The aims of our studies and assessments are: 1 - to evaluate the risks linked to woody vegetation on dikes and their nearby environment. Particularly, we measure and model in these conditions the root system of the most common tree species and its impact on dike structure and durability. More than ninety stumps embedded on canal or flood protection dikes were excavated throughout France. Root systems structure and architecture depend on the tree species and age and on site conditions: type of materials, soil texture, structure, compaction and fertility, water availability and climate. 2 - to study vegetation and biodiversity natural dynamics mechanisms, 3 - to determine and sort by priority all social and ecological issues; 4 - to propose management plans, tools or recommendations to help all stake holders (river and dike managers, foresters, decision makers, NGOs, local population) finding the best compromise between risks control (included dikes safety) and all other issues. We designed such management plans and directives for many French rivers. Issues concerning trees were each time particularly sensitive.