The demography of trout lily (Erythronium americanum Ker.) in Nova Scotia

Abstract

The age structures of both native and transplanted populations of the perennial herb, ‘trout lily’ (Erythronium americanum), were analysed and found to have age-independent mortality rates. Cohort survival was greatest in populations growing on hardwood forested flood plains (60%), less in populations from gently sloping terraces with pit-and-mound microrelief (53%) and smallest (45%) for colonies on slopes steeper than 15°. The former habitat-type is the optimum for trout lily in Nova Scotia and in it the proportion of flowering bulbs can reach 35%. The second named habitat is widespread and characterised by fewer flowering bulbs (5–10%). In the latter habitat flowering bulbs are uniformly rare. Trout lily bulbs tend to be sterile until at least their eighth year. The high mortality rates of populations on steeply sloping, hardwood forested ground ensure minimal survival of bulbs beyond their sixth year. In the other two named habitats sufficient numbers of bulbs reach ages of 8 or 9 years for some to make the translation from the sterile to the flowering form. In all the habitats studied in Nova Scotia, propagation is typically by either runners or, less importantly, daughter bulbs, with the peak of activity in the bulbs third and fourth years. The plants of flood plains showed the greatest rates of vegetative propagation, by cohort, but many of the bulbs from colonies growing on steep slopes lacked runners or daughter bulbs. As all bulbs for the transplant experiments came from a single clone it can be concluded that trout lily plants in Nova Scotia have a sufficiently large genetic endowment for them to behave in the same manner as native populations of the species in the several habitats represented in the province.