Beyond the usual climate? Factors determining flowering and fruiting phenology across a genus over 117 years

Premise: Although changes in plant phenology are largely attributed to changes in climate, the roles of other factors, such as genetic constraints, competition, and self-compatibility, are underexplored.  Methods: We compiled >900 herbarium records spanning 117 years for all 8 nominal species of the winter-annual genus Leavenworthia (Brassicaceae). We used linear regression to determine the rate of phenological change across years and phenological sensitivity to climate. Using a variance partitioning analysis, we assessed the relative influence of climatic and non-climatic factors (self-compatibility, range overlap, latitude, and year) on Leavenworthia reproductive phenology.  Key Results: Flowering advanced by ~2.0 days and fruiting ~1.3 days per decade. For every 1°C increase in spring temperature, flowering advanced ~2.3 days and fruiting ~3.3 days. For every 100 mm decrease in spring precipitation, each advanced ~6-7 days. The best models explained 35.4% of flowering variance and 33.9% of fruiting. Spring precipitation accounted for 51.3% of explained variance in flowering date and 44.6% in fruiting. Mean spring temperature accounted for 10.6% and 19.3%, respectively. Year accounted for 16.6% of flowering variance and 5.4% of fruiting, and latitude 2.3% and 15.1%, respectively. Non-climatic variables combined accounted for <11% of the variance across phenophases. Conclusions: Spring precipitation, alongside other climate and climatically-related factors, were dominant predictors of phenological variance. Our results emphasize the strong effect of precipitation on phenology, especially in moisture-limited habitats preferred by Leavenworthia. Amongst the many factors that determine phenology, climate is the dominant influence, indicating the effects of climate change on phenology are expected to increase.