Functional Analysis of European Wetland Vegetation

Riverine marginal wetland vegetation was studied at thirty-two hydrogeomorphic units of sites used by the European Community project "Functional Analysis of European Wetland Ecosystems", these units were situated in England, France, Ireland and Spain. Fieldwork was carried out between May 1991 and August 1993. The aim of the work was to develop a system of analysis of wetland vegetation using functional attributes which could be used to predict the effect of anthropogenic perturbation. Grime's C-S-D established-phase strategy theory was used as the framework for this study. Analysis of plant species abundance, using DCA (detrended correspondence analysis) and PCA (principal components analysis), revealed the extent of variation in the plant species composition between the hydrogeomoq)hic units. A majority of the hydrogeomorphic units could be assigned to CORINE biotope categories (the European Community categorisation system of sites of nature conservation importance); most sites were water fringe vegetation (53) or humid grassland (37). Eight morphological traits were measured from one hundred and forty-four common plant populations from the hydrogeomorphic units. Non-hierarchical classification of populations by traits was carried out using sum of squares and centroid dissimilarity algorithms. It was determined that the most efficient classification was into three groups. Each of these three groups was associated with different parts of the C-S-D strategy space. The results strongly suggested that morphological traits can be used to classify plants into functional groups which have differing ecological properties. Using twelve traits, linear and multiple discriminant analysis were used to distinguish objectively between populations with a selected strategies determined from the work of Grime. Competitive and stress-tolerant populations were found to be significantly different using twelve traits. Stepwise multiple regression identified the important traits for predicting competitive ability (C) and stress tolerance (S). Significant predictors of the C-strategy were height of plant and the dry weight of leaves; and of the S strategy, the dry weight of stems and the weight per seed. Use of these predictive equations permitted calculation of C and S for the one hundred and forty-four populations that were studied. The mean C and S scores of the populations present in each hydrogeomorphic unit were used to determine the functional vegetation type (FVT) in terms of competitiveness (CFVT) and stress-tolerance (SFVT). CFVT and SFVT were inversely correlated (r = -0.73, P<0.001). A greenhouse experiment was carried out to determine the effect of competition (phytometer), disturbance (cutting) and stress (saturated soil conditions) on the morphology of six common wetland plants. The stress treatment was too weak to have much effect on the morphology of the species. The ranking of the species in terms of C and D (disturbance-tolerance) showed a degree of similarity with the strategy designation of Grime. The competitive ability of the test species, using the phytometr)' method, was significantly related to the field determined C score (r = 0.80, P<0.05). Eleven state variables, defined as measurable variables of biotic communities which have a particular range of values for each type of vegetational community, were measured in the studied wetlands. Using PCA, the major gradient in state variables was most strongly correlated to biomass. However, using CCA (canonical correspondence analysis), constraining the axes to be linear combinations of CFVT and SFVT, a different gradient in state variables was identified. This gradient was related to a high canopy, large stem area with great distance between stems and dominated by a few species at high CP/T-low SFVT values and high stem density, species richness and density of reproductive structures at low CFVT-high SFVT values. Using stepwise multiple regression, state variables could significantly predict CFVT (P<0.0001). Common CORINE biotopes were related to the CCA ordination diagram of FVT and state-variables. 3 biotopes (humid grassland, mesophile grassland and reed beds) were related to certain areas of the CFVT-SFVT gradient. Sedge beds ranged across much of the gradient, this could be due to the taxonomic diversity of the biotope. The results suggested a certain degree of comparability between the strategy, state-variable and phytosociological biotope units in the studied wetlands. (Abstract shortened by ProQuest.).