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Factors Affecting Spotted Knapweed (Centaurea stoebe) Seedling Survival Rates

Published online by Cambridge University Press:  20 January 2017

Anastasia P. Maines ,
David G. Knochel  and
Timothy R. Seastedt
Anastasia P. Maines
Affiliation:
Department of Ecology and Evolutionary Biology and Institute of Arctic and Alpine Research, University of Colorado Boulder, Boulder, CO 80309
David G. Knochel
Affiliation:
Department of Ecology and Evolutionary Biology and Institute of Arctic and Alpine Research, University of Colorado Boulder, Boulder, CO 80309
Timothy R. Seastedt*
Affiliation:
Department of Ecology and Evolutionary Biology and Institute of Arctic and Alpine Research, University of Colorado Boulder, Boulder, CO 80309
*
Corresponding author's E-mail: [email protected]
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Abstract

Predicting site vulnerability to nonnative plant establishment remains a difficult goal. Seedling survival is an important component of population dynamics and can affect the success of control strategies. Field manipulations allow potential causal mechanisms of site vulnerability to be evaluated under realistic environmental conditions. We conducted field studies to determine the effects of plant competition and differing precipitation regimes on spotted knapweed seedling survival. We also examined the effect of herbivory on rosette survival and growth. Seeds were sown into plots with vegetation intact or removed at three sites. Seeds were also sown into plots where plant competition and precipitation were manipulated in a factorial design at a single site. Field studies demonstrated that site accounted for much of the variation in emergence rate, while herbivory and plant competition affected seedling survival rates. We observed a wide range in emergence rates, with site averages ranging from 13.1 to 42.5%. Survival the following year ranged from 0.5 to 9.4% of sown seeds. Rosette survival was significantly higher when herbivores were excluded from plots. Below average precipitation reduced seedling survival; however, even with supplemental water, dry-down of exposed sites resulted in low seedling survival. Of the 8,000 seeds added to plots in one study, by autumn, only eight plants resulted, seven of which survived in watered plots with intact vegetation. Collectively, these results show that seedling survival is a critical phase in spotted knapweed population dynamics and can vary among habitats on the basis of plant competition and precipitation. Furthermore, herbivory affects all stages of the lifecycle from the seedling onward. The observed differences help explain the reported variability in seedling survival in the literature and inform efforts to control spotted knapweed using plant competition and biological controls.

Keywords

Spotted knapweed, Centaurea stoebe L. ssp. micranthos (Gugler) HayekHerbivoryinvasive plantsplant competitionseedling survivalspotted knapweed
Type
Research
Information
Invasive Plant Science and Management , Volume 6 , Issue 4 , December 2013 , pp. 568 - 576
Copyright
Copyright © Weed Science Society of America 

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Footnotes

Current address: Department of Integrative Biology, University of Colorado Denver, Denver, CO 80217

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