Drought affects the competitive interactions between Fagus sylvatica seedlings and an early successional species, Rubus fruticosus: responses of growth, water status and delta C-13 composition

Competitive interactions between European beech (Fagus sylvatica L.) seedli ngs and the early successional species Rubus fruticosus, and the role of wa ter availability, are reported and discussed in relation to management prac tices and climatic changes in beech ecosystems of Central Europe. Responses of growth, water status, gas exchange and carbon isotope composit ion (delta C-13) to two competition and three irrigation treatments were ex amined in a factorial-design glasshouse study. Under regular irrigation, coexistence with R. fruticosus did not significan tly affect growth, water potential and gas exchange of beech seedlings. How ever, moderate water shortage caused a twofold reduction in beech biomass a nd changes in root: shoot ratios. Drought lowered transpiration rates and p redawn water potentials (below the xylem embolism threshold) for F. sylvati ca; delta C-13 of leaves and fine roots increased (discrimination was reduc ed). By contrast, significantly lower delta C-13 of R. fruticosus foliage i ndicated an improved water status. Competitive interference intensified the effects of reduced irrigation. Water availability regulates the competitive interactions between beech see dlings and R. fruticosus. Natural regeneration of beech seedlings may be in hibited by interference from a species such as R. fruticosus, especially du ring summer drought, as predicted by actual climate models.