Sugar gum woodland in Wanilla Conservation Park, regenerating by epicormic regrowth, c. 3 years after the Wangary fire. Photo: Peter Lang.

In January 2005, the Wangary wild fire swept rapidly across southern Eyre Peninsula under conditions not dissimilar to those of the recent Kangaroo Island and Mount Lofty Ranges fires, and with reports of particularly intense and hot burns.

The Wangary fire burnt vegetation quadrats at nine different sites, which had been surveyed only the previous year as part of the Biological Survey of South Australia program. This provided an ideal opportunity to investigate post-fire recovery and changes to plant and animal species composition. The quadrats were re-surveyed using the same methods in 2007, three growing seasons after the fire. Findings were published by State Herbarium botanist Peter Lang and (the then) manager Peter Canty, together with Robert Brandle, in the following report:

P.J. Lang, P.D. Canty & R. Brandle, Biological impacts of the 2005 wildfire on southern Eyre Peninsula: monitoring post-fire recovery within three years using Biological Survey of South Australia sites. (12.7mb PDF)

Less than three years on, the vascular plant species richness had increased substantially from pre-fire levels in nearly all sites, with species losses outweighed by gains. The total species count for all sites rose by 43 (from 150) for indigenous species and by 19 for alien species (from 25). However, an index based on cover scores, showed a large disparity in responses of alien and indigenous species, with a post-fire jump of 136% for alien species compared to only 11% for indigenous species.

The report also documents and illustrates the regeneration modes observed — re-sprouting, seedlings or both (something that we plan to pursue in a future blog). Some sugar gums, for example, retained their major branches intact and had been able to regenerate quickly by epicormic growth. Some were killed in their upper parts and were re-sprouting basally, whilst others were completely destroyed and had to rely on seedling recruitment to regenerate.

Sugar gum open woodland with dense and diverse understorey, well recovered 15 years after Wangary fire, Wanilla Land Settlement Conservation Park. Photo: P. Lang.

Sugar gum (Eucalyptus cladocalyx) is a very distinctive eucalypt that is endemic to South Australia, with three isolated populations on Eyre Peninsula, Kangaroo Island and in the southern Flinders Ranges, now treated as different subspecies (see also the Flora of South Australia chapter on eucalypts; 33.8mb PDF). Recent DNA sequencing (both nuclear and chloroplast genes/markers) confirms that it has no close relatives. It is also ecologically significant, as a dominant tree for distinctive plant communities with varied and, often, species rich understories.

Concerns were raised about the impact of the Wangary fire on sugar gum plant communities, and these may be highly relevant for the recent Kangaroo Island fires, which also burnt large areas of sugar gum woodland. It seems that on certain soil types and where the fire was particularly intense, mass regeneration from seed occurred and that the highly successful adaptive response of this eucalypt may cause problems.

The following comments were made on page 39 of the report:

Sugar Gum forms a unique community both structurally and floristically that is of high conservation importance. It is valuable as plant and animal habitat, due in part to its structural characteristics in readily producing hollows, abundant fallen timber and, beneath its umbrella-like canopies, much open space which provides for a variety of diverse understorey types.

Depending on the severity and frequency, fire can have deleterious impacts by consuming a substantial amount of fallen timber and destroying hollows. In addition, where major seedling recruitment of Sugar Gum occurs, the structure of the resulting community will be changed substantially due to crowding and consequent overshadowing and nutrient/water competition. This effect has been observed for Sugar Gum regeneration in the Flinders Ranges over a 20 year period of following a severe wildfire in Mount Remarkable National Park. This fire led to the development of many dense stands of thin-stemmed trees, understorey suppression and a much reduced capacity for hollow formation. In both the Tucknott Scrub sites (KOP00501 and KOP00601), there was a dense and extensive establishment of seedlings from 10 cm to 2 m tall […]. Without intervention, it is expected that over the ensuing decades these will produce a similar crowded overstorey structure as observed at Mt Remarkable; indeed it is highly unlikely that natural thinning could produce a typical Sugar Gum community structure with well-spaced large trees in the lifetime of these stands. Failure to restore this structure will affect recovery of dependent wildlife species.

