Massive bushfires are occurring unnaturally, often in native forests in south-eastern Australia, prompting the collapse of ecosystems and rendering logging unviable, according to a new study published overnight in the journal of the National Academy of Sciences in the US.  Since 2003, Victoria has been hit with three mega-fires, blazes that burn over 1 million hectares, but in the period of European settlement before that there was just one, in 1939, according to research led by Professor David Lindenmayer, one of the world’s leading forest ecologists.  Fires, exacerbated by climate change, are now so common that it is unlikely that the mountain ash forests set aside for logging on an 80-year rotation will ever reach maturity and, as a result, logging has become unviable in native forests, the report says.