LAUSR

Plant collections are, by their very nature, records of phenology— the study of cyclical events in an organism’s life cycle including growth and reproduction phases that occur over the course of the year. These phases, which are called phenophases, are represented in plant collections with such features as young flower buds, senescing leaves, and even bare branches on a herbarium sheet. In combination with the collection date and locality information present on the specimen label, collections provide valuable data about plant phenology. Phenology is not a new science, but it has taken on additional importance in recent decades as a metric for studying the impacts of global climate change on species. As the climate warms and weather patterns are altered, it becomes increasingly vital to quantify the effects of these changes on plants and animals. Certain taxa, of plants in particular, are quite sensitive to temperature, precipitation, and other environmental variables, with the timing of their growth, reproduction, and senescence advancing or becoming delayed depending on the conditions to which they are exposed. Shifts in phenology can have cascading effects through the ecosystem. For example, the timing of when a forest leafs out signifies the start of the growing season and with it the progression of nutrient and water cycles. Likewise, if plants flower earlier in warmer springs but their insect pollinators have not yet emerged, plant and pollinator populations themselves can be negatively impacted. At the landscape scale, even small changes in phenology can have substantial consequences. Longterm data that capture the variability inherent to plant phenophases are foundational to phenological studies. Systematic records of phenology are rare, however, so researchers have been creative in using records that were collected for purposes other than phenological research. Herbarium specimens have proven to be especially robust sources of historic and recent phenological data, and, thanks to global efforts to image specimens and create digital records for information that was previously available only in analog format, more and more of these data are freely available online. The urgency of biodiversity research relating to environmental change, the ready availability of phenological data, along with continually improving computational capabilities, make this an ideal time to be conducting phenological research. In this special issue, “Emerging Frontiers in Phenological Research,” nine research groups have come together to present innovative phenology projects, all of which make use of, or can be applied to, herbarium specimens. Digitized herbarium specimens most often require the addition of phenological classification to be useful for phenological research, and this can be resourceintensive and timeconsuming. Lorieul et al. (2019) describe advances in phenological scoring of herbarium specimens using computer neural networks, thereby streamlining the process of annotating specimens for phenophases. The authors demonstrate the usefulness of this method using plant species from numerous bioregions that exhibit a variety of phenological characteristics. Computer neural networks proved to be most accurate when annotating coarserscale phenophases (e.g., 50% flowering and 50% fruiting; 96.3% accurate) and slightly less accurate, although still very useful, for finescale phenophases (up to 84.3% accurate). Finescale phenophases may be necessary for addressing certain research questions, although as Pearson (2019) models, binary annotations (e.g., flowering/not flowering) provide nearly as much value as more precise estimations of finescale