Sundaland

Sundaland, also called Sundaica or the Sundaic region, is a special area in Southeast Asia. Long ago, when sea levels were lower, this area was a bigger piece of land. It includes places like Bali, Borneo, Java, and Sumatra in Indonesia, along with nearby small islands. It also includes the Malay Peninsula on Mainland Southeast Asia. This area is important for studying plants and animals because many unique species live there.

Extent

Sundaland is a special area in Southeast Asia. Long ago, when sea levels were lower, it was connected to land. It includes places like Borneo, Java, Sumatra, and the Malay Peninsula, along with nearby waters such as the Java Sea and the Gulf of Thailand.

When glaciers covered large areas with ice, sea levels dropped, and more land became visible. During these times, islands like Borneo, Java, and Sumatra were connected to each other and to mainland Asia by land bridges. As sea levels rose, these areas became separate islands. The borders of Sundaland are marked by deep ocean areas and a line called the Wallace Line, which separates it from another region called Wallacea.

Modern climate

All of Sundaland is close to the equator, including parts of central Sumatra and Borneo. In these tropical areas, rain is more important than temperature for the climate. Most of Sundaland gets more than 2,000 millimeters of rain each year, and there are no real dry seasons.

The warm, shallow seas of the Sunda Shelf, which stay above 28 °C, help shape weather patterns far away. They play a big role in global air movements and can affect weather during special times of year.

Modern ecology

The islands of Sundaland get lots of rain, which helps forests grow with tall trees all year. In some places, the forests get shorter and have fewer trees as you move north. The forests that are still standing are special because they have very tall trees and orangutans. When forests are cut down, the plants and animals there change.

Long ago, during a cold time called the last glacial period, the sea level was lower, and all of Sundaland was connected to Asia. This is why many animals from Asia, like elephants, monkeys, apes, tigers, tapirs, and rhinoceroses, live there today. When the sea levels rose, it separated the animals that used to live together. Each island now has its own mix of animals because of this. The biggest islands, Borneo and Sumatra, have the most different kinds of animals.

History

The name "Sunda" has been used since ancient times, appearing in old writings from around 150 AD. In the 1800s, explorers started studying the seas around Southeast Asia. A Dutch scientist in 1921 suggested that the shallow seas were once land that flooded many times as ice melted.

The term "Sundaland" was first used in 1949 for the underwater land that connects parts of Southeast Asia. Scientists have studied the climate and plants of this area by looking at tiny sea creatures, pollen, and other clues from the ocean floor and caves.

Sundaland has been a key place for animals and plants to evolve since the early Miocene period. The islands of Borneo, Java, and Sumatra have protected many species during cold periods in the past million years.

Early research

The name "Sunda" goes back to antiquity, appearing in Ptolemy's Geography, written around 150 AD. In an 1852 publication, English navigator George Windsor Earl advanced the idea of a "Great Asiatic Bank", based in part on common features of mammals found in Java, Borneo and Sumatra.

Explorers and scientists began measuring and mapping the seas of Southeast Asia in the 1870s, primarily using depth sounding. In 1921 Gustaaf Molengraaff, a Dutch geologist, postulated that the nearly uniform sea depths of the shelf indicated an ancient peneplain that was the result of repeated flooding events as ice caps melted, with the peneplain becoming more perfect with each successive flooding event. Molengraaff also identified ancient, now submerged, drainage systems that drained the area during periods of lower sea levels.

The name "Sundaland" for the peninsular shelf was first proposed by Reinout Willem van Bemmelen in his Geography of Indonesia in 1949, based on his research during World War II. The ancient drainage systems described by Molengraaff were verified and mapped by Tjia in 1980 and described in greater detail by Emmel and Curray in 1982 complete with river deltas, floodplains and backswamps.

Data types

The climate and ecology of Sundaland throughout the Quaternary has been investigated by analyzing foraminiferal δ¹⁸O and pollen from cores drilled into the ocean bed, δ¹⁸O in speleothems from caves, and δ¹³C and δ¹⁵N in bat guano from caves, as well as species distribution models, phylogenetic analysis, and community structure and species richness analysis.

Climate

Perhumid climate has existed in Sundaland since the early Miocene; though there is evidence for several periods of drier conditions, a perhumid core persisted in Borneo. The presence of fossil coral reefs dating to the late Miocene and early Pliocene suggests that, as the Indian monsoon grew more intense, seasonality increased in some portions of Sundaland during these epochs. Palynological evidence from Sumatra suggests that temperatures were cooler during the late Pleistocene; mean annual temperatures at high elevation sites may have been as much as 5 °C cooler than present.

Most recent research agrees that Indo-Pacific sea surface temperatures were at most 2-3 °C lower during the Last Glacial Maximum. Snow was found much lower than at present (approximately 1,000 meters lower) and there is evidence that glaciers existed on Borneo and Sumatra around 10,000 years before present. However, debate continues on how precipitation regimes changed throughout the Quaternary.

Ecology

Sundaland, and in particular Borneo, has been an evolutionary hotspot for biodiversity since the early Miocene due to repeated immigration and vicariance events. The modern islands of Borneo, Java, and Sumatra have served as refugia for the flora and fauna of Sundaland during multiple glacial periods in the last million years, and are serving the same role at present.

Savanna corridor theory

Dipterocarp trees characteristic of modern Southeast Asian tropical rainforest have been present in Sundaland since before the Last Glacial Maximum. There is also evidence for savanna vegetation, particularly in now submerged areas of Sundaland, throughout the last glacial period. However, researchers disagree on the spatial extent of savanna that was present in Sundaland.

Paleofauna

Before Sundaland emerged during the late Pliocene and early Pleistocene (~2.4 million years ago), there were no mammals on Java. As sea level lowered, species such as the dwarf elephantoid Sinomastodon bumiajuensis colonized Sundaland from mainland Asia. Later fauna included tigers, Sumatran rhinoceros, and Indian elephant, which were found throughout Sundaland; smaller animals were also able to disperse across the region.

Human migrations

People moved from East Asia to places like Taiwan and then to Maritime Southeast Asia. Some think an area called Sundaland may have been where their languages began, but most experts agree they came from Taiwan.

Studies show that people moved when sea levels rose, changing the land and forcing them to find new homes. These changes happened because of climate change, and people had to adapt to new places and ways of living.