A 20-year record of the western prairie fringed orchid (Platanthera praeclara): Population dynamics and modeling of precipitation effects

Abstract

Western prairie fringed orchid (Platanthera praeclara) populations may be highly variable over time. It is thought that soil moisture, and potentially disturbance, play important roles in determining abundance and flowering in this species. We present data for a P. praeclara population in southwestern Minnesota that has been monitored annually for 20 years. The number of flowering orchids varied over this period from 0 to 722. We provide an empirical test of an earlier model of precipitation effects during phenological life stages of the orchid, finding that the model was no better than a simple null model that ignored variability in precipitation. We re-examined the relationship between number of flowering orchids and precipitation during phenological life stages based on a modern information theoretic (AIC), multimodel inference approach, and a larger data set. The models indicate the importance of precipitation during three phases of orchid life history: (1) mature growth in the previous year; (2) postsenescence; and (3) emergence, explaining >70% of the variation in the number of flowering orchids. We also evaluated the effect of prescribed burns on this orchid population. Although we found no effect of fire on the number of flowering orchids, plants were shorter in burn years. This difference was not significant, however, once variation in precipitation was taken into account.