Langfristige Veränderung der Blühhäufigkeit seltener Geophyten in Pfeifengraswiesen: zeitlicher Trend oder Einfluss von Wasserstand und Wetter?

Abstract

The long-term population dynamics of Orchis coriophora, O. morio (Orchidaceae), and Gladiolus palustris (Iridaceae) were studied in a nature reserve at the border of Lake Constance. The studied species inhabit wet meadows, which were irregularly flooded during summer. Since the 1970s these meadows were mown for conservation reasons. The aim of this paper is to examine (1) whether the population size increased because of the management practice and (2) whether variation in flowering frequency was related to water level fluctuations of Lake Constance, precipitation, and air temperature. To census the population size the number of flowering plants of the three species was counted yearly from 1969 and 1972 to 1998 respectively. The study shows that irregular flooding was an important factor decreasing flowering frequency of O. morio and G. palustris. Furthermore, the number of flowering plants of G. palustris decreased after years with high air temperature and high precipitation. Two of three species showed a clear temporal trend. Orchis morio decreased dramatically. Only the population size of G. palustris increased which can be interpreted as a result of the management practice.