Untersuchungen zur Neuansiedlung von drei seltenen Xerothermrasenarten in artenarmen Dominanzbeständen von Festuca rupicola Heuff.

Abstract

Wahl, S.; Partzsch, M.: Investigations into the introduction of three rare xerothermic plant species into species-poor stands dominated by Festuca rupicola. – Hercynia N.F. 41 (2008): 99 –119.Recently developed porphyry outcrops are caused by anthropogenic impacts near Halle (Saale). They characteristically differ from prehistorically outcrops in that they are now dominated by species-poor xerothermic grassland communities. In line with ecological regeneration investigations, we wish to evaluate the possibility of introducing three rare xerothermic species (Muscari tenuiflorum, Filipendula vulgaris and Pseudolysimachion spicatum) into Festuca rupicola dominated stands. The target species are commonly found in neighbouring, more species-rich outcrops. The three species are bloomed and fruited rich throughout the open field, but it is hard to find seedlings. Germination biology investigations revealed that F. vulgaris and P. spicatum become viable for germination on reaching maturity and prefer medium-temperature conditions (20 °C by day and 10 °C by night). M. tenuiflorum shows a morphophysiological dormancy, germinates in the following spring, and, favours the lower temperatures of 8 °C by day and 4 °C by night. F. vulgaris and P. spicatum became rapidly established under standardized conditions in the climate chamber but not in the open field. In contrast, M. tenuiflorum did not develop in the climate chamber due to its dormancy and the warm experimental conditions, but establishment was successful in the open field. Emergence of individuals was highest in the subplots without vegetation, intermediate in the plots with gaps and with clipped vegetation, and low in the plots with intact vegetation. The development of M. tenuiflorum was very slow, with an annual production of only one single leaf for the whole investigation period. In the 1st year the individuals were, on average, 1.5-5 cm high, with best growth in the gaps, in the 2nd year the individuals averaged 6-7 cm, and in the 3rd year the individuals averaged 5-7 cm, the highest measurements being in the plots without vegetation. However, there were no significant differences between the plots with different levels of disturbance in the three years. Survival percentages of M. tenuiflorum declined from year to year: In the 1st year survival was high in the plots without vegetation, gaps, and clipped vegetation (62-80 %), and low in the plots with intact vegetation (27 %). In the 3rd year survival was highest in the plots without vegetation (30 %), intermediate in the gaps and plots with clipped vegetation (ca. 20%), and low in the plots with intact vegetation (2 %). Mortality between the years varied: between the 1st and 2nd years ca. 50 % of individuals died in the plots with gaps, clipped vegetation and intact vegetation, while only 20 % died in the plots without vegetation. Between the 2nd and 3rd years 85 % died in the intact vegetation; in the other plots between 38 and 52 % died. Certain conclusions can be drawn from the results with relevance to nature conservation: The present form of land use, which implies a lack of grazing, represents the greatest obstacle to the establishment and thus reintroduction of rarer xerothermic species. Disturbance of the grassland communities provides regeneration niches. Small clearings formed by the burrows of small mammals and the tracks of sheep and goats can aid the emergence and establishment of certain plant species. A successful approach toward regenerating species-poor xerothermic grasslands may therefore involve the reintroduction of traditional land use measures.