Sulfur cinquefoil is native to Eurasia and has invaded meadows and grasslands of North America. It occurs in intermountain valleys of the Rocky Mountains, including a nature reserve in northwest Montana that supports a mosaic of mesic fescue and xeric needlegrass grassland communities. We did tests to determine germination requirements, followed the fate of mapped sulfur cinquefoil from 1998 to 2005 to determine vital rates, and used a matrix modeling framework to analyze population-level dynamics. Sulfur cinquefoil plants were highly fecund; large plants produced > 10,000 seeds that require light for germination. The survivorship curve of the 1999 cohort suggested low juvenile but high adult survival. Simulations indicated that a 10% decline in survival would decrease population size more than a 10% decline in recruitment. Annual recruitment, growth of nonreproductive plants, survival, and flowering frequency of sulfur cinquefoil were all higher in the three needlegrass sample plots compared with the one fescue plot, and projected equilibrium sulfur cinquefoil populations were approximately 12 times larger in needlegrass than fescue grasslands. Our results suggest that biological control agents that negatively affect survival, such as root borers, might be more effective at controlling established sulfur cinquefoil populations than those that diminish seed production. Our results also suggest that sulfur cinquefoil might have more potential to become dominant in xeric grasslands and demonstrate the need for doing multiple demographic studies over a variety of habitats because the same species will respond differently in different habitats.

Nomenclature: Sulfur cinquefoil, Potentilla recta L.; fescue, Festuca idahoensis Elmer and Festuca scabrella Hook.; needlegrass, Stipa comata Tri. & Rupr.