Lure of fertile soils endangers native bush at Mt Wilson, Mt Irvine, Mt Tomah

They are some of the most fertile soils in the Mountains and for many decades have been a magnet for Sydneysiders wanting to create beautiful gardens.

Tall eucalypts with an understorey of tree ferns at Mt Wilson are typical of the ecological system declared endangered.

Tall eucalypts with an understorey of tree ferns at Mt Wilson are typical of the ecological system declared endangered.

But land clearing has taken its toll on the volcanic basalt caps of Mts Irvine, Wilson and Tomah, to the point where the NSW scientific committee has just declared the native forests an endangered ecological system.

The committee noted that the forests have been extensively cleared since the early days of white settlement and now only exist in small remnants.

“Less than half of the remaining area is in conservation reserves,” the committee wrote. “Areas outside reserves are close to urban or rural residential areas and are subject to ongoing clearing for residential development and development of other infrastructure.”

The forests were also susceptible to weed invasion because they are close to urban and rural residential areas and because of the high quality of the soil.

“Proximity to urban areas also constrains fire management, leading to altered fire regimes with potentially adverse impacts. Some areas may be burnt at short intervals to maintain fire protection zones for urban areas.”

Other areas had also been used for grazing, with native species trampled or eaten, leaving them vulnerable to weed invasion.

“Blue Mountains Basalt Forest ... is eligible to be listed as an endangered ecological community ... as, in the opinion of the Scientific Committee, it is facing a very high risk of extinction in NSW,” the report concluded.

Such a listing will help protect the remaining ecology, according to Greg Steenbeeke, senior threatened species officer with the Office of Environment and Heritage.

“Where there is a development application or some other form of situation where the vegetation community is going to be under threat, the listing needs to be taken into account,” he said. “There needs to be appropriate and adequate assessment of environment impact [before any development approval].”

If development in the endangered community can’t be avoided, or damage can’t be minimised, the third option was offsetting through tools such as biobanking, Mr Steenbeeke said.

Under biobanking, anyone who is going to damage, destroy or reduce the biodiversity of a part of an endangered community must assess the impacts and, subject to the relevant approvals, can protect another area of the same ecosystem in roughly the same location.

“That way, the environmental loss is offset,” he said.

They can buy land themselves or buy biobanking credits and that way effectively pay others to protect and manage the land in perpetuity. 

“There’s also philanthropists,” Mr Steenbeeke said. “Some organisations are looking to invest in particular endangered ecological communities. You can enter into an arrangement where you keep ownership of the land and they will pay you to look after the environment.”

Blue Mountains Basalt Forest is usually a tall eucalypt forest, with mature trees more than 30 metres tall, with a dense shrub or small tree layer, often including tree ferns. The major areas of distribution are the basalt caps of Mounts Irvine, Wilson, Bell, Tomah, Banks, Caley and Hay.

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