Dating Aboriginal Scarred Trees in north eastern Australia

This week and next I’m back in Weipa (NE Australia) working on a research project with Alngith People — Traditional Owners of the western Weipa Peninsula — as well as Dr Kathryn Allen (Monash University), to collect cores from Aboriginal scarred trees in the region.  The work we’re doing involves applying dendrochronology, dendroecology and radiocarbon dating techniques to date Aboriginal scarred trees, understand growth rates on a particular species of tree and to collect new data about environmental change in the region over the past few centuries.  In this post I want to outline the context and primary focus of the project, with another to follow on the methods and approaches we’re using as well as some secondary issues that we’re exploring.

What are scarred trees?

‘Scarred trees’ are simply trees that have some evidence of scarring as a result of people in the past removing bark or wood, engraving designs or motifs or cutting into trees for various reasons, including to collect food. In Australia, scarred trees have typically been created by Indigenous peoples. South eastern Australia is well known for the often large and imposing canoe scars carefully carved into the trunks of majestic river gums, and which are a common sight near waterways and wetlands. However, it is less well known that scarred trees are found in many parts of Australia and indeed, in many other parts of the world including in North America and Europe.

Scarred trees are a physical reminder of how Indigenous peoples in the past lived and are often of high importance to Indigenous communities in Australia today: they provide a link to the past and are generally a type of heritage place that communities try to preserve and protect where possible. Scarred trees are highly vulnerable to destruction via natural decay and fire while development is also a major threat as mining, urban expansion and so on see widespread clearance of otherwise undisturbed areas of forest and woodland across the country. This is particularly the case in western Cape York Peninsula where mining has considerable impacts on the local environment and where the foreseeable future is one that is dominated by ongoing mine expansion.

Scarred trees on Western Cape York

Many thousands of scarred trees occur on Aboriginal lands around Weipa, with well over 1,500 recorded on the Weipa Peninsula alone (1, 2). They are regularly found by archaeologists and Traditional Owners completing assessments before mining clearances and are frequently cut down and moved to make way for mining development. In the past few years, some Traditional Owners have chosen scarred trees of special importance and have placed these into monuments in the local area, in part to prevent them from being destroyed by mining (3).

Scarred tree monument at Ruchook Cultural Ground, Weipa

According to local Elders, there are several different types of scar tree. Some scars were created by people cutting timber to make spear throwers or woomera as well as other  tools (4). The scar tree that is most commonly found in the Weipa area are ‘sugarbag’ scars which were created by people cutting into trees to collect the honey and wax of the stingless native bees. In the early days, a stone axe was used to create a small hole near a sugarbag hive and then a thin, spongy branch was inserted into this hole to soak up the honey. These holes would then be sealed up again so that people could come back at a later time to collect more of the honey or wax. We’ve recently suggested that this approach was a form of resource management or ‘domiculture’, or a set of economic practices and ethics that were — and still are — a major feature of Aboriginal cultural traditions in the region (5).

In the late 1800s Europeans bought iron hatchets and axes and these were also used in the collection of sugarbag right through the 1900s. Indeed, Napranum Elders who grew up in the Weipa Mission remember their parents collecting honey and exchanging this with the Missionaries who would place it into a tank beneath the Mission Superintendent’s house. It was mixed with water as a cordial-like drink, and was eaten on porridge and damper every day. Sugarbag is still collected regularly by local community members today, using similar methods to those used by their parents and grandparents.

How old are scar trees?

On western Cape York Peninsula, scars mostly occur on one species of tree — the Cooktown ironwood — which as the name suggests is a tree whose timber is extremely dense and hard and is well known to be quite difficult to cut. This tree is also quite slow growing, with one study suggesting that a tree that was about 35 cm in diameter at chest height had taken between 180 and 300 years to grow, with growth rates of about 0.12 cm each year (6). What this means is that average sized ironwoods are likely to be at least several hundred years old and that the very large trees with 60 cm or more in diameter may in fact be much older than we had previously thought. Scars have been recorded on ironwoods of all shapes and sizes, and even found on ironwoods that have long since died, so  it is likely that some scarred trees date to the period before Europeans arrived in the region.

There have been no previous attempts to discover the age of scarred trees in the region and only one other study in Australia that has attempted to do so (7), though this was highly destructive and required that the tree be felled — which is not always an option when it comes to managing Indigenous heritage sites.

