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  • 1.
    Huels, Joerg
    et al.
    Justus-Liebig-University Giessen, Germany.
    Otte, Annette
    Justus Liebig University Giessen, Germany.
    Eckstein, R. Lutz
    Justus-Liebig-University Giessen, Germany.
    Population life-cycle and stand structure in dense and open stands of the introduced tall herb Heracleum mantegazzianum2007In: Biological Invasions, ISSN 1387-3547, E-ISSN 1573-1464, Vol. 9, no 7, p. 799-811Article in journal (Refereed)
    Abstract [en]

    Populations of the introduced Heracleum mantegazzianum consist of dense central stands, which gradually give way to open stands towards the margins. To analyse whether open stands are due to unsuitable conditions or represent the invading front for further spread, we studied life-cycle, population dynamics, stand structure and soil conditions of open and dense stands over two transition periods. Populations decreased during the first interval but increased after the extremely dry and warm summer of 2003 during the second interval. Open stands had shorter generation times, lower height, smaller proportions of small individuals and were less in equilibrium with the environment than dense stands. In open stands, growth to higher stages was most important, while in dense stands delayed development (self-loops) had a strong effect on population growth; stasis and fecundity contributed most to the difference in lambda between stand types. By petiole extension H. mantegazzianum may raise its leaves just above the resident vegetation. Therefore, younger stages develop faster in open stands, whereas strong competition by conspecific adults leads to longer generation times and a higher proportion of small individuals in dense stands. Disturbance due to extreme climatic conditions in summer 2003 equalised population dynamics of both stand types. Life-cycle variation between stand types makes it difficult to infer simple management rules. However, our data suggest that small and/or open stands of H. mantegazzianum may eventually serve as initials for further spread after land-use changes, whereas dense stands are stable and may represent sources of propagules.

  • 2.
    Klinger, Yves P.
    et al.
    Liebig University Giessen, Germany.
    Harvolk-Schöning, Sarah
    Liebig University Giessen, Germany.
    Eckstein, Rolf Lutz
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Hansen, Wiebke
    Liebig University Giessen, Germany.
    Otte, Annette
    Liebig University Giessen, Germany.
    Ludewig, Kristin
    Liebig University Giessen, Germany.
    Applying landscape structure analysis to assess the spatio-temporal distribution of an invasive legume in the Rhön UNESCO Biosphere Reserve2019In: Biological Invasions, ISSN 1387-3547, E-ISSN 1573-1464, Vol. 21, no 8, p. 2735-2749Article in journal (Refereed)
    Abstract [en]

    Landscape composition and structure may strongly affect the spread of invasive species in landscapes. Landscape analysis provides a powerful toolset for assessing invasive species invasions over time and for planning control measures. We applied a combination of aerial mapping and landscape analysis to assess the invasion of the legume, Lupinus polyphyllus, in the Rhön UNESCO Biosphere Reserve. The Biosphere Reserve contains different types of large and well-connected grasslands threatened by lupine invasion. We assessed the changes in lupine distribution between 1998 and 2016 in a strictly protected part of the Biosphere Reserve by means of landscape structure analysis. The area invaded by L. polyphyllus doubled from 1998 to 2016. While the number of lupine stands decreased by 25%, stand size on average increased by 300%; stands also became less compact during that period. Furthermore, the degree of invasion of different grassland types changed. In 1998, all investigated grassland types were invaded to equal extents, whereas in 2016, large and well-connected mesic grasslands located close to roads were more heavily invaded than small and remote wet grasslands. Our results show that landscape composition plays an important role for the spread of lupine. Specifically, invasive stand characteristics, such as stand size, form, and connectivity, are crucial for driving the invasion of lupine. Therefore, in addition to landscape composition, invasive stand characteristics should be included in the planning of conservation measures. Overall, aerial mapping combined with landscape analysis provides a cost-effective and practical tool for landscape managers to prioritize invasive control measures.

  • 3. Loydi, A.
    et al.
    Donath, T. W.
    Eckstein, Rolf Lutz
    Justus-Liebig University, Giessen, Germany.
    Otte, A.
    Non-native species litter reduces germination and growth of resident forbs and grasses: allelopathic, osmotic or mechanical effects?2015In: Biological Invasions, ISSN 1387-3547, E-ISSN 1573-1464, Vol. 17, no 2, p. 581-595Article in journal (Refereed)
    Abstract [en]

    Non-native plant species may contain allelopathic substances that might help to out-compete native vegetation. These allelochemicals may be released from live or dead plant tissues and be accumulated in the soil. We tested whether non-native species leaf litter and their leachates reduced seedling establishment and growth of native species. We subjected seeds of six native species to the effect of litter leachates of three of the most important invasive plants in Europe and to mannitol solutions with similar osmotic potential in germination chamber experiments. Additionally, we measured the effect of the same litter on emergence and growth of the native species in an outdoor pot experiment. Litter leachates delayed and reduced germination and affected initial root growth of all native species. The effects of leachates were significantly higher than those of mannitol, indicating the action of toxic, most probably allelochemical substances. Emergence of seedlings in pots was also reduced, but total biomass per pot was not affected and biomass per seedling increased. Allelochemicals may affect germination and early stages of seedling recruitment. However, these negative effects seem to cease shortly after germination, when other mechanisms such as competition may be more important. Consequently, litter-borne allelochemicals are unlikely to drive the invasion of the studied non-native species, but they may contribute to maintain mono-dominant stands reinforcing invasion success.

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