Improving the efficiency of genetic selection in Sitka spruce using spatial and competition factors

Sitka spruce ( Picea sitchensis (Bong.) Carr.), is a highly valuable commercial tree species in Ireland, UK and elsewhere in Europe but there is relatively little information available in relation to the performance of improved material. The primary objective of this study was to explore the genetic variation in competitive ability and determine how a spatial model improved the accuracy of genetic estimates over time for Sitka spruce. To achieve this, the study employed competition index (Hegyi’s I) and spatial analysis on height and diameter data from genetic improvement trials in Ireland. A total of 54 half-sib families of Sitka spruce were included in the study. The trials had been established to identify superior genotypes among the plus trees which had been included in the improvement programme in Ireland. The study revealed that spatial heterogeneity significantly affects the genetic estimates for Sitka spruce. The results indicated that spatial analysis could provide valuable insights into the genetic trials of Sitka spruce and improve the accuracy of genetic evaluations. Heritability increased by 104% for diameter at breast height (DBH) using a spatial analysis approach, compared with a more traditional non-spatial model approach. It was found that thinning practices can affect the response of genetic performance to spatial heterogeneity. In addition, genetic variation in competitive ability was observed. The results highlight the importance of considering spatial dependence in the design but more importantly in the analysis of genetic trials and provides a framework for future research on the genetic improvement of Sitka spruce populations.