Changing Climate Drives Divergent and Nonlinear Shifts in Flowering Phenology across Elevations

• Published in: Current biology 2020-02, Vol.30 (3), p.432-441.e3
• Main Authors: Rafferty, Nicole E., Diez, Jeffrey M., Bertelsen, C. David
• Format: Article
• Language: English
• Subjects: Altitude; Arizona; circular statistics; Climate Change; communities; Flowers - growth & development; Flowers - physiology; Magnoliopsida - growth & development; Magnoliopsida - physiology; metacommunities; plant-pollinator interactions; plasticity; precipitation; Reproduction; Seasons; semi-arid ecosystems; subpopulations; temperature
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2019.11.071

Climate change is known to affect regional weather patterns and phenology; however, we lack understanding of how climate drives phenological change across local spatial gradients. This spatial variation is critical for determining whether subpopulations and metacommunities are changing in unison or diverging in phenology. Divergent responses could reduce synchrony both within species (disrupting gene flow among subpopulations) and among species (disrupting interspecific interactions in communities). We also lack understanding of phenological change in environments where life history events are frequently aseasonal, such as the tropical, arid, and semi-arid ecosystems that cover vast areas. Using a 33-year-long dataset spanning a 1,267-m semi-arid elevational gradient in the southwestern United States, we test whether flowering phenology diverged among subpopulations within species and among five communities comprising 590 species. Applying circular statistics to test for changes in year-round flowering, we show flowering has become earlier for all communities except at the highest elevations. However, flowering times shifted at different rates across elevations likely because of elevation-specific changes in temperature and precipitation, indicating diverging phenologies of neighboring communities. Subpopulations of individual species also diverged at mid-elevation but converged in phenology at high elevation. These changes in flowering phenology among communities and subpopulations are undetectable when data are pooled across the gradient. Furthermore, we show that nonlinear changes in flowering times over the 33-year record are obscured by traditional calculations of long-term trends. These findings reveal greater spatiotemporal complexity in phenological responses than previously recognized and indicate climate is driving phenological reshuffling across local spatial gradients. •Flowering time is diverging among communities across an elevational gradient•Divergence reflects nonlinear shifts in flowering phenology over three decades•Climatic variables have also changed differently across space and over time•Changing climate is driving phenological reshuffling across local spatial gradients Using 33 years of data, Rafferty et al. test whether flowering times have diverged for neighboring communities comprising 590 species across an elevational gradient. Divergent and nonlinear shifts in flowering time are related to elevation-specific changes in temperatu