How Will Climate Change Affect the Future Habitat Suitability of Douglas-fir in Romania?

Abstract

Climate change is expected to substantially alter the distribution of forest tree species, requiring reliable tools to support adaptive forest management. Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), one of the most productive and economically valuable conifer species cultivated in Europe, has attracted increasing interest as a potential alternative to native conifers under future climatic conditions. This study assessed the historical baseline and future climatic habitat suitability of Douglas-fir in Romania using an ensemble species distribution modelling approach. Species occurrence data were combined with bioclimatic variables from WorldClim, and ensemble predictions were generated using four modelling algorithms. Future habitat suitability was projected under two climate scenarios (SSP245 and SSP585) for three time periods (2041-2060, 2061-2080, and 2081-2100). Temperature seasonality (BIO4) and precipitation seasonality (BIO15) were identified as the most influential variables controlling the potential distribution of Douglas-fir. Model performance was high, with Random Forest providing the best predictive accuracy (AUC = 0.94; TSS = 0.76). Historical baseline habitat suitability was highest in western, north-western, and north-central Romania, while eastern and south-eastern regions were characterized by predominantly poor or unsuitable conditions. Future projections indicated contrasting trends between climate scenarios. Under SSP245, climatically suitable habitats persisted throughout the century, although highly suitable areas gradually declined. In contrast, SSP585 projected a marked deterioration in habitat suitability, with the disappearance of the good and excellent suitability classes by the end of the century and the expansion of poor suitability across most of Romania. Despite these projected changes, western Romania is expected to remain the most favourable region for Douglas-fir cultivation. The results provide valuable information for climate-adaptive forest management, assisted migration, and the selection of suitable planting areas and reproductive material under future climate conditions.