Beiträge zur Populationsdynamik von Antennaria dioica (L.) Gaertn. im Bereich der mittleren Schwäbischen Alb

Abstract

Occurrence of Antennaria dioica is decreasing in the area of Schwäbische Alb (Southern Germany). The reasons of this decrease were studied. The surviving populations of this plant were mapped in dry grasslands. From existing sites data concerning slope and exposition, the soil depth and the pH-value of upper soil and the composition of the vegetation were recorded. The population biology of the plants was examined in respect to vegetative and generative life form development. The life form development of particular plants and groups of plants was tracked in all areas in order to show the population dynamics. From 1991 to 2007 some sites were therefore continuously observed several times a year. Due to plagiotropic growth the plant grows near the surface of the ground and its spreading is therefore restricted. A. dioica is not able to survive long periods of drought. Flowering of A. dioica depends on sufficient water supply in preceding years. The fructification is highly dependent on the distance of sexes of the dioecious plant. Isolated populations generally do not produce fruits at all. For long-distance dispersal the plant uses anemochorous achenes, which however do not depart very far from the flowering elder plant. In natural conditions only very few seedlings develop. In most locations surviving seedlings were not discovered. Reasons for the decrease of A. dioica may be change in the pasture regimes. Due to felting the biomass close to the soil surface biomass is increasing. Because of strict plagiotropic growth of the species the plant is not able to outcompete accompanying vegetation. High growing plants and compact turfs of grasses cannot be overgrown. A second observed reason for the local decrease of A. dioica may be the increase of long lasting dry seasons as a result of climate change. In order to conserve the species on the Alb specific nature management is necessary in order to maintain habitats suitable for the plant.