Gary Bacon’s October 2025 Report

Report on the Dig Tree Site

Approvals for Botanising Project

The Council of the Royal Historical Society of Queensland (RHSQ) approved in April 2025 a proposal that the Dig Tree Reserve (the Reserve) be botanised pro bono and voucher specimens of in situ plants be collected and deposited within the Queensland Herbarium (QHerb), cognisant that no formal collection had previously been made.

Linkages were established with the QHerb and an itinerary developed. The botanising of the Reserve was effected 19-20 August 2025.

History Depot Camp 65.

This is the site on the Cooper Creek of the Burke and Wills expedition Depot Camp 65 from which Burke, Wills, King and Gray journeyed to the Gulf of Carpentaria in 1861. The depot party remained at this camp of 17 weeks and returned to the Darling River after burying supplies near the 'Dig' Tree. Burke, Wills and King returned to this depot during the evening of 21 April, the day that the depot party departed. Burke and Wills perished some weeks later near Innamincka.

The loss of seven men including the leaders was, in the view of later historians, ‘the direct result of the deadly and irretrievable- error of placing the incapable man in the responsible position! Carlyle's " unutterably fatal man put in the high places of men"! Nevertheless, the three blazed icon coolibahs, remain as a memorial to the first north-south continental crossing expedition and a symbol of the perseverance and hardships endured by the early explorers.

The Reserve

The land surrounding the icon trees is under the trusteeship of the RHSQ and located within the 7275 square kilometre Nappa Merrie property owned by Morella Agriculture, a family business operated by the Coulton family. The Reserve was first gazetted in 19642 covering about one acre. Following a further survey in the site was gazetted in 19873 as R7 being lot 1 on plan CPR4 an area of 4470 square metres in the Parish Oontoo, County Cooper, on the bank of Cooper Creek in south-west Queensland (Attachment 1).

The Burke and Wills Dig Tree was entered on the Queensland Heritage Register in 2003. The Reserve was entered 2016 on the Australian Heritage Database.

In 2020, the Dig Tree Visitor Experience Redesign Project refurbished the site with a path and boardwalk to protect the roots of the heritage-listed trees. Interpretive signage was installed with replicas of the carved blazes (Attachment 2). The project was funded by RHSQ, Bulloo Shire Council, the Commonwealth Government’s ‘Australian Heritage Grants Program’ and the Queensland Government’s Department of Environment and Science ‘Heritage Grants Program’, and Department of State Development ‘Building Our Regions Program’. In 2024 RHSQ installed Wi-Fi to allow payment of the Conservation Fee ($20 per vehicle, $60 per bus, valid for six months) via a QR Code4.

Currently the Reserve is managed by the RHSQ with the active support of Nappa Merrie Station and the Bulloo Shire Council, with an on-site Ranger (Colin Mace).

Climate

Cooper Creek, an ephemeral water source, was named by explorer Charles Sturt in 1845, during his expedition to locate an inland sea after Sir Charles Cooper, the then Chief Justice of South Australia. The local Yandruwandha people refer to it as Kooropari. It originates as the Barcoo and Thomson Rivers on the Great Divide in central Queensland and drains into Kati Thanda/Lake Eyre having a drainage area of 296 000 sq km (Attachment 3).

The Reserve on Nappa Merrie has a subtropical desert climate (Köppen: BWh) (Attachment 4) and experiences very hot, slightly wetter summers and mild, very dry winters5. It lies within the 100mm annual isohyet.

The Trees

The iron-link fenced Reserve contains within twelve trees of which ten are coolibahs (Eucalyptus coolabah) including the Dig Tree, Brahe’s Tree and Face Tree. Two adjacent to the Face tree are bean trees (Lysiphyllum gilvum) (Attachment 5).

The significant trees measured and material collected on this site are referred to in this report as:

#1 Dig Tree — the tree now known as the Dig Tree, with three blazes (two grown over), Coordinates -27 37 26.2S, 141 14 32.79E, 76.3m AMSL;

#2 Brahé’s Tree — the tree identified by Dave Phoenix’s research6 as that originally blazed by Brahé (the ‘DIG’ blaze now grown over);

#3 Face Tree — the tree carved by John Dick in 1898;

#4 & #5 – two Bean trees adjacent to #3.

All five trees are located on the northern bank of Cooper Creek, at Bulla Bulla Crossing, six kilometres from the Nappa Merrie homestead.

Tree Taxonomy

Australian desert vegetation is a mosaic of plant communities made up of species with varying evolved tolerances to significant environmental stress (including exposure, drought, temperature, nutrition). The eucalypts are the quintessential native flora that have evolved to cover the diversity of environments over the whole continent7. The total number of eucalypts is debatable, usually quoted as over 900 distinct species. Taxonomists have had a veritable field day from the first naming of a Eucalypt by the French botanist Charles Louis L'Héritier de Brutelle in 1788. The name "Eucalyptus" comes from the Greek words eu (meaning "well") and kalyptos (meaning "covered"), referring to the operculum (a cap) that covers the flower buds.

