The survival of an endangered wattle species that exists on one mountain in the Hunter relies on fire and climate cycles over hundreds of years, research shows.
"This is mind-blowing stuff," said Dr Stephen Bell, a University of Newcastle botanist and adjunct lecturer.
"It makes you realise that, for some species, it is important to look at much longer time-scales than say five to 10 years when managing them."
The last major fire on Mount Dangar in the Hunter Region occurred in the late 1950s.
Dr Bell said the role of fire in trees such as acacia dangarensis is "only now being more fully understood".
"Acacia dangarensis occurs only on Mount Dangar near Sandy Hollow," Dr Bell said. "Like most other wattles, it requires hot fire to sufficiently crack the coats of fallen seed waiting in the soil."
Such cracks allow the entry of water for germination.
The population of acacia that grew from the 1950s fire is "now aging and dying".
"A similar hot fire event will be required to rejuvenate the population," Dr Bell said.
"However, while existing trees continue to flower and fruit there is no urgency in this. But it is something that needs to be acknowledged and planned for by authorities, in the event that wildfire moves across that landscape."
Dr Bell said fire suppression to protect surrounding properties "may ultimately lead to the demise of this species".
"The last major fire event likely occurred at least 200 years prior to the 1950s wildfire, around 1750," he said.
This was shown through research into historical wet-dry weather cycles and tree-growth ring analysis.
The writings and collections of historical explorers and botanists on Mount Dangar since 1825 show that acacia dangarensis was not present above ground on the mountain, until it was first discovered and recognised as a new species in 1979.
"We believe that the presence of acacia dangarensis above ground is driven by centurial-scale cycles in climate and fire," Dr Bell said.
The species had persisted over the centuries through a "soil seed bank".
That is, seeds dispersed in surrounding soil.
The acacia dangarensis species, which has no common name, is listed as critically endangered.
It is endemic to NSW and confined to the summit and surrounding slopes of Mount Dangar in the Goulburn River National Park.
The total population is estimated to be at least 20,000 plants, extending over 112 hectares.
It is not known to occur in any other spot, despite considerable surveys around the Hunter in recent years.
The small tree grows up to 10 metres, with golden-yellow flowers that bloom from August to September.
As well as frequent and very severe fires, its threats include lack of fire causing the population to deteriorate.
"Without fire-driven rejuvenation of these populations, persistence in the area over the long term comes into question."
This places limits on successful pollination.
Storms, weeds such as prickly pear and goats also threaten the species.
A targeted strategy for managing it has been developed under the NSW government's Saving Our Species program.
Most Protected
Another wattle, acacia pendula, is also being managed through this program and other strategies.
Dr Bell said the acacia pendula population in the Hunter was "probably the most legally protected threatened entity in the region".
The species, commonly known as the weeping myall, is listed as an "endangered population" in the Hunter, and also forms part of a "critically endangered ecological community".
Fewer than 1000 trees were thought to occur in the Hunter Valley at the time of its threatened species listing in 2005. It has been recorded at many locations in and around the Muswellbrook and Singleton areas.
This population is thought to occur naturally in spots stretching from Warkworth to Wybong, however there is some uncertainty about its origins. "We researched the history of collection, observation and habitat of this widespread semi-arid species," Dr Bell said.
"It did not make ecological sense for populations in the Hunter to be naturally occurring, particularly when we looked at the range of habitats in which it occurs.
"We found that historical explorers did not mention the presence of this species in their journals until after they left the Hunter."
Root Suckering
Researchers said the species may have been introduced through stock movements from the Liverpool Plains in the 1800s.
"Once here, these plants failed to reproduce sexually," Dr Bell said.
They didn't produce seed, but instead "persisted in the landscape through suckering from their roots".
More populations have been discovered in recent years, as stock grazing pressures have eased in properties set aside for conservation offsets.
This has allowed these root suckers to develop into trees and thickets, which were otherwise kept low through grazing.
Root suckering is asexual reproduction that involves plants regenerating tissues and parts, such as shoots springing from the roots.
Further research is examining how the root-suckering spread of this species is affecting plant diversity in surrounding threatened ecological communities.
Researching the ecology of threatened Hunter plant species has taught Dr Bell that "there is still an awful lot we still need to learn about life processes and the ecosystems in which these species occur".
"Discovering how different plant species deal with multiple stressors (fire, drought, grazing etc) is crucial to know how to manage a species into the future. However, perhaps more importantly we need to step back sometimes to put things into context, and look at managing the whole landscape."
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