PARENT SESSION
Poster Session 31: Rare, Threatened, and Endangered Species
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Population dynamics of American Ginseng along an ice storm canopy disturbance gradient in sugar maple forests of south-western Quebec (Canada).

Thibeault, Julie^*,1, Gagnon, Daniel¹, Nault, Andrée^{1, 2}, ¹ Université du Québec à Montréal (UQAM), Montréal, Québec, Canada² Biodôme de Montréal, Montréal, Québec, Canada

ABSTRACT- In January 1998, a severe ice storm damaged the tree canopy of 1.8 million ha of forests in south-western Quebec (Canada). The resulting increase in solar radiation in the understory, which may prove to be detrimental to shade-tolerant species, is of particular concern in the case of endangered understory species like American Ginseng (Panax quinquefolius L.).To assess the impact of such a disturbance on ginseng population dynamics, a demographic study was conducted in four natural populations of south-western Quebec. Study sites were located along a gradient of canopy disturbance by the 1998 ice storm, as measured by light penetration in the understory. In each population, approximately 300 plants were monitored from 1999 to 2001 to record individual growth, fecundity and mortality. For each population, transition matrices were built for two time-intervals (1999-2000 and 2000-2001), which yielded different demographic parameters allowing comparisons among populations (including asymptotic growth rate () and elasticity values of each possible transition). Our results indicate that, in sites most affected by the ice-storm, population growth rates () were the lowest. In these sites, seed production, seedling recruitment and seedling survival were generally lower while plant mortality (especially in adult plants) was generally higher. The negative impact of canopy disturbance may have been direct (by increasing the irradiation of ginseng plants) or indirect (by stimulating the growth of a dense shrub layer, by increasing competition by other herbs, shrubs and saplings, and by creating suitable conditions for the development of fungal disease). Even though large plants remaining in the same size-class were the transitions most contributing to the population growth rate, higher elasticity values for fecundity were associated with higher values. Therefore, restoration efforts to increase ginseng population growth rates should aim at increasing seed production and recruitment. In addition, the two least disturbed sites had population growth rates not significantly lower that 1 for one time-interval, indicating that low disturbance intensity can be beneficial to ginseng populations. This project has been funded by the Quebec Ministry of Environment and WWF.

Key words: Panax quinquefolius L., canopy disturbance, population dynamics, transition matrices