September 2020 Speaker Report: Plant and Animal Responses to Fire - by Craig Welden

 

Our September speaker’s address on “Fire in the Landscape” couldn’t be more timely or relevant to the past 16 months. But rather than speak about the raging wildfires of last summer, Craig Welden explained the numerous elements involved in successful controlled burns, and the plant and animal responses to them when carried out with due consideration.

As a Senior Scientist at Healthy Land and Water and coordinator of the Queensland Fire and Biodiversity Consortium, Craig has developed extensive skills and knowledge in fire management, weed and pest control, and flora and fauna surveying. 

He spoke of quite a few critical considerations and questions to be answered for successful “burns” and results.

Different areas require site specific planning for their vegetation and fauna, for example, dry vine thicket; brigalow, riparian and rainforest areas do not tolerate fire well at all. Are there exotic weeds in the mix that need intense concentration; how much heat will the native plants tolerate to regenerate; when was it last burnt; what are the expected flora and fauna results if there is no fire and will a plant or animal species become overly dominant, stifling diversity? Other factors to consider include seasonal and weekly weather predictions, the need to vary the months for burning, and nearby areas needing to be left unburnt to offer food and habitat while the burnt areas recover; so much to consider!

Craig also explained some of the unique interactions between Australian native plants and animals with fire: i.e. certain fungi will sprout on black burnt logs; hakeas and banksias release their seeds due to fire heat and smoke; some insects lay their eggs in (sometimes warm!) ashes; frogs and others escape by burrowing into the soil or under logs;  birds feed on insects escaping from ground flames.

The plants that regrow after fire are generally divided into “seeders” and/or “resprouters”, and the latter can be from lignotubers, rhizomes, or epicormic shoots under tree bark. Most eucalypt shoots emanate from deep under the bark and can therefore withstand more radiant heat and flame than other species. Some species require (are obliged to have) fire to sprout and so are called “obligate seeders”. Most of these adult species are killed by fire and their new seedlings are vulnerable to a second fire occurring too soon.

The takeaway message was that wisely controlled fire is integral to the Australian landscape, has been practised for centuries, and affords the recovery and continuation of a vast number of flora and fauna species.

Craig brought copies of two issues of excellent fire information booklets entitled “Living With Fire: Fire Ecol-ogy”, and “Fire Regimes”, which feature many photos taken by Craig himself, and from which I will include here a few major points and observations.

“Fire Regimes” describes 10 broad vegetation types in southeast Queensland, and outlines the recommended frequency, area, season, and intensity of controlled burns for each one. 80°C is a temperature which enables hard coated seeds to crack open, while 120°C kills most seeds and species. Post fire regrowth can be quite positive, especially following rain, with seed germination, seedling growth, and some prolific plant flowerings. 

“Fire Ecology” covers the effect fires have on the burnt flora, fauna (including insects) and soil biota. One major negative side effect on native animals is that open clear burnt understory terrain allows easier feral animal predation. On the other hand, some native fauna prefers the resultant new vegetation after cool fires. But it seems reptiles are more abundant in areas of fewer fires. With frogs, some prefer burnt sites (Litoria frycineti), others (Litoria olongburensis) do not. Ants of 16 taxa showed up strongly in areas burnt annually which was shown by research north of Gympie, along with long-horned beetles at those frequently burnt sites.

Fire also affects, alters, and changes the soil. It burns away surface organic matter, alters nutrient availability and the pH, depletes soil nitrogen, and moisture retention, so rain run-off erosion is more likely. However, indications are that many fungi, soil fauna, and bacteria do recover fairly quickly after a low intensity fire, although that can be quite variable depending on remaining leaf litter.     

(Report by Lauren Marlatt)