The aim of this study was to determine bryophyte richness and species composition in Tasmanian buttongrass moorland, and the effect of environmental variation, in particular time since fire, on bryophyte diversity. Almost nothing has been published on bryophytes in this landscape, despite buttongrass moorland covering approximately 8% of Tasmania and being a key vegetation community in the Tasmanian Wilderness World Heritage Area. Characterised by vegetation dominated by Gymnoschoenus spaerocephalus, a large, slow-growing, pyrogenic and tussock-forming sedge, buttongrass moorland is a highly fire-adapted ecosystem and frequently burned. Uncontrollable buttongrass fires spread into other habitats, especially on windy days or when the fuel is particularly dry. However, buttongrass moorlands are also seasonally water-logged, potentially being under water for months, and some areas are subjected to frosts and snow-cover.
This study occurred across a range of scales, from a statewide survey down to the local level. For the statewide survey of bryophytes in buttongrass moorland, 100 sites were located across Tasmania, including the far south, south-west, west, north-west, central and north-east, and across a range of altitudes (10 m - 810 m). Two-hour time sampling of bryophytes was performed at these sites. At the regional scale, two areas were used, Lake Pedder in Tasmania’s south-west and Lake St. Clair in the central highlands for complementary studies; a space for time study and a before-after control-impact study. Both sought correlations between the length of time since the site was burned and bryophyte richness and composition. Two much more localised studies were established in the buttongrass moorlands surrounding Lake St. Clair, where the effects of canopy removal and grazing on bryophyte cover were examined. The effects of fire on bryophytes were investigated further by comparing changes to bryophytes after burning, which alters the soil nutrient status and light levels, and changes to bryophytes through slashing the buttongrass canopy, which alters only light levels. This was done by comparing three recently burnt sites to three sites that had had the canopy mechanically removed through slashing. Also examined at the local level was whether bryophytes were being grazed by vertebrate herbivores after fire in the buttongrass moorlands.
On a statewide scale, overall bryophyte composition was quite uniform across the 100 buttongrass moorland sites, with no differences based on location, although altitude was found to be significantly correlated with composition. On a regional level, fire did not significantly affect bryophyte species richness or composition. In the space-for-time study, liverwort diversity was significantly related to buttongrass age, but this was due to the effects of just a few older sites with higher liverwort richness. The surprisingly poor correlation with fire was supported by the results from the sites established as a before-after control-impact study, even though these sites were not analysed collectively due to design limitations. In contrast, there was a significant difference in the vascular plant species found in the buttongrass moorlands around Lake Pedder compared to Lake St. Clair.
In the two localised studies, bryophytes were not significantly affected by an increase in light levels or found to be eaten by vertebrate herbivores. It is possible that the fruiting capsules of bryophytes were being eaten, because what appeared to be evidence of herbivory was observed on the large fruiting capsules of the moss Pleurophascum grandiglobum in a buttongrass moorland plain separate to this particular study. Bryophytes were not found to be significantly affected by an increase in light levels after fire or after mechanical slashing of the overstorey, although there was a significant difference in the effects on bryophytes between the two treatments during the first year.
A relatively limited suite of bryophytes may be able to deal with the challenges associated with life in the Tasmanian buttongrass moorlands. The current management regime of periodic prescribed burning in some areas would appear to be adequate to maintain bryophyte species diversity in this vegetation type, providing a variety of time since fires is retained to facilitate liverwort diversity.