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

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