Forest management alters the growing conditions and thus further development of trees. However, quantitative assessment of forest management on tree growth has been demanding as methodologies for capturing changes comprehensively in space and time have been lacking. Terrestrial laser scanning (TLS) has shown to be capable of providing three-dimensional (3D) tree stem reconstructions required for revealing differences between stem forms and growth allocation. In this study, we used TLS-based 3D reconstructions of tree stems to investigate how forest management (i.e., varying thinning treatments and the following growth effects) has affected stem size and form of Scots pine (Pinus sylvestris L.) trees. The results showed that intensive thinning resulted in more stem volume and therefore total biomass allocation and carbon uptake compared to the moderate thinning. Scots pines growing in plots from which suppressed trees were removed (i.e., thinning from below) had larger bottom part of stems (i.e., volume accumulated more below 50% of tree height) compared to Scots pines growing in plots from which part of the dominant trees had been removed (i.e., thinning from above). Furthermore, intensive thinning, especially from below, produced less variation in relative stem attributes characterizing stem size and form. Thus, it can be concluded that thinning intensity, type, and the following growth effects have an impact on post-thinning stem growth as well as stem form of individual Scots pine trees. Our study presented detailed measurements on postthinning growth of Scots pines that have been laborious or impracticable before the emergence of TLS technology. Moreover, TLS-based stem reconstructions provided variety of attributes characterizing stem growth allocation that have not traditionally been feasible to obtain. The study demonstrated that TLS technology can be used to generate new knowledge for supporting forest management and silviculture as well as improving ecological understanding of boreal forests.