Results and discussions

Regression tree technique has failed to read the data structure due to collinearity effect. The so-called “statistical hazards” is identified from the extremely high correlation coefficients (R2): ec vs B, Na, Cl; Na vs K, Li; NH4 vs K, Li. Only three branches are extracted from the procedure, involving air temperature (atemp), elevation (elv), and B (Boron concentration), which is very difficult to explain (Figure 2). However B is presumably has the strongest control to the data structure as it closely correlates with EC along with Na and Cl. Li and K both have strong correlation with Na and NH4.
Table 3 A correlation diagram showing several variables that has extremely high (0.98-0.99) R2