DISTRIBUTION, DISTURBANCE TOLERANCE AND CONSERVATION OF STACKHOUSIA-GUNNII IN TASMANIA

Although being possibly widespread on the mainland of Australia, where it is recognised as part of the Stackhousia monogyna Labill. complex, S. gunnii Hook.f. is an endangered species in Tasmania, with only 10 known extant populations, all in the drier parts of the southern Midla nds. These populations occur largely on roadsides or lightly grazed pa ddocks in vegetation that was originally either Themeda triandra grass land or Eucalyptus pauciflora woodland. An ordination of floristic dat a from sites with and without S. gunnii showed that the species occupi es a floristically distinct environment. The floristic differences bet ween stands of S. gunnii relate partly to the presence or absence of t ree cover and substantially to precipitation. The groups of species th at preferentially occur with S. gunnii are geophytes, non-geophytic he rbs and exotic plants, while those that are concentrated elsewhere inc lude shrubs, grasses and non-geophytic graminoids. Permanent transects were monitored over a 4-year period at seven sites with varying grazi ng, firing and disturbance. The number of shoots varied markedly betwe en years in all sites, but not synchronously, even when transects were in close proximity. Although shoot numbers increased after fires occu rred on several ungrazed transect lines, they decreased on one grazed line. Deep mechanical disturbance of one site resulted in a dramatic d ecrease in shoot numbers in the following year. However, they increase d steadily over the following 2 years. Shoot emergence occurred at twi ce the expected rate on bare ground in all years and at all sites, and a substantial proportion of shoots was confined to this type of surfa ce. However, shoots were also recorded in fewer numbers in grass cover , herb cover and non-vascular plant crusts. Like some other threatened plants of grassy ecosystems, S. gunnii seems to be rare because it ca nnot survive with heavy grazing disturbance, ploughing and fertilisati on, and, at the other extreme, because it is susceptible to eliminatio n in the absence of environmental conditions and disturbances that cre ate bare ground.