Ecological valence of expanding European ash (Fraxinus excelsior L.) in the Bohemian Karst (Czech Republic)

In 2002 a study focused on the evaluation of height and density of expanding natural regeneration of Fraxinus excelsior L. (FE) was carried out on Velká hora Hill, a locality in the Bohemian Karst (Český kras). The examined area is located in Karlštejn National Nature Reserve and takes up around 31 ha. The parent rock is limestone. The expansion depends on soil and exposition conditions and relates to the water balance gradient. FE reached the highest densities (up to 6,000 individuals/400 m2) on Velká hora's peak plateau on medium-deep, heavy-textured decarbonized soils. The lowest expansion (508 individuals/400 m2) was found on slopes fully exposed to south (S) with water retention capacity lower than 20 mm. In total, the average density was 1,190 individuals/400 m2. FE natural regeneration reached the highest average heights (around 210 cm) on Fageto-Quercetum illimerosum mesotrophicum, the smallest heights on Carpineto-Aceretum saxatile. Average height in the locality was 47 cm. No relation was found between FE natural regeneration height or density and the distance of a fertile specimen. The distance exceeded 70 m only in 3.4%. FE seeds could be detected almost everywhere at the area. FE is capable to establish itself on any location of the studied locality except ecologically extreme parts of rock steppe without forest and Fagus sylvatica L. stands occupying S slopes. On less favourable sites it is capable to use the protection of other tree species and as a low growing tree it can eventually dominate the site. In more favourable conditions it expands on the whole area, where it can dominate the undergrowth already at 1-m height. If the forest sites are left to natural development, a distinctive change in the tree species composition could take place in a short time period. Such a change could have an essential impact on light conditions, energy flux and species composition of plant and animal communities.