Assessing accuracy in citizen science-based plant phenology monitoring

In the USA, thousands of volunteers are engaged in tracking plant and animal phenology through a variety of citizen science programs for the purpose of amassing spatially and temporally comprehensive datasets useful to scientists and resource managers. The quality of these observations and their suitability for scientific analysis, however, remains largely unevaluated. We aimed to evaluate the accuracy of plant phenology observations collected by citizen scientist volunteers following protocols designed by the USA National Phenology Network (USA-NPN). Phenology observations made by volunteers receiving several hours of formal training were compared to those collected independently by a professional ecologist. Approximately 11,000 observations were recorded by 28 volunteers over the course of one field season. Volunteers consistently identified phenophases correctly (91 % overall) for the 19 species observed. Volunteers demonstrated greatest overall accuracy identifying unfolded leaves, ripe fruits, and open flowers. Transitional accuracy decreased for some species/phenophase combinations (70 % average), and accuracy varied significantly by phenophase and species ( p