Burning Issues

Over the years, we have published several blogs concerning orchids and fire. At the beginning of the year, Renate Faast spoke at the NOSSA February meeting. John Eaton wrote an extensive summary of her talk which is reprodued here as it appeared in the 2019 March edition of the Native Orchid Society of South Australia Journal, Volume 43 Number 2.

Renate’s take home message was that we cannot make sweeping statement about orchids and fire, each species responds differently and we need to take this into account when planning proscribed. This was something that Dr Michael Duncan also brought out in his 2009 report following the Victorian Black Saturday fires – see Orchids and Fire.

An interesting aside to Renate’s research was her observations of white-winged choughs – see the paragraph Not All Relationships are Friendly.

Stipi fire 3Guest Speaker Notes                                John Eaton

At our February 26th meeting, thirty NOSSA members were treated to a stimulating talk by Dr Renate Faast from the University of Adelaide – our first guest speaker for 2019.

Renate acknowledged the support her project received from an Australian Research Council (ARC) grant under the Linkage Program which promotes national and international research partnerships between researchers and publicly funded research agencies – in Renate’s case – support from the University of Adelaide, SA Museum, SA Water, Forestry SA, The Australian Orchid Foundation, the Nature Foundation of SA, The Environment Institute and the SA Government.

Mixed Messages

Renate had been getting mixed messages from the field observations people had made following prescribed burning or bushfires. This ARC grant enabled her to study the impacts of prescribed burning on native terrestrial orchids.

Renate found that the response of orchids to controlled burns suggests that there are winners and losers amongst orchids: Naked sun orchids responded really well to a controlled burn with 6 plants growing to 83 plants. REALLY good news for that species of orchid but the reality is more complicated than that and this study suggests that there are no generalisations that can be drawn with any confidence about regeneration following prescribed burns or bushfires! In view of the complex interactions between orchids and other plants, and between orchids and bird-and-animal grazers, orchids rely on so many things to go right in order to set seed and recruit new plants into a population. With the exception of a few self-pollinating species, most orchids rely on pollinators for seed production. For non-clonal species, releasing seed is the only way to ensure the species’ long-term survival!

Not all relationships are friendly

Over 80% of orchid flowers had been grazed at some sites. No flowers means no seeds. Renate’s film clips embedded in her PowerPoint dramatically showed the extent of orchid predation by birds such as white-winged choughs and currawongs. They picked off the flowers quite deliberately, leaving behind an intact stalk. Five flowers were grazed every 10 sec (that’s at a rate of 30 flowers/min!) And there are all the other orchid grazers such as roos, deer and rabbits as they move through a patch, often only grazing part of the stem, in a far less targeted and thorough way, compared to these birds. All of these interactions play a key role in whether seeds are released to keep the population viable.

The Mount Bold Fire prompt

160219 Anita Marquart Melangyna collatus on Caladenia rigida

While engaged in her PhD research into reproductive ecology of spider orchids, Renate heard that a fire at Mt Bold had led to a “profusion” of Caladenia rigida flowers! The Victorian bushfires had also prompted changes to prescribed burning practises in South Australia. The combination of these two events led Renate to explore the effect of fire on the interactions orchids have with other plants and animals – leading her to ask such questions as:

  • Does fire promote the flowering of spider orchids (e.g. Caladenia rigida, C. behrii, C. tentaculata) and Glossodia major?
  • If there are more flowers following fire, will they be pollinated and will they set seed?
  • How does burn timing influence this response?
  • Do all species respond in the same way?

These are all critical issues to consider if we are to ensure a self-sustaining orchid population in the future.

1710 JH Arachnorchis tentaculata sm

Seasonal Factors

There are seasonal influences on the effects of a burn. The response to a summer bushfire could be quite different from cooler season burns in autumn and spring. And even if some orchids are stimulated to flower, it doesn’t necessarily mean that they will end up producing and releasing more seed – which is what really matters for the long-term survival of the orchid population.

Orchid monitoring was carried out in several sites and included 1 autumn, 3 spring burns and 4 adjacent unburnt control sites across the Mt Lofty Ranges (NE of Adelaide). Renate followed the fate of 4 species by tagging up to 150 plants for each species. Renate’s presentation focused on the Millbrook sites where she studied C. rigida and G. major before and after a prescribed burn conducted in Autumn 2013. Unfortunately and fortuitously, her control site also became a bushfire site following the Sampson Flat Fire in January 2015. Fortunately, the Autumn burn site was not affected by the Sampson Flat Fire, so became something of a control site! Renate found that 97% of C. rigida did not emerge after the Autumn prescribed burn compared with 8% at the unburnt control affected site. Flowering was not promoted and no tagged plants flowered. A similar but less severe effect was recorded for Glossodia major.

Will these orchids recover in subsequent years?

Annual monitoring up until 2017, revealed that over one third of C. rigida plants did not re-emerge for 5 consecutive years after the autumn burn. Unfortunately, these plants are likely to have been killed by this burn, probably because the fire was conducted as the orchids were about to emerge. Interestingly, spring burns did not have a detrimental impact on the orchids studied, however, a proportion (18 – 28%) of C. rigida plants may also have been killed by the summer bushfires.

One of the more striking findings out of this research was the large increase in pollination for C. rigida following the bushfires – up to 65% of flowers (protected from grazing) produced a seed pod – an unprecedented rate for Renate’s research. It seems that in the sparse blackened landscape with very few other plants in flower, C. rigida had most of the attention for pollinators. However, the removal of understorey cover also meant that grazing rates were higher after the fires, and most of the flowers that were not protected inside cages were eaten. This meant that there was no actual benefit to the orchids, as there was no increase in seed release. All of these responses were short-lived, and by spring 2016, pollination, grazing and seed release rates were much the same as before the fires.

Arachnorchis behrii 1

Arachnorchis behrii (Pink Lipped Spider Orchid)

Renate’s Conclusions:

All species are not equal – fires may benefit some species others don’t fare so well;
All fires are not equal;
Autumn burning may be detrimental to SOME species;
Bushfire may benefit seed release, only if grazing pressure is low – and
Flowering was not promoted by any fire.
More research is needed on other species, and in different habitats.

Therefore, Renate pointed out that no generalisations can be made about her observations!

Some good news that has come out of this research:

  • Burn practices are changing, with land managers taking into account the timing of prescribed burns, and bestattempts are made to avoid late autumn burns in areas containing threatened (early-emerging) orchids;
  • Impacts of fire on reproductive success appear to be short-term

Renate’s hope is that one day, the message will get out there that while some orchids can respond well to burning, this isn’t the case for all species – and that we still have a long way to go before we will really understand the complexities that underlie these different responses with any degree of predictability. Renate also warned that over a third of SA’s orchids are threatened with habitat loss, weed invasion, pollinator loss, grazing and fire regimes.

Renate’s address was followed by a flurry of burning questions and observations. It is hoped that we NOSSA members will use Renate’s conclusions to guide and inform our own anecdotal field observations and test our underlying assumptions and prejudices about the effects of burning on orchid viability – especially as we enter an unprecedented and potentially species-destroying period of human – induced global warming.

Stipi fire 2

 

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