Landscapes & Botany along The Botanists Way

The Bell Range, which Bells’ Line of Road largely follows, runs from Bell to Kurrajong Heights and is one of only a few continuous east-west ridge systems to breach the Blue Mountains escarpment. As a major watershed, the range offers a relatively easy path dividing the catchments of the Colo River to the north and the Grose River to the south. Both rivers flow through rugged gorges in wild country which is protected as dedicated wilderness within Blue Mountains National Park (Grose Wilderness) and Wollemi National Park (Wollemi Wilderness).

Most of the Way traverses Triassic age sandstones of the Sydney Basin: Hawkesbury Sandstone east of Mount Tomah and Narrabeen Sandstone in the west. Short sections traverse other rock types: Quaternary alluviums and Triassic shales in the lowlands around the Hawkesbury River, Triassic shales along the Bell Range around Bilpin, basalt on Mount Tomah and Permian sediments in the Lithgow Valley.

Major landscape features along The Botanists Way include (from the east) the riverine plains of the Hawkesbury River, the Hawkesbury River itself, the foothills of the Blue Mountains escarpment, the high ridge running north-south through Kurrajong Heights (which is associated with the Kurrajong Fault and Lapstone Monocline and forms the eastern Blue Mountains escarpment), the Bell Range, the basalt tops of Mount Tomah and Mount Bell, the edge of the Newnes Plateau, the western escarpment of the Blue Mountains and Lithgow Valley.

The botanists’ way of looking at the Australian bush has much in common with the Aboriginal view of the landscape. Both see an intricate, interconnected world where the plants, animals, rocks and terrain features all combine in the story of the land’s creation.

The way in which the same landscape can be read by different storylines is an intriguing part of the Australian experience. To the botanist’s eye, the changes in vegetation along the Botanists Way tell the story of the changing land beneath.

The Botanists Way climbs from close to sea level on the Hawkesbury River to 1000 metres on Mount Tomah, crosses the Blue Mountains plateau at a slightly higher altitude, then descends to the Lithgow Valley at 900 metres.

From west of Kurrajong to the foot of Mount Tomah along the Bell Range, the Way travels along a ridge-top of shale. Apart from providing an almost level line of travel, this thin layer of soft sedimentary rock also produces a corridor of fine silt soils through a landscape dominated by craggy sandstone.

The sandstone breaks down into some of the world’s poorest soils, but the shale weathers into earth that can hold both nutrients and moisture. These more productive soils support intensive orcharding and farming through the Bilpin-Berambing area, as well as tall forests where remnants of the original vegetation survive beside the road. Prominent amongst the taller trees are Smooth-barked Apple (Angophora costata), Grey Gum (Eucalyptus punctata), Turpentine (Syncarpia glomulifera) and Sydney Blue Gum (E. saligna). In places you can see a dense understorey of moisture-loving plants, in contrast to the prickly, hard-leaved shrubs typical of the sandstone expanse.

Mount Tomah and other nearby prominent hills including Mount Irvine, Mount Wilson, Mount Bell, Mount Tootie and Mount Banks, are capped by thin layers of basalt – the last remnants of extensive lava flows that spread over the landscape about 18 million years ago. The basalt soils are even richer than those on shale, so the vegetation too takes a step up the productivity ladder. It was the rich soils that prompted the development of the many exotic gardens on ‘The Mounts’.

The natural vegetation of ‘Fern Tree Hill’ (Mount Tomah) and other high altitude, high rainfall basalt caps is a mix of tall open forest and rainforest. The tall open forest has a canopy of huge eucalypts like Brown Barrel (E. fastigata) and Ribbon Gum (E. viminalis) over a thick understorey of rainforest plants. The eucalypts rely on the very occasional fire to regenerate, so if there is no fire for long enough (the lifespan of the big eucalypts - several hundred years) the rainforest will take over.

The most protected parts of the basalt mountain-tops and slopes are covered by the most extensive rainforests in the Blue Mountains. These are warm temperate rainforests, dominated by trees of coachwood (Ceratopetalum apetalum), Sassafras (Doryphora sassafras) and Possumwood (Quintinia sieberi), with rough treeferns (Cyathea australis) prominent in the understorey.

Travelling west, and after descending from Mount Tomah and rounding Mount Bell, Mount Banks comes into sight to the south of the road and the landscape changes character again. Narrabeen sandstone now dominates, with poor soils and very broken terrain. The vegetation is visually varied, with low open forests of Hard-leaved Scribbly Gum (E. sclerophylla) and Black Ash (E. sieberii) and expansive heathlands on the areas most exposed to wind and sun, particularly on the cliff-tops of the Grose Valley.

Dotted over the landscape are smooth-looking expanses of hanging swamp and sedgeland. These occur where bands of shale within the sandstone block the downward movement of water which then moves horizontally to emerge on the surface where the layers intersect the hillslope, creating wet areas. The stately white trunks of Blue Mountains Ash (E. oreades) poke up out of the deep gullies, sometimes quite close to the road. Blue Mountains Ash are vulnerable to fire, and some are just bare, dead skeletons after hot wildfires in 1994 and 2002.