Trends in Vegetation at Kosciusko. II. Subalpine Range Transects, 1959-1978

Abstract

Changes in vegetation during the 20-yr period from 1959 to 1978 were measured along permanent transects and on photographic quadrats in four subalpine areas at elevations between 1660 and 1770 m at Kosciusko: Thompsons Plain, Wragges Creek, The Piper and Piper West. The plant communities sampled include more or less natural tussock understorey vegetation in mature subalpine woodland; disclimax tussock, disclimax intertussock and more open vegetation with large bare areas, all in sites formerly dominated by woodland; and disclimax ground-water vegetation with shrubs, derived from Sphagnum bogs.

On the dense tussock transects under woodland the vegetation underwent little change, except for an increase in the number and abundance of species of major and intermediate herbs within the snowgrass tussocks; strong competition from the perennial snowgrasses and other herbs suppressed the development of shrubs. On the disclimax tussock transects there was a progressive decrease in the amount of bare ground to minimal values, corresponding with increases in the cover of herbaceous species and shrubs. the increases in shrubs being generally proportional to the amount of bare ground initially exposed.

On the disclimax intertussock transects there was a substantial decrease in the amount of bare ground owing to the increased cover of snowgrasses, shrubs and colonizing minor herbs. The cover provided by major non-gramineous herbs remained low, but showed signs of increasing towards the end of the period of measurement. On some transects, the shrubs began to senesce without regeneration as competition from the perennial herbs increased.

The bare transects on which there were initially large areas of bare ground continued to lose soil. The main colonizers under these conditions were leguminous shrubs.

On the ground-water transects the initial cover of short, grazing-adapted herbs was replaced by tallergrowing sedges and shrubs, with some adjacent regeneration of Sphagnum moss.

The results of the transect and associated quadrat measurements were supplemented by other observations throughout the Kosciusko National Park, on the variable regeneration of snowgum, and on the regeneration of kangaroo grass.(Themeda australis) in the Poa-dominated sod tussock grasslands in lower-subalpine cold air plains. The contrasting condition of subalpine vegetation in the Snowy Plains area, just outside the Park, was also recorded.

Trends and associated plant successions reflect the effects of the last 20 years' protection from burningoff and livestock grazing and the occasional periods of unfavourable weather including drought, prolonged snow cover and low temperatures. The vegetation trends, which are still continuing, are generally beneficial to water catchment and nature conservation values. Grazing potential has suffered through the replacement of minor herbs by less palatable grasses and shrubs, and although palatable major herbs have increased these could not sustain grazing at the previous stocking rates. Unless grossIy disturbed, some of the associated plant successions are likely to continue for at least another 30 years before near-climax stages are reached, and on severely disturbed sites subclimax conditions may persist indefinitely.