Population Trends in Northern Monkshood, Aconitum noveboracense, at Four Sample Intervals Over Fifteen Years

摘要

Aconitum noveboracense A. Gray ex Coville (northern monkshood) is a federally threatened plant species of the blue-flowered Aconitum section (Napellus) that occurs in Iowa, Wisconsin, Ohio, and New York, with most populations in Iowa. Monitoring of 12 populations in Iowa over a 15-year period showed substantial periodic variation in all population parameters, although less variation in adult density. Variation among sites was only detected for the proportion of quadrats with fruiting plants, and overall, adult and juvenile density. Our analysis provided a mixed view of the status of this species. On one hand, after a substantial decline between the 1994/95 and 2001/02 sample intervals, overall population density and density of each life stage increased and nearly recovered between the 2001/02 and 2004/05 sample intervals. Conversely, all our measures of reproduction - number of fruits/plant, proportion of quadrats with fruiting plants, number of fruitsode - indicated reduced vigor, as in the same intervals these measures declined and did not recover. Soil temperature was highly correlated with juvenile and adult density. Measuring additional biotic and abiotic factors should be incorporated into future monitoring. Local-scale abiotic factors that could influence variation in adult and juvenile density include light levels, drought, distance to cold air vents, soil moisture, nutrient levels, and humidity. Biotic factors, particularly herbivores, pollinator availability, and garlic mustard (Alliaria petiolata (M. Bieb.) Cavara & Grande), are also likely to have an impact on the Iowa Aconitum populations.