Fritillaria gentneri (Gentner’s fritillary) is a rare member of the lily family (Liliaceae) that is endemic to southwestern Oregon and northern California. Across its range, there has been an overall trend of declining flower production in recent years. A number of factors likely contribute to fluctuations in reproductive output, including changes in habitat quality, population genetics, dormancy patterns, herbivory, disease, and climate. In an attempt to clarify the role of climate and environmental variables, non-parametric multiplicative regression (NPMR; Hyperniche v. 2.0) was used to assess which variables affected the number of flowering plants at 57 sites monitored from 2008-2016. We used a Gaussian weighting function with a local mean estimator in a forward stepwise regression of our response variable against the predictors, then expressed fit as a cross-validated R2 (or xR2). Monthly climate data from 2007-2016 were acquired from the PRISM climate group for precipitation, minimum and maximum temperature, dew point temperature, and minimum and maximum vapor pressure deficit. Monthly averages were consolidated into seasonal means to be used as predictive variables; previous year’s values were included as predictive variables as well. In addition to climate variables, our model incorporated elevation, potential direct incident radiation (PDIR), and heatload.
Modeling efforts to date revealed that climate influences F. gentneri population size and flower production. Results for a F. gentneri population at a long-term study site (Pickett Creek) indicated that dry, warm summers positively influenced flowering. Examining a larger dataset of F. gentneri occurrences that have been monitored annually for flowering plants, and represent the species’ full range in southwestern Oregon, we found that other variables may be influencing reproductive effort. Spring precipitation and previous spring's minimum temperature appear to be influencing the number of flowering plants. Understanding how a changing climate and other variables affect reproductive output of F. gentneri will be important for assessing implications for the species’ recovery.