Overstorey tree species regulate colonization by native and exotic plants: a source of positive relationships between understorey diversity and invasibility

Authors

  • Kathleen S. Knight,

    1. Department of Ecology, Evolution, and Behaviour, University of Minnesota, 100 Ecology Building, 1987 Upper Buford Circle, St. Paul, MN 55108-6112, USA,
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  • Jacek Oleksyn,

    1. Department of Forest Resources, University of Minnesota, 115 Green Hall, 1530 Cleveland Avenue N., St. Paul, MN 55108-6112, USA,
    2. Institute of Dendrology, Polish Academy of Sciences, Parkowa 5, PL-62-035 Kórnik, Poland,
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  • Andrzej M. Jagodzinski,

    1. Institute of Dendrology, Polish Academy of Sciences, Parkowa 5, PL-62-035 Kórnik, Poland,
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  • Peter B. Reich,

    1. Department of Forest Resources, University of Minnesota, 115 Green Hall, 1530 Cleveland Avenue N., St. Paul, MN 55108-6112, USA,
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  • Marek Kasprowicz

    1. Department of Plant Ecology and Environmental Protection, Adam Mickiewicz University, Umultowska 89, PL-61-614 Poznań, Poland
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Kathleen S. Knight, USDA Forest Service, 359 Main Road, Delaware, OH 43015, USA. Tel.: +1 740-368-0063; E-mail: laca0023@umn.edu

ABSTRACT

The North American woody species, Prunus serotina Ehrh., is an aggressive invader of forest understories in Europe. To better understand the plant invasion process, we assessed understorey plants and Prunus serotina seedlings that have colonized a 35-year-old replicated common-garden experiment of 14 tree species in south-western Poland. The density and size of established (> 1 year old) P. serotina seedlings varied among overstorey species and were related to variation in light availability and attributes of the understorey layer. In a multiple regression analysis, the density of established P. serotina seedlings was positively correlated with light availability and understorey species richness and negatively correlated with understorey species cover. These results suggest that woody invader success is adversely affected by overstorey shading and understorey competition for resources. Simultaneously, however, invader success may generally be positively associated with understorey species richness because both native and invasive plant colonization respond similarly to environmental conditions, including those influenced by overstorey tree species. Identification of characteristics of forests that increase their susceptibility to invasion may allow managers to target efforts to detect invasives and to restore forests to states that may be less invasible.

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