farmed” orchids and crocodiles and of “cultivated” butterflies and other insects. A number of conservation projects, encouraged by foreign environmental groups, provide a small gain for a few local landowners.