Assessing the invasive potential of Eucalyptus globulus in Australia: quantification of wildling establishment from plantations

Eucalyptus globulus is one of the most widely planted temperate hardwood species in the world, and in Australia there are 538,000 hectares growing in plantations. Although it has been reported as invasive, quantification of E. globulus invasion is rare. We conducted surveys at two geographic scales to assess the level of, and factors influencing, wildling establishment from industrial E. globulus plantations in Australia. We surveyed 290 km of plantation boundary, both within (22 %) and outside (78 %) the species native range. In areas of relatively high establishment, a density triggered paired plot approach (plots with and without wildlings) was used to assess fine-scale factors influencing establishment. We recorded 4,939 wildlings (17/km), 98 % of which occurred within 10 m of the plantation edge (maximum 175 m). Establishment varied between regions, ranging from 1.2 to 39.6 wildlings/km. Generalized linear models showed that the probability of a wildling being present increased with plantation age, that wildling abundance was higher along burnt transects, as well as sites that received regular, relatively high rainfall and had lower mean annual temperatures. The only fine-scale/local factor influencing wildling presence was the reproductive output of the plantation. The current level of E. globulus establishment in Australia is low in comparison to other invasive forestry trees. However, given the relatively young age of the Australian estate, local and regional variation in establishment, and potential future changes in plantation management, monitoring is warranted. Implications for assessing the general invasiveness of Eucalyptus and possibilities for E. globulus wildling control are discussed.