The root systems of Fraxinus excelsior and Fagus sylvatica and their competitive relationships

Following reports from field foresters on so-called 'beech regeneration dieback', the root systems and competitive relationships of sapling-stage mixtures of beech (Fagus sylvatica L.) and ash (Fraxinus excelsior L.) were investigated in vivo and in vitro. Ash has a plate-root system from an early age, and beech a heart-root system. The distribution of ash roots is determined by competition for light under a closed overstorey of beech while the distribution of beech roots changes if there is competition with ash roots. In a replacement series experiment in a greenhouse, interspecific competition for water strongly reduced growth and survival of beech saplings. It is concluded that this competition for water could be the reason for beech regeneration dieback on sites where it occurs.