Flowering regimes of terrestrial orchids: unpredictability or regularity?

Abstract

Abstract. Empirical data on many species of terrestrial orchids suggest that their flowering pattern over the years is extremely irregular and unpredictable. A long search for the reason has hitherto proved inconclusive. Irregular flowering was attributed to costs associated with sexual reproduction, to herbivory, or to the chaotic behaviour of the system represented by difference equations describing growth of the vegetative and reproductive organs. Data on the seasonal growth of leaves and inflorescence of Dactylorhiza majalis are used here to test alternative explanations of the irregular flowering patterns of orchids. These patterns are found to be extremely rare in our data set. Neither costs of reproduction nor grazing seem to explain the rare events of a transition from flowering one year to sterility or absence the next year. These transitions are almost exclusively characteristic of one of four experimental sites, the only unmown site, where the mean leaf area and incidence of flowering in the whole population is also in decline. It is therefore hypothesized that irregular flowering regimes may be characteristic of sites with temporarily or steadily declining populations and that they are usually not present in prosperous ones ‐ at least for D. majalis.

Inter-annual variability in flowering of orchids: lessons learned from 8 years of monitoring in a Mediterranean region of France

“…1B). These results are in accordance with the previous findings on the variability in the inter-annual records of orchid numbers in northern Europe (Tamm 1991;Kindlmann and Balounova 1999;Oien and Moen 2002;Tali 2002;Brzosko 2003). Inter-annual fluctuations in orchid abundance are mainly induced by variations in climate, in particular temperature and rainfall (Wells et al 1998;Pfeifer et al 2006Pfeifer et al , 2011Pfeifer et al ).…”

Habitat demands and population characteristics of the rare plant species Gladiolus imbricatus L. in the Frenštát region (NE Moravia, the Czech Republic)

“…Geophytes show annual variation in the percentage of generative individuals, which is connected with intrinsic population dynamics, reproductive costs, herbivory and environmental factors. None of these alone, however, unambiguously explains annual shifts from sterility or dormancy to fertility (Tamm 1991, Kindlmann & Balounová 1999Pfeifer et al 2006). There have been number of studies analysing the distribution, phytosociological and habitat conditions of the sword lily in the Czech Republic (Zelená 1967;Sedláčková 1978Sedláčková , 2005Barabasz 1998;Falkowski 2002;Hänel & Müller 2006;Rombel-Bryzek 2007) but a comprehensive study focused on local reasons behind population changes is lacking.…”

Orchid Biology: Reviews and Perspectives, VIII

“…Only after a dormant period (a year or two) is there an increased probability that a plant will appear above ground and flower ( Fig. Kindlmann and Balounovi (1999) report that in vigorous populations of Dactylorhiza majalis large investments in reproduction did not cause plants to be vegetative or dormant in the following year. Kindlmann and Balounovi (1999) report that in vigorous populations of Dactylorhiza majalis large investments in reproduction did not cause plants to be vegetative or dormant in the following year.…”