A study of the ecology of Tasmanian sphagnum peatlands

The ecology of Sphagnum peatlands in the southern hemisphere has been poorly understood. Comparisons with northern hemisphere literature suggest that Tasmanian Sphagnum peatlands are limited in their morphology and geomorphic expression, possibly due to relatively low effective precipitation. While Sphagnum bogs tend to occupy nutrient poor situations in the northern hemisphere, in Tasmania they do not occur on the poorest substrates, despite climatic suitability. To provide data on spatial variability of Tasmanian Sphagnum mires, a survey of 137 sites across Tasmania was carried out. Plant species composition and cover, peat depths and height of hummocks were recorded. Climatic data were generated by using the computing package BIOCLIM. Peats from a subset of samples were analysed for their nutrient composition. Eight ecologically distinct groups spanning an almost continuous gradient from high to low altitude sites were recognised. Floristic variation between sites along this gradient can largely be explained by location along secondary gradients of nutrient availability and disturbance (fire). In a glasshouse experiment, the dry matter biomass of S. cristatum showed no significant relative effects when subjected to drought, fertiliser or shade treatments, either singularly or interactively. Shade resulted in a reduced biomass of Sphagnumassociates, suggesting that shade affects the competitive ability of other species. Monitoring of exclosure and control plots provided data which suggest that grazing may result in the maintenance of conditions suitable for Sphagnum by altering interspecific competition. The effects of grazing appear to be more pronounced at lower altitude, high productivity sites than at higher altitudes. There was no evidence to suggest that marsupials graze Sphagnum moss. Monitoring of a site subjected to a low intensity burn provided some short-term data on this disturbance event. Initial effects varied according to the vegetation present, which influenced the local severity of the fire. The most significant change appears to be a drying out of the peatland, which has resulted in a decline of Sphagnum. Macrofossils from peat cores have enabled a possible model of Sphagnum peatland succession in Tasmania to be developed. Succession appears to be multi-directional, with micro-successional changes occurring across mires in response to extremely local events. While the major successional pathway suggested by these cores is from Sphagnum/Restiad to Sphagnum mires, progressfon to sites dominated by herbs and shrubs is possible.