The predominant natural vegetation of the higher ridges is eucalyptus forest. Heath-like vegetation is present on plateau edges above cliffs. The sheltered gorges often contain temperate rainforests. There are also many hanging swamps with button grass reeds and thick, deep black soil. Wollemia nobilis, the "Wollemi pine", a relic of earlier vegetation of Gondwana, is found in remote and isolated valleys of the Wollemi National Park. The main natural disasters to afflict the area are bushfires and severe storms. In recent years the lower mountains has been subjected to a series of bushfires which have caused great loss of property but relatively little loss of life. The upper mountains had not had a major fire for some decades until December 2002 (the Blackheath Glen Fire) and November 2006 when an extensive blaze in the Grose Valley threatened several communities including Bell and Blackheath (the Lawson Long Alley Fire). This latest fire burned for almost a month but was extinguished without loss of human life or property. A program of winter burning seems to have been quite successful in reducing fires in the upper mountains.