AGU: Geophysical Research Letters

 

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Warming temperatures affect seed dormancy, delaying the onset of spring vegetation south of 35°N

Warming climates are thought to advance the timing of spring leafing, flowering, and bud-burst in northern areas, but the delayed responses of vegetation phenology to rising temperatures in more southern regimes are poorly understood. Using satellite and climate data from 1982 to 2005, Zhang et al. (2007) found that from 40°N northward, spring onset has advanced by 0.32 days each year. These regions have sufficient winter chilling duration, so a decrease in chilling days by warming winter temperatures has little impact on the thermal requirements for spring onset. However, south of 40°N, the shortened winter chilling days are insufficient for certain seeds to overcome their dormancy, causing a delay in the onset of spring conditions. The authors found that vegetation green-up onset changes progressively from an early trend at 40°N to a later trend through a latitude transition zone from 40° to 31°N, with the cusp of this switch occurring around 35°N. Below 31°N, the onset of spring has been delayed by 0.15 days each year. Furthermore, the transition zone shifts poleward by 0.1 latitude degree per year.

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