2.9 Statistical analyses
One-way repeated-measures analysis of variance (RM ANOVA) was used to assess the effect of girdling on respiration of leaves and branches. We used linear mixed effect modelling to assess differences in St and Ss in leaves and bark before and after girdling (fixed effects), accounting for tree number, sample position and sampling date (random effects). Linear mixed effect modelling was also used to account for tree number, sample position and sampling date (random effects) when assessing differences in D x and D bprior and after girdling (fixed effects). Student’s t-tests were used to assess differences in D G+ before and after girdling. We report the marginal R2 (proportion of total variance explained through fixed effects) and conditional R2 (proportion of total variance explained through fixed and random effects) of the mixed effect model.
Regression analyses were used to determine the effect of girdling on the relationships between whole-tree fluxes of H2O and CO2 and environmental drivers, namely PAR, Tair and VPD prior to and after girdling. Single factor ANOVA and Fisher’s LSD test were used to assess the effect of sample location (base, top) on the daily amplitude of expansion and contraction in D x, D b, andD Gempir. These tests also included comparing pre-girdle (6 to 10 May) to post-girdle (20 to 24 May) measurements. Violation of the condition of homogeneity of variance of these data was tested (Barlett’s chi-square) and rejected in all cases as p >0.05.