Fire plays an important role in grasslands and grassy woodlands – but can burning save the Button Wrinklewort?
The Button What?
The pleasingly named Button Wrinklewort (Rutidosis leptorrhynchoides) is a native daisy, with a yellow button-like flower. Once widespread in the grasslands and grassy woodlands of eastern Australia, it is now only known from a few small populations around the ACT, and several in central Victoria. This decline has been driven by land use changes and loss of habitat.
Back in 2011 (in my good old undergraduate days), I did a small research project with fellow student Amy Macris looking into the effects of fire on the Button Wrinklewort, and how it could be used to better manage this endangered species.
Why is fire important?
The ACT Government’s current management guidelines (ACT Government 1998) recommend that burning should be avoided in Button Wrinklewort populations to prevent losing any of the existing plants – but this policy could actually be doing more harm than good.
Many of the areas where Button Wrinkleworts have survived are frequently burnt as part of their management, such as railway reserves. In some cases, when management techniques changed from burning to slashing or herbicides, the Button Wrinklewort population subsequently declined (Scarlett and Parsons 1990).
Many grassland plants are adapted to frequent fires, and some require burning to stimulate flowering or release seed dormancy (Lunt 1994). Others rely on fire to create gaps in the dominant grasses, which in the absence of fire can become too dense and smother any seedlings that germinate (Coates et al. 2006; O’Bryan et al. 2009; Prober et al. 2008; Prober et al. 2007). Button Wrinkleworts are known to prefer open grasslands – a study by Morgan (1997) found that they need gaps of at least 30cm to germinate, and plants growing in larger gaps (>100cm) have better survival, growth and reproductive rates.
Fire can also help to control exotic weeds that out-compete plants like the Button Wrinklewort. Studies have shown that unburnt or grazed sites tend to have a greater proportion of exotic species than regularly burnt areas (Stuwe and Parsons 1977; Lunt and Morgan 1999). But others have shown that fire can stimulate growth of some exotic species – especially those that are fire tolerant or that invade following disturbance (Henderson and Hocking 1997; Lunt and Morgan 1999).
We wanted to know if burning in a woodland would have an overall positive or negative effect on the Button Wrinklewort population, either directly or indirectly through influencing germination or competition.
The study site – Stirling Park, Yarralumla
One of the largest remaining populations of Button Wrinkleworts (approx. 70,000 individuals) occurs in Stirling Park, on the south side of Lake Burley Griffin in the centre of Canberra. The park is bordered by residential areas, so it is necessary to conduct regular fuel reduction burns to protect the surrounding houses from bushfire. In May 2011 the ACT Government planned to burn a small area of the park, providing an opportunity to study the effect of burning on the Button Wrinklewort population.
We set up 12 plots in the area where the burn was planned, and 12 additional plots in a neighbouring area to act as controls. The two areas are shown on the map (burn area in red, control area in brown). The plots were placed in areas where Button Wrinkleworts were already growing, because they have a very patchy distribution across the park.
What did we do?
At each of our 24 plots, we estimated percentage cover by recording everything that intersected a vertical line placed at 10cm intervals along a five metre transect. We classified the ground cover as either Button Wrinklewort, bare ground, litter, native grass, native forbs, shrubs, trees, or weeds. We also counted the number of Button Wrinkleworts in the area one metre either side of the transect. There was a strong correlation between the percentage cover estimates and the number of individuals we counted, showing that the transect method provided a good estimate of the population.
A few weeks after the burn, we estimated the fire severity using the same transect method, but at each 10cm we classified the ground as burnt or unburnt. The burn was very patchy so for the analysis we split the treatment plots into heavily burnt (7 plots, >10% burnt) and lightly burnt (5 plots, <10% burnt).
What did we find?
After the fire, there was a slight reduction in the cover of Button Wrinkleworts but this was not significant. We noticed that even when all the above-ground material was burnt, most plants were beginning to resprout from rootstock. The reduction in cover was probably due to this loss of above-ground material, so the plants were less likely to intercept the transect.
We also found that in the heavily burnt plots there was a significant increase in the amount of bare ground, and a reduction in the cover of native grass and weeds. This may indirectly benefit the Button Wrinklewort in the longer term by reducing competition and forming gaps that are important for germination and survival.
In such a short time-frame, it was impossible to tell whether burning has a positive or negative effect in the long term. Any benefit to the Button Wrinklewort population would probably only be visible after several years, as the fire may stimulate increased flowering and seed production as well as providing a ‘germination niche’. There could also be a delayed negative effect, as the grasses and weeds may also get a positive boost from the burn.
Three years on, what has changed?
In September 2014, Lynette Matthews, another student from CIT (Canberra Institute of Technology), repeated the monitoring to see what changes had occurred in the three years since the initial burn. Unfortunately, in that time two of the plot markers in the burnt area had been lost, leaving only four unburnt and six burnt plots. Given the already limited number of samples, this meant that the results were less reliable.
Using the transect method, Lynette found that the percentage cover of Button Wrinklewort had declined in the treatment and control plots, with the biggest decline in the heavily burnt plots. However, the actual number of plants in the plots had increased, with the greatest relative increase in the heavily burnt plots (although they had the lowest absolute numbers). This discrepancy may be at least partly explained by sampling error and the fact that the monitoring was done by different people.
Lynette noticed that there were three age groups of plants: mature plants, seedlings (less than 8 leaves), and young plants which were assumed to have germinated post-fire. Compared with 2011, there was a huge increase in the number of seedlings across all sites, but this was not related to the burn and is more likely to be the result of increased rainfall over the last few years.
The fire did not seem to have stimulated weed growth – in fact, there was an overall reduction in weed cover. This was probably due to weed control programs being carried out in the park.
What did we learn?
As a student project with very limited sampling, the results of this study should be taken with a grain of salt. This was my first foray into the world of ecological research, and it taught me a very important lesson about how difficult it is to account for the inherent variability of ecological systems. It also taught me the importance and challenges of long-term monitoring.
The results of the initial study seemed to suggest that fire did not have any negative effect, and may have a positive effect in the long term. After three years however, there seems to have been a decline in the Button Wrinklewort population (although sampling error made this difficult to confirm), and other changes to the ecosystem were probably more likely to be due to rainfall or other management actions (i.e. weed control) rather than the burning.
The effect of fire on the Button Wrinklewort is still unclear, so it should still be used with caution. Future burns planned in Stirling Park in 2015/2016 will provide an opportunity for further investigation with a greater sample size.
The results of the initial study were published in Australian Plant Conservation (Volume 20 number 4) available here.
ACT Government (1998) Button Wrinklewort (Rutidosis leptorrhynchoides): An endangered species. Action Plan No. 8. E. ACT. Canberra.
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