This repository contains the island-level dataset and R scripts supporting the manuscript “Climate and volcanic activity modulate area–distance effects on plant diversity along the temperate–subarctic island volcanic arc.” The dataset includes species richness (SR), standardized phylogenetic diversity metrics (SES.MNTD and SES.MPD), and all environmental and geographic predictors used in the analyses. The island × species matrix (provided without species names, raw floristic checklist is available upon reasonable request). R scripts reproduce all regression, ordination, and structural equation modelling analyses presented in the manuscript.