Contrasting Spatial Genomic Structure in Two Widespread Grassland Species Across Norway Supports Species‐Specific Seed Sourcing

ABSTRACT

Ecological restoration typically relies on locally sourced seed material, yet seed sourcing in many countries is based on broad administrative regions rather than empirical genetic data. Whether these generalized zones reflect biologically meaningful population genomic structure, particularly among co‐occurring species used together in restoration, remains poorly understood, thus limiting genetically informed restoration practices. Here, we use genome‐wide double‐digest RAD sequencing (ddRAD‐seq) to examine spatial population genomic structure in two widespread perennial grassland species commonly used in restoration in Norway: Silene dioica , an obligately outcrossing species with limited seed dispersal, and Achillea millefolium , a polyploid complex characterized by high gene flow and dispersal capacity. Analysis of 17 populations of S. dioica (355 individuals; 19,200 SNPs) and 23 populations of A. millefolium (428 individuals; 21,294 SNPs) across broad latitudinal and climatic gradients in Norway revealed strikingly contrasting patterns of genetic structure. Silene dioica showed moderate spatial structure, significant isolation‐by‐distance, and multiple geographically coherent genetic groups, indicating spatially restricted gene flow and supporting the delineation of multiple seed transfer zones. In contrast, A. millefolium showed weak population differentiation, extensive admixture, and little geographic structuring, but significant isolation‐by‐environment, with annual precipitation emerging as the strongest environmental predictor of genomic differentiation independently of geographic distance, justifying the delineation of three broad genomic zones. Because species‐specific life‐history traits likely contributed to these patterns, a single generalized seed‐sourcing framework can be inadequate even for sympatric species restored together. While the structured genomic patterns in S. dioica support localized seed sourcing, the high connectivity in A. millefolium supports broader transfer zones. Overall, our study highlights the importance of incorporating genomic data into restoration planning by aligning seed transfer distances with species‐specific connectivity to reduce genetic risks and maintain evolutionary potential under environmental change.