The Detrended Correspondence (DCA) module uses the same algorithm as Decorana (Hill & Gauch 1980), with modifications according to Oxanen & Minchin (1997). It is specialized for use on 'ecological' data sets with abundance data; samples in rows, taxa in columns.
Eigenvalues for the four ordination axes are given as in CA, indicating their relative importance in explaining the spread in the data.
Detrending is a sort of normalization procedure in two steps. The first step involves an attempt to 'straighten out' points lying in an arch, which is a common occurrence. The second step involves 'spreading out' the points to avoid clustering of the points at the edges of the plot. Detrending may seem an arbitrary procedure, but can be a useful aid in interpretation.
Missing data is supported by column average substitution.
References
Hill, M.O. & H.G. Gauch Jr. 1980. Detrended Correspondence analysis: an improved ordination technique. Vegetatio 42:47-58.
Oxanen, J. & P.R. Minchin. 1997. Instability of ordination results under changes in input data order: explanations and remedies. Journal of Vegetation Science 8:447-454.