Die Xerothermrasenart Veronica spicata L.: Populationsstruktur, Etablierung und pflanzliche Interaktionen
Populationsstruktur, Etablierung und pflanzliche Interaktionen
Schlagworte:biodiversity, competition, facilitation, endangered species, establishment, semi-dry grasslands
The high biodiversity of xerothermic grasslands in Central Germany developed due to traditional land use over centuries. The political upheaval in 1990 led to an abandonment of grazing in consequence of economical reasons and to a gradually depletion of former species-rich communities. Especially the dominance of particular grass species like Festuca rupicola results in a strong decline of dicotyledonous species. As a characteristic species of xerothermic grasslands the rare and endangered Veronica spicata was chosen as study species in order to investigate how many populations still exist in Central Germany`s porphyry landscape, how big and vital they are, which chances of establishment V. spicata shows in grass stands with different densities of F. rupicola and how the dicot interacts with the co-existing grass F. rupicola.
The following methods were used: 1) In the field, population sizes and plant parameters like number and length of leaves, number and length of infructescences, generative biomass, seed traits of V. spicata and the plant communities in which this species occurs, were estimated. 2) Establishment was examined in a pot-experiment, with F. rupicola-individuals growing in different densities (F0, F1, F2, F3; six replications). In each pot 20 seeds of V. spicata were sown in summer; germination, mortality and growth performance were controlled. 3) Another pot-experiment was conducted in order to investigate the plant-plant interactions between V. spicata and F. rupicola in different mixtures (V3F6, V6F3) and monocultures (V9, F9; per each six replications). The above-ground biomass, growth height, number and length of leaves and flowering stems, length of infructescenes (V. spicata) or panicles (F. rupicola) and seed traits were determined and the intensity and importance of interactions were calculated by using the Relative Interaction Index (RII) and the Index of Interaction Importance (Iimp).
Results showed that from the former 12 populations of V. spicata only seven were relocated: two of them were large and stable with ca. 600 individuals, three were mediate populations with ca. 50 till 90 individuals and two were very small with ca. 10 individuals. Veronica spicata was found in Filipendulo-Helictotrichetum as well as in Festuco-Brachypodietum, but showed no difference in growth performance between the two plant communities. Leaf length and seed weight significantly negatively correlated and the generative biomass significantly positively correlated with population size. In terms of establishment, V. spicata did not show significant differences in germination and mortality in the grass-stands with different densities but the survival likelihood was higher in the pots with F. rupicola-individuals. Without F. rupicola the dicot developed better in terms of growth height and diameter of rosettes. With regard to interactions, V. spicata grew significantly better in monocultures than in mixtures, but F. rupicola did not show any differences. Thus, the dicot stronger responded to interspecific than to intraspecific competition. Both interaction indices suggested competition against the dicot and neutral till facilitative effects to the grass.
In order to counteract the recent decline of V. spicata the reintroduction of a traditional grazing regime of the xerothermic vegetation is necessary, because browsing by animals reduces the competition ability of grasses and woody species and the damage by trampling creates new niches for establishment of actually endangered xerothermic species.