Swiss stone pine (Pinus cembra) is a viable solution for afforestation in the high mountain zone, at the upper limit of the forests, due to the species adaptation ability to the limiting climatic conditions. The aim of this study was to analyse the genetic variability, inheritance rate and juvenile-adult correlations, in a 26 years full-sib (10x10 complete mating design) trial, in order to predict the genetic gain of forward selection. In the spring of 2023, measurements and evaluations were carried out for all the existing trees, for Survival rate (Sr), growth (Diameter as breast height- Dbh, Trees' height- Th, Trees' volume- Tv) and quality traits (Forks, stem slenderness- Ss, branches' diameter- Bd, branches' finesse- Bf, defoliation- Def). The 90 cross-pollinated (CP) families registered 50% of Sr whereas the other 10 selfcross-pollinated (consanguineous) registered just 11% of Sr, and the majority of those trees are dominated and face extinction in the next years. Juvenile-adult correlations were highly significant (p<0.001), indicating that early selection (at the age of 14 years) might be efficient. At the trial age, based on the medium to high heritabilities, the forward selection of the best 10% individual trees from the top 20 of the 90 CP families, for Dbh, could be applied, which ensure at least 9.2% of genetic gain.

Swiss stone pine (Pinus cembra) is a feasible solution for increasing the resistance of future mixed spruce–pine stands to windfall at the upper altitudinal limit of Romanian forests. This study aims to analyze the adaptability of ten full-sib families in two different environmental conditions and their evolution in time for predicting forward selection. At a seedling age of 33, evaluations were carried out for survival rate (Sr), growth (diameter at breast height—Dbh, and trees’ height), and branch traits, as well as for stem straightness. The high level of genetic variability, inheritance rate, and trait–trait correlations, registered in both trials, ensure the success of the breeding program. The Swiss stone pine shows a very good adaptation on high-sloping lands from the upper altitudinal limit of Romania’s forests, with the cross-pollinated (CP) families registering a 28.5% better survival in the Rodna trial (34° slope) compared to the Păltiniș experiment (7° slope). The consanguineous families registered only an 11% Sr in Păltiniș, while in the Rodna trial, the Sr was four times higher (in both trials, consanguineous trees were dominated). The juvenile–adult correlations of growth traits were significant, indicating that early selection could be efficient. The forward selection of the best 10% of CP families for Dbh could be applied, ensuring a 9% to 15% genetic gain.

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.