The spatial distribution of non-native plant invaders in a pine–eucalypt landscape mosaic in south-eastern Australia Original Research Article

Factors influencing the spatial distribution of two major species of non-native plants, blackberry (Rubus fruticosus) and radiata pine (Pinus radiata) wildlings in a fragmented forest landscape in south-eastern Australia were quantified. A total of 1067 plots within three broad groups of sites was surveyed for these two non-native plant species. The sites were in large continuous areas of native eucalypt forest, an extensive plantation of P. radiata, and sites in patches of remnant eucalypt forest embedded within the pine plantation. In the case of the 507 plots located within patches of remnant eucalypt forest, an array of variables (e.g. distance to surrounding pine plantation, and floristic and structural attributes) was measured and used in statistical analyses of non-native plant occurrence. P. radiata wildlings were totally absent from plots in large continuous areas of native eucalypt forest, but present at 5% of plots within patches of eucalypt remnants embedded within the pine plantation. Logistic regression showed that the occurrence of P. radiata wildlings in the eucalypt remnants was significantly higher in plots where the neighbouring pine plantation had been established for a long time, plots that were dominated by dry eucalypt forest types, and plots with a limited cover of ground vegetation. The occurrence of R. fruticosus differed significantly (P<0.001) between the groups of sites; 59% of plots in the pine plantation, 41% in the eucalypt remnants, and 7% in continuous areas of native forest were invaded. For the eucalypt remnants, the occurrence of this species was significantly greater in plots close to the surrounding pine plantation, with fewer species of native shrubs, in wet eucalypt forest types, and with low values for both eucalypt basal area and rock cover. The results of this study indicate that even though non-native plant invasion is already relatively extensive in the study area, it is likely to further increase. The array of factors influencing the spread and establishment of P. radiata wildlings and R. fruticosus indicate that the control of these non-native plants will be extremely difficult in the existing plantation estate. However, the adoption of some simple protocols could make it feasible to limit their spread to newly established areas of the pine plantation estate.