Genetic diversity of European larch (Larix decidua Mill.) seed sources in Romania: implications for their conservation and sustainable use

Background European larch ( Larix decidua Mill.) populations in the Romanian Carpathians represent unique gene pools, yet their genetic integrity is increasingly threatened by fragmentation and the introduction of reproductive material of unknown origin. Aims This study assesses the genetic diversity and population structure of several seed sources represented by five natural populations, ten plantations, and two seed orchards in Romania. Results Our molecular analysis reveals that plantations exhibit significantly higher genetic diversity and reduced genetic distances compared to natural stands. This "diversity paradox" is attributed to the use of mixed genetic material from diverse Austrian and Central European (e.g. Czech Republic, Slovakia) seed sources, confirming the success of early breeding programs in maintaining a broad genetic base despite their primary focus on timber production. In contrast, natural populations show reduced genetic diversity, significant heterozygote deficiency, and strong genetic differentiation, with some populations exhibiting signatures of historical bottlenecks, indicating long-term isolation and limited gene flow. Management Implications Our results have clear implications for seed sourcing strategies. The extensive use of non-native reproductive material may contribute to the genetic admixture and erosion of locally adapted gene pools. In this context, the use of local seed sources should be prioritized, particularly within the native range, while the deployment of mixed material should be approached with caution. The continuous genetic monitoring of seed orchards and plantations is also necessary. Conclusions While plantations serve as vital reservoirs of adaptive variation for timber production, the protection of the unique, site-specific natural gene pools remains a conservation priority aiming to maintain a high evolutionary potential of the species in the face of climate change.