Analyses of the flowering time with climatic variables for each county cluster (model 1).

Response variables were year (yr), precipitation (precip), the lowest average monthly minimum temperature in the calendar year prior to flowering (min_T), the highest average monthly maximum temperature in the calendar year prior to flowering (max_T), range of minimum temperatures for the months previous to flowering of that calendar year (range_minT), range of maximum temperatures for the months previous to flowering of that calendar year (range_maxT), plant origin (native or nonnative; “origin”). Two-way interactions between these variables are listed by variable names separated by an ‘*’. Precipitation is in centimeters and temperature is in degrees Celsius. We applied a sequential Bonferroni adjustment within each cluster. *P<0.05, **P<0.001, *** P<0.001, **** P<0.0001, for tests of significant difference of parameter values from 0.