Transforming environmental variables 
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Palmer (1993) recommends logarithmic transformations of soil nutrient concentrations when undertaking vegetational analysis "because a 1unit difference in nutrient concentration is probably much more important at low concentrations than it is at high concentrations".
Linear transformations of variables will have no effect on the results of a CCA. Therefore, changing the units of a variable (e.g. centimeters to millimeters) or the base point (e.g. elevation above a fixed point to elevation above sea level) will have no effect.
See also Selecting Environmental variables Linear combinations of environmental variables
