Celebrating Biodiversity on World Environment Day 2020
World Environment Day is an international opportunity to raise issues requiring environmental action. This year, the theme is biodiversity!
Through our own experience here in South Australia with the recent massive bushfires across South Australia concerns about the recovery of biodiversity from the fires is in the front of mind for many members of the community.
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.
International Fascination of Plants Day, 18th May, has been celebrated since 2012 and has provided a focus for plant enthusiasts to share their interest and passion for the amazing world of plants. Last year events across 51 countries were held. While we are still primarily working from home the Staff and Honorary Research Associates of the Science and Conservation programme at the Botanic Gardens and State Herbarium (South Australia) decided to celebrate by sharing some of the plants they find fascinating!
Griffithsia monilis, a small, annual alga with delicate chains of ruby coloured cells, looking like sweets good enough to eat, spectacular under the microscope—Bob Baldock
Cephalotus follicularis (Albany Pitcher Plant), is a single species in its own family and endemic to near where I grew up in south Western Australia. These carnivorous plants are fascinating because they are not closely related to any of the other carnivorous plants such as Drosera (sundews)—Michelle Waycott
Ginkgo biloba, Royal Botanic Gardens Kew, on its 250th anniversary in 2012, with admiring cohort of ‘geriatric teenagers’—Pam Catcheside
Capparis spinosa ssp nummularia, I’m fascinated by the way the flowers change from bright white (to attract pollinators at night) to pink once its too late—Helen Vonow
Rhizanthella gardneri, an underground orchid. These fascinating plants flower where no-one can see them and only some animals can find them—that’s not an orchid! —Robyn Barker
CC BY 2.0 Fred Hort
Ptilotus sp. (mulla mulla), amazing combination of texture, colour and shape in this smoky pincushion—Teresa Lebel
Two bearded orchids from Mark Oliphant Reserve. One is Calochilus robertsonii, a bearded orchid. The other is Pterostylis plumosa, a bearded greenhood. Both are trying to trick insects into pollinating them. I like the thrill of the hunt of trying to find them 🙂 —Andrew Thornhill
Reflections—an ordinary little stump can be turned in to an intriguing complex pattern—Teresa Lebel
Acrotriche fasciculiflora (Mt Lofty Ground-berry) is fascinating for its cauliflory, with flowers packed around the base of its main stems, an adaptation for pollination or fruit dispersal by small vertebrates perhaps?—Peter Lang
Washingtonia robusta (Cotton Palms), native to Mexico, can be seen emerging from the skyline in older suburbs and rural towns in drier districts. An occasional though generally benign weed, it appeared in gardens and parks in the later 19th and early 20th centuries—Laurie Haegi
Tillandsia ‘Houston’ (T. stricta x T. recurvifolia) are fascinating because of their novel growth habit (air plants) and because they lend themselves so readily to decorative use around the home—Manfred Jusaitis
Hakea aenigma, found only on the western lateritic sands of Kangaroo Island, is sterile and unable to fruit. It resprouts after fires from suckers over distances of more than 30 km. A single plant that is an evolutionary dead-end but surviving for perhaps thousands of years—Bill Barker
Nuytsia floribunda, The West Australian Christmas Tree, is a parasitic plant that is actually a mistletoe! It has a unique way of parasitising the roots of nearby plants, a set of hard and sharp ‘shears’ cuts through the root so Nuytsia can attach feeding points to enable it get water and minerals from its hosts—Ainsley Calladine
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.
(1) J. Kellermann, Nomenclatural notes and typifications in Australian species of Paliureae (Rhamnaceae). (2.6mb PDF)
This is the first paper resulting from the ABRS funded research project on the plant family Rhamnaceae, undertaken by State Herbarium botanist Jürgen Kellermann and colleagues from around Australia. The nomenclature of the species of Hovenia and Ziziphus occurring in Australia is reviewed, including the role of the Paul Hermann herbarium in London; some plant names are typified. A key to the the Australian species, as well as line drawings are also provided.
(2) E.M. Davison, D. Giustiniano & J.F. Haska, Clarification of the type locality of Amanita peltigera (Agaricales, Amanitaceae), phylogenetic placement within subgenus Amanitina, and an expanded description. (2.3mb PDF).
The authors examined the native mushroom Amantia peltigera with molecular and morphological methods. They show that the type collection is from South Australia, not Western Australia, as stated in the original publication. They place the species in a phylogeny of the genus and provide a revised description and illustrations of A. peltigera.
Amanita peltigera, collected on Kangaroo Island. Photo: J.F. Haska.
To access content of all volumes of Swainsona and the Journal of the Adelaide Botanic Gardenssince Vol. 1 (1976), please visit the journal’s web-site at flora.sa.gov.au/swainsona.