Global climate change exposes perennial plant species to increasingly variable environmental conditions, intensifying the need to understand the genetic mechanisms underlying phenotypic plasticity. Phenotypic plasticity, the ability of a genotype to express varying phenotypes while exposed to different environmental conditions (Sommer, 2020), is especially critical for long-lived species such as Populus tremula, which encounter diverse climates throughout their lifespan. This study uses bioinformatics tools and methods to investigate the genetic basis of heritable plasticity in Populus tremula using clonal replicates from the Swedish Aspen (SwAsp) Collection, planted in two contrasting environments: Ekebo and Sävar. Plasticity scores and genotypic estimates were used to estimate if there were significant plastic responses and look at a clone’s genotypic performance. Plasticity was assessed through genotype-by-environment (GxE) interactions, differences in genotype responses across environments. RRMMs were fitted with both fixed and random effects to identify associations between the dataset’s variables and genotype association was done as a part of a larger GWAS study to identify loci associated with trait variation. It can be concluded that the consistent clone-level differences for both traits across locations and time suggest a heritable basis for environmental responsiveness and performance. The RRMMs captured significant variations connected to clones and GxE interactions implying that variation in plasticity is not random and at least partially under genetic control. The genotype association results further illustrated and gave insight into the different underlying genetic architectures of plasticity and genotypic performance. Plasticity showed no significant associations, similar to polygenic inheritance patterns, while genotypic performance, revealed a significant SNP associated with CAF-1, suggesting partial control by major regulatory genes. While the study did not estimate heritability in the formal quantitative genetics sense, the structure and output of the results suggest that phenotypic plasticity is at least partially under genetic control in Populus tremula.