Rapidly increasing areas of eucalypt forests are dying from Bell Miner Associated Dieback (BMAD).

Dieback associated with over abundant psyllid insects and Bell Miners (or bellbirds) in coastal forests has just been listed as a key threatening process under the Threatened Species Conservation Act.

Current trials on private and government land are testing methods of controlling bellbird habitat in the forest understorey.

"An estimated 2.5 million hectares of forest is now vulnerable across all land tenures along the NSW coast," Northern Rivers Private Forestry Development Committee executive officer, John Macgregor-Skinner, said.

The cause, effect and timing of the dieback are not fully understood and vary between different tree species, however, disturbed eucalypt forests, where bellbirds occupy a modified and uniform understorey, often Lantana, are characteristic sites.

Bellbirds are a native honeyeater with their distinctive bell-like call.

They live in forests along the coast and Great Dividing Range between Gympie in Queensland and Melbourne.

Bellbirds live in well organised colonies and chase out any birds they see as a threat to either their nests or food sources.

The sugary exudate shelter, or lerp (similar to scale), of the larval stage of psyllids is a major food source for them.

Certain psyllids of the Glycaspis genus specific to particular eucalypts are known to cause BMAD.

Under normal environmental constraints, psyllid populations remain at low to moderate levels and a number of small birds such as pardalotes and thornbills and other predators - spiders and invertebrates - feed on them.

Where over abundant populations of bellbirds drive out other birds, psyllid numbers soar.

This leads to insect induced tree stress and the emergence of dieback.

Plague proportions of psyllids and bellbirds precede the eventual death of the host trees.

There is hope from trials and research, now indicating possible methods to combat dieback.

Mr Macgregor-Skinner says preliminary trial results indicate that reduction of dense forest understorey causes bellbirds to disperse, breaking the cycle.

"Management trials are now aimed at reinvigorating forest health by manipulating bellbird habitats," he said.

Current trials are measuring whether dieback affected trees recover after clearing of the understorey.

Methods being tested include herbicide treatment using the splatter gun technique, the use of machinery and fire to remove Lantana, and the adoption of silvicultural techniques including enrichment planting and regular low intensity fire to maintain grassy understorey.

Mr Macgregor-Skinner says while it is difficult to separate cause from effect, drought, harvesting, forest structure change, road construction and changing fire and grazing regimes have all been suggested as additional contributing factors in the northern region of the State.

A working group of local landholders, community and conservation groups, and representatives of industry and government agencies has assessed and mapped the extent of the dieback on private property, National Park and State forest in the Richmond Range area.

"The survey estimated that 20,000 hectares were infected with the dieback," Mr Macgregor-Skinner said.

"Since this assessment, dieback has expanded its range and larger areas of forest are now dying."

Contact John Macgregor-Skinner, Murwillumbah, (02) 6672 2770, www.bmad.com.au