Does an early spring indicate an early summer? relationships between intra-seasonal growing degree day thresholds

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 thresh...