Canopy traits reveal climate-associated genetic differentiation in a California oak common garden

Abstract

Background and Aims. Phenotypic variation in plant populations reflecting historical climate adaptation may affect performance under future climates. In long-lived trees, height and stem diameter are commonly used to assess growth, but these measures may not fully capture complementary structural and functional dimensions of performance, such as canopy development and vigor. We investigated whether canopy traits reveal climate-associated genetic differentiation in Quercus lobata. Methods. Using drone-based remote sensing of 1,395 12-year-old Quercus lobata trees from 601 families in a common garden, we quantified canopy volume and greenness, using the Normalized Difference Vegetation Index (NDVI). Previous analyses indicated that trees originating from warmer climates grew more in common gardens than those from cooler climates. To assess whether canopy traits showed similar patterns, we tested for family-level variation in each trait and associations with climate of origin. Key Results. Canopy volume and greenness showed significant genetic variation among families and significant associations with climate of origin. Trees from hotter climates had greater canopy volume and greenness than trees from cooler climates. Conclusions. These covarying traits provide novel evidence of climate-associated genetic differentiation in tree performance, consistent with historical climate selection. Trees originating from climates with hot summers, moderate winters, and low precipitation performed best in the garden, suggesting that they will perform better than trees adapted to cool, wet conditions under future climate change.