A Population Study of Hyacinthoides non-scripta:
Density dependence, Phenology and Environment

Abstract

This study investigated different factors affecting seed production in the English bluebell, Hyacinthoides non-scripta, and the role of density and phenology during their reproductive stage. The study sought to understand processes such as pollination facilitation, i.e. positive density dependence, and the complex interaction of density acting on different stages, and even parts, of the plant. A simulation model was developed to investigate population growth and spread under varying degrees of density dependence. Data were collected during the flowering season in 2015, from woodland surrounding Durham University (North-East England, UK), to investigate the impacts of conspecific density, flowering phenology and environmental factors on seed production (used here as a proxy for plant fitness).
The unspecialized manner of bluebell dispersal leads to extremely slow spread and influences the spatial structure of the population. Population simulation using baseline parameters (excluding density dependence except for on adult survival) predicted the population to take more than 100 years to reach plant densities and population sizes seen in the field, indicating that new populations of bluebells may take many years to establish and expand. The model also highlighted the importance of seedling survival and fertilisation for population growth and spread, and the necessity for high adult survival for population existence.
Data from the field suggest that flowering date is an important plant trait that is likely to be subject to strong selective pressure; as plants starting their flowering in the first two weeks of the flowering season produced more than double the number of seeds produced by later plants. Aspect was the most important environmental factor. Data from several years are needed to verify the model further, and determine if the trends seen in the data are common for the English bluebell in the North-East of England, or are the result of a non-optimal growth season.