Ludwigia grandiflora ssp. hexapetala and L. peploides ssp. montevidensis have invaded many types of fresh water ecosystem in France leading to serious problems of management of these macrophytes. The prediction of extracted plant biomass quantities for every control method could considerably help in plant removal and selecting management choices. The paper presents results of the research program "Biological Invasions" granted by the French Environmental Agency concerning the Ludwigia species (2003-2006): "Characterization of the relations between biotopes, plant populations and human activities: Implications for management". The objective of this work is: (1) to compare environmental variables in the western part of France where colonised water bodies are widespread, (2) to link these parameters with the evaluation of standing crops and (3) to propose implications for management planning and control methods. Measured dry biomass of Ludwigia spp. varied from 200 g DM m(-2) in shallow lakes to 4,500 g DM m(-2) in a meander of a eutrophicated river. Results depend on the scale of the analysis: within sites, between-sites, at different seasons or years. In sunny conditions, optimal for these plants and in nutrient rich areas, biomass is high. In general, exposure to wind, waves and currents reduces the standing crop. For plant production as well as removal work, the status of plant development and water level, are key factors.
