Introduction

Weitin River valley, New Ireland, Papua New Guinea. (Photograph by Jim Mori)

Like the lowland rain forests, the montane forests of New Britain and New Ireland are rich in endemic species. However, unlike the lowlands, the karst topography of the montane forests is too steep for plantations. The montane forests therefore are relatively intact yet under increasing threat of being logged or degraded as a result of increasing populations.

Location and General Description

The narrow Vitiaz Strait separates the Huon Peninsula of northeastern New Guinea from the island chain known as the Bismarck Archipelago, which is dominated by two islands: New Britain and New Ireland (both exceed 400 kilometers (km) in length). The montane rain forests ecoregion includes the mountainous regions above 1,000 meters (m) of New Britain and New Ireland. New Britain and New Ireland are both long and narrow and contain several mountain ranges that trap rainfall. The climate of the ecoregion is tropical wet but varies in amount of average annual rainfall from about 3,000 to more than 6,000 millimeters (mm).

Despite the close proximity of the Bismarck Archipelago to New Guinea and the existence of small islands that appear to be the remnants of a land bridge, the island archipelago was never connected to the mainland. The islands breached the ocean surface in the late Miocene (8-10 million years ago) as the result of volcanic uplift, and many active volcanoes still exist (particularly on New Britain). Most of the islands are made up of both volcanic (acidic) soils and limestone. Limestone makes up 30 percent of New Britain and nearly 40 percent of New Ireland, or the entire northern half. The mountain ranges on New Britain and New Ireland often are isolated from each other by lowlands. The key mountain ranges of New Britain are the Whiteman, Nakanai, Baining, and Willaumez ranges. Key ranges in New Ireland are the Hans Meyer, Verron, and Lelet ranges.

The boundary between lowland and montane vegetation is gradual and placed at different altitudes by various authors. The discrepancies arise because the authors look at combinations of changes in forest structure, species composition, and degree of cloud cover. The boundary for the ecoregion is 1,000 m, marking a point of transition where the height of the forest diminishes, tree leaves become smaller and thicker, and tree crowns become smaller. Temperatures in the montane forest decrease with altitude, and humidity generally increases. Paijamans listed the occurrence of tree genera characteristic of lower montane forests, including Araucaria, Lithocarpus, Castanopsis, Syzygium, and Ilex. Beech (Nothofagus) and oak trees are found on mainland New Guinea and New Britain but are absent from New Ireland. The high-elevation forests of New Ireland are dominated by Metrosideros salomonensis (Myrtaceae) 10-20 tall.

Biodiversity Features

No comprehensive, modern botanical datasets exist for the Bismarcks, and much of the area is unknown in terms of biodiversity for any taxa. However, southern New Ireland has been surveyed botanically at two montane sites at 1,200 and 1,800 m. Findings from these two sites suggest that the trees of New Ireland montane forests are less diverse than expected, but the diversity and abundance of epiphytes from 1,000 to 1,600 m are impressive. Johns listed several montane regions within New Britain and New Ireland as areas of high biological importance based on their flora: Lelet Plateau, southern Namatanai, Hans Meyer Range of New Ireland and Willaumez Peninsula, Whiteman Range, Nakanai Mountain, and Mts. Sinewit and Burringa of New Britain.

There are forty-five mammal species in the ecoregion. Most of these species are bats (thirty-six) in four families (Pteropodidae, Emballonuridae, Rhinolophidae, Vespertilionidae), followed by rodent species (Muridae). No mammal species is strictly endemic to the ecoregion, but eight are near endemics (Table 1). Several species are listed as threatened (VU or higher) by IUCN: New Guinea pademelon (Thylogale brownii), Gilliard's flying-fox (Pteropus gilliardorum), large-eared sheathtail-bat (Emballonura dianae), Bismarck trumpet-eared bat (Kerivoula myrella), New Britain water-rat (Hydromys neobrittanicus).

The ecoregion includes the highland portions of the New Britain and New Ireland 'Endemic Bird Area' (EBA). The New Britain-New Ireland montane rain forests contain thirty endemic and near-endemic bird species (Table 2). Two of these species are listed as threatened (VU or higher) by IUCN: yellow-legged pigeon (Columba pallidiceps) and Bismarck owl (Tyto aurantia). There is little doubt that the Bismarck Archipelago contains undescribed birds, especially at higher elevations in the Hans Meyer, Nakanai, Baining, and Whiteman ranges. All four ranges are listed by Beehler (1993) as biologically important areas for Papua New Guinea (PNG).

Current Status

The ecoregion is largely intact. Steep slopes and smaller trees probably are the reason these forests are in good shape. The montane forests of the Bismarcks are crucial for capturing fresh water from the clouds and supplying it to streams and thus for maintaining water resources for communities year-round. The thick humus layer in montane forests acts as a sponge that collects moisture and releases it in a more uniform fashion than a bare hillside would so that even in dry periods water reaches the streams. Two protected areas overlap with the ecoregion (Table 3).

Types and Severity of Threats

There is the threat of logging operations extending into the montane forests from the lowlands. Logging also leads to the proliferation of nonnative species, which often outcompete native species.

Justification of Ecoregion Delineation

We delineated two ecoregions to represent the montane and lowland evergreen moist forests in the New Britain and New Ireland island complex: the New Britain-New Ireland lowland rain forests and the New Britain-New Ireland montane rain forests. The 1,000-m contour of the digital elevation map (DEM) was used as the transition between lowland and montane ecoregions. We placed the [[Admiralty Islands lowland rain forests into a distinct ecoregion, following Stattersfield et al. MacKinnon combined these three ecoregions into a single subunit (P3p). Udvardy placed these ecoregions in the Papuan biogeographic province of the Oceanian Realm.

Additional information on this ecoregion

• For a shorter summary of this entry, see the WWF WildWorld profile of this ecoregion.
• To see the species that live in this ecoregion, including images and threat levels, see the WWF Wildfinder description of this ecoregion.
• World Wildlife Fund Homepage