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Climate, size and flowering history determine flowering behaviour of

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Marion Pfeifer, W. Heinrich, G. Jetschke

Institute of Ecology, Jena

Flowering behaviour of the individuals as well as annual flowering frequency of a population of Himantoglossum hircinum are investigated using data collected in a long-term project (1976-2001) in Germany. The long-term data set includes information about size, life-span and flowering activity of about 13600 H. hircinum individuals observed and individually marked on a permanent plot (1.8 ha) in a nature reserve. Additional data taken in the last plant year contain information about fruit-set and correlations between life-history traits.

Flowering behaviour of orchids is often irregular and various hypotheses were proposed to explain that pattern including irregularity because of costs associated with reproduction and herbivory (Whigham and O’Neill 1991, Kindlmann 1999, Kindlmann and Balounova 1999, 2001), because of the chaotic behaviour of the system (Inghe, 1990) or because of external conditions (i.e. climatic variability). Which factors determine the flowering behaviour of the population and individuals in a given year and over their lifetime, and thus overall flowering patterns on the population level. Age might be an important factor, but more important seems to be plant size (leaf area, leaf number), which was described as a good predictor of flowering probability in a variety of studies (Snow and Whigham 1989, Wells and Cox 1989, Zimmerman and Aide 1989, Calvo 1990b, Primack and Hall 1990, Whigham and O’Neill 1991, Carey 1998, Willems and Melser 1998), but see also Hutchings (1987a). There is evidence from a number of studies that weather has an influence on the flowering behaviour of the individuals and consequently on the flowering frequency of the population of terrestrial orchids (Hutchings 1987a, Inghe and Tamm 1988, Wells and Cox 1989, Kull and Kull 1991, Carey 1999, Brzosko 2002). However, other authors found no relationship between weather conditions and flowering ecology (Wells and Cox 1991, Whigham and O’Neill 1991).

The talk will be about the influence of age, size, reproductive effort (flowering history) and climatic conditions on flowering dynamics of an orchid species. Flowering performance of the individuals and of the population is highly variable and annual flowering frequency of the population never exceeds 14%. Individuals mostly flower only once, but a few flower up to four and more years. Few individuals flower in a succession of years and mortality after flowering is high. Flowering probability is strongly determined by plant size in a given year, while there is nearly no recognizable influence of age. Costs of reproduction are high resulting in a decrease in leaf number the year after flowering and a FBF value of 24%. Weather can explain around 60% of the yearly variation in proportion of plants with 8-15 leaves and thus has a strong, but indirect influence on flowering percentage. Drought in winter has a direct, negative influence on the flowering initial. Mean fruit-set appears to be very low and there is a significant correlation between size and reproductive activity.

Additional Keywords: reproduction - costs - size class distribution - long-term dynamics – life history - terrestrial orchid – principal component analysis – flowering behaviour

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