Mass recruitment of sugar gum seedlings (orange-coppery coloured foliage in mid-distance) amongst sparse existing trees, Tucknott Scrub Conservation Park, c. 3 years after the Wangary fire. (Foreground seedlings are golden wattle). Photo: P. Lang.

Recent observations on southern Eyre Peninsula, now 15 years on from the Wangary fire, show that those predictions are proving correct. In some places, particularly lowland areas with sandier soils and heathy vegetation, sugar gum plant communities have regenerated well and still retain their diverse open structure (see first two of above images). Elsewhere, however, in hilly areas such as in Charlton Gully, and the disturbed woodlands of Tucknott Scrub Conservation Park, the previous woodland structure with large well-spaced trees supporting diverse and species-rich understories has been lost. Instead there are now masses of closely crowded young erect trees resembling woodlots with understorey plants mostly eliminated by overshadowing and competition for nutrients and water.

Dense sugar gum regeneration near Tucknotts Scrub Conservation Park, 15 years after Wangary fire. Photo: K. Pobke.

Dense regeneration of golden wattle (Acacia pycnantha) has a similar effect, but only for a limited period due to its relatively short life span. It is a very different scenario though for sugar gums which can persist for centuries. While some natural thinning of sugar gum may still occur as the trees continue to age, we should not expect that they will return to the original structure as they reach maturity: it is well known in forestry practice that initial spacing affects resultant tree habit and size. As well as supressing understorey, the greater density of smaller and less spreading mature trees is likely to result in reduced and delayed hollow production, which is another concern since the availability of hollows can be a limiting factor for many wildlife species.

Observations of older post-fire sugar gum regeneration in Mount Remarkable National Park, and some massed post-grazing recruitment of red gum in the Mount Lofty Ranges, support the Eyre Peninsula observations that natural thinning is not going to return these formations to a more open woodland structure within the time frame of human life-spans at least, and probably much longer. This raises the issue of how the original open vegetation structure arose and was maintained, and whether active management involving selective thinning is now warranted as a conservation measure.

Dense sugar gum regenerated from seed 15 years after Wangary fires, showing deep leaf litter and lack of understorey, Tucknott Scrub Conservation Park. Photo: K. Pobke.

Prepared by State Herbarium botanist Peter Lang

(acknowledging helpful discussions with DEW ecologists Jason Van Weenen and Kat Pobke).

Eucalyptus leptophylla, regenerating by regrowth from lignotuber, after fire in Billiatt Conservation Park, Murray Mallee. 18 June 2014. Photo: P.J. Lang.

The eucalypts are the epitome of resilience in surviving and regenerating after a bushfire. What first appears to be blackened and destroyed forests of tree trunks, returns as thousands of new shoots all over tree trunks and branches. It is almost without a doubt that the eucalypts have come to dominate Australia with the help of fire, given their ability to quickly recover from it. What do the eucalypts do that many of the other plants don’t, and what can we expect to see happen to eucalypts in the South Australian areas that have been burnt?

First of all, there is more than one way that eucalypts recover from fire. Some species recover by sprouting new leafy shoots all over their trunks and branches. This is called epicormic regrowth and is possible because many eucalypt species have buds buried deep below their bark that are protected from fire. It is triggered by the plant being under stress. Quickly regrowing leaves all over the burnt structure means that it is essentially functioning as a tree again and this is a massive advantage over other plants that have to regenerate from seed, to become a sapling, and then a tree, a process that can take years.

Eucalyptus cladocalyx, regeneration by epicormic regrowth, nearly 3 years after fire in Wanilla Conservation Park, Eyre Peninsula. 24 Sep 2007. Photo: P.J. Lang.

