Cupressus arizonica Greene (Arizona cypress) is a neotropical tree species with populations in Mexico and the American southwest. Despite being a long-lived, ring-forming tree species, C. arizonica is unrepresented in the International Tree Ring Databank (ITRDB) and other published dendrochronology literature. In northern Arizona, C. arizonica often inhabits shady microclimates near ephemeral (seasonal) water sources, occupying a poorly studied niche. In this study, we quantify key aspects of the species’ relationship to climate both during and prior to ring formation to evaluate relationships between growth and seasonal climate variables. We collected cores (2 cores/tree) from C. arizonica individuals (N=9) at a site in Coconino County AZ, north of Sedona. Crossdating of the C. arizonica chronology was verified by comparing it to local Pinus edulis chronologies from the ITRDB and to annual gridded climate data from PRISM. We conducted linear regressions of tree-level ring width indices versus individual monthly climate variables (precipitation, temperature, humidity, and drought indices) spanning 24 months prior to cessation of ring growth. Coefficients of determination (R2) and effects parameters were evaluated to identify important climate predictors and the time periods over which they influenced growth.
Results/Conclusions
Average ring width of the C. arizonica study trees over the last 50 years was 0.56 mm. Regression models revealed that ring width was most closely related to drought index (scPDSI) during the summer of ring formation (R2 > 0.25). Ring width was only weakly related to the other climate variables, though measures of vapor pressure deficit and precipitation could be important in mid-to-late summer of the year of ring formation (R2 > 0.1). The site is located on an ephemeral stream, so weak correlation with winter precipitation suggests runoff from upstream precipitation may be a more meaningful water source early in the growing season. The effect of summer drought points to the limiting effect of hot, dry conditions, while the importance of late summer rainfall and humidity suggests that monsoon rains help to alleviate drought stress. Unlike other conifer species that show a multi-year lagged response to climate, C. arizonica’s growth was nearly independent (R2<<0.1) of climatic conditions in the year prior to ring formation. Though, additional work is required to evaluate the role of upstream winter precipitation to radial growth. Overall, our results suggest a seasonal decoupling of C. arizonica growth and local precipitation in our study population.