Warm winters may shorten the growing season of plants that rely on cold weather cues, a study finds. Though previous research has shown that warming climate has accompanied early spring growth in many plant species, approximately a quarter of plants in temperate regions do not follow this pattern. Professor Jianchu Xu at the Kunming Institute of Botany, the Chinese Academy of Sciences published on Nov. 29 of 2010 in the Proceedings of the National Academy of Sciences (PNAS).

To investigate this inconsistency, Jianchu Xu and colleagues used satellite images to track seasonal plant growth in the Tibetan Plateau between 1982 and 2006, and correlated the onset and end of steppe and meadow plant growth to monthly temperature data. Spring growth in both landscapes began earlier from the early 1980s until the mid 1990s, the authors found, but despite continued warming, plants delayed spring growth in the last decade. Though warmer temperatures also delayed the onset of winter cold, the region’s net growing season decreased by three weeks or more from 2000 to 2006.

The authors suggest that warm winters may delay the fulfillment of plants’ chilling requirement, or the combination of time and cold that signals the arrival of spring. THEY propose that continued warming may reverse current trends toward extended growth seasons in other plant species. If recent trends continue, Tibetan pastoralists may have to adapt to a shorter growing season, which may limit fodder availability during certain parts of the year.

（image by Xu Jianchu）