The growth and form of ash (Fraxinus excelsior) in mixture with cherry (Prunus avium), oak (Quercus petraea and Quercus robur), and beech (Fagus sylvatica)

The effects of mixing ash (Fraxinus excelsior L.) with cherry (Prunus avium L.), oak (Quercus petraea (Matt.) Lieb., and Quercus robur L.), and beech (Fagus sylvatica L.) were investigated using a balanced two-component competition experiment. In general, two patterns of growth were observed. Firstly, in the ash–cherry experiment, two rapidly growing species altered their stem form and showed a plastic response to interspecific competition, and both species maintained a position in the upper canopy. Secondly, in the ash–oak and ash–beech experiments, a two-tier canopy formed with ash in the upper canopy, and interspecific competition resulted in an early nursing effect on the ash. In both patterns of growth, competition affected stem diameter and the shape of the tree with few, and only short-lived, effects on height. The maximum relative yield totals were 1.78 for ash–cherry, 1.77 for ash–oak, and 1.44 for ash–beech, indicating that the mixtures studied may be more productive in their early phase of growth than equivalent areas of pure species.