Assessing the drivers and the recruitment potential of Eucalyptus globulus in the Iberian Peninsula

In the last century, eucalypts became one of the most popular fast-growing species in the world for production purposes. Eucalyptus globulus Labill. is currently one of the most extensively cultivated species. The Iberian Peninsula (Iberia) holds the largest concentration of E. globulus plantations, distributed mostly along the Western and Northern coasts. The naturalization of E. globulus is now a concern in many regions across the introduced range, so it is important to identify the local and regional drivers that influence the recruitment of E. globulus wildlings. Likewise, it is important to understand how this recruitment relates both with the current and the potential distribution of plantations. We analyzed wildlings count data from 4169 transects surveyed with Google Street View along roadsides adjacent to E. globulus plantations across Iberia. These data were used to calibrate a probability map of wildling recruitment, using a species distribution model developed with biomod2. The probability map was compared with both the current and the potential distributions of E. globulus. Finally, we performed a logistic regression to model the relationship between the environmental suitability for E. globulus recruitment and the suitability for plantations in Portugal and Spain. We recorded a total of 6721 wildlings in 1363 transects (33% of the total transects). Overall, wildling density was 85.3 +/- 4.1 wildlings ha(-1), ranging from 0 to 5882 wildlings ha(-1). Regional variables had greater influence than local variables on wildling recruitment. Higher annual precipitation and lower temperature seasonality were positively related to recruitment abundance, reflecting wildling sensitivity to water deficits and extreme temperatures. At a local scale, the northern aspect and bare soil also presented a positive relationship with recruitment abundance. Recruitment potential was higher in areas with Atlantic influence along the northern and western coasts of Iberia, where plantations are already present. Nearly half of the area potentially suitable for E. globulus plantations was unfavorable for recruitment. However, we found a positive correlation between plantation suitability and recruitment suitability. This work may assist forest management by identifying zones where E. globulus recruitment is enhanced outside plantations for a better allocation of resources for monitoring and control actions.