The methods give site index-that is, tree-growing potential- in terms of the height,. in feet, that free-growing cottonwoods in well-stocked forest stands will reach at the age of 30 years. While 50 years is the customary age for expressing site index; 30 years was chosen because it is close to the average for the stands from which data were secured and because most cottonwood trees are log size by 30 years.

The first method provides a fast field classification of sites from determinations of soil texture, internal drainage, and inherent moisture conditions.

The second method requires the soil to be identified according to standard soil series and phase.

A weakness of both methods is that they rely heavily upon human judgment. Attempts have been made to predict cottonwood site index from soil variables that can be objectively measured, but the variables initially tested did not prove to be very well correlated with site index. The present subjective methods are offered only until more objective measures can be developed.

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