The promise of digital herbarium specimens in large-scale phenology research

The online mobilization of herbaria has made tens of millions of specimens digitally available, revolutionizing investigations of phenology and plant responses to climate change. We identify two main themes associated with this growing body of research and highlight a selection of recent publications exemplifying: investigating phenology at large spatial and temporal scales and in understudied locations and testing long-standing theories and novel questions in ecology and evolution that were not previously answerable. We explore strengths and limitations of using digitized herbarium specimens in phenology research, including: issues of sampling; reliability, transferability, and biases; and ethical and social justice considerations. This field will see further breakthroughs as herbaria around the world continue to mobilize and digitally interlink their collections. New developments will likely come from advances in technology, international collaborations, and including understudied plant taxa and regions such as the Arctic and the tropics. Advances in technology are already improving digitization workflows and speeding the collection of phenology data from digital specimens.