Weather and herbivores influence fertility in the endangered fern Botrychium multifidum (S.G. Gmel.) Rupr

Fluctuations in local weather conditions and other stochastic processes are important factors affecting species population persistence. We studied two differently sized populations of the rare and declining fern species Botrychium multifidum for 4 and 5 years, respectively. Individually marked plants in permanent plots were followed to detect trends in population size, reproductive success and dormancy in relation to local precipitation and temperature. Our applied logistic regression model suggests that the shortage of precipitation during summer decreases fertility in the next year in both populations. Invertebrate herbivory of the fertile part of the plant additionally diminishes the output of spores. We found the population size to be stable with a very low percentage of each population composed of juvenile plants. Stochastic processes and low recruitment could easily lead to the extinction of these populations.