SUBMERGED PLANT-SURVIVAL STRATEGIES IN RELATION TO MANAGEMENT AND ENVIRONMENTAL PRESSURES IN DRAINAGE CHANNEL HABITATS

The abundance of submerged weeds, in relation to management regime and environmental factors, was surveyed during 1992 and 1993 in drainage channels located in four geographically-distinct areas of Britain. The aim of the study was to ascertain, using a multivariate approach, the degree to which species survival strategy and vegetation could be rel ated to disturbance and stress pressures on plant survival. Indices of disturbance and stress were constructed from combined environmental d ata for each site. A species ordination using Canonical Correspondence Analysis showed that the combined disturbance variable explained more of the variability that did stress. Two main groups of species could be distinguished. The larger group scored low on the disturbance gradi ent and these species, with different tolerances to stress (especially light-limitation), appeared to be those better-adapted to habitats wi th low disturbance (e.g. Potamogeton pectinatus and Potamogeton lucens ). The smaller group comprised species which tended to occur in sites with higher disturbance (e.g. regular cutting) such as Callitriche sta gnalis. Using the terminology of strategy theory, most of the dominant species could be classed as 'competitive/disturbance tolerators (CD)' or variants of this established-phase strategy. The limitations are d iscussed of applying the strategy approach at species level in a defin ed habitat-type which shows a high degree of uniformity between sites, such as artificial drainage channels.