2.6 Statistical analysis
All data analyses were completed using JMP Pro 12 (JMP, 2012). Sap flux
density across years and zones was determined using a paired t-test. The
zone was defined as a riparian buffer, mid-hillslope, and
upland-hillslope. The t-test was selected, and the significance level
was set to α < 0.05 to determine which year or zone was
statistically different from each other. The power model was used to
determine the nonlinear relationship between daily VPD and sap flux
density. The explanatory and response variables in the bivariate plots
were log-transformed to produce the power model, y
=axb. The effects test was used to determine if the
evaporative demand changed across the zones and if there was an
interaction between VPD and the zones. VPD was log transformed to
reflect the power function of the relationship between VPD and species
sap flux density. P values < 0.05 indicate that the
independent variables and/or their interaction were significantly
related to sap flux density.