Fire has been an integral part of central Australian arid ecosystems for thousands of years. Fire is used by humans as a hunting aid, for signalling presence, for warmth and for cooking. Fire has a positive effect on germination of ephemeral plants, and is also known to be important for germination of many tough-coated seeding plants in central Australia (such as Hakea sp. and Greveilla sp.). As a result, many plant species have evolved to cope with periodic fire disturbance.
However, in central Australia, Buffel Grass (Cenchrus ciliaris) has changed the way that the land burns and so fuel reduction burning and slashed firebreaks are more important than ever. Buffel Grass grows fast following heavy rains, it generally out-competes native grasses (producing a thick monoculture), and when it burns – it burns hot and fast. Consequently, the presence of Buffel Grass can be problematic for controlling fire.
Lately (or not so lately?), Alice Springs has seen a spurt of fire in the Todd River, which has got many residents concerned about the fragility of the old River Red Gums (Eucalyptus camaldulensis). The death of River Red Gums in the Todd River is saddening, as it means a loss of habitat for many of the amazing hollow-nesting birds and bats in the region. But there is a sentimental value to the beauty of the trees as well, which many long-term residents are keen to protect. Several of the large trees have cultural value to local Indigenous groups, which also warrants their protection from fire.
Removal of Buffel Grass around large River Red Gums (and other large trees) is one of the main ways that we can protect them. As a result of big summer rains, we have a huge fire risk with thick Buffel Grass growth around town and rural areas and there is a need for fuel reduction through slashing, spraying or prescribed burning.
Slashing is effective at removing Buffel Grass but it can be time-consuming and costly over large areas and is non-discriminatory (slashes the native grasses and herbs as well). It is best-suited to large and flat grassland areas that require quick fuel reduction.
Spraying can be effective at killing Buffel Grass but doesn’t remove the biomass and nor does it remove the fire hazard. Spraying as a technique is only effective when the Buffel Grass has green pick that is then able to absorb chemical for purposes of killing the root system. At this time of year, much of the Buffel Grass is dry and needs to be chipped out with a mattock if working at a small scale. Chemical is expensive and so is the time needed to spray large areas of Buffel Grass. With the loss of funding to programs such as Green Army – where does the funding come from to support such endeavours? In this case, the town largely relies on groups such as Landcare, as well as individual residents to volunteer their time and do the hard yards. Adopt an area or a tree and go from there!
Fuel reduction by prescribed burning an essential component of fire management, and in most cases the aim is to reduce the ground cover by 60 to 80 %. Such prescribed burning can be effective for a year or two in protecting large trees and habitats from large-scale fires, as well as preventing the spread of large fires. Prescribed burning needs permits and trained fire teams to conduct appropriately and becomes tricky within municipal areas – so it isn’t a reliable venture for protecting the large gums in the Todd River.
Want to know how you can help protect the River Red Gums? Read more about the recent suggestions in Fiona Walsh’s article (http://www.alicespringsnews.com.au/2017/07/30/save-our-trees-reduce-buffel-call-000-collaborate/).
If fire takes hold, what is the consequence for our wildlife and the ecosystem as a whole?
In terms of the soil, there will be an immediate loss of soil organic matter, and nutrients will be mobilised following a fire. These nutrients have the potential to be relocated downslope (hillside fires) or downstream (riverside or river island fires). There is an immediate loss of groundcover (plants) and leaf litter, which in turn can make an area susceptible to erosion, and result in wetter soils (fewer plants to absorb water through the roots).
Many central Australian birds (such as Cockatoos, Nightjars and Owls) rely on large tree hollows for nesting space. Following a fire, general bird abundance in the area will remain stable; however the loss of hollows can result in a long-term reduction in the population of hollow-nesting species. The loss of a small number of trees may not affect the ecosystem balance to a huge degree, while a large loss of trees may be consequential.
Bat population stability following fire depends on the insect population. Invertebrate population is extremely variable in time and space with or without fire. It is driven by environmental factors such as temperature, rainfall and insolation; and therefore the effect of fire is extremely difficult to determine. As a result, the effect of fire on bat populations will depend on a host of environmental factors as well.
Mammals can experience some initial mortality as a direct result of fire, and in the period following fire there can be increased predation due to lack of cover, and emigration from burnt areas. Patch burning can alleviate the risk to mammals to some extent – leaving intact patches of habitat for mammals to retreat to can be effective at protecting mammal populations.
For reptiles, the effect of fire on populations will depend on the amount of leaf litter and hollow logs left intact for shelter and foraging for food. Patch burning can provide useful refuges for skinks, lizards and snakes, and therefore populations can recover quickly after small and patchy fires. If a large tree with hollows does fall, it’s important to remember that while their hollows may no longer be useful as bird nesting sites, if left in place, they will provide useful habitat for many of the native reptiles in time.
So while fire can leave scars on the land and reduce the number of old hollow-bearing trees, in healthy ecosystems fire is important to regeneration of ephemerals and the wildlife can cope readily with small-scale and patchy fires. It’s the large fires that take hold in fuel-rich areas that are a concern, and fire in fragile systems such as rivers can result in a change in nutrient levels and erosion on the banks. The sentimentality of the beautiful old River Red Gums means that fire in Todd is an unwelcome event that we would like to avoid, which means removing Buffel Grass before a fire takes hold.
Want to do your bit? There are several keen Landcare (https://www.alicespringslandcare.com/ ) groups in Alice Springs that are removing weedy species to make way for the native forbs, which is proving successful at preventing the spread of large fires. Join a group near you!