Long-term data provide context for interpretation of ecological interactions

Background/Question/Methods

Long-term studies can provide important insights into ecological processes and interactions that cannot be gained from shorter investigations. Important but infrequent events such as mast flowering or late spring frosts can have significant demographic consequences and can have cascading trophic consequences for interacting species of pollinators, herbivores, and parasites, but may not be easily understood without long-term study.  The drivers of these infrequent events can be environmental or ecological in nature, and the frequency with which they operate will determine the time needed to understand their consequences. I use the data from a 42-year ongoing study of phenology at the Rocky Mountain Biological Laboratory to show that late spring frosts that can kill young flower buds of some wildflower species have occurred at intervals as long as nine years, or as short as 1 year, so interpreting their frequency and consequences requires long-term data. In some cases proxies can be used to extend our understanding of some infrequent events. Elucidating the environmental drivers of some of these phenomena, such as frost kills of buds and mast flowering, creates the potential to use long-term climate records to hind-cast their frequency in the past.

Results/Conclusions

Loss of flowers has consequences for pollinators, seed predators, and parasitoids, in addition to the demographic consequences for the plants. I used stream gauge data from back to 1913 and weather station data back to 1909 to gain a larger context for my contemporary observations.  Access to four decades of observations led to a recent insight that there is a decadal cycle in the phenology of our study species and in the flower abundance of some of them. Studies encompassing fewer than one of these cycles run the risk of mis-interpreting the nature of affected ecological interactions. Frasera speciosa (Gentianaceae) exhibits mast flowering, apparently in response to a rainfall cue (unusually heavy summer precipitation).  It required 32 years of data before I had 8 data points that allowed me to gain this insight, and 28 years to be able to model mast flowering in Veratrum californicum (Melanthiaceae).  The long-term environmental data provide a better understanding of the history of these cycles, and we can use this new temporal framework to understand how species interactions may be affected on this long-term temporal scale.