Abstract
Tree-growth patterns encode valuable information about forest dynamics, ecological processes, and environmental changes. However, extracting this information requires precise visualization of tree-ring boundaries. While species with distinct tree-ring boundaries (e.g., conifers and ring-porous hardwoods) have been extensively studied, diffuse-porous and semi-ring-porous species remain understudied, despite their ecological importance. Addressing this knowledge gap requires improved tree-ring visualization techniques for these challenging species to enable their reliable measurement and crossdating. In this study, we evaluated the effectiveness of various sample preparation and imaging techniques for enhancing tree-ring visibility in 62 temperate tree species sensu lato from East Asia and North America. We compared three preparation methods: increment cores surfaced with a core microtome with and without chalk, and double-stained thin sections. These were combined with four imaging techniques: visible light microscopy and fluorescence microscopy using ultraviolet (UV), green fluorescent protein A (GFPA), and red fluorescent protein 1 (RFP1) filters. The results demonstrated that double-stained thin sections under visible light yielded the clearest tree-ring boundaries, followed by chalked surfaced cores under visible light. Among the fluorescence techniques, UV fluorescence imaging outperformed GFPA and RFP1 fluorescence. Although double-stained thin-section preparation requires greater expertise, it is a reliable, relatively fast, and cost-effective approach that can expand the scope of dendrochronological studies and support broader applications in forest management, climate research, and biodiversity conservation.