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An understanding of plant population dynamics in response to natural and anthropogenic influences is critical for rare species management. We present a long-term study and population viability analysis of a federally threatened monocarpic, Cirsium pitcheri, endemic to the Great Lakes, in northern Michigan. Population growth rates of C. pitcheri were highly variable; only four of the 14 year-pairs studied during the 19 yr study period indicated a growing population (λ > 1). Elasticity analysis showed population growth was sensitive to seedling recruitment. We manipulated light and litter levels in the growth chamber to simulate natural succession or invasive plants and to determine their effects on seedlings and ultimately, population performance. The absence of shading and litter increased seedling emergence from 8% to 42%, but no simulated population had less than a 5% risk of extinction over a 25-year period. These populations are, strictly speaking, non-viable. Population viability and conservation of this species are linked to recruitment, including seedling success. Control of plant and animal invasive species and addition of greenhouse transplants to increase recruitment may help reverse population declines.

Pitcher's thistle (Cirsium pitcheri) is a federally listed monocarpic plant species endemic to the shoreline dunes of Lakes Huron, Michigan and Superior. Individual plants may require 4–8 y to mature, after which they flower and die. This life history and the lack of vegetative modes of reproduction make an understanding of seed and seedling ecology critical for preservation and restoration of Pitcher's thistle. We report conditions necessary to overcome seed dormancy and the effects of light, seed mass and depth of burial (0, 2, 4 or 8 cm) on seed and seedling success from laboratory experiments in controlled growth environments. Seeds of Pitcher's thistle are dormant when dispersed, but a combination of low temperatures and afterripening can break dormancy. Germination over 30% was obtained with at least 24 wk of low temperature moist stratification; 25% germination occurred after 6 mo of storage at room temperatures. Light suppressed germination of nondormant seeds. Although burial is required...