Browsing by Subject "earthworms"

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    Common buckthorn (Rhamnus cathartica), European earthworms, and ecosystem management: Invasion and restoration in Minnesota’s deciduous forests
    (2015-05) Roth, Alexander
    Common buckthorn (Rhamnus cathartica) and European earthworms are problematic invasive species in forests of the upper Midwest United States, and it is hypothesized that these two species may have a facilitative relationship. To better understand their invasion, it is necessary to understand how they interact with biotic and abiotic filters, as well as with each other. We established a greenhouse microcosm experiment to investigate the effects of important biotic and abiotic factors on buckthorn establishment and further explored the relationship between buckthorn and earthworms using a 24-plot field study. Using insights from our greenhouse results, we manipulated factors affecting plant colonization in a buckthorn removal experiment in order to improve buckthorn removal and ecosystem restoration efforts. Greenhouse results showed that the presence of earthworms increased buckthorn abundance and biomass across all light and leaf litter treatment levels, supporting the hypothesis that earthworms facilitate buckthorn invasion in upper Midwest forests. Results from the field study, conducted across a naturally-occurring gradient of buckthorn abundance, suggest that buckthorn, in turn, facilitates earthworms in this study system. Plots with higher buckthorn abundance had higher earthworm biomass, with linear regression, mixed model, and path analysis results supporting the directionality of the relationship. Together, these results lend support to a co-facilitative relationship between the two organisms. Co-facilitation my increