Ecology of Indonesian Papua Part One. Andrew J. Marshall
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Papua’s other great rivers drain the ragged southern scarp of the central range in the eastern half of Papua. Among these, the Digul is the greatest, followed by the Catalina, which in the mountains becomes the famous Baliem that drains the Grand Valley of the Baliem, discovered in the late 1930s by explorer-pilot Richard Archbold. Scores of lesser rivers sweep heavy gravels southward toward the muddy Arafura Sea. These turbid and unstable rivers tumble out of the mountains, with torrential flows in the mountain gorges, and heavily braided channels in the flats that spread out from the bottom of the ranges. As one moves westward, one finds river after river, each shorter than the preceding, until the central mountains pinch off the alluvial plain at the bottom of the Bird’s Neck.
LAKES
Papua has a few prominent lakes. Lake Sentani, near the Papuan capital Jayapura, was apparently created by tectonic movement related to the uplift of the coastal Cyclops Mountains just to the north. The lower Mamberamo features Lake Rombebai, the largest lake in Papua, as well as smaller Lake Bira. These are swampy backwater lakes. At the western end of the central cordillera we find the Paniai Lakes in an interior highland basin. Lake Yamur, on the Bird’s Neck, is home to a freshwater shark. Finally, highlands lakes (Anggi Gigi and Anggi Gita) are found in the Arfak Mountains of the Vogelkop.
SWAMPS,MANGROVES, AND SAVANNAS
The vast lakes plain of the Mamberamo Basin is dominated by seasonally inundated swamplands of various types. There are great coastal swamplands along much of the southern coast, from the Casuarina coast in the southeast to the swamplands south of Timika, far to the west. Indonesia’s largest mangrove ecosystem is nestled in the head of Bintuni Bay, which separates the Vogelkop (Bird’s Head) Peninsula from the more southerly Bomberai Peninsula. Elsewhere in Papua, swamps can be found in many alluvial localities where drainage is impeded, around lowland rivers, and in and around Dolok (Yos Sudarso) Island in the far south. In the far southeast, by the Papua New Guinea border, is a swath of savanna that ranges westward to Dolok Island—part of the great Trans-Fly savannas that have the look of Australia rather than New Guinea. This is a highly seasonal low-rainfall zone that toggles from an inundation season to a burning season.
COASTS
Papua’s abundant coastline is not uniform. In the northeast, one finds hilly country reaching the coast, which features a mix of white sand beaches and rocky shorelines. Long stretches of beach dominate in the north, backed by coastal hills. The eastern shore of Cenderawasih (formerly Geelvink) Bay features swamps and mangroves, whereas the western shore is more rugged and hilly. The north side of the Vogelkop is rugged, whereas the south side is low and swampy. Much of the southern and southeastern coastline are low and silty, with dark sand beaches backed by casuarinas, with swamplands further inland. The most spectacular coastlines are found on the south side of the Bird’s Neck, between Arguni Bay and Etna Bay. Here one finds tropical karstic fjordlands that feature coastal mountains rising to more than 1,000 meters, steep cliffs, deep embayments, and scenery galore.
ISLANDS
Papua has more than a thousand fringing islands, from tiny to quite large. The Raja Ampat Islands range off the western coast of the Vogelkop Peninsula, and include Waigeo (3,155 km2), Salawati (1,632 km2), Misool (2,041 km2), Batanta (453 km2), and Kofiau (150 km2), among others. This remarkable archipelago supports the world’s richest coral reefs and considerable endemic forest biodiversity (e.g., Wilson’s Bird of Paradise, Red Bird of Paradise, Waigeo Brush-turkey). The islands of Cenderawasih Bay include two isolated oceanic islands with distinct island faunas (Biak/Supiori, 2,497 km2, and Numfoor, 311 km2), as well as the mountainous land-bridge island of Yapen (2,227 km2). In addition, there are the Padaido Islands southeast of Biak, and Num Island west of Yapen, and a number of small coastal islands in the south and west portions of the Bay. Small islands also dot the north coast and fringe the Fakfak and Triton Bay region. Papua’s largest island is Dolok (11,192 km2), which is a vast mudbank outwash from the silt-laden rivers of the southeast coast. It is often forgotten because of its unpre-possessing nature and isolation, and its minimal distance from the mainland.
Ecological Setting
New Guinea is the northern quadrant of the Australian tectonic plate; thus this island is geologically one with the Australian continent. And yet in spite of geological linkages, there are considerable environmental differences. In particular, Australia today is dry and temperate, whereas New Guinea is tropical and perhumid. These two fundamental distinctions can explain much of the differences between these sister biotas, north and south.
Climatologically, Papua is remarkable mainly for its cloudiness. It is perhaps one of the cloudiest places on earth. Spanning latitudes from the equator to 12 degrees south latitude, Papua’s equatorial climate is seasonally dominated by the Northwest Monsoon and the Southeast Trade Winds. In most parts of Papua, the effects of the Northwest Monsoon dominate in the period from November to March, bringing rain and unsettled weather. The Southeast Trade Winds tend to bring cool and dry weather, and predominate from April until September. That said, Papua has many microclimates. Rainfall regimes range from low in the southeast (less than 2,000 mm/year) to extremely high on the southern scarp of the Central Cordillera (more than 5,000 mm/year). The highest rainfall on record for Papua is from Tembagapura town, which receives 7,500 mm/year on average. In the wetter areas, the typical seasons are reversed, and the most rain falls in the April–October period. In fact, the wettest sites receive rain from both the monsoon and the trades, and they tend to be found in the mountains along the southern front of the Central Cordillera. Moreover, annual accumulation in the very wettest areas tends to show great variability. This variability can exceed the mean annual accumulations recorded for typical medium-rainfall sites.
Seasonally, temperature varies little. Elevation is the key to temperature in equatorial zones. This "lapse rate" is equivalent to 5 C per 1,000 m elevation. Thus, at sea level, in the forests near Timika, one will encounter an unpleasant combination of high humidity and warm temperature day and night on all but the coolest days of the austral winter. By contrast, at 4,000 m in the Sudirman Range one must expect regular night frosts during the dry season, when the skies are clear. Above 4,500 m periodic snowfalls are common. And glaciers cap the highest peaks of the Jaya Mountains (formerly the Carstensz Range). These glaciers expanded outward and downward during the Pleistocene cooling, melted altogether by 6,000 years BP, and returned during the recent cooling, only to begin retreating again in the last century.
The elevation-temperature equation is a defining environmental phenomenon in mountainous Papua. This allows essentially distinct biotas to inhabit adjacent patches of land, separated only by elevation. It certainly explains much of the species-richness of Papua (beta diversity).
Rain shadows exist in some interior valleys (such as the Baliem), on the Bomb-erai Peninsula, and in the Trans-Fly of the far southeast. Rainfall is also slightly attenuated along the northern coast, from the mouth of the Mamberamo east to Jayapura. Much of the interior receives well in excess of 3,000 mm/year.
Papua is a land in flux. Significant chronic disturbance is produced by ongoing mountain-building in contest with rainfall-driven erosional processes, as well as by periodic vulcanism, human-caused and naturally occurring fire regimes, plus El Niño droughts. Over the long history of human occupation, swidden agriculture has disturbed large swaths of habitat, most of which is now regenerated forest. Thus historical disturbance is a dominant factor dictating the distribution and pattern of today’s vegetation. Much of what appears to be "virgin rainforest" is, in fact, the product of recent and not-so-recent patch disturbance. This is abundantly evident when conducting plot-based plant surveys in the forest. Thus any attempt to characterize forest types is a rough generalization, and at best a qualitative assessment with minimal predictive power at the taxonomic scale.
FOREST TYPES
Closed forest is the default vegetation type over virtually the entirety of Papua except perhaps in the southeast (although the fire regime that produces savannas there may be anthropogenic). Papua’s forests are highly species rich, with minimal stand dominance by particular tree species, and with remarkable history-driven variation from site to site, even within single catchments. One-hectare stands of forest typically