Investigating the invasiveness of Eucalyptus globulus in Portugal: site-scale drivers, reproductive capacity and dispersal potential

Plantations of Eucalyptus globulus Labill. have expanded rapidly over the last four decades across temperate parts of the globe. There has been growing concern about the potential invasiveness of this species. Portugal grows more E. globulus than any other country (by area). This study investigates poorly understood factors that may influence wilding establishment and spread from Portuguese plantations. We assessed: site-scale factors influencing the presence and abundance of E. globulus wildlings along plantation edges, as well as the size and reproductive state of these wildlings; and the dispersal distances and developmental state of wildlings away from the plantations edge. We found 1630 E. globulus wildlings in 129 survey plots (10 × 10 m) established along the edge of 67 plantations. Half of the surveyed wildlings were taller than 1.3 m. The presence and abundance of E. globulus wildlings was mainly influenced by factors such as soil cover, the age of mother-trees and their reproductive output. Around 8% of the surveyed wildlings were reproductive, including wildlings less than 1.3 m tall. The proportion of reproductive wildlings was mainly influenced by wildling size, the location relative to the plantation edge and the annual number of frost days. In 49 survey transects outside plantations we found 641 E. globulus wildlings up to a distance of 76 m. Establishment distance was associated with natural drainage lines and the dominant wind direction. We discuss the relevance of the results in terms of the potential invasiveness of E. globulus .