title: Trends toward an earlier peak of the growing season in Northern Hemisphere mid-latitudes.
abstract: Changes in peak photosynthesis timing (PPT) could substantially change the seasonality of the terrestrial carbon cycle. Spring PPT in dry regions has been documented for some individual plant species on a stand scale, but both the spatio-temporal pattern of shifting PPT on a continental scale and its determinants remain unclear. Here, we use satellite measurements of vegetation greenness to find that the majority of Northern Hemisphere, mid-latitude vegetated area experienced a trend toward earlier PPT during 1982-2012, with significant trends of an average of 0.61 day yr(-1) across 19.4% of areas. These shifts correspond to increased annual accumulation of growing degree days (GDD) due to warming and are most highly concentrated in the eastern United States and Europe. Earlier mean PPT is generally a trait common among areas with summer temperatures higher than 27.6 ± 2.9 °C, summer precipitation lower than 84.2 ± 41.5 mm, and fraction of cold season precipitation greater than 89.2 ± 1.5%. The trends toward earlier PPT discovered here have co-occurred with overall increases in vegetation greenness throughout the growing season, suggesting that summer drought is not a dominant driver of these trends. These results imply that continued warming may facilitate continued shifts toward earlier PPT and cause these trends to become more pervasive, with important implications for terrestrial carbon, water, nutrient, and energy budgets.
authors.affiliation: College of Urban and Environmental Science and MOE Laboratory for Earth Surface Processes, Peking University, Beijing, 100871, China.
authors.forename: Chongyang
authors.initials: C
authors.lastname: Xu
authors.affiliation: College of Urban and Environmental Science and MOE Laboratory for Earth Surface Processes, Peking University, Beijing, 100871, China.
authors.forename: Hongyan
authors.initials: H
authors.lastname: Liu
authors.affiliation: Lamont-Doherty Earth Observatory, Columbia University, Rt 9W, Palisades, NY, 10964, USA.
authors.forename: A Park
authors.initials: AP
authors.lastname: Williams
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS-UVSQ, CE Orme des Merisiers, 91191, Gif sur Yvette Cedex, France.
authors.forename: Yi
authors.initials: Y
authors.lastname: Yin
authors.affiliation: College of Resource Science and Technology, Beijing Normal University, Beijing, 100875, China.
authors.forename: Xiuchen
authors.initials: X
authors.lastname: Wu
mesh_terms: D057486:Carbon Cycle; D057231:Climate Change; D005060:Europe; D010788:Photosynthesis; D012621:Seasons; D013696:Temperature
keywords: climatic warming; dryland; mid-latitudinal biomes; peak photosynthesis timing; phenological shifting; seasonality