Forest Structural Complexity Regulates Vertical Microclimatic Stratification

Understanding how forest structure mediates the influence of incoming solar energy into microclimatic conditions is essential for predicting their resilience under climate change. We investigated how structural complexity and solar energy interact to shape vertical microclimatic stratification across canopy, understory, and ground layers in native and exotic forests on Terceira Island (Azores, Portugal).,Across 19 plots spanning broad gradients of elevation and structural complexity, we quantified forest architecture using terrestrial laser scanning, and recorded temperature and relative humidity at three vertical strata from August 2023 to June 2025. From these data, we derived daily means and ranges of temperature and vapour pressure deficit (VPD), and modelled their responses to the interactions between structural attributes and total daily incoming solar energy using linear mixed-effects models.,Forest microclimates emerged from stratumspecific interactions between vegetation structure and solar energy. Greater structural complexity consistently buffered the effects of solar radiation on temperature and VPD variability in the canopy and understory, supporting global evidence that dense, vertically complex canopies moderate microclimatic extremes. In contrast, canopy openness amplified thermal and moisture variability across all strata, although this effect weakened towards the forest floor in structurally complex stands. Elevation strongly attenuated temperature and VPD responses, while slope and aspect intensified energy-driven fluctuations, highlighting the combined influence of radiative and terrain-mediated aerodynamic processes.,No single structural attribute universally governed microclimatic stability. Instead, microclimatic conditions arose from the combined effects of forest architecture, solar energy, and topography, with distinct mechanisms dominating each vertical layer. By quantifying how forest architecture modulates microclimate responses to incoming solar energy, this study provides a mechanistic causation for restoration strategies aimed at preserving structured microclimatic refugia under ongoing and future climatic change.