An ecophysiological study in the field layer of ash coppice. III. Influence of diminishing light intensity during growth on Geum urbanum and Cirsium palustre

The adaptability of Cirsium palustre, a shade avoiding species, and Geum urbanum, a species avoiding exposed conditions in the ash coppice cycle, to a change from a high to a low light intensity was studied, in order to simulate the changes taking place in the light climate in a deciduous woodland in spring. Both the vegetative rosette phase and the generative phase were considered. In the rosette phase a rapid adaptation to the low light intensity took place in both species in a similar way. In the generative phase Geum adapted much better after the plants had been transferred from a high to a low light intensity. The dry weight increase of Cirsium ceased after the transfer, whereas Geum continued to grow. The leaf area ratio was much higher after the transfer, giving better assimilation in limiting light conditions. Cirsium when continuously grown in a low light intensity also had a high leaf area ratio, but the stems were too weak to support themselves, in contrast with Geum. So in the vegetative phase both species can be considered shade tolerant, but Cirsium palustre is not shade tolerant in the generative phase.