There is no need here to cover the subsequent tortuous divisions of ‘eucalypts’ into three genera - Eucalyptus, Corymbia and Angophora and the latest addition, Blakella8. The coolibah tree has never left the Eucalyptus genus.

Nevertheless, the coolibah tree has itself been front and centre of taxonomic debate9 ever since Baron Ferdinand von Mueller first described the species as Eucalyptus microtheca (ex Greek, ‘micro’ = small and ‘theke’ = container; referring to the small fruit of the species, amongst the smallest in the genus). He collected it as botanist in the Northern Territory on the 1855-56 Great Northern Expedition led by A C Gregory, who became the first Queensland Surveyor-General.

Unbeknown to Mueller at the time was that his classification comprising a single species across a very broad geographic distribution included a group of closely related taxa that subsequently were split into separate species and associated varieties and sub-species.

Gillan10 provides a fulsome detailed time journey through the maze of taxonomic development of Coolibah and serves to clarify why the nomenclature encountered in the literature can be so confusing. This taxonomic separation commenced in 1934 with the first comprehensive revision of the Eucalyptus by W F Blakely who recognised Eucalyptus coolabah (ex aboriginal term). However, the binomial Eucalyptus microtheca continues to be broadly used11 even by the Queensland Heritage Register12 for the Dig Tree itself.

The botanical collection made for this report uses the current EUCLID 13naming, viz. Eucalyptus coolabah Blakely & Jacobs, and morphological differences to Eucalyptus microtheca F.Muell succinctly described by Booker and Kleinig14 as ‘E.coolabah is very similar to E.microtheca in most respects but has conspicuous, whitish branches and more exerted valves of the fruit’. A fuller comparison of the major trees ascribed as coolibahs across Australia is provided in Attachment 6.

The Kew Herbarium type specimen for a Cooper Creek coolibah (E. coolabah Blakely & Jacobs) was collected from the Kopperamanna Mission, South Australia, distant hundreds of kilometers from the Reserve. The closest coolibah specimen held at the Queensland Herbarium was sampled some 3.2km from the Reserve

The Bean tree native to Cooper Creek has also received the attention of taxonomists over time. Currently Lysiphyllum gilvum (F.M.Bailey) Pedley APNI is the preferred name15 with Homotypic Synonyms Bauhinia cunninghamii f. gilva F.M.Bailey and Bauhinia gilva (F.M.Bailey) A.S.George.

Tree Measurements

Vegetative material was collected into plant presses from each of the five principal trees on the Reserve for future identification and housing in the Queensland Herbarium.

A number of measurements were recorded for each tree including Diameter (main trunk and at bifurcations), Height and Crown spread. These data were inserted into standard Tree Biomass and Carbon capture allometric equations with variables:

Density: 1150kg/m316, Quadratic Paraboloid form factor: 50%17, Carbon: 50% Dry wood, Below Ground Biomass = 26%18 Above Ground Biomass, CO2 sequestered (uptake) = 22/14 Carbon content (chemistry).

Tree age was determined using an average 0.23 cm diameter annual increment using the mean of Queensland low rainfall woodland growth rates19. Estimates of diameter growth taken from measurement of bark covering the 1898 carving on Face tree #3, ie the last 127 years, align 82% with the default increment.

The results are tabled in Attachment 7. The largest icon coolibah tree, DIG #1, is estimated to contain an above ground Carbon content of 3.9 t and has sequestered 14.4 t of carbon dioxide over its 500+ years. The Register of the National Estate20 and local Shire pamphlets state the age of the DIG tree between 200 to 250 years old, clearly an underestimate.

Tree Heath

All icon trees are in good health with vigorous expanding new leaf in the crowns. No ill effect of the full submergence of all the Reserve biota under the massive April floods was apparent. Some additional silt deposition was evident on the upper plateau surface and a little sheet erosion on the steep bank into Cooper Creek. One gall of Apiomorpha floralis of no concern was found on a fallen twig on the ground.

The Dig Tree was previously treated successfully for pests and diseases by a professional tree surgeon from the Queensland Department of Primary Industry and is in good condition. Cement had been inserted on one side of the base of the tree for stabilisation purposes. The inscriptions have been obscured over time by regrowth and the only clearly remaining blaze is LXV.

Other plants collected

The opportunity was taken to collect voucher specimens of ground cover for later identification and deposit within the Queensland Herbarium. A colourful array of small covers are now incrementally populating the surface of the Reserve following the recent flood and follow on rains. The locals are adamant that the season will be one of the best if not the best in a life time.

Three particular plants of botanical and historical interest were collected; whole plants including rhizomes of the desert fern Nardoo/Ngardu (Marsilea drummondi), pods of the native Bauhinia Bean Tree (Lysiphyllum gilvum) and stalks of the thicket shrub Lignum (Duma florulenta Synonym Muchlenbeckia cunninghamii). The original explorers ate nardoo and the beans of the native bauhinia.

Infrastructure

Pictures of all infrastructure are contained within the accompanying PowerPoint Presentation.

The record breaking April flood at its peak is estimated to have covered the whole site including the Information Shelter on the rise above the Reserve proper by upwards of 10-20 metres.

