Does an Early Spring Indicate an Early Summer? Relationships Between Intraseasonal Growing Degree Day Thresholds

Abstract

Spring heat accumulation plays a major role in the timing of events such as leaf-out, leaf expansion, flowering, and insect hatch in temperate systems. Accordingly, heat accumulation can serve as a proxy for the timing of plant and insect phenological activity and can be used in a predictive way when the timing of heat accumulation thresholds being reached can be anticipated. This has strong value for a host of planning and management applications. If relationships exist between earlier-and later-season thresholds at a location, then the timing of later-season phenological events that are forced by the accumulation of warmth could be anticipated based on when earlier-season thresholds are met. Using high-resolution daily temperature data, we calculated the coherence in pairs of spring-season heat accumulation (growing degree day) threshold anomalies over 1948-2016. Overall, relationships between thresholds spanning the entire spring season were relatively low, while later season thresholds exhibited much higher correlations. This pattern is generally the result of decreasing variability in heat accumulation with season progression. However, correlation strengths did not follow latitudinal or gradients, revealing that within-season heat accumulation and interannual variability in threshold timing are unique to the specified base temperature and thresholds being compared. We show that the relationships between earlier-and later-season heat accumulation thresholds were sufficient to accurately predict the timing of phenological events in plants in two case examples. Plain Language SummaryIn several recent years, spring has arrived especially early across much of the United States. Warm temperatures occurred earlier than average, and consequently, many trees and crops put on leaves or flowered days or weeks ahead of normal. Whether an early start to spring season weather conditions-and subsequently, plant and insect activity-leads to similarly early initiation of later-season events in plant and insect life cycles is not well understood. In some locations in the United States, the timing of the arrival of warm spring temperatures is a strong predictor of when biological events that occur in the middle and later part of spring would occur: an early start to spring will mean that later events will continue to occur ahead of schedule. In many other locations, the relationship is not as strong. These findings are important for scheduling management activities later in the season. For example, insect pest managers might use information regarding whether warm temperatures in the beginning or middle of spring are occurring ahead of schedule to plan whether crews should be dispatched earlier than usual. Key Points: • The ability to anticipate the timing of late spring phenological events using the timing of early-season heat is variable across the United States • Locations exhibiting strong relationships between the timing of early-season and later-season thresholds vary by base temperature • As the season progresses, relati...

Changing Lengths of the Four Seasons by Global Warming

“…Plants that survive false springs may not be able to grow successfully due to weak resistance to future stress (Allstadt et al., 2015). The seasonal effect is not limited to acting on itself; it spreads to other seasons and even brings about long‐term consequences; for instance, early springs are likely to indicate early summers (Crimmins & Crimmins, 2019), early growth due to advanced onset of spring may face a shortage of water in the remainder of the growing season (Buermann et al., 2018), and short and warm winters can exacerbate the occurrence of false springs (Allstadt et al., 2015). The chain reactions complicate the effects of seasonal changes.…”

Biologically‐Relevant Trends in Springtime Temperatures Across the United States

“…Our aim was to evaluate and compare trends in multiple heat accumulation thresholds representing various points in the spring season across the continental United States. Spring‐season heat accumulation does not happen at a constant rate; warmth accumulates rapidly during warm spells and stalls out during cold periods (Crimmins & Crimmins, ). Geographic patterns in the variability in heat accumulation at a location are a function of latitude, elevation, topography, sun angle, and atmospheric circulation (James & Arguez, ; McKinnon et al, ; Stine & Huybers, ).…”