Distribution of Eucalyptus globulus Labill. in northern Spain: Contemporary cover, suitable habitat and potential expansion under climate change

Abstract The goals of this study were to analyze the current status of eucalypt plantations in northern Spain and to assess current and future potential expansion of these plantations under climate change. The findings showed that the area occupied by Eucalyptus globulus has increased greatly (by 4.6 times) in northern Spain in the last 50 years, to reach the current cover of 389033.57 ha. This area represents 18.22% of the total area of wooded land, although the proportion varies widely in different provinces (0.28% in the inland province of Ourense and 44.76% in A Coruna). In order to assess the current and future species distribution for two climate change scenarios, species distribution models were fitted to data on 53 spatially-continuous environmental variables (terrain, climate, soil and hydrographical variables) derived from 3014 plots with presence of eucalypts and included in the third Spanish national forest inventory. The Random Forest machine learning method proved to be the best approach for modelling eucalypt occurrence, which was found to be related to 18 variables. Climate, soil and terrain were the most important variables in the model (explaining respectively 51.2%, 34.2% and 10.1% of the variation). Future projections were made for 2050 and 2070 by considering representative concentration pathway (RCP) scenarios 4.5 and 8.5 and applying the BCC-CSM1.1 model of the IPCC’s 5th Assessment Report, which forecasted a significant increase in the suitable habitat in the inland areas of Galicia (northwest Spain) and a slight reduction in the other three autonomous communities in northern Spain (Asturias, Cantabria and Euskadi). The current suitable habitat in forest land and other natural and seminatural areas (SHNET) includes an area of 830885.41 ha available for potential expansion of eucalypt, of which a total of 296356.71 ha is currently occupied by native broadleaved forest, mainly in Galicia (185420.12 ha). In addition, an increase in SHNET of up 398810.27 ha is expected by 2070 in the worst climate change scenario (RCP 8.5), so that pressure on the native forest will mainly increase in the inland areas of Galicia. In natural protected areas, eucalypts currently occupy an area of 7840.40 ha, which represents 7.10% of the SHNET included in natural protected areas in the study zone (110428.78 ha). The largest such area (5032.65 ha) is in Galicia and represents 7.42% of the SHNET in natural protected areas in the region (67836.64 ha). In the future, this amount will increase by between 59.16% and 87.89% in Galicia but will decrease by between 18.41% and 30.59% in the other autonomous communities in northern Spain, with the exception of the RCP 8.5 scenario for 2070, in which an increase of 4.42% is forecast. The research findings demonstrate the significant presence of eucalypt in natural protected areas and the possibility of expansion of eucalypts in Galicia in the absence of effective control.