Abstract: Ordination and GLM/GAM are both important methods to explore the relationship between plant species and environment.Generally,ordination methods,based on linear model,are suitable for dealing with the vegetation within a comparatively short environmental gradient,while those based on unimodal model are more suitable for tackling with the vegetation distributing along a longer gradient.PCA,CA/RA series and CCA series are the most commonly used ordination methods.Involving the environmental data in the analysis,CCA series could demonstrate the relationship between plant species and environment clearly.After modification,DCCA and PCCA are considered to be ideal ordination methods at present.Essentially,General Linear Model (GLM) and General Additive Modal (GAM) were using the high power polynomials of environmental variables to fit the response of plant species to environment.So,the models for delineating the relationship between species and environment have been enhanced through the introduction of GLM and GAM in recent years.GLM is basically driven by model,while GAM is more driven by data.In comparison,ordination can obtain the main environmental gradient and provide the general information of species assembling and plant community in the study area.GLM and GAM have advantages in probing deeply into the relationship between plant species and environment.In practice,the two kinds of methods can yield better results when used in combination.

Key words: Ditch wetland, Emerged plants, Nitrogen and phosphorus, Non-point source pollutants