Soil moisture results
- Soil samples taken in April show that the average soil moisture content at the surface was 1.4% and at 20cm depth it was 3.4% - so pretty dry already and reflective of the early end to the wet season.
- There was no evidence to suggest any difference in soil moisture between treatments based on whether the plots were burnt or not.
Tagged plants results
At the start of the experiment, we tagged 289 plants and re- measured them over time. Included in the 289 plants were 144 feathertop plants, 58 weeping Mitchell grass plants and 87 curly bluegrass plants which were fairly equally spread throughout the 16 experimental plots.
Measurements on these plants included the maximum width of the base of each plant, the width perpendicular to that, and estimated percentage of the base that was moribund (dead). From these measurements the area of living basal area for each plant was calculated. The number of seed tillers present on each plant at each visit was recorded as well as whether any plants had died.
The results showed that only three of the 289 tagged plants died. All three were feathertop plants that were burnt in July.
According to Table 1, burning strongly stimulated seed tillering in curly bluegrass but did not seem to have any impact on tillering in weeping Mitchell grass or a strong influence on seed tillering in feathertop.
Table 1: Average number of seed tillers per plant
At Start (July17)
At End (Apr18)
Unburnt weeping Mitchell
Unburnt curly bluegrass
July burnt weeping Mitchell
July burnt feathertop
July burnt curly bluegrass
Sept burnt weeping Mitchell
Sept burnt feathertop
Sept burnt curly bluegrass
The tagged plants had more living basal area at the start of the experiment in July 2017 than at the end in April 2018 and this was true even for plots that were never burnt (see graph below). Given that the plants were protected from grazing for the entire experiment, this suggests that the 2017/18 Wet Season was harder on all species compared to the year before.
Although all plants (both burnt and unburnt) decreased in basal area, it is apparent that the impact was much higher on those plants that were burnt in July (orange bars) and September (grey bars):
Table 2 shows the change in average living basal area per plant broken down by species and burning treatment. The only plants that increased in basal area between the start and end of the experiment were feathertop wiregrass plants that weren’t burnt. It would appear that the September burn had a bigger impact on basal area than the July burn but more statistical analysis is required.
Table 2: Change in average living basal area per plant
Burnt in July
Burnt in Sept
Research conducted in western Queensland showed that high mortality rates of feathertop can be achieved when a moderately hot fire is applied to feathertop in July or August. This timing maximises the period that the shallow-rooted feathertop plants are drought-stressed. Success appears to be highly dependent on having very low or no soil moisture before and after burning – if there is soil moisture present at the time of burning, or within six weeks after burning, the burnt plants can re-sprout and mortality rates can be as low as 10-30%.We are currently considering repeating the experiment in August, as historical records indicate that it is not uncommon for Newcastle Waters to receive rain in November, to see whether the early end to the wet might help us kill more feathertop this year. This timing should ensure the soil moisture is low enough to burn, but also reduces the chance of receiving rain within six weeks after burning.
We still have a large amount of biomass, ground cover and species composition data to analyse which may provide further insights into the impact of the burns on both the feathertop and also the desirable 3P species. Stay tuned!
Last updated: 23 September 2019