Phenology: response, driver, and integrator1

Abstract

Whether out of necessity for survival, or simple enjoyment, humans have long been interested in the seasonal cycles of nature. The observation and recording of the timing of annual spring events, for example, is an ancient practice that was undoubtedly important to the success of early gatherers and farmers. But the study of phenology eventually expanded beyond its practical origins. Its purpose has ranged from documenting nature's patterns, to scientific inquiry into the mechanisms behind phenological events, to applications in agriculture, and most recently to understanding the ecological consequences of climate change. The longest records of this kind are for the flowering of cherry trees in Kyoto, Japan, where observations stretch back over 12 centuries (Arakawa, H. 1955. Twelve centuries of blooming dates of the cherry blossoms at the city of Kyoto and its own vicinity. Geofisica pura e applicata 30:36–50), and the Marsham Phenological Record (Margary, I. D. 1926. The Marsham phenological record in Norfolk, 1736–1925, and some others. Quarterly Journal of the Royal Meteorological Society 52:27–54), which is the longest continuous record of multiple spring events from a single location. Although neither of those records was initiated for the purpose of understanding future environmental changes, both are now valuable resources for studies of ecological responses to climate change. The recent resurgence in interest in phenology has united the lay public and scientists in the study of climate change. The study of the annual timing of events such as spring flowering, or arrival of migratory birds, for instance, embodies one of the clearest and most inherently appreciated manifestations of organism–environment interactions. There is also growing appreciation among ecologists for the role of phenology as a driver of ecological dynamics, as opposed to simply a response to environmental conditions. As such, phenology is a discipline that contributes fundamental insights into ecology at the individual level, but also scales up interactions to the population, community, and landscape levels. Our Special Feature on phenology highlights this range of approaches and perspectives in this rapidly developing field. In this Special Feature, we highlight a breadth of theoretical and empirical perspectives concerning contemporary phenology that were identified by the USA National Phenology Network (USA-NPN), the origins of which trace back to a meeting among scientists representing multiple disciplines held in Tucson, Arizona, in August 2005 (Betancourt, J. L. et al. 2005. Implementing a U.S. national phenology network. Eos 86:539). Perspectives represented at that meeting ranged from observational studies such as remote sensing of continental-scale events to experimental manipulations of 2 × 2 m plots, from studies of historical records to current events, and from studies of plants to animals (more information available online).2 The papers in this Special Feature thus illustrate the diversity of perspectives from which phenology is currently being studied, from satellite-based observations to counts of individual flowers in small plots, and from the analysis of long-term records to experimental manipulations. These perspectives include the relationship between phenology and carbon cycling (Kudo et al.); the importance of long-term records with an example derived from the work of Henry David Thoreau (Miller-Rushing and Primack); using remote sensing to understand the large-scale implications of phenology to net primary production (Rich et al.); an example of how long-term ecological studies can be used to elucidate the impacts of climate change on flowering plants, especially in sensitive areas such as the alpine meadows of the Rocky Mountains (Inouye); and insights into individual-based phenological responses to climate change across a range of life history events following experimental warming in the Arctic (Post et al.). We hope this Special Feature will draw attention to the resurgence of activity in phenological research, point to the extraordinary value of recording long-term phenological data, and engender appreciation for the role of phenology as a driver of complex ecological dynamics.