Burning at Night.

At many places across the State forests of the Central Highlands there were large and dense stands of silver wattle (Acacia dealbata) whichhad replaced the original mountain ash (E. regnans) forests because of repeated bushfires in 1926, 1932 and 1939.

By the early 1970s, silvicultural knowledge had grown after the pioneering work by foresters like Jack Gillespie, and the methods of regeneration by clearing of overstorey, burning of slash and seeding or planting were well known, but the problem of reforesting sites in dense growth of wattle remained.

Firstly, a fixed-wing aircraft flying from Sumner Spur was used to spray chemical herbicide mixed with diesel to kill the wattle.

Two FCV bulldozers then dragged heavy chains to bring down the dead stems, which was followed by a spectacular slash burn to prepare the site.

But burning the wattle slash hot enough to create a receptive seed bed was a problem.

Unlike Fuel Reduction Burning (FRB), which required a slow moving and low intensity fire, slash burning required a very hot fire, usually in late summer to early autumn when there was still a risk of bushfires.

One solution to reduce the risk was to burn at night when the temperature was falling, the relative humidity was rising, and the wind had dropped off.

The area to be burnt was prepared by surrounding it with a solid earth break and a road to provide access for vehicles and tankers.

It required great skill, as well as a bit of courage, to light these burns and choose the moment of ignition. The wattle slash fuels needed to be very dry (<10% moisture content) but for the adjoining areas to be wetter (preferably >20%) to create a fuel moisture differential. A bit of light rain in the days before the burn was a big help.

High intensity slash burns are risky, and the final decision was made late on the day by the District Forester.

The burn was lit on dusk by crews with drip torches, beginning in the centre to develop a strong convection column to draw the hot fire inwards. More fire was then added around the perimeter until the whole thing was alight.

As the fire died down crews could then relax, and at around midnight there was often a convivial cook-up around a small campfire. A skeleton crew remained until dawn.

In a few days an aircraft would spread coated eucalypt seed on the receptive seedbed to regenerate a new forest.

Burning at night was once common but seems rare these days.

These amazing photos are from the Gregor Wallace collection and were taken at a night slash burn on Britannia Range near Powelltown on 4 March 1970.