Chorizanthe orcuttiana is an endangered annual herbaceous plant species endemic to San Diego County, CA. Populations of C. orcuttiana are disjunct and display wide range of demographic patterns despite their narrow geographic distribution. We present demographic patterns of C. orcuttiana in relation to its microclimate characterization during pre-germination (July-November) and germination periods (December-January). We selected four populations to ask: 1) Are there any differences in microclimatic conditions at four experimental locations which might be driving the demography of C. orcuttiana? 2) What are the patterns of similarity and dissimilarly between the four experimental locations? 3) Which climatic variables best describe the differential climatic regimes of the four experimental locations? Three (EO12, EO14 and NPS) of the four sites are restricted to 2.5 km2 on Point Loma peninsula, whereas the fourth (EO16) is located 25 km north of the peninsula. Sites EO12, EO14 and EO16 host extant populations of C. orcuttianawhile NPS serves as a control site without historical records of the species. In 2015, EO12 and EO16 hosted >1000 individuals while EO14 had approximately 170 plants. Microhabitat at each site was characterized by continuously recording soil temperature, soil moisture, air temperature, and relative humidity at 4-hr frequency between July 2014 and February 2016. Wavelet analysis and linear discriminant analysis (LDA) were used to obtain pairwise comparisons among sites and to identify the variable that best explained the variability, respectively.
Differences in microclimatic conditions were discovered via pairwise comparisons of study sites for each response variable (r2 = 0 to 0.5). Each site displayed unique microclimatic regime during the study period. Sites EO14 and NPS consistently had higher air temperature and soil temperature when compared to EO12 and EO16. Relative humidity though was highest at EO12 followed by EO16, and soil moisture was highest at EO16. The LDA analysis showed that most of the variability among experimental locations is explained first by soil moisture and then by soil temperature, whereas air temperature and relative humidity explain the least variability. Data suggest that the annual demographic patterns of C. orcuttiana are likely shaped by the continuum of hourly changes in soil moisture and soil temperature during pre-germination and germination periods. Multi-year data, however, are also being generated to validate these patterns.