2.4. Data analysis
All the above-mentioned data were analysed for single effect of
the factors (tree species, zones, compass directions and soil
depths) as well as for all the interactions, using GenStat 5
Release 8.11 (Rothamsted Experimental Station). Data from
the sensors which did not display HR were removed; this
made the design unbalanced, and as a result the Restricted
MaximumLikelihood (REML) method was used for the analysis.
The test of effects was carried out using Wald tests with chisquared
distribution used for calculating significance levels
(Piepho et al., 2003). Since the analysis revealed two-way and
three-way interactions between factors, we then analysed
separately data for each factor using one-way ANOVA, and
statistical differences given refer to 5% probability levels. We
also assessed the potential effect of temperature gradients on
diel fluctuations of soil water potential by regressing temperature
values against offset values.