Changes in urban plant phenology in the Pacific Northwest from 1959 to 2016: anthropogenic warming and natural oscillation.

In the Pacific Northwest of the USA, winter and spring temperature vary with the Pacific Decadal Oscillation, making effects of anthropogenic warming difficult to detect. We sought to detect community-level signals of anthropogenic change in a legacy plant phenology dataset. We analyzed both incomplete data from 1959 to 2016 on spring phenology of 115 species and more complete 1996-2016 data on spring and fall events for 607 plant species.