Detrended correspondence analysis is an extension of correspondence analysis (CA) aimed at addressing a deficiency of correspondence analysis. The problem is known as the “arch effect” – a non-monotonic relationship between two sets of scores derived by CA.
The basic idea is to split the first dimension into several intervals and to subtract the mean score of the second dimension from its values in each interval separately. This approach has been criticized by some authors because of loss of valuable information in course of such “detrending”. So, this method should be used with caution.