Photoperiod compensates for decreased temperature sensitivity in deciduous forest greenup

Abstract:

The timing of leaf emergence in temperate and boreal forests is changing, which has profound implications for a wide array of ecosystem processes and services. However, the factors that control observed changes are not well understood. Here we use a continuous development model that quantifies the relative importance of bioclimatic forcing variables in controlling the timing of leaf emergence in deciduous forests of North America. Results reveal strong biogeographic variation in the time period that controls leaf emergence that covaries with the relative importance of photoperiod versus temperature in controlling this process. The results demonstrate that photoperiod control on leaf emergence is dominant in warmer climates but modest in colder climates, with a sharp transition near 10 ^oC mean annual temperature. These results suggest that apparent changes in the sensitivity of trees to temperature are modest and reflect a trade-off between decreased sensitivity to temperature and increased photoperiod control.