The presence or absence of iron axe marks does give us a general estimate of the age of a scar and it is likely that scars with sharp and distinct axe marks were made after the late 1880s. However, many scars do not have clear axe marks suggesting they might be older than this. The techniques we are using potentially allow us to place scarring events into a 5-10 year time bracket allowing both community members and us to place specific trees into a particular historical context.

There are a number of reasons we are interested in developing a technique to effectively date scarred trees:

  1. Having information about the probable age of a scarred tree will help to better manage these sites when difficult decisions about development are being made. For example, Traditional Owners may wish to manage scarred trees made in the 1960s, 1920s or 1850s in very different ways.
  2. It will provide historical information that can feed into a range of community heritage work including educational and interpretive projects.
  3. It will contribute to more academic research questions about the history of the region, particularly in terms of understanding what life was like for Indigenous people between the early 1800s and the mid 1900s and the ways in which the arrival of settler-invaders influenced Indigenous wellbeing.

So, this week we’re trying to relocate scarred trees on Alngith Country that have been recorded over the past 8-10 years. Next week, we’ll be selecting those trees that Alngith People want to core. Over the coming week I’ll post more information on the method we’re using and some images and video from the field.

Further reading:

I’m yet to upload my own publications here but if you are looking for a copy of something I’ve written just contact me and I’ll send it to you via express carrier pigeon.

1) Morrison, M.J., D.A. McNaughton and J. Shiner 2010 Mission-Based Indigenous Production at the Weipa Presbyterian Mission, Western Cape York Peninsula (1932–66). International Journal of Historical Archaeology, 14(1), pp.86–111.

2) Shiner, J. and M.J. Morrison. 2009 The contribution of heritage surveys towards understanding the cultural landscape of the Weipa bauxite plateau. Australian Archaeology, 68, pp.52–55.

3) Barkley, R. et al. 2008 Collaboration and innovation in the management of cultural landscapes in mining contexts, western Cape York, far north Queensland. Historic Environment, 21(3).

4) Morrison, M.J. et al. 2012 New approaches to the archaeological investigation of culturally modified trees: a case study from western Cape York Peninsula. Journal of the Anthropological Society of South Australia, 35, pp.17–51.

5) Morrison, M.J. and Shepard, E. [Forthcoming] The archaeology of “sugarbag” production: post-contact Indigenous economic diversification within colonial intercultural settings in Cape York Peninsula, north eastern Australia. Journal of Field Archaeology.

6) Cook, A.D. et al. 2005 Sustainable harvest rates of ironwood, Erythrophleum chlorostachys, in the Northern Territory, Australia. Australian Journal of Botany, 53, pp.821–826.

7) Long, A. et al. 2002 The origin and date of two scarred trees at Horsham Saleyards, Horsham, Western Victoria. A report to Horsham Rural City Council and Goolum Goolum Aboriginal Cooperative, Horsham.

Australian Indigenous archaeology and cultural heritage wrap, 5 March

I try to keep a close eye on new papers, books and so on relevant to Australian Indigenous archaeology and collate much of this information in Zotero. I thought it might be worth irregularly posting a list of new materials that I’ve noticed. If there’s some interest, I’ll turn this into an open Zotero group. This is by no means comprehensive, just a list of the items that I stumble across and that might be of interest to others.

I will avoid commenting on items; the authors speak well enough for themselves.

Continue reading

Spatial statistics and the archaeology of sugarbag scarred trees

This past few months I’ve been prompted into working on some scarred or culturally modified tree data that I recorded near Weipa  during a series cultural heritage consultancy projects between about 2003 and 2007. The reason for looking at this again was that I was fortunate enough to be hosting/supervising Masters student Emily Shepard from Portland State University who was out here on an EAPSI scholarship to work on this material with me. It was a great chance to blow the dust off some good data  collected under trying circumstances during many months in the field. It’s not often you get a chance like that.

A tree felled to obtain honey and wax

The project we’ve been working on has involved looking at ‘sugarbag’ scarred trees. These are trees scarred by Aboriginal people cutting holes (or apertures) to access honey and wax from the nests of various species of Australian native stingless bee. Alun Salt wrote a great post about some of my work on CMTs here last year and it’s well worth a read. The question Emily and I have been looking at this past few months involves using the data I collected to identify trends and patterns that give us some insight into the intensity of wild honey collection. Emily has worked through and made sense of the original data, re-analysed photos and completed most of the statistical analyses. I turned my attention to spatial statistics, a mildly terrifying method, but one that I think more archaeologists should employ.

