A photographic guide to spring phenology in woody plants of Western North America

Studies of spring budburst frequently rely on observations from branch cuttings kept under controlled environmental conditions to test for species-level variation. While this approach provides a more mechanistic understanding of how budburst in adult trees responds to differ- ent environmental cues, it is critical that observations are standardized across species and studies. Standardized guides, such as the BBCH (Biologische Bundesanstalt, Bundessortenamt, CHemische Industrie) scale, were developed to provide a consistent definition of each phenological stage of spring budburst. But given the diversity in species bud morphology, architecture, and observers’ interpretations, making consistent observations across growth stages is still challenging. To address these challenges, we developed a photoguide of the principal growth stages of budburst and leafout for our focal community, photographing BBCH stages 0 to 17 for woody plant species in western North American temperate forests.