Douglas-fir Performance in Romania: Growth Insights from Common Garden Experiments

Abstract

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) is one of the most important non-native conifers introduced to Europe, valued for its rapid growth, versatile timber, and resilience under climate change. In Romania, the Douglas-fir was introduced at the end of the 19th century and later tested in international provenance trials. A total of 55 provenances originating from North America and Europe, from Romanian common garden experiments established in 1977, were evaluated in this study. We assessed growth performance using tree volume, slenderness index, and basal area as indicators of productivity and stability. Linear mixed models revealed that provenance significantly influenced tree volume and basal area at two testing sites, whereas the slenderness index was more strongly affected by site conditions. At the third testing site, provenance effects were weak, highlighting the dominance of the environmental factor. Strong provenance × location interactions indicated an instability in growth performance across sites. Among North American sources, interior provenances such as Idaho performed consistently well across sites, while coastal provenances from Washington and British Columbia achieved superior productivity at specific locations. Romanian provenances, including Toplița, Piatra Albă, and Anina Buhui, also ranked among the best performers, underlining their adaptive potential. Correlation analyses showed positive relationships between tree volume and basal area, while both growth traits were negatively associated with the slenderness index. Geographic origin variables explained part of the variation: longitude correlated positively with productivity, whereas higher elevation of origin was linked to slower growth and greater slenderness. Our results emphasize the importance of matching seed sources to planting conditions and highlight the potential of Douglas-fir for Romanian forestry.