PS 23-40 - The effect of climate on masting patterns in a long-lived monocarp Frasera speciosa (Gentianaceae)

Background/Question/Methods

Climate change affects the phenology of flowering plants by changing the timing and magnitude of weather cues like temperature and precipitation. There is variation in flowering synchrony within populations and periodicity (years between flowering events), with mast flowering being the most dramatic example. Climate change could potentially change the intensity, frequency, and variability of cues for synchrony of flowering, potentially breaking down or strengthening the synchronization of flowering and altering potentially adaptive processes like pollinator efficiency, seed predator satiation, or resource dynamics. Frasera speciosa is a long-lived herbaceous monocarp in the Rocky Mountains that is thought to be a masting plant. We used a long-term dataset to ask: Does Frasera fit the strict definition of masting? What is the level of synchrony, periodicity, and intensity of flowering? Are these trends changing over time and correlated with changes in climate variables?

We used a 42-year (1979 – 2021) flowering stalk census of Frasera speciosa in Colorado to analyze the synchrony, periodicity, and magnitude of flowering (range: 2 - 28,757 stalks). We explored correlations between flowering and climate variables, including average monthly precipitation and summer temperature. We explored spatial autocorrelation using a Mantel test to quantify spatial synchrony across a 12.3km transect.

Results/Conclusions

Overall, few signs of strict masting were found. Using a hurdle model, we did not find a bimodal pattern of masting, as would be suggested by theory on plants with similar life history to Frasera. These results resemble “putative” masting according to a definition of types of masting behavior; this is the most common classification for plants labeled as “masting” in literature. Time-series analysis showed no clear periodicity, contrary to earlier suggestions. We found a negative correlation between flowering intensity and average spring precipitation with a three-year lag. We also found a positive correlation between flowering intensity and average spring temperature with a four-year lag. There was also a positive relationship between flowering and growing degree days in the spring with a three-year lag. A Mantel test showed that there was no spatial autocorrelation between plots. Longer, warm, dry spring conditions three to four years before a flowering event seem to increase flowering intensity.