Pollen Analysis of Digger's Creek Bog, Kosciuszko National Park: Vegetation History and Tree-line Change

Abstract

Digger's Creek Bog, an Empodisma minus–Callistemon pityoides–Sphagnum cristatum shrubby subalpine peat bog, alt. c. 1690 m, not far below local altitudinal tree-line, began development > 10 000 years before present as an Astelia sp.–Carex alpine soak. Surrounding vegetation was a grassy alpine herbfield with many Asteraceae, Apiaceae and Gentianella diemensis, corresponding to the regional Club Lake Zone C, dated to the same period. Astelia died out c. 6500 years before present approximately at the Club Lake C/D 1 boundary, marked by spread of Pomaderris in subjacent montane forests. Thereafter, shrubs, mainly Myrtaceae and Epacridaceae, and Restionaceae (Empodisma and Restio australis) dominated the bog. Epacris cf. paludosa and C. pityoides seem to have been the earliest shrubs to invade, Baeckea, probably B. gunniana, and Richea continentis reaching maximum prominence 5000–3000 years before present. Sphagnum was uncommon until recently. Regional arboreal pollen enable comparisons with other sites in south-eastern Australia but immigration of the tree-line species Eucalyptus pauciflora subsp. niphophila (snowgum) is not well expressed in the pollen spectra. Surface and near-surface counts of this species are higher than at any preceding time, and correspond most closely to surface counts in adjacent young snowgum woodland. The co-occurrence of weed pollens, probably associated with the late 19th and early 20th century practice of summer pasturing stock on the alpine–subalpine tract, suggests that pasturing and burning, responsible for widespread severe fires on this range, led both to the formation of dense even-aged snowgum woodland that had been open and patchy at this altitude, and a spread of Sphagnum on the bog surface.