Spring and summer patterns in flowering onset, duration, and constancy across a water-limited gradient

Community-level flowering patterns can be characterized by onset, duration, and end as well as constancy, the degree to which species commence, cease, and reinitiate flowering within a season. In the mountainous Sky Islands region of the southwestern United States, flowering onset is clearly influenced by elevation in the spring, but much less so in the summer season. We evaluated whether these flowering metrics reflect these dissimilar patterns between distinct spring and summer seasons regarding the influence of the elevation and moisture gradient. •

We characterized flowering onset, end, duration, and constancy by plant functional type and their relationships to climate variables in spring and summer. We also evaluated the influence of climate on seasonal flowering patterns. •

Gaps in seasonal flowering occur frequently in this system in both seasons and among all plant functional types. In both seasons, annual plants exhibit the shortest flowering durations and highest constancies, and plants at low elevations, inhabiting environments with variable moisture conditions, show a greater tendency for longer flowering durations and lower constancy than high-elevation plants. Spring flowering characteristics are most influenced by the total amount of October-March precipitation as well as temperatures in these months, whereas summer flowering characteristics are influenced by the timing of summer-season precipitation, and next by the total amount of summer precipitation. •

Flowering metrics, especially constancy and duration, show similar patterns in spring and summer and vary across elevation and moisture gradients. These patterns have substantial implications for plant and animal communities.