The vegetation and flora of Three Hummock Island, western Bass Strait

Abstract

A survey of the vegetation of Three Hummock Island Nature Reserve recorded 289 vascular higher plant species, 60 of which were introduced. Of the native flora, six are classified as rare or vulnerable. Clarke Island, at a similar latitude in Eastern Bass Strait, has a significantly richer flora, including an element of Mainland Australian/Bassian flora for which the island is the southernmost limit. In contrast, there are no species known from Three Hummock Island that do not occur on mainland Tasmania. The greater length of time during which the land bridge at the eastern end of Bass Strait was exposed is, therefore, reflected in the flora. Three Hummock Island was cut off for a much longer period with no land connections to the north, therefore has a more insular Tasmanian flora. Climatic differences may have exacerbated the contrast. Nine vegetation mapping communities are defined, the largest proportion of the island being covered by Myrtaceae-dominated scrub. The main changes in the vegetation since the time of European discovery have been the clearing of much of the relatively fertile calcareous sands for grazing and the consequent loss of most of the Eucalyptus viminalis forests, an increased fire frequency and the introduction of exotic plants. Fire and weeds are the major vegetation management issues on the island.