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(American Journal of Botany. 2006;93:1018-1028.)
© 2006 Botanical Society of America, Inc.

Population Biology

Population age structure and reproductive behavior of the monocarpic perennial Heracleum mantegazzianum (Apiaceae) in its native and invaded distribution ranges1

Jan Pergl5, Irena Perglová, Petr Pysek and Hansjörg Dietz

2Institute of Botany, Academy of Sciences of the Czech Republic, CZ-252 43 Pruhonice, Czech Republic; 3Department of Ecology, Faculty of Science, Charles University, Vinicná 7, CZ-128 01 Praha 2, Czech Republic; 4Institute of Integrative Biology ETH, Universitätsstrasse 16, CH-8092 Zürich, Switzerland

ABSTRACT

Many invasive species are benign in their native region—are there interactions between their key traits and the new habitats that explain invasion success? The giant perennial herb Heracleum mantegazzianum is a problematic invader in Europe and is also naturalized in North America. We compared its population structure and reproductive behavior in the native (W. Caucasus) and invaded (Czech Republic) areas in managed (pastures) and unmanaged sites. The age structure of the populations and age at flowering were analyzed using herb-chronology, a method based on counting annual rings in the secondary xylem of roots. The species was strictly monocarpic; most plants in unmanaged sites in the invaded range flowered in the third and fourth yr (maximum 12 yr). In unmanaged habitats, plants from the native range flowered later than those from the invaded range. In both ranges, flowering was delayed in managed sites where the population density was higher and most plants flowered around the fifth year. Reproductive output of individual plants was neither related to population density nor to age at flowering. More favorable climatic conditions in the invaded region, together with increased chances for dispersal in a densely colonized central Europe, seemed to allow the massive invasion.

Key Words: biogeography • Caucasus • Czech Republic • demography • habitat type • Heracleum mantegazzianum • herb-chronology • invasive alien plant






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