"Single-species management has the potential to impinge on other biodiversity attributes," Dr Bell said.

Dr Bell gave the example of removing an invasive weed to improve habitat for a threatened native shrub.

"This may inadvertently remove essential habitat for a threatened frog," he said.

Biodiversity is dynamic and cyclic, responding to variables such as fire, flood and drought. These factors favour some species but temporarily remove others.

These cycles vary in duration across "all forms of life".

"Sometimes we need to acknowledge these changes as a major component of a biodiverse landscape.

"For example, wildfire will often enable germination and growth of plant species that have been hidden as seeds in the soil for many decades."

A few years after fire, they will again disappear into the soil.

Some species operate on time scales across centuries.

They can appear in the landscape only after rare events and can "persist for many decades" until they naturally deteriorate with age.

Dr Bell, who is researching numerous threatened species, said new flora and fauna are still being discovered and described in the Hunter.

"For example, over the past 10 years or so there have been three new eucalypts and several shrub species newly described for the Hunter, most of which are endemic to our region.

"This is on top of other species discovered and named in the decade before that [2002-2012], about a dozen or so of which are now listed as threatened."

A new frog species - Mahony's toadlet - was discovered in 2016 near Newcastle Airport.

And, in recent years, the Hunter River turtle was split off as a subspecies of the Murray River turtle.

Compared to a couple of decades ago, Dr Bell said biodiversity was well supported by legislation and regulation and had "greater recognition in the general community".

"There is now legal protection for numerous species and their habitats. Biodiversity offsetting is creating additional non-national park conservation areas in private ownership, but still regulated by government.

"Their long-term value will be determined by how well they are managed.

"You cannot just fence off an area and not monitor and manage feral pests, weeds, fire regimes and woody regrowth."

The main threats to biodiversity are associated with humans.

These include land clearing, development, agriculture, weed invasion, feral pests, invasive pathogens and diseases, misuse of fire and illegal collecting.

"Often, several threats operate simultaneously and feed off each other - high weed invasion might lead to higher fire frequency and severity for example," he said.

"All of these threats are essentially why certain species are considered threatened."