Draft 22/8/2005
MOUNTAIN OCCUPATION PROJECT
MIRES OF THE AUSTRALIAN CAPITAL TERRITORY
Snowy Flat and Ginini Bogs, Brindabella Range, Australian Capital Territory.
Geoffrey Hope, Mike Macphail and Ben Keaney.
Department of Archaeology and Natural History
Australian National University
Abstract
The stratigraphy of two similar subalpine mires at around 1600m altitude have been investigated using radiocarbon and pollen analyses. They represent the northernmost Sphagnum –Richea peatlands in the Brindabella Range, which borders the western side of the Australian Capital Territory and New South Wales and is the northern extension of the Snowy Mountains. The chronologies of both Snowy Flat Bog and Ginini Bog are not yet fully understood, but one bog seems to provide a record from the early Holocene to present, while the other only commenced its most recent peat accumulation about 4000 years ago.
Key Words. Peatlands, subalpine, fire histories, Sphagnum
Address for correspondence Professor G. S. Hope, Dept Archaeology and Natural History, RSPAS ANU Canberra 0200
Introduction.
Climate
Geology and soils
Vegetation
Both bogs are dominated by low shrublands of Richea continentis- Baeckia gunniana over extensive Sphagnum hummocks intergrown by restiads, especially Empodisma minus. Wet areas support tiny stands of Carex gaudichaudiana fen with Myriophyllum in shallow sandy ponds. The bog grades onto msteeper slopes with snow daisies, grass, alpine gentians and shrubs such as Mirbelia oxylobioides and Hakea microcarpa. Although Poa grasslands surround the sites, snow gum, Eucalyptus pauciflora, forms a ring of woodland on the slopes.
Taxa noted in the Mire complex. A = Grass bog, B = shrub bog and ponds.
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Species / A / B*Acetosella vulgaris / 1
Acaena novae-zelandiae / 1
Aciphylla simplicifolia / 1
Anthoxanthum odoratum* / 1
Asperula scoparia / 1
Baeckea gunniana / 5
Baeckea utilis / 2
Baloskion australe / 2 / 4
Brachyscome scapigera / 1
Callistemon sieberi / 2
Carex gaudichaudiana / 1 / 3
Celmisia paludosa / 1 / 1
Celmisia tomentella / 1
Chionogentiana sp / 2
Comesperma ericinum / 2
Cotula alpina / 1 / 1
Craspedia glauca / 2 / 1
Danthonia alpicola / 1
Deyeuxia gunniana / 2
Empodisma minus / 6 / 3
Epacris breviflora / 1 / 4
Epacris paludosa / 2 / 1
Epilobium billardierianum subsp. cinereum / 1
Eriocaulon scariosum / 1
Euphrasia caudata / 1
Galium nigrans / 1
Geranium molle / 1
Hakea microcarpa / 2
*Hypochaeris radicata / 2
Isoetes muelleri / 1
Isolepis crassiuscula / 1
Isolepis fluitans / 2
Juncus brevibracteus / 2
Lagenifera montana / 1
Lobelia gibbosa / 1
Luzula sp. / 2 / 1
Lycopodium fastigiatum / 2 / 1
Myriophyllum pedunculatum / 2
Olearia ?algida
Oreobolus pumilio / 3 / 1
Oreomyrrhis ciliata / 2
Plantago antarctica / 1
Poa clivicola / 1
Poa costiniana / 1
Poa sieberiana var. cyanophylla / 1
Pratia pedunculata / 1
Ranunculus graniticola / 2
Richea continentis / 5
Scleranthus fasciculatus / 1
Sphagnum montanum / 3 / 4
Stylidium graminifolium / 2
Utricularia dichotoma / 1
Wahlenbergia ceracea / 1 / 1
Wahlenbergia communis / 1
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Stratigraphy and dating.
1. Snowy Flats 35°33.93’S 148°51.85’E
Altitude: 1618 metres Area of deposit: 12 ha
Area of catchment: 185 ha Max. altitude of catchment: 1856 m
Location. Snowy Flats bog lies 1.4km north of the summit of Mt Gingera at the head of Snowy Flat Creek, which flows north through the bog then east to the Cotter River. The bog has not been intensively studied, although it was cored in 1973 by G. Singh and others. The Sphagnum bog has been included in a survey of Sphagnum bogs (Whinam and Chilcott 2002).
It was visited on 18/3/2001 by Environmental Reconstruction (ANU Geography and Archaeology) and the sediment stratigraphy tested. Three transects of peat depths were established by pushing a rod down to gravel or stone. Transect 1 traversed the bog on the western tributary, while transect 2 and 3 traversed Snowy Flat. The deepest sections were found on a bench on the eastern side of the bog in Transect 3, the depth reducing to the west and the lowest part of the valley. The western marginal Sphagnum bog (nearest to Pryors Hut) has an average depth of 165cm. On the eastern side is a very well developed Sphagnum area which had a maximum depth of 220cm, about 60cm of which was Sphagnum. This site was cored and samples taken for dating on 28 March 2001.
