Burning for Brolgas
..and some grazing, too
There's hope for wetland managers tackling a serious problem throughout the north – choking grasses. CSIRO Sustainable Ecosystems and QPWS have been testing fire and grazing as tools to knock dense Para grass Brachiaria mutica in the Townsville Town Common Conservation Park, north Queensland. The results are promising, attracting interest from production and conservation land managers.
Funded by the NHT through the Burdekin Dry Tropics NRM Board.
← The Townsville Town Common was once an important breeding site for Brolgas (P Merritt)
How it happened Brolgas breed as separate pairs in the Wet Season then in the Dry, join flocks to feed and roost in coastal and inland wetlands. Bulkuru sedge tubers, a key food, were once abundant on the Townsville Town Common. Up to 100 breeding pairs were reported in the Wet and flocks of 1000s in some Dry seasons, but by the mid 1980s flocks totalled less than 500. Today, no Brolgas breed on the Common. And in the Dry? Townsville BOCA and Birds Australia members count the Town Common Brolgas each October for the North Queensland Crane Count, and their maximum tally since 1997 is 18 birds.
Double whammy How can a Conservation Park virtually lose its icon bird? Likely the Common's potential to support breeding Brolgas and Dry season flocks is permanently lower due to drainage and building in the Bohle Basin, limiting water flows to the Common wetlands. But even this potential is on hold, with wetter parts of the Common locked up in a dense blanket of Para grass that chokes out Bulkuru sedge and inhibits Brolgas feeding or roosting. Para took over after cattle were removed in the 1970s, clogging swamps and adding to fire fuel loads. The build-up was perhaps compounded by public opposition to controlled burning so close to town.
With its high profile and lost waterbirds the Town Common is an ideal site for the CSIRO and QPWS, with community support, to test control methods for use across many weed-invaded wetlands in northern Australia.
Testing the tools
← Plot 12 with dense Para grass, August 2004, before grazing and burning. Townsville city, and hinterland ranges, in the background (CSIRO Sustainable Ecosystems)
The trials In the Dry season (August 2004) the project team marked and fenced 12 x 6ha Para grass plots. Over the next few months some were left alone (the ‘do nothing’ option); some burnt; some grazed; and some burnt, then lightly grazed. Cattle were removed before the first major rains, to avoid disturbing breeding Magpie Geese. Vegetation, birds and mammals were identified and measured/counted at every stage.
← Plot 7 four months after burning (CSIRO Sustainable Ecosystems)
The results The short-term one-season trial was a success. Compared with the ‘do nothing’ plots, burnt or grazed plots had 25% living grass ‘mat’ (biomass); burnt-and-grazed plots had 4%. Native plant diversity increased, with native sedges and grasses notably more frequent.
Brolgas feeding on burnt plots, August 2004 (CSIRO Sustainable Ecosystems) →
Bird diversity and numbers also rose, except for a few species that favour dense grass. Some Para grass tussocks were completely killed by fire. But heavy grazing for only one season, without fire, left a heavy mulch likely to suppress native plant growth the following Wet.
The next steps
Para on the Common is expected to reinvade after only a one-off treatment. Next, the project will repeat the trials to find –
- Does annually burnt and/or grazed Para come back seriously after every Wet, or progressively decline after several seasons of control?
- How will different combinations of control methods succeed and interact, over time?
- What will be the most effective and cost-efficient control program for wetland conservation combined with production, and for conservation-only properties which often ban grazing?
- Can the methods be applied to similar weeds like Olive Hymenachne (Hymenachne amplexicaulis), a Weed of National Significance?
Ozcranes thanks Dr Tony Grice of CSIRO Sustainable Ecosystems, Townsville for allowing us to report project results. For more information, email Dr Grice or visit the Burdekin NQ Dry Tropics NRM Board.
Moves to fence off wetlands will likely increase the number of Brolga and Sarus Crane sites affected by dense growth – more in Ozcranes Fencing pages. Links to other useful sites for crane and wetland conservation are in Ozcranes Resources.