Comparison of common lilac (Syringa vulgaris) phenology timing between historical data and current Project BudBurst citizen science data: challenges and lessons learned.
Observing the timing of plant phenology provides a way to monitor and predict effects of ecological change on plants. This study compared historical data for common lilac dating from 1956-2003 with recent lilac phenology data collected by Project BudBurst citizen scientists from 2007-2013. Due to the lack of accessible growing degree day data, it was not possible to directly examine climate effects on phenology timing. Instead, we compared geographic distribution patterns between historical and Project BudBurst data to explore what factors might contribute to the timing of phenophase dates between data sets. T-tests were performed on latitude, longitude, and day of year of observation (Julian date) for first flower and first leaf between the two data sets. Differences between latitude were not significant for first flower and first leaf (p = 0.789, p = 0.489, respectively) but there was a difference between longitude for both variables (p\u3c0.001). Mean observation dates for Project BudBurst were 9.5 days earlier for first flower (significantly different, p = 0.0001) and 2.3 days earlier for first leaf (no significant difference, p = 0.063) but the difference in longitude and the small sample size of the Project BudBurst data set makes these findings questionable. Because of the effect of longitude, we suggest future analyses of data by regions. Additional Project BudBurst observations in the western U.S. would allow better comparisons in that region and encouraging observations near historic sites would take advantage of a long, rich data set
