Understanding the breadth and complexity of changes in phenology is limited by the availability of long-term historical datasets with broad geographic range. We compare a recently discovered historical dataset of plant phenology observations collected across the state of New York (1826-1872) to contemporary volunteer-contributed observations from the New York Phenology Project (2009-2017) to evaluate changes in plant phenology between time periods. These multi-site, multi-taxa phenology data matched with temperature data uniquely extend historical observations back in time prior to the major atmospheric effects of the Industrial Revolution. The majority of the 36 trees, shrubs and forbs that comprised our analyzable dataset flowered and leafed out earlier in contemporary years than in the early-to-mid 19th century. This shift is associated with a warming trend in mean January-to-April temperatures, with flowering and leafing advancing on average 3 days/°C earlier. On average, plants flowered 10.5 days earlier and leafed out 19 days earlier in the contemporary period. Urban areas exhibit more advanced phenology than their rural counterparts overall, insect-pollinated trees show more advanced phenology than wind-pollinated trees and seasonality and growth form explain significant variation in flowering phenology. The greatest rates of temperature sensitivity and change between time periods for flowering are seen in early-season species, particularly trees. Changes in the timing of leaf out are the most advanced for trees and shrubs in urban areas. These paired community/citizen science observations across two centuries illustrate how long-term monitoring and public participation in science efforts are invaluable for ecological forecasting and discovery.
