The study was focused on the development of 2-year-old beech seedlings under Scots pine stands thinned to different degrees. Along two growing seasons we measured water, light and nutrient availability and above- and below-ground development of beech seedlings, ground vegetation and pine. Pine action on beech development seemed to be essentially through modulation of the light transmission while it did not seem to exert a severe belowground competition. At the difference of pine, and depending on the species composition, the ground vegetation was able to compete strongly for water and nutrients and reduce considerably beech establishment and growth. Dicotyledonous species are generally less competitive than monocotyledonous one and particularly grasses. Therefore to promote beech establishment under Scots pine stands, forest managers have to control and make a compromise between pine competition for light and ground vegetation competition for water and nutrients which increases with increasing light.