Abstract
<jats:p>Tree crown architecture — the 3-D density, distribution and inclination of leaves within a tree crown — modulates within-crown light environments and can strongly affect optical signals linked to canopy structure and photosynthesis. Tree crown economics posits that (1) measurable crown architectural traits co-vary to describe a tradeoff between light capture and water-use efficiency, and (2) crown traits strongly affect crown-scale processes. However, empirical evaluation of these hypothesized relationships at the crown-scale across environmental gradients remains limited. Here, we combine tower-based photography with NEON Airborne Observation Platform (AOP) LiDAR and imaging spectroscopy to evaluate relationships among sunlit mean leaf angle (MLA), top rugosity, plant area index, accumulative plant area density in the upper 50% of the crown (APAD50), and crown-scale near-infrared reflectance of vegetation (NIRv) across nine eastern U.S. broadleaf deciduous forest sites and seven species. We found that (1) crowns with more vertically-inclined sunlit leaves (higher MLA) tended to have a greater proportion of plant area distributed in the upper half of the crown (higher APAD50), and (2) increases in both these traits were associated with lower crown-scale NIRv. Inter-specific patterns in crown traits and NIRv were broadly consistent with known species successional strategies, while site-level variation within Liriodendron tulipifera suggested possible acclimation of crown traits and NIRv along a moisture gradient. By leveraging NEON’s unique capacity to quantify crown architecture and associated spectral reflectance across wide environmental gradients, this study provides one of the first cross-site empirical evaluations showing that crown architectural traits are linked to crown-scale reflectance, and lays a foundation for future tests connecting crown economics to measured carbon and water exchange.</jats:p>