Strategy analysis of submerged lake macrophyte communities: an international example

Abstract

The plant strategy approach was used to assess relationships between the submerged macrophyte vegetation and environmental (natural and anthropogenic) pressures acting in four contrasting lakes: Lake Nasser (Egypt), a large man-made water body, and three North European natural or semi-natural lakes, Steinsfjord (Norway), and Loch Dee and Laird's Loch (Scotland). These lakes provide a high-variance data set over large physical, geographical and climatic gradients. Two complementary approaches were used to classify the established-phase strategy types of populations of euhydrophytes found in these water bodies. The relative contribution of each strategy element to the “community strategy” of the whole lake euhydrophyte flora was determined using a simple strategy index technique. The overall set of strategies prevailing in the submerged macrophyte community of each lake was visualised by plotting the percentage occurrence of each strategy type into the appropriate compartment of the triangular established-phase strategy model of Grime (1979). Comparisons were drawn both between lakes and, in the case of Steinsfjord, between the lake euhydrophyte communities present on five sampling occasions over a 58-year period. The strategy approach provided insight into the interaction between environmental pressures (such as trophic state and water level regime) and the macrophyte communities. Thus a high incidence of stress-tolerant traits occurred in the plants of habitats stressed by low nutrient availability in conjunction with low pH. Competition- and disturbance-tolerant traits were more frequent in the plant communities of two productive lakes impacted by regular fluctuation of water level.