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Title: A new phenological metric for use in pheno‐climatic models: A case study using herbarium specimens of Streptanthus tortuosus

Herbarium specimens have been used to detect climate‐induced shifts in flowering time by using the day of year of collection (DOY) as a proxy for first or peak flowering date. Variation among herbarium sheets in their phenological status, however, undermines the assumption thatDOYaccurately represents any particular phenophase. Ignoring this variation can reduce the explanatory power of pheno‐climatic models (PCMs) designed to predict the effects of climate on flowering date.


Here we present a protocol for the phenological scoring of imaged herbarium specimens using an ImageJ plugin, and we introduce a quantitative metric of a specimen's phenological status, the phenological index (PI), which we use inPCMs to control for phenological variation among specimens ofStreptanthus tortuosus(Brassicaceeae) when testing for the effects of climate onDOY. We demonstrate that includingPIas an independent variable improves model fit.


IncludingPIinPCMs increased the modelR2relative toPCMs that excludedPI; regression coefficients for climatic parameters, however, remained constant.


Our protocol provides a simple, quantitative phenological metric for any observed plant. IncludingPIinPCMs increasesR2and enables predictions of theDOYof any phenophase under any specified climatic conditions.

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Author(s) / Creator(s):
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Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Applications in Plant Sciences
Medium: X
Sponsoring Org:
National Science Foundation
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