A new method and insights for estimating phenological events from herbarium specimens

Premise of the Study A novel method of estimating phenology of herbarium specimens was developed to facilitate more precise determination of plant phenological responses to explanatory variables (e.g., climate). Methods and Results Simulated specimen data sets were used to compare the precision of phenological models using the new method and two common, alternative methods (flower presence/absence and ≥50% flowers present). The new "estimated phenophase" method was more precise and extracted a greater number of significant species-level relationships; however, this method only slightly outperformed the simple "binary" (e.g., flowers present/absent) method. Conclusions The new method enables estimation of phenological trends with greater precision. However, when time and resources are limited, a presence/absence method may offer comparable results at lower cost. Using a more restrictive approach, such as only including specimens in a certain phenophase, is not advised given the detrimental effect of decreased sample size on resulting models.