Phenology is the study of recurring life‐cycle events, classic examples being the flowering of plants and animal migration. Phenological responses are increasingly relevant for addressing applied environmental issues. Yet, challenges remain with respect to spanning scales of observation, integrating observations across taxa, and modeling phenological sequences to enable ecological forecasts in light of future climate change. Recent advances that are helping to address these questions include refined landscape‐scale phenology estimates from satellite data, advanced, instrument‐based approaches for field measurements, and new cyberinfrastructure for archiving and distribution of products. These breakthroughs are improving our understanding in diverse areas, including modeling land‐surface exchange, evaluating climate–phenology relationships, and making land‐management decisions.

ABSTRACT:With abundant evidence of recent climate warming, most vegetation studies have concentrated on its direct impacts, such as modifications to seasonal plant and animal life cycle events (phenology). The most common examples are indications of earlier onset of spring plant growth and delayed onset of autumn senescence. However, less attention has been paid to the implications of continued warming for plant species' chilling requirements. Many woody plants that grow in temperate areas require a certain amount of winter chilling to break dormancy and prepare to respond to springtime warming. Thus, a comprehensive assessment of plant species' responses to warming must also include the potential impacts of insufficient chilling.When collected at continental scale, plant species phenological data can be used to extract information relating to the combined impacts of warming and reduced chilling on plant species physiology. In this brief study, we demonstrate that common lilac first leaf and first bloom phenology (collected from multiple locations in the western United States and matched with air temperature records) can estimate the species' chilling requirement (1748 chilling hours, base 7.2°C) and highlight the changing impact of warming on the plant's phenological response in light of that requirement. Specifically, when chilling is above the requirement, lilac first leaf/first bloom dates advance at a rate of −5.0/−4.2 days per 100-h reduction in chilling accumulation, while when chilling is below the requirement, they advance at a much reduced rate of −1.6/−2.2 days per 100-h reduction. With continental-scale phenology data being collected by the USA National Phenology Network (http://www.usanpn.org), these and more complex ecological questions related to warming and chilling can be addressed for other plant species in future studies.

Measuring the onset of deciduous tree leaf flush and subsequent development during the spring season in temperate climates can be accomplished using multiple ground and satellite-based techniques. Although all these measurements are valid (i.e. record a real characteristic related to plant development), they typically are poorly interrelated due to incompatible levels of spatial representation and differing methodologies. Given recent and likely future impacts of climate change on spring leaf development, the need to reconstruct past patterns, and the lack of standardised vegetation change measurements around the world, more work is needed to determine the relationships among the various measures, and the degree to which they may serve as substitutes for each other. In this article, we use observations and measurements at two phenology 'super-sites' in eastern North America and four other supporting sites to evaluate the relationships among multiple spring leaf development measures, and explore strategies to standardise their intercomparison. The results show infrequent significant correlations among 10 satellite-derived 'start of season' (SOS) measures (which suggests they are often not detecting the same phenomena), along with more common significant correlations among six ground phenology measures. However, when ground phenology and satellite-derived SOS are compared, there are few significant correlations, even at sites with extensive native species phenology available. Modelled phenology, based on daily temperature data (Spring Indices First Bloom date) does as well as any of the direct native species measures, and is well suited to facilitate intercomparisons. In order to effectively compare ground-based and satellite-derived SOS measures, approaches that use limited numbers of individual plants face considerable challenges. Given that satellite-derived measures are areal and at a scale of 250 m and larger, we suggest collecting ground phenology data at the same areal scale in order to make effective comparisons.

Here we present, for the first time, a glossary of biometeorological terms. The glossary aims to address the need for a reliable source of biometeorological definitions, thereby facilitating communication and mutual understanding in this rapidly expanding field. A total of 171 terms are defined, with reference to 234 citations. It is anticipated that the glossary will be revisited in coming years, updating terms and adding new terms, as appropriate. The glossary is intended to provide a useful resource to the biometeorology community, and to this end, readers are encouraged to contact the lead author to suggest additional terms for inclusion in later versions of the glossary as a result of new and emerging developments in the field.

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