Seed dispersal by animals is a major mechanism by which plant species spread over long distances. Furthermore, ungulates are said to be particularly relevant vectors in forest habitats. Based on coupled floristic and browsing surveys, we described and analyzed the causes of the spatio-temporal progression of the rare epizoochorous species Cynoglossum germanicum over 30 years in a large forested area. Paradoxically, although rare and protected, C. germanicum displayed a strong colonization dynamic. It was absent in the initial 1976 survey, but occurred in 20 plots in 1981 and 120 plots in 2006, only in the northern part of the forest, which had the highest deer populations. In 1981, the probability of occurrence of C. germanicum did not depend on browsing pressure whereas results for 2006 showed that it increased significantly with past browsing pressure. In a second step, a multiple logistic model linking C. germanicum presence with browsing pressure and ecological site variables (soil water reserve, Ellenberg indicator values) proved that its distribution not only depended on its ecological requirements (notably for nitrogen) but also remained dependant on past browsing pressure. C. germanicum not only benefited from epizoochorous dispersal by deer but also due to the presence of toxic proteins in its tissues also avoids deer browsing once settled. Factors not well controlled such as browsing pressure can however emerge as possible causes of rare plant species progressions.