A diagram showing the relationships among forcing change (FC, difference in spring forcing (degree days) between baseline and warmer temperatures at species event with baseline temperatures OCi), expected response (NE, difference between climatic conditions of baseline and warmer temperatures in reaching species forcing needs with baseline temperatures, i.e., spring forcing at OCi), growth temperature (FC/NE, average temperature at species event with warmer temperatures), and phenological lag (NC, difference between expected NE and observed NO responses with warmer temperatures).

Observed responses and phenological lags (least square means ± standard errors) in leafing and flowering (left and right set of bars in each pair, respectively) by research approach (observation and experiment), species origin (native and exotic), climatic region (boreal and temperate), and growth form (tree, shrub, herb, and grass) extracted from reported plant phenological changes in spring.

Phenological lags are calculated from the differences between observed responses and those expected from species-specific changes in spring temperatures. Different letters indicate means differ significantly (p<0.05).

Mean values of climatic, phenological, and biological variables by species event (leafing and flowering), research approach (observation and experiment), species origin (native and exotic), climatic region (boreal and temperate), and growth form (tree, shrub, herb, and grass).

Growth temperature=temperatures at species event with warmer climate, forcing change =warming-induced changes in spring forcing experienced by individual species, spring warming=average spring temperature changes, and phenological lag= phenological difference due to effects of phenological constraints.

Final stepwise regression coefficients and variable influence on observed phenological responses by Akaike information criterion (AIC).