Discovering the ecological structure of different macrophyte groups in rivers using non-parametric and parametric multivariate ordination techniques

This paper analyses various methods of ecological ordering that are often used in modelling the
relationship between vegetation and habitat. The results of direct gradient ordination by Canonical
correspondence analysis (CCA), which is based on correlation, were compared with Non-metric
multidimensional scaling (NMDS), which is based on rank analyses. Both tools were also compared
with Detrended correspondence analysis (DCA), which is a popular indirect gradient analysis method.
The macrophyte assessment was conducted at 98 river locations in the lowland regions of Poland.
Each of the surveyed locations falls within a consistent abiotic category: small to medium-sized
lowland rivers with a sandy bottom. Habitat elements analysed included limnological variables and
geographic parameters, and the botanical survey focused on submerged macrophytes, including
vascular plants, as well as bryophytes and algae. Firstly, it was shown that various analytical tools for
determining the importance of ecological factors (Monte Carlo test, BIOENV) identify slightly diferent
signifcant factors responsible for the development of macrophytes in rivers. Secondly, considerable
similarity was found in the structure of macrophyte communities generated on NMDS and DCA
biplots, while macrophyte communities were presented very diferently based on CCA. Thirdly,
the ecological preferences of aquatic plants based on one-dimensional analyses primarily refected
the results of CCA, whereas they did not always follow the ecological pattern revealed by NMDS.
Finally, by conducting separate studies for non-vascular plants and vascular macrophytes, it was
confrmed that diferent ecological drivers are responsible for the development of particular groups of
macrophytes