Changes in the distribution and density of bitou bush (Chrysanthemoides monilifera subsp. rotundata (DC.) T.Norl.) in eastern Australia

Bitou bush (Chrysanthemoides monilifera subsp. rotundata (DC.) T.Norl.) is a South African shrub that has invaded large areas of coastal south-eastern Australia. It is widespread along the coast, where it negatively impacts native plants and ecological communities. Detailed spatial information is critical for making informed management decisions, particularly to assist in setting on-ground priorities and allocating resources, and to evaluate the effectiveness of weed management. The distribution of bitou bush was mapped previously in New South Wales; this paper presents an updated assessment of the distribution and density of bitou bush in Australia for 2008. The data were collated from a range of land managers and community groups, and analysed to determine area, density and spatial changes in bitou bush distribution. Mapping data were also analysed with respect to conservation areas in New South Wales, and national bitou bush containment lines, established to prevent northern and southern spread. The total area of bitou bush in Australia increased by 20% since 2001; 83% of the increase consisted of infestations with less than 10% cover. However, this spread has been offset by a 43% reduction in infestations with greater than 40% cover. Some of the overall increase in area may be attributed to a more comprehensive survey methodology, as this study may have captured sparse infestations that were not recorded in previous surveys. The distribution of bitou bush was found to be highly coastal, with 90.3% of bitou bush within 2.5 km of the coastline. The area of bitou bush in conservation areas in New South Wales decreased by 21%, including a 56% decrease in infestations with greater than 40% cover. Management in national containment zones has successfully restricted bitou bush Changes in the distribution and density of bitou bush spread and significantly reduced its density in these nationally significant areas. Continued support for strategic control programs will ensure the spread of bitou bush in Australia is contained.