Neil Gibson

Dynamics of a Tasmanian bolster heath string fen

The string fen at Newdegate Pass, Mt. Field, Tasmania consists of dams composed of bolster heath and peat derived from bolster heath, and flark ponds with concave sides and usually rocky floors. The bolster heath has a smooth surface which consists of a complex mosaic dominated byDonatia novae-zelandiae, Carpha rodwayi andDracophyllum minimum. The floors of the ponds usually support no macrophytes. The ponds situated on strong flow lines have shallower dams which are more often breached than those where flow is more diffuse. The ponds ultimately drain by tunnelling through the humified peat below the live roots of the bolster heath, and the exposed floors are colonized by bolster heath species. The underlying block stream has a topography partly independent from that of the string and flark features, which shift in both time and space.

A comparison of the cushion plant communities of New Zealand and Tasmania

Abstract Communities dominated by species of cushion plants are widespread in the alpine and subalpine zones ofNew Zealand and Tasmania. In New Zealand this vegetation type contains six major associations. These are described as alpine herbmoor, cushion bog, high alpine cushion moor, alpinc cushion herbfield, and rock and river shingle cushion communities, their distributions being closely related to particular geomorphic environments. In Tasmania there are four major associations. These are described as AbrotancHa cushion heath, high mountain cushion heath, mosaic cushion heath, and Donatia cushion heath, their distributions being most closely related to altitude, precipitation, and rock type. Ofthe six New Zealand cushion associations, herbmoor and cushion bog have the highest proportion ofspecies also occurring in Tasmania. The differences between Tasmanian and New Zealand cushion associations largely result from differences in topography. Tasmania lacks the rock and river shingle environments, complet...

Dynamics of a Tasmanian cushion heath community

Little is known of the dynamics of the alpine cushion plant communities of Tasmania. The present study investigates the nature of the short (5 yr) and long (850 yr plus) term dynamics within one such community at Newdegate Pass, Tasmania. This involved observations of permanent plots, quadrat sampling of cushion heath in different stages of a secondary succession and cuticular analysis of a core through the cushion peat. Data from the peat core showed the contin- ued presence of the cushion heath community at this site for at least 850 yr, while the regeneration patterns indicated commu- nity composition was largely achieved by species accumula- tion rather than species replacement. Over a 5-yr period there was little or no change in total percentage cover yet a surpris- ingly high degree of interspecific competition for space in areas of complete plant cover. These observations best fit non equilibrium models of community succession and stability.

Causes and consequences of variation in snow incidence on the high mountains of Tasmania, 1983-2013

Alpine plant species are considered to have a precarious near future in a warming world, especially where endemic on mountains without a nival zone. We investigated how and why snow patch vegetation and snow incidence varied over recent decades in Tasmania, Australia. Landsat images between 1983 and 2013 were used to calculate the proportion of clear days with snow visible on Mt Field. We compared average annual snow incidence on 74 Tasmanian alpine mountains for 1983–1996 with that for 1997–2013 using the small subset of Landsat runs in which most of Tasmania was clear of cloud. We related the temporal data from Mt Field to Tasmanian climatic data and climate indices to determine the predictors of change. We recorded plant species and life form cover from quadrats in transects through a snow patch on Mt Field in 1983, 2001 and 2014, and mapped decadal scale changes in boundaries and shrub cover at five other snow patches across the extent of the Tasmanian alpine areas from aerial photographs. The incidence of snow fluctuated between 1983 and 2013 at Mt Field with no overall trend. Snow incidence was less on lower elevation alpine mountains in the period 1997–2013 than in the period 1983–1996, but showed a weak opposite trend on mountains higher than 1350 m. The contrast in trends may be a consequence of the effect on lapse rates of stronger frontal winds associated with a steepening of latitudinal pressure gradients. At Mt Field, bare ground decreased, cover of cushion plants and tall shrubs increased and obligate snow patch species were persistent. The trends we observed in both vegetation and snow incidence differ markedly from those observed on mainland Australia. The increase in shrub cover and decrease in bare ground on Mt Field were unexpected, given the constancy in incidence of snow. These results may relate to ongoing recovery from a fire in the 1960s, as the shrub species that have increased are fire-sensitive, obligate seeders and there has been no indication of warming since 1983 in the climatic record for western Tasmania. There is a possibility that some Tasmanian alpine areas might act as long-term refugia from general warming.