APRIL Meeting 2017
Dr Ben Miller, fire ecologist and Director of Science at Kings Park, has worked in areas such as fire ecology, restoration ecology, rare plant conservation and ecosystem management.
Ben’s talk looked into the role that fire ecology plays in the management of bushland in Kings Park. Most of the Park (300ha out of a total area of 400ha) is Banksia woodland, consisting of Banksia attenuata and Banksia menziesii together with Jarrah and Marri and some (increasing) Allocasuarina fraseriana. The Banksia woodlands of the Swan Coastal Plain are now listed as a Threatened Ecological Community. Fire is the biggest risk to the Park, and this risk needs to be managed well. The big fire of 2009 threatened buildings and the Botanic Garden.
Ben talked about a very common weed in Kings Park, Perennial Veldt Grass Ehrharta calycina – about what makes it such a virulent weed and why it is that fire favours its own recruitment over that of native species. He also explained how the profit motive caused its introduction to the Park in the early 20th century (stock fodder).
The policy of the Botanic Gardens and Parks Authority (BGPA) includes a fire ecology program, which aims to determine the impacts of fire on biodiversity, weeds and fuels in the Banksia woodlands, and the likely effects of a drying climate. There is a deficit of data necessary to understand the effects of fire on biodiversity, vegetation structure and weed abundance, and also the effect of burning on the fire hazard itself.
A current study in Kings Park, over 20 to 25 years, aims to determine the effects of different intervals between burning – i.e. short (5 to 6 years), medium (10 to 12 years) and no burning at all, and to see whether these are affected by weed-treatment in the growing season before the burn.
A study site was set up with 6 blocks, each containing 7 quadrats and 3 transects. There were four areas:
- Burnt with weed-control
- Burnt with no weed-control
- Unburnt with weed-control
- Unburnt with no weed-control (the experimental control)
In 2015, the Department of Parks and Wildlife burnt the specified 6ha area, in the same way they would normally do a fuel-reduction burn.
Two years after the experimental burn it was found that, in the burnt areas without weed control, weed cover increased enormously, whereas in the burnt, weed-controlled areas, weed-cover was about the same as before, and the native plants (including a native grass) did better. Overall, burning in this area which had last burnt in 1989 was good for the bush as long as there was weed-control.
Ben then talked about the results of previous experiments in shrublands near Eneabba to determine the optimum interval between burns. The result was that a “minimum tolerable fire interval” was ten years. However, after a winter with only 80% of the average rainfall, that minimum interval rose to 14 years. This has implications for climate change.
An interesting finding from that study was that Banksia attenuata that is a small tree in Kings Park may take the form of a shrub in the sandplain habitat near Eneabba, and therefore exhibit a different response to fire.
There has also been research at Kings Park on lethal temperatures for seeds, both in the field, using optic fibre technology, and in the oven. One counter-intuitive result was that dry seeds are more fire-tolerant than seeds that have absorbed moisture.
We learnt that fire ecology is complex, and that much more research has to be done in order to understand the role of fire in bushland management, such as the subject of optimal fire intervals and the effect of grazing by native animals. Fire interacts to compound the many other threats to bushland such as climate change. Another example is that weeds make the fire risk worse and fire makes the weed problem worse.
Popular opinion on the role of fire on the bush tends to be polarised and emotional, but research such as Ben outlined to us is helping to make the debate more rational and bush management more effective.
Mike Gregson