Other eucalypt species grow from lignotubers. A lignotuber is woody swelling at the base of a tree trunk. This structure can often be buried deep within the soil, another way of protecting a plant from fire. While the plant above the ground will be destroyed by a fire, the underground material remains untouched. New shoots appear from the lignotuber and the plant begins growing again from the ground up.

A third way that eucalypts can regenerate is from seed, and some eucalypts can only regenerate this way. This strategy involves plants growing from seedlings into adults, setting seed which falls to the ground and forms a seed bank. A fire then removes the adult plants and new seedlings are generated from the seed bank that then repeat the cycle. The risk of this strategy is that a second fire will occur while plants are seedlings or saplings that haven’t reached a stage to make new seeds, thus removing the species because there is no back-up seed bank. Eucalyptus regnans, the mountain ash of Victoria and Tasmania which is the tallest flowering plant in the world, is an obligate seeder.

Eucalyptus angulosa, regeneration from seed, nearly 3 years after fire in Murrunatta Conservation Park, Eyre Peninsula. Photo P.J.Lang.

With that quick crash course in regeneration strategies of eucalypts we can now turn our attention to South Australian species and what we can expect to see from them after a fire. In 2006 Dean Nicolle from the Currency Creek Arboretum published a paper that summarised the regenerative strategy of every eucalypt species. Below are two tables that are a subset of Dean’s work and give details for each native South Australian eucalypt in the Kangaroo Island (Table 1) and Adelaide Hills (Table 2) 2019/2020 fire zones. (A “combination sprouter”, listed in the tables below, can regenerate from both, epicormic shoots as well as from lignotubers.)

The good news is that not one of those eucalypt species is an obligate seeder and so the threat of a second fire in the next few years removing a species from these areas is not high. The majority of eucalypts in these areas have lignotubers and should successfully regenerate. There are things we need to be observant about though. We think that these fires were extremely hot in some areas, perhaps hotter than has ever been experienced before. While eucalypts are adapted for fire we are uncertain at what maximum temperature plants can survive and regenerate. Past fires have indicated that if the thermal tolerance of species is exceeded then they will not regenerate.

Compiled by State Herbarium botanists Andrew Thornhill and Peter Lang.

Table 1. Regeneration strategies of eucalypts of Kangaroo Island.

Table 2. Regeneration strategies of eucalypts from the Adelaide Hills.

In a previous blog, we introduced three species that often occur after fire.

Other attractive species likely to be seen on Kangaroo Island and elsewhere are branched everlasting, Coronidium adenophorum (F.Muell.) Paul G.Wilson, purple daisy bush, Olearia rudis (Benth.) Benth., as well as ironstone mulla mulla, Ptilotus beckerianus (F.Muell.) F.Muell., this last species appeared in hundreds in post 2007 fire scars near the Ravine des Casoars.

Coronidium adenophorum, Olearia rudis & Ptilotus beckerianus (from LEFT to RIGHT). Habit of plants with flowers and new seedling (for O. rudis). Photos: SA Seed Conservation Centre.

Contributed by State Herbarium botanist Martin O’Leary.

Orange disc fungus, Byssonectria fusispora, surrounded by mosses. Photo: D. Catcheside.

Fungi are essential in all ecosystems, acting as recyclers, helpers of almost all plants and improving soil health.  After fire, much of the organic material in soils may have burnt, leaving a blackened mass of fine, silty particles and ash. The ash is highly alkaline and unfavourable for plant regrowth. The fungi help in restoration of soil health, as recyclers of burnt litter and wood and as partners with plants in re-establishing the vegetation.

Two disc fungi, orange Pulvinula archeri, brown-lilac Peziza tenacella. Photo: D. Catcheside.