Contents of a 'sugarbag'. The brown material is wax which contains small pockets of rather delicious honey

Spatial statistics are simply tools in a Geographic Information System (GIS) that use statistics to “cut through the map display and get right at the patterns and relationships in the data” (Mitchell 2009:2). They do require reasonable familiarity with using GIS software, as well as access to decent software that can perform the analysis. I found it quite challenging to begin with, partly as I’ve had no formal training in statistics or GIS, but if you need to identify patterns in the way archaeological data are distributed then it’s well worth the investment of time. There are a bunch of more simple tools archaeologists can use to find patterns in their data, such as proximity analysis, and these give good insights on simple questions such as ‘what is the relationship between site location and distance to water’. Resulting data can be quickly and easily exported to conventional statistical software. But GIS can do a lot more than make maps and summarise basic patterns such as this.

Cluster analysis is something that I’ve been interested in for some time, in part because my Doctoral research involved looking at clusters of midden sites and trying to make sense of them. With the scarred tree data, we were interested in discovering whether we could find clusters of similar variables in our dataset of >1500 sugarbag scars. We did.

We looked at the frequency of scars across our study area. Figure 1 shows aggregated number of scars within 500 metre raster cells.  This is a great means of visualising datasets in a relatively simple manner and helped us to identify general areas of high frequency scarring. However, it doesn’t provide a clear indication of whether there are finer or more localised trends within this dataset, or whether the things we think are ‘clusters’ meet tests for statistical significance.

Sugarbag scarred tree frequency
Figure 1: Frequency of sugarbag scar trees, 500 m raster cell size (click through for larger image)

We then used two local statistical measures to further explore whether there are any specific clusters of high scar frequencies. We used Anselin’s Local Moran statistic and the very nicely named Local Getis-Ord Statistic (or Gi*). I won’t go into details of how these work, but see this guide for a start if you’re interested. Figure 2 shows the resulting data. What we were looking for particularly were areas where both techniques pointed to a a number of cluster points in relatively close proximity to each other. You can see a few of these in this image.

Sugarbag scars - clusters of high frequency
Figure 2: Distribution of statistically signfiicant clusters of high frequencies of sugarbag scars

I suspect the results are probably not that exciting to look at without any more detailed context, but the approach has enabled us to identify clusters in the data that weren’t noted from visual inspection alone. Given some success here, we decided that it was worth  exploring clustering of other variables and the one that we had most success with was identifying clusters of larger scar aperture area, shown in Figure 3.

Clusters of high aperture areas
Figure 3: Clusters of high aperture areas

The result indicated the high frequency scarring locations broadly correlated with large aperture sizes and that there were even more subtle trends we needed to think about. I won’t go into what we think the results mean, partly because we haven’t completed our paper yet, but these methods provide a useful insight that can be used alongside other standard statistical tests that archaeologists often use.

Our dataset is not perfect: it’s uneven and there are major gaps which have limited our ability to take these analyses any further.  Despite that, I think these tests are still worth exploring for  archaeological spatial data. I’m especially fascinated by the potential of these kinds of tests for picking out clusters in more evenly distributed data, such as looking for clusters of particular artefact types or sizes within large surface scatters.

I’ve picked out a few books and articles below that I found really quite useful and that are worth reading if you’re interested in exploring this material in more detail. There is surprisingly little written about spatial analysis and spatial statistics in archaeology, which I find baffling given our love affair with conventional statistics.

Some useful sources

McCoy, M.D. and Ladefoged, T.N. 2009 New Developments in the Use of Spatial Technology in Archaeology. Journal of Archaeological Research, 17(3), pp.263-295.
Mitchell, A. 2005 The ESRI Guide to GIS analysis, Volume 2: Spatial measurements and statistics. Redlands, California: ESRI press.
Schwarz, K.R. and Mount, J. 2006 Integrating spatial statistics into archaeological data modelling. In M. W. Mehrer and K. L. Wescott, (eds), GIS and archaeological site modelling, pp.163-190. London: Taylor and Francis.
Wheatley, D. and Gillings, M. 2002 Spatial technology and archaeology: the archaeological applications of GIS. New York: Taylor and Francis. (see Chapter 6)