Decadal-scale vegetation dynamics above the alpine treeline, Mount Rufus, Tasmania

Abstract

Alpine areas by definition have summer temperatures too cool to support trees. Concerns have been raised that trees may invade these distinctive habitats where global climate change results in an increase in summer temperatures beyond the threshold limiting tree growth. In 2016, we investigated changes in the treeline and vegetation immediately above it by resampling quadrats and rephotographing from the set points established in the Alpine Treeline Ecotone Monitoring Program on Mount Rufus, Tasmania, in 2006. Within the study area, the only species with the potential to reach a tree height > 3 m is Eucalyptus coccifera Hook.f. The height, density, basal diameter and diameter at breast height were recorded for all E. coccifera within the study area, together with an estimate of percentage cover of each vascular plant species. No change was found in the location of the treeline over the 10-year period, although E. coccifera height and density above the treeline did increase. The vegetation on the north-facing slope shifted to a composition more closely related to the forest below the treeline, while on the south-facing slope forest species reduced in abundance and the vegetation became more dominated by alpine species. Historical aerial photographs suggest that there has been a minor and inconsistent establishment of E. coccifera plants at higher altitudes since 1953. The area was burned by bushfire in 1965, making it difficult to separate the effects of putative climate change and recovery after the fire event on vegetation changes, although data from Lake St Clair suggest a local constancy of mean growing season temperatures and rainfall.

Seventy-five years of vegetation change after fire in Tasmanian alpine heathland

“…These two studies largely took place in coniferous heaths, which are dominated by slow-growing shrub species from the Gymnospermae that are commonly dominant in the western and central mountains; however, most of the Tasmanian and mainland Australian alpine heath is dominated by shrub species in the Angiospermae (Kirkpatrick 1997). Harrison-Day et al (2016) documented Orites acicularis and Eucalyptus coccifera expansion in angiosperm-dominated alpine vegetation between three and five decades after fire on Mount Rufus in central Tasmania. Kirkpatrick et al (2002a) examined the long-term impacts of fire in angiosperm alpine heath on kunanyi in the south-east of Tasmania, re-sampling plots that were first placed 31 and 16 years after fires burnt parts of the study area in 1947 and 1962.…”