Gradient Analysis: The Use of Species and Synthetic Indices

Gradient analysis by means of species indices and stand synthetic values provides a very fruitful approach to ecological investigation. Bivariate analysis of unweighted and variously weighted stand averages shows that there is little practical difference between the results obtained at the gradient level using tree species frequency, density, basal area, and various combinations of these measures. Although they are highly significantly correlated, there is considerable variation between weighted stand values and the unweighted stand means. Several alternative methods of deriving species sociologic indices are demonstrated to give very similar species indices along the primary sociological dimension in southern Wisconsin upland forests. An iterative technique for maximizing the information content of sociologic dimensions is suggested.