Trans-Fly savanna and grasslands

Trans-Fly savanna and grasslands
Name	Trans-Fly savanna and grasslands
Ecozone	Australasia
Biome	Tropical and subtropical grasslands, savannas, and shrublands
Borders	Southern New Guinea freshwater swamp forests, Vogelkop-Aru lowland rain forests
Area	26,539
Country	Indonesia, Papua New Guinea
State	Papua (province), Western Province (Papua New Guinea)

Trans-Fly savanna and grasslands is a distinctive ecoregion spanning the southern lowlands of the island of New Guinea. It is situated primarily within the Western Province (Papua New Guinea) of Papua New Guinea and the Papua (province) of Indonesia, forming a vast, seasonally flooded plain. This region represents one of the largest areas of tropical savanna in the Australasia ecozone, characterized by a unique blend of flora and fauna with affinities to both Australia and New Guinea.

Geography and location

The ecoregion occupies the flat alluvial plains of the Digul River, Fly River, and Morehead River drainages, extending from the Oriomo River in the east to the Bensbach River near the border with Indonesia. Its southern boundary is defined by the coastline of the Torres Strait and the Arafura Sea, while to the north it transitions into the Southern New Guinea freshwater swamp forests. The landscape is predominantly a low-lying plain with extensive wetlands, including the massive Lake Murray and the floodplains of the Strickland River.

Climate and ecology

The climate is tropical monsoonal, with a pronounced dry season from May to October influenced by the southeast trade winds from the Coral Sea. Annual rainfall ranges from 1,200 to 1,600 mm, with most precipitation occurring during the northwest monsoon. This strong seasonal rainfall pattern drives the defining ecological process of extensive seasonal flooding, creating a dynamic mosaic of grasslands, wetlands, and woodlands. Fire is a natural and recurring disturbance, maintained by lightning strikes and traditional human management, which helps maintain the open savanna structure.

Flora and vegetation

The vegetation is a complex mosaic dominated by grasslands of Imperata cylindrica and Themeda species, interspersed with open woodlands and patches of monsoon forest. Common woodland trees include Eucalyptus species such as Eucalyptus tereticornis, along with Melaleuca and Corymbia. Scattered stands of Melaleuca leucadendra form distinctive swamp forests in permanently wet areas. The ecotone with the Vogelkop-Aru lowland rain forests supports a greater density of trees including Acacia and Banksia, reflecting the region's connection to the ancient Sahul Shelf.

Fauna and wildlife

The fauna exhibits a remarkable mix of Australasian and endemic species. It is a critical habitat for migratory birds traveling the East Asian-Australasian Flyway, including large populations of the broiga and the Australian bustard. The wetlands support significant populations of the New Guinea crocodile and the pig-nosed turtle. Mammals include the agile wallaby, the southern common cuscus, and the endangered New Guinea singing dog. Notable bird species include the black-faced monarch, the red-billed brush-turkey, and the palm cockatoo.

Conservation and threats

Key protected areas include the Tonda Wildlife Management Area in Papua New Guinea, a Ramsar site and one of the largest protected areas in the country, and the Wasur National Park in Indonesia. Major threats include habitat conversion for large-scale agricultural projects, such as the Merauke Integrated Food and Energy Estate, unsustainable logging, and potential mining impacts from operations like the Ok Tedi Mine. Climate change poses a long-term threat through altered fire regimes and sea-level rise affecting coastal margins. Invasive species, particularly the rubber vine and feral pigs, also degrade native habitats.

Human use and cultural significance

The region is sparsely populated by indigenous groups including the Boazi people, the Suki people, and the Marind people, whose livelihoods are traditionally based on hunting, fishing, and shifting cultivation. The savanna is managed through customary fire-stick farming to maintain resources for game like the ruk and wallaby. The area holds profound cultural significance, with landscapes featuring in the creation myths of the Marind-anim and sites like the Bensbach region being important for traditional ceremonies. Modern economic activities are limited but include some cattle ranching and artisanal fishing.

Category:Ecoregions of Indonesia Category:Ecoregions of Papua New Guinea Category:Grasslands of Oceania