Wednesday, 19 February 2014

Molonglo High Plains - Ancient History of the Molonglo High Plains

Molonglo High Plains

This is one of a series of posts dealing with the Molonglo High Plains (Hoskinstown, Rossi, Forbes Creek and other areas to the west of the old volcano Palerang).  The entire series is at:

Molonglo High Plains: 2013

Ancient History

We know a surprising amount about the history of our local region because of core samples from the nearby Lake George Basin.

The region emerged from shallow seas more than 150 million years ago. The surrounding mountains resulted from volcanic action from that time and as part of the general uplift of the eastern highlands about 80 million years ago. However, it has changed slowly over the past 50 million years. Against the backdrop of familiar landmarks, climate, vegetation and animal types have gone through a number of distinct stages.

50-30 Million years ago: wet, warm

When the land bridge between Antarctica and Australia finally sank about 50 million years ago, the Yandyguinula valley was a much wetter and warmer place. Like much of the rest of the country (and Antarctica), it was covered in lush rainforests. The Yandyguinula, probably shrouded in perpetual mist and flowing heavily, periodically flooded some of the lower valleys as it cut its way through the dense conifer rainforest.

The forest canopy towered up to 50 metres above the ground. It consisted of the Southern Conifers (today, descendants of the northern family include the Kauri, Bunya, Hoop and Norfolk Pines while the southern family, known as Podocarps, include the Huon and Celery-top Pines) and the Southern Beeches ( the Antarctic Beech, Nothofagus moorei, is still found in Queensland rainforests). These trees are very ancient with the Kauri Pine still closely resembling fossil records from 175 million years ago.  The Beeches spread to this country across Antarctica from South America about 90 million years ago.

In the understorey were ferns, cushion plants, rhododendrons, orchids, hollies, ancestors of the willows and the gums. Leopard -like Wakeleo stalked the forests with Tasmanian tigers and carnivorous kangaroos. Large toothed platypus, possums, numbats and bilbies lived in the forest.

From this and earlier periods, remnant species still survive in our region.

30- 5 Million years ago: drier, colder

About 30 million years ago, Antarctica drifted lower to the south pole and world temperatures began to drop. The sea level fell, temperatures began to drop and Australia began to dry. The great Pine forests began to retreat to the Eastern seaboard. Casuarinas (probably developing from early willows) slowly replaced the Southern Conifers in the new dry woodlands, while gum trees thrived in the drier climate. As more extensive grasslands developed and the forests became more open, large marsupial browsers and flightless birds appeared.  It was a time of giant marsupial browsers including the bear sized Nehelos and the Diprotodon.

The north-south Lake George Fault began to slowly rise during this period. Over 20 million years, it rose about 100 metres, impeding the westward flow of both the Yass, Molonglo and Yandyguinula Rivers. The Yass River, with a small catchment, was not able to cut through the new range and pooled into Lake George. The Molonglo, helped in part by the Yandyguinula, cut through the range near Balcombe Hill. During the periodic ice ages at times of very low rainfall, even the Molonglo failed to keep up with the gradual rise along the fault. At these times of drought, the Molonglo formed a lake on the Hoskingtown Plain.

5 Million Years Ago

About 5 million years ago, the Lake George Fault ceased to rise. This coincided with another dramatic ice age. The Molonglo drained through the fault and the plain started to dry out. By this stage, the forests in the region consisted of a mix of casuarina canopy with a fern and podocarp understorey (on the higher peaks in the ACT the mountain plum pine (Podocarpus lawrencei) still clings to rocks). The forests survived in the mountains and hills, extending onto the plains during periods between ice ages (there have been 20 ice ages in the past 2 million years). During colder, drier periods, the plains became open forests and grasslands.


100,000-180 years ago: fire stick agriculture

To the north of Lake George, in sandstone, is the footprint of one of the giant marsupial browsers. Next to it is the footprint of a man.

When aborigines settled the continent, they brought with them knowledge of fire stick agriculture, which they used as an integral part of hunting and everyday life. The introduction of systematic burning co-incided with the extinction of many of the forest casuarinas and podocarps (although it is not certain whether these are related or are both aspects of a different event as yet undiscovered). The forests were replaced by grasslands and eucalypts and the Casuarinas and podocarps “retreated” into the wetter mountains.

The intensity of aboriginal occupation probably varied with climatic factors. During ice ages, traces of carbon in the fossil record become rare in the face of the permanent snow which settled on the Great Divide and the Black Ranges. During warmer interglacial periods, fire stick agriculture returned to the plains and foothills, but only rarely was felt in the wetter ranges. As the next fire tolerant range of species became widespread in the lower and mid ranges, remnants of the Casuarina forests held fast to the river banks or joined earlier remnant species in the high wetter valleys and ridges of the ranges.

About 30,000 years ago the last of the giant marsupial browsers became extinct and the last of the Tasmanian tigers retreated permanently from this area. The region was left to the grey kangaroo, the red-necked wallaby, the koala and a range of smaller marsupials including the native cat and the possum. Bush turkeys led mostly solitary lives while quail and emu lived in large family groups.

The Yandyguinula and Molonglo were a series of marshy ponds. Protected by stands of casuarina and tea tree the ponds were a haven for ducks and swans. During warmer periods, brolga from the interior may have lived on the river (but there is doubt about whether this continued into modern times).

Along the river stretched the permanent grassed walking tracks of the aborigines. Early settlers found these trails kept free of obstruction and well burnt. Of necessity, the trails were used by the first shepherds, adopted by the settlers and mapped by the surveyors. Today, our roads follow those same trails.

180 years ago to present

The first three white Australians to ride across the Hoskingtown Plain in the 1820’s were all native born “cornstalks”, selected by Governor Macquarie. The young men had no difficulty communicating with the aboriginal people they met and reported back to Sydney about a rich environment. They also reported seeing numerous fires of the aboriginal inhabitants of the five high plains in the Hoskingtown, Queanbeyan and Canberra regions. However, within a decade, aboriginal people from the region had withdrawn to the central Canberra plains and the Tidbinbillas and encounters with aborigines living traditional lives became infrequent.

With the cessation of fire stick agriculture, the Eucalypt and Acacia populations exploded. Within a decade, the tended woodlands of the aborigines became impenetrable scrub. Resourceful foresters logged many of the mountain giants. The casuarinas along the river were removed  for fencing and yards. Rumours of gold led to the declaration of gold reserves along the rivers. The wetlands disappeared and the banks of creeks and rivers became sharply delineated through erosion.  Koalas and bush turkeys were shot out for sport and tucker.

Attempts to plant orchards, run dairies and intensively farm small selections were frustrated by years of drought and the loss of settlers to flood, influenza and war. Farms further away from permanent water were abandoned. Presently, many survive only as collections of hearth stones and isolated stands of exotic trees, but the region is starting to repopulate.

(In different forms, this document was prepared based on discussions - and arguments - with Rhys Jones (an eminent Australian expert in prehistory who lived on the Hoskinstown Plain) and research at the National Library of Australia as well as discussions with others with local knowledge and published in the 1990s.  Information was drawn from many local people.)

Peter Quinton

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