Trends in Vegetation at Kosciusko. 1. Grazing Trials in the Subalpine Zone, 1957-1971

Abstract

This paper examines vegetation changes in the absence of fires at Kosciusko during the 14 years following the general withdrawal of livestock grazing at Kosciusko in 1958 on two pairs of plots on subalpine grassland at Dainers Gap (elev. 1700 m) and in the Hotel Kosciusko Water Reserve (elev. 1660 m). One plot in each pair was experimentally grazed. and the other plot was ungrazed. The vegetation of the Kosciusko Reserve was in a relatively natural condition, characterized by continuous forb-rich snowgrass associated with regenerating snowgum woodland. At Dainers Gap the snowgrass was less continuous, and there was no snowgum regeneration.

In the Kosciusko Reserve the main effect of grazing was to reduce the cover of the large palatable forbs. This change appeared to be largely reversible within 6 years after the 8 years of grazing treatment was discontinued.

At Dainers Gap the tussocks spread laterally in the absence of fire. on both the grazed and ungrazed plots. Under grazing (5 sheepjha/season), small grazing-adapted herbs maintained themselves on the intertussock spaces, but in the absence of grazing they were largely replaced by taller-growing species, many of which appeared only after this treatment had ceased. Shrubs, although uncommon, increased rapidly in size, especially on the grazed plot where competition from herbaceous species was reduced. On the grazed plot the area of bare soil did not decrease appreciably but on the ungrazed plot it decreased on all but the largest bare patches where the lateral spread of tussocks and shrubs was not sufficient to cover them. Under grazing the standing crop on the intertussock spaces at Dainers Gap remained at low levels of about 0.3 kg/m². but when not grazed for 10 years it increased to about 1 kg/m², with a resultant increase in surface soil organic matter and decrease in bulk density.

During the one season when sheep were weighed at monthly intervals. they gained weight at both sites at the start of the grazing season until the supply of the relatively palatable and nutritious herbs and grass inflorescences was exhausted, then lost weight as mature snowgrass leaves became the main part of their diet. Seasonal weight losses of sheep increased over the 15 years of the experiment as most of the major forbs were eliminated by grazing from the Kosciusko Water Reserve plot, and the area of minor herbs was reduced at Dainers Gap by the encroachment of snowgrass tussocks onto the intertussock spaces.

At Dainers Gap in the absence of grazing and fires; water catchment and nature conservation values improved but. without fire, unpalatable snowgrasses and shrubs increased and the value of the area for grazing was reduced. With grazing, the previously unsatisfactory conditions for water catchment and nature conservation were maintained. At the Kosciusko Water Reserve nature conservation and grazing values were reduced by grazing. Introduction Transhumant grazing increasingly became a major issue in the use and management of the Snowy Mountains, following completion of the Hume Dam in the early 1920s and the report by Byles (1932) documenting the deterioration of parts of the Hume