A phytoecological study of the mire Northern Kisselbergmosen, SE Norway. II. Identification of gradients by detrended (canonical) correspondence analysis

The vegetation of a poor mire is sampled by two procedures; 800 randomly placed sample plots made up the R data set, 765 subjectively selected plots in 153 sample plot series made up the S data set. DCA ordination and constrained ordination by DCCA of the data sets and subsets showed the existence of three coenoclines in the material: (1) the coenocline along the mire expanse: low to high median depth to the water table—mire margin gradient, (2) the poor-rich coenocline, dependent on a complex-gradient in substrate chemistry, and (3) a coenocline attributed to variation in peat productivity. Thus the assumption of Fennoscandian mire scientists embedded in numerous systems for classifying mire vegetation, that three gradients are the most important in the mire ecosystem, is partly confirmed. In the investigated area, two of the gradients normally considered make up one complex coenocline (1), and a fourth coenocline (3) has to be added. The effects of sampling techniques on correlations between coenoclines and on ordination results are discussed, and an improved sampling technique is suggested. The major faults of DCA: (1) the tongue effect, and (2) the instability, are described and discussed. It is concluded that if due attention is taken to reveal effects of the faults of the method, DCA is among the best ordination methods currently available.