BALLINA'S linchpin koala population would be decimated within 25 years if the Pacific Highway's route through the Blackwall Ranges is given federal approval, new modelling has shown.
Earlier this month the NSW Planning Minister approved the Woolgoolga to Ballina upgrade, leaving Federal Environment Minister Greg Hunt the final gatekeeper.
But a new study by koala biologist Dr Stephen Phillips has predicted the fate of the population of 200 genetically diverse koalas is more acute than previously thought under the proposed route which cuts through the colony's eastern cell.
Dr Phillips used a sophisticated computer program, Vortex, designed specially for conservation modelling and used by global conservation authorities.
Using conservative losses of six or seven koala a year predicted in his Ballina Shire-wide koala study, Dr Phillips's modelling revealed the group of 80 koalas which the highway would dissect would not survive the impacts on their habitat.
But what Dr Phillips did not expect is that the larger colony of 120 koalas to the west would also face "functional extinction" by 2035.
"What I was interested in is if the displacement of a small number of animals in that population would tip over the entire population," Dr Phillips said.
"The smaller of the two population cells would collapse as a result, but what I didn't expect was the bigger population would collapse about 20 years later because of the lack of replenishment from the eastern population."
The Blackwall Range population is widely recognised as a very robust ancestral source colony, which has fed the surrounding Lismore, Ballina, and Byron shire populations to the north and west.
It is healthy, unlike the Lismore population, which are known to be inbred and suffer more from diseases such as Chlamydia - and "without doubt" the most important population in Ballina Shire, if not the region.
Dr Phillips said with koala populations already on a gentle decline, the massive impact of the Pacific Hwy on this significant population could easily become the "final straw" for the entire koala population north of the Richmond River.