A group of fungi whose spores germinate almost immediately after fire are the disc fungi (e.g. Peziza and Pulvinula, image above). These act as colonisers. Their fine thread-like hyphae bind soil particles, stabilising the soil and helping to reduce erosion. They change the highly alkaline ash (with a pH of up to 10) to soils which are approximately neutral (pH 7). Structurally, the hyphae form a network, a ‘scaffolding’, improving soil aeration and water percolation. The often dense carpets of disc fungi covering the bare soil not only reduce erosion but also provide protection for small plants such as mosses, grasses and herbs (see top image). As the fungal hyphae and plant roots grow their developing networks increase movement of gases and water through the soil. Other groups of fungi are saprotrophs, breaking down and recycling burnt litter and wood.

Coprinellus angulatus, a saprotrophic fungus (left image). Stereum hirsutum, a saprotroph on wood (right image). Photos: D. Catcheside.

Pam Catcheside and Danielle Calabro with a sclerotium of Laccocephalum mylittae. Photo: D. Catcheside.

There is a definite succession of fungi after fires.

Amongst the first to appear, often only a day or two after fire, are strange, hard, mushroom-like fungi with pores, not gills in the genus Laccocephalum (see image at bottom of this post). Their fruit-bodies grow from an underground storage-organ called a sclerotium. The sclerotium of Laccocephalum mylittae, native bread, was eaten by Aborigines (image on right). It may weigh up to 20 kg.

Yellow, orange, brown and black disc fungi appear. Some species fruit only in the first year after fire, others in the second and some for several years. As litter builds up recycling fungi break it down returning nutrients to the soil.

Mycorrhizal fungi (e.g. from the genus Laccaria, image below), which form symbiotic relationships with plants become re-established, collecting nutrients and water for the partner plant and receiving energy-giving sugars in return. Gradually, the web of life with all its complex communication systems regains momentum, habitats are re-established, insects and other animal life return and natural cycles continue.

We observed this pattern after the 2007 bushfires on Kangaroo Island. Since Flinders Chase National Park is relatively self-contained, weeds which often invade bare areas did not threaten the native systems. Keeping out weeds after a fire is a major concern.

Laccaria sp., a mycorrhizal fungus. Photo: D. Catcheside.

Another concern is that it takes time for the bush to re-establish itself, some studies showing that it takes at least five years but this time lapse varies with different habitats. We have found that most groups of fungi have returned to pre-fire levels. It is now 12 years since the last major fires on the island and Kangaroo Island has shown itself to be resilient.

Laccocephalum sp. showing swollen sclerotium. Image of herbariumspecimen PSC3033 before drying. Photo: D. Catcheside.

Further reading

Atlas of Living Australia. Geopyxis carbonaria (Alb. & Schwein) Sacc.

Catcheside, P. (2009). Phoenicoid discomycetes in Kangaroo Island. Fungimap Newsletter 38: 5-8.

George, P. (2008). Fungimap survey on Kangaroo Island. Fungimap Newsletter 36: 13-15.

Kalotas, A.C. (1996). Aboriginal knowledge and use of fungi. In Orchard, A.E. (Exec. Ed.), Mallett, K. & Grgurinovic C. (Vol. Eds.). Fungi of Australia, Vol. 1B: Introduction-Fungi in the Environment. (Australian Biological Resources Study, Canberra).

McMullan-Fisher, S. J. M., May, T. W. & Keane, P. J. (2002). The macrofungal community and fire in a Mountain Ash forest in southern Australia. Fungal Diversity 10: 57-76.

Robinson, R.M. (2009). Laccocephalums on Kangaroo Island. Fungimap Newsletter 37: 6-7.

Robinson, R. (2007). Laccocephalum mylittae – Native Bread. (Dept of Environment & Conservation: Manjuimup). [Fungus Factsheet 18/2007].

Spooner, B. & Roberts, P. (2005). Fungi. (Collins: New Naturalist Library).

Yales, D. (2019). Fire-spawned forest fungi hide out in other organisms, study finds. PHYS.ORG website.

Written by State Herbarium Hon. Research Associate Pam Catcheside.