A standardized photographic guide to woody plant spring phenology

Measuring plant phenology--the timing of recurring life history events such as leafout and flowering--sounds tantalizingly simple, but is complicated by the reality that different people often interpret the same event (e.g., budburst or leafout) differently. Researchers have worked to overcome this with a series of guides that explicitly describe each phenological event in great detail. One of the most widely-used scales is the BBCH (Biologische Bundesanstalt, Bundessortenamt und CHemische Industrie), which defines several principal growth stages and breaks down each stage into events within stages (e.g., first leaves separated). Yet, even with clearly described stages aimed at standardizing measurements of the same events taken by different observers, there can still be variation in observers' interpretation of events. Thus, photographs of each defined stage, for each species of interest, can help standardize observations further. Here we present a photographic guide to the BBCH stages of 31 woody species common to northeastern North American temperate forests.