Table 1 Distance, moss depth and peat depth on three transects.
Trans 1 / Trans 2 / Trans 3Dist / SD / D / Dist / SD / D / Dist / SD / D
0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0
8 / 0 / 141 / 8 / 0 / 6 / 8 / 30 / 172
16 / 40 / 145 / 16 / 37 / 128 / 16 / 0 / 159
24 / 50 / 154 / 24 / 36 / 97 / 24 / 50 / 188
32 / 51 / 210 / 32 / 33 / 100 / 33 / 45 / 200
40 / 34 / 170 / 40 / 36 / 55 / 37 / 20 / 182
48 / 55 / 146 / 44 / 0 / 50 / 41 / 43 / 195
56 / 0 / 47 / 50 / 20 / 20 / 48 / 82 / 208
56 / 10 / 140
64 / 64 / 183
72 / 55 / 171
80 / 48 / 153
88 / 50 / 124
96 / 50 / 104
104 / 62 / 99
112 / 30 / 72
120 / 0 / 5
128 / 53 / 57
136 / 0 / 52
148 / 0 / 0
A core was taken with a D section auger at 32m along Transect 3, in Richea-Epacris-Empodisma-Sphagnum bog. This was subsequently extended to 212cm with a Livingstone piston corer.
Depth cm / Sediment
0-65 / Sphagnum
65-80 / Peaty Sphagnum with roots
80-160 / Brown amorphous peat with many roots and wood at 150cm
160-195 / Black clayey amorphous peat with lenses of sand
195-200 / Coarse angular sands with clay
200-210 / Black sloppy mud with fibrous debris
>212 / Boulders or granite bedrock.
Dating samples were taken at 90-100, 180-190cm ( ASF1-3) and fine fraction bulk dates ASF1 and 3 submitted. An AMS date was submitted from peaty basal gravels at 205-7cm, with ABA pretreatment of <150 micron fraction.
Results:
Depth / Age / Lab No90-100cm / 250 ± 70 / ANU 11463
180-190cm / 7130 ± 70 / ANU 11464
205-7 / 5480 60 / OZI 143
Pollen diagram
Pollen samples were taken at 5cm intervals through the 210cm section and prepared by standard means. Samples were counted every 10cm. Charcoal was also analysed at the same interval, using the point method of Clark 1982.
The pollen diagram and upper date at shows that the Sphagnum cushion is less than 100 years old and that the top 70cm is within settlement time. There is a noteable reduction in eucalypt and increase in grass associated with settlement, suggesting that impact byearly grazing was pronounced, although there is slight recovery. The site has been mainly a Sphagnum bog throughout its history but the section may not be continuous and requires further dating. The basal sandy clays coincide with low eucalypt and high grass and daisy records so may reflect a tree line below the level of the site. Ponds were more widespread in the lower half of the section, as indicated by Haloragaceae. Fire has been present at most levels but the higher concentrations 170-130cm may represent more concentrated peat rather than more frequent fires
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Ginini Flats 35°31'S 148°46'E
IBRA AA006AC, RAMSAR
Altitude: 1590 metres
Area of deposit: 125 ha
Area of catchment: 1790 ha
Max. altitude of catchment: 1762 metres
Ginini Bog lies at the head of a creek on the crest of the Brindabella Range on the northeastern summit slopes of Mt Ginini about 800m east of the ACT-NSW border. Mt Ginini is formed from a contact metamorphic hornfels rocks underlain by the Gingera granidiorite batholith (MacPherson 1998). Granidiorite outcrops on the southern side of the bog and corestones are scattered through it. The climate is sub-alpine but McPherson (1998) has identified active periglacial activity at the summit of Mt Ginini, in areas he believe may have been exposed by intense fire. The mire occupies a broad flat between moderate slopes which are covered by dense snowgum woodland over a papilionaceous shrub layer. Ginini Bog is the northern section of a complex of wet grassland and other swamp areas such as Cheyenne Flats, Snowy Flats and Gingera Flats which occur on other streams on the eastern slopes, assisted by an extension of the range at this point to form a relictual plateau about 2km in extent. This area receives snow in winter and has distinctly denser vegetation than the steep exposed western slopes of the range.