Information shelter: Slopes a little off plump in direction of flood flow. Dirt floor eroded in places. All posters salvaged and cleaned. Ranger Col can excavate and re-stand the wall posts with aid of Nappa Merrie machinery. Back wall ought be hinged on top to allow flow of water through at next flood. This principle is used when fencing across water ways using galvanised iron sheets. Some residual funds are available from B&W Society.

WiFi cabinet and solar panels unit: All electronics are destroyed from flood water and require replacement. Solar panels need testing but outwardly are intact. Little gain from relocation. Security camera useful as a vehicle monitoring and deterrent.

Toilet block: Partly excavated, unusable and a new modern chemical version ought be erected asap.

Tracks into and car park area at Reserve: Minimal erosion.

Formed walking track on Reserve: All intact and no erosion.

Memorial cairns: All intact.

Boardwalks, railings and information boards: All intact.

Footnotes

It is a pleasure to acknowledge the critical support of fellow travellers Carol Bacon, Caroline Fewtrell and Geoff Thompson and the insightful on-site assistance of Ranger Colin Mace.

References

1 = Mason, A. (1895). Geographic History of Queensland. Dedicated to the Queensland People. p197-199. Government Printer, Brisbane. Saenger.P. Trees associated with the Burke and Wills Expedition, Chapter 16 in Australia’s Ever-changing Forests: Proceedings of the Eighth National Conference on Australian Forest History. Stubbs,B.J. et al. (ed.). © 2012, ISBN 978-0-9757906-2-5

2 = Queensland Government Gazette dated 2 July 1964. p1083.

3 = Queensland Government Gazette dated 24 January 1987. p285.

4 = https://www.thedigtree.com.au/, https://www.thedigtree.com.au/dig-tree-reserve

5 = Beck, H. E. et al. (2023). High-resolution (1 km) Köppen-Geiger maps for 1901–2099 based on constrained CMIP6 projections. Nature. https://www.nature.com/articles/s41597-023-02549-6 . Climate statistics for Australian locations- Ballera Gas Field. Bureau of Meteorology. DCCEEW. https://en.wikipedia.org/wiki/Nappa_Merrie Retrieved 19 July 2025.

6 = Phoenix, D.G. (2017). More like a picnic party: Burke and Wills: an analysis of the Victorian exploring expedition of 1860-1861. PhD thesis, James Cook University. https://researchonline.jcu.edu.au/50833/ Retrieved 19 July 2025.

7 = Hill, R. et al. (2016). Evolution of the eucalypts – an interpretation from the macrofossil record. Australian Journal of Botany. 64. p600-608.

8 = Crisp, M.D. et al. (2024). Perianth evolution and implications for generic delimitation in the eucalypts (Myrtaceae), including the description of the new genus, Blakella. Journal of Systematics and Evolution 62 (5) p942-962.

9 = WRIGLEY, J. & FAGG, M. 2012. Eucalypts: A Celebration, Sydney, Allen & Unwin

10 = Gillen, J.S. 2017. Coolibah (Eucalyptus coolabah Blakely & Jacobs) of the Diamantina and Warburton River systems in north eastern South Australia. Report by Australian National University to the South Australian Arid Lands Natural Resources. https://cdn.environment.sa.gov.au/landscape/docs/saal/2_coolibah_final_hmeditfinal_1.pdf

11 = Boland, D.J. et al. (1992). Forest Trees of Australia. CSIRO Publications, Melbourne. Cronin, L. (2013). Cronin’s Key Guide Australian Trees. Allen & Unwin, Crows Nest.

12 = Queensland Heritage Register. https://apps.des.qld.gov.au/heritage-register/detail/?id=601073

13 = EUCLID, (2020) Eucalypts of Australia Contributors: AV Slee, MIH Brooker, SM Duffy, JG West. Fourth Edition Centre for Australian National Biodiversity Research Canberra. https://apps.lucidcentral.org/euclid/text/intro/about.htm

14 = Brooker, I. and Kleinig, D. (2004). Eucalyptus An illustrated guide to identification. Reed New Holland. p155.

15 = https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:505338-1

16 = Cause, M. et al. (1989) Queensland Timbers Their nomenclature, density and lyctid susceptibility. Dept Forestry Tech Pam No2. p33.

17 = Oluwajuwon, T.V. et al (2025) Describing and Modelling Stem Form of Tropical Tree Species. Forests 16(1) p 29; https://doi.org/10.3390/f16010029

18 = Raison, J. et al. (2003) Spatial estimates of biomass in ‘mature’ native vegetation. Australia National Carbon Accounting System, Technical Report No. 44. 56p.

19 = Ngugi, M.R. et al. (2015) Growth rates of Eucalyptus and other Australian native tree species derived from seven decades of growth monitoring. J. For. Res. 26(4). p 799–810.

20 = https://apps.des.qld.gov.au/heritage-register/detail/?id=601073

Attachments

Fig 1: Dig Tree Reserve Identification Survey

Fig 2: Location of planned new access path, boardwalks, and interpretative signage, 2019