Diversity of exotic vascular plant species on Moreton Island in subtropical Australia: increase over 100 years

There have been significant increases in the richness of exotic vascular plant species over the past century on Moreton Island, Australia. In total, 120 exotic species (including eight declared plants) in 90 genera and 42 families were collected and collated through field surveys during 2008–2010 and from the Queensland Herbarium collections. One-hundred years ago, no exotic vascular plant species were recorded. Sixteen years later, 14 exotic species in 14 genera from 11 families were collected. A half century later (1973–1975), a detailed vegetation survey recorded 66 exotic species (including five declared plants) belonging to 57 genera from 30 families. This increase coincides with a history of increasingly frequent wild fires, increasing human activities and greater presence of feral animals. The most significant increase occurred after the 1973–1975 surveys, namely an increase of 54 more species, equivalent to an 81.8% increase. These latter species included 17 (31.5%) woody species, 11 (20.4%) graminoid species and 26 (48.1%) forb species. The Sorensen similarity index (ISS) of total exotic species between the surveys of 1973–1975 and 2008–2010 was intermediate (ISS = 0.62). Index for woody species (ISS = 0.60) was also intermediate. Indices for annual graminoids (ISS = 0.53) and perennial forbs (ISS = 0.40) were all relatively low between the studies. Perennial graminoids and annual forbs had high similarity indices, namely, 0.75 and 0.72, respectively. The invasiveness of these plants was also assessed and it was shown that the ‘highly invasive’ and ‘generally invasive’ species were relatively few in number. The findings highlight the rapid increase and change in exotic vascular plant species on Moreton Island and the need for a more robust understanding of the exotic species’ dynamics of the island in order to inform weed management and native vegetation protection services.