Ginini Bog is better studied than most other subalpine bogs and is included as an example of the lower altitude subalpine Sphagnum bogs of southern montane New South Wales. These include Rennex Gap and many small subalpine sites in the Snowy Mountains and the Brindabella Ranges of the ACT, which generally occur above 1150 m with increasing frequency. This site is described by Costin (1972) as one of the largest and best preserved Sphagnum bogs in Australia, and it is noteable for the extensive stands of Richea continentis, which occurs in the Victorian and Tasmanian subalpine.
At Ginini, subalpine heath, comprising Epacris paludosa, Richea continentis and Baeckea gunniana, overtops the rushes Baloskion australe and Empodisma minus. The taller plants overgrow an almost complete cover of Sphagnum. This surface is slightly raised away from the valley sides and individual hummocks are 50 cm above hollows. On the margins of the bog are shrubs and small trees of Leptospermum lanigerum. Along creek lines are tussock Poa and Juncus sp. With herbs such as Ranunculus and Epilobium species.
The mire slopes quite steeply from the northwest and becomes shallower to the east on granite. The depth of peat varies considerably with an average of 75cm under moss hummocks up to 80cm in height. Grey pebbly clay underlies the peat. The peat is considerably humified near the base but contains some Sphagnum remains and possible Richea wood. The base of a peat section has been dated by Costin (1972) at 3280 ± 70 years BP (GRN 2491) and wood above at 3050 ± 80 (GRN 2492).. The date is remarkably young, and raises the possibility that the mire may have eroded or burnt and then regenerated. Sediments in the swamp could be used to interpret the response to firing by the woodland and bog communities. New techniques of carbon particle analysis and tree scar recording have been researched at this site to provide a history of fire from about 1820. (Banks 1982, Clark 1983). Clark (1983) studied the growth of Sphagnum hummocks, concluding that fast apparent growth took place, but could be reversed after heavy snow compressed the hummocks.
Serious fires have been common in the catchment, and the distribution of other Sphagnum bogs is possibly limited to the wettest areas by burning. Some removal of surface Sphagnum (for filler in acetylene tanks) occurred in 1940, and a prominent trench was dug in 1938 on the northern slope. The site lies in Namadgi National Park and is also protected as part of the Cotter River catchment, the water supply for Canberra. Faunal studies are continuing on this mire as it is a northerly habitat for the Corroboree Frog and access is now discouraged to protect the fauna.
The section from which Costin obtained his dates is exposed in the old peat trench. A fresh section was cleaned and samples taken at approximately 10cm intervals below the overlying 30cm of fresh moss. Samples below 80cm, down to 120cm, were taken with a bucket soil auger. These were made up with standard methods and counted for pollen and charcoal. A new date on ABA washed <175 micron fraction was run that confirmed the age of Costin’s levels (114-115cm 3170 ± 70 BP ANU 12021). Preliminary pollen studies confirm that the site has supported a Sphagnum bog throughout its history.
Ginini Bog was badly burnt by two consecutive fires which passed over it in February 2003. Post-fire monitoring plots have established a 2.2m sediment sequence about 150m south of the trench close to the base of the slope. It is hoped to complete the pollen diagram from the trench site and also study the deeper section which may have an older basal age. The monitoring program will establish the rate of rehabilitation of the moss cover.
Discussion
The most equivalent bog studied is the Cotter Source Bog, at the head of the Cotter River about 25km south east of Snowy Flat (Hope 1996). It is about 100m higher, and more exposed, than Snowy Flat. It spans about 9500 years.
Acknowledgements. Tanya Whiteway, Alan Wade, Amanda Carey, Ecowise
References
Argue, D. 1995. Aboriginal occupation of the Southern Highlands: Was it seasonal? Australian Archaeology 41, 30-36
Banks, J. 1982. The dynamics of the snow gum (Eucalyptus pauciflora). Ph.D. Thesis. Australian National University, Canberra.
Clark, R.L., 1980 Sphagnum growth on Ginini Flats, A.C.T. Unpubl. Report to NSW National Parks and Wildlife Service.
Clark, R.L., 1983: Fire History from Fossil Charcoal in Lake and Swamp Sediments, Ph.D. Thesis, Canberra, Australian National University.
Clark, R.L., 1983: Pollen and charcoal evidence for the effects of Aboriginal burning on the vegetation of Australia, Archaeology in Oceania 18(2), 32-37.
Clark, R.L., 1986: The fire history of Rotten Swamp, A.C.T., Canberra, Unpublished Report to ACT Parks and Conservation Service, CSIRO, Canberra.
Clarke, P.J. and Martin, A.R.H. 1999. Sphagnum peatlands of Kosciuszko National Park in relation to altitude, time and disturbance. Aust. J. Botany 47, 519-536.
Costin, A.B., 1972: Carbon-14 dates from the Snowy Mountains area, southeastern Australia, and their interpretation, Quaternary Research 2, 579-590.