Adaptability of twelve European provenances of Pinus cembra in two different branches of the Carpathians

Swiss stone pine (Pinus cembra L.) is a promising species for afforestation at the upper altitudinal limit of the forests due to its adaptability to more difficult climatic conditions. The study aims to analyze the genetic variability, testing site influence, trait-trait and juvenile-adult correlations across two 27-years-old provenance trials. The primary goal was to identify the best-performing provenances, set the suitable breeding strategies, and predicting the optimal age for forward selection. In the spring of 2024, measurements and evaluations were made for survival, diameter at breast height, tree height (Th), volume, fork occurrences, stem straightness, defoliation, branches diameter and finesse. The results indicated a high level of genetic variability, particularly within provenances, suggesting strong potential for selective breeding and adaptability. In each trial, three provenances were selected for reproduction in the same provenance region and under similar environmental conditions as the trials where they were performed. However, due to significant testing site and site x provenance interactions, extreme caution is recommended when transferring forest reproductive materials. Low QST values highlight the need for maintain high genetic diversity, a serious issue for the long-term resilience of this species. The observed juvenile-adult growth traits correlations and the time-to-time evolution of the 12 provenances indicate that early selection, even at the juvenile stage (17 years), could be effective. Forward selection of the top 30 % trees from the best three provenances, for Th, is recommended to enhance genetic gain. These findings provide valuable insights for developing breeding strategies and optimizing afforestation efforts in high-altitude regions.