The Effects of Forest Management on the Genetic Variability of Plant Species in the Herb Layer

The change of the genetic structure of three plant species of woodland clearings, Senecto sylvattcus, Dtgttalts purpurea and ScrophuVarta nodosa has been studied in relation to the management of these clearings.Despite a lack of allozyme variation between and within populations of Senecto sylvattcus increase of the light accessibility to the forest floor by thinning has let evolve a winter annual type in addition to the common summer annual type. In contrast to the latter type the fruits of the former one germinated without cold treatment; seedlings developped a winter hardiness, but they took more time to flower and fruit than the summer annual type. In addition the winter annual type was physiologically differentiated in individuals with high and low chlorophyll content, the latter being correlated with a high magnesium and a low iron content of the leaves.All populations of the biennial Digitalis purpurea consisted of plants with glabrous and hairy flower stalks, the latter being the recessive homozygote. Mowing of herbs and gresses, but not of shrubs and young trees in woodland clearings extended the survival of the populations for some more generations, and gave rise to a selection in favour of the glabrous genotype of D. purpurea.Populations of the perennial Scrophularia nodosa contained iron efficient and inefficient plants. The ability to change the pH around the root seems to be coded by a single gene. In addition to this acidification Fe-efficiency was further determined by the Fe-translocation from the root to the shoot. Genotypes with a slow Fe~translocation were inferior in flower and seed production and unable to produce seeds if ploughing of woodland clearings before afforestation had diminished the soil organic matter of the A_o-horizon.