Methodological foundation for the demographic research of dog’s tooth violet (Erythronium dens-canis L.)

Abstract

Little is known about the life history, demography, and population dynamics of Erythronium dens-canis L., although it is listed as an endangered species in a large part of its distribution range. The aim of our research was to establish methods to study the population biology of E. dens-canis. We wanted to clarify the question of how to classify individuals into age-state categories for a perennial species whose shoots do not appear simultaneously at the beginning of its growing season. Our studies were carried out in three sites in Zala county (Hungary). A total of 377 individuals of E. dens-canis were measured at least once in 2020, of which 255 plants (67.6%) were measured twice, in March and April.
Significant differences were observed in the demographic structure of the three Erythronium populations, both in terms of location and time. In the three sample sites, nearly 99% of the reproductive individuals were already present aboveground at the time of the first survey, whereas a significant number of juveniles emerged only afterwards. Our results suggest a significant seasonal effect on the reproductive rate of E. dens-canis. While in 2020 no seedlings were found in the quadrats of the sample plots, juvenile plants were present in significant numbers in all three sites.
The classification into age-states is unambiguous for reproductive individuals but shows moderate uncertainty for juvenile and vegetative adult plants depending on the time of the survey. To increase the accuracy of the classification, leaf size estimates were made by analysing the species-specific leaf shapes. Characteristics of each population were also considered by determining the size of the smallest flowering individuals in each group and the boundaries between adult and juvenile categories were set using these values. In all three sample sites, more than three quarters of the juvenile and adult vegetative plants were categorised into the same age-state category during both surveys. Since the boundary line between these two categories is based on the size of reproductive individuals, which are the first to sprout in the populations, it can be assumed that the accuracy of the classification increases over time, as plants that sprout later may reach or approach their maximum leaf area in the meantime. An additional advantage of choosing a later time for surveying is that in April the success of reproductive individuals in fruit-set can be determined at the same time. However, late surveys could be hampered by the withering, disappearance, or damage of the plants, which becomes more frequent as the plants approach the end of their growing season.