Project 03A: ACTewAGL/ACT National Parks 2003-


State of the mountain mires of the Australian Capital Territory after fires 14-22 January 2003

Researchers: Prof. Geoff Hope, Dr Alan Wade and Dr Jennie Whinam

Summary: The mountains of the ACT support substantial areas of mires in interfluves and valley heads, as well as areas of boggy riparian vegetation along streams. They include valley fill deposits with sedge fens at lower altitudes (800-1000m), shrubby Sphagnum cristatum –epacrid shrub bogs in the subalpine and wet tussock grasslands. Almost all the montane mires in the ACT have been affected by the January 2003 fires with the burnt area varying from 55-100% of the mire surface. Surveys of major wetland areas have been carried out by field visits from vehicles or helicopter and some aerial inspection.

In general the vegetation in the burnt swamp areas has been reduced to ash or charred remnants with the exception of Sphagnum moss hummocks, which have partly remained although the moss has mostly been killed. However the fibrous root mat has mostly survived as the peat soils have not caught fire except in a isolated patches. Some regeneration of sedges, grasses and other monocots is taking place. Shrubs have mostly been killed except for resprouting of some myrtaceous species.

The mires so far visited will recover, but at a slow rate. A shift towards sedge and grass dominance will increase runoff during showers, which may increase stream incision. Peat growth (organic matter accumulation) may be negative due to more exposure and better aeration of the peat, which will also provide a habitat for wind-borne weeds such as thistles. The 2003 fires will accelerate the trend towards loss of shrub-moss bog that probably commenced when the mires were disturbed by cattle grazing and pastoral fires in the late 19th century. Research is being undertaken to assess the extent of the loss. Some simple remedial measures to encourage regrowth on the remnant dead Sphagnum hummocks might be helpful, and consideration should be given to returning the hydrology to pre-fire state.

Mire Histories
Current research based on carbon dating, fossil pollen and spores, and microscopic charcoal suggests that the mires of the ACT post-date the last period of glaciation which occurred from 26-16,000 years ago (Barrows et al 2001) and owe their origin to the post-glacial amelioration of climatic conditions. At the end of the Pleistocene most montane streams lay above the treeline and their channels had been infilled by sands and gravels. Increasing temperature and precipitation around 12-9000 years ago allowed subalpine plants to stabilise the catchments permitting the establishment of many swamp plants on the river flats. The plants blocked streams and the wet conditions initiated peat accumulation. However there is no clear correlation between the basal dates and mire altitude. The oldest sites, Nursery and Cotter Source, lie in very different settings (Table 1).

Table 1. Dates for the Initiation of Peat Formation in ACT and nearby NSW Montane Site
Site Name, Locality

(years BP)

Cotter Source A, Mt Scabby, ACT
9040± 80
Hope unpubl.
Ginini Bog, Mt Ginini, ACT
Costin unpubl
Micalong Swamp, 35 km E Tumut
Kemp (1993)
Mulloon Swamp, 25km W of Braidwood
3440 ± 90
Hope, unpubl
Nursery Swamp, 40km SW Canberra, ACT
Hope unpubl.
Rotten Swamp, NE of Mt Kelly, ACT
Clark 1986
Snowy Flat, Mt Gingera, ACT
7,130 ± 70
Macphail, unpubl
Yaouk Swamp, Scabby Nature Reserve
9250 ± 40
Keany, unpubl

The reasons for the variation in ages for the initiation of peat are not yet understood. The younger sites (Rotten Swamp and Ginini Bog) have probably lost earlier peat fills, possibly by fire. Yaouk Swamp, and possibly Snowy Flat, have basal peaty clays that are early Holocene, but seem to lack sediments from the last few thousand years. A suggestion is that since wet sclerophyll forest expanded in the mid-Holocene to altitudes beyond present limits, wetter conditions than present may have occurred from 9000 to about 4000 years BP. This may have been a time of consistent peat formation. Perhaps some peatlands did not grow well after 4000 years ago or there have been erosional events since that time. Only Cotter Source Bog possibly provides a fairly complete record of the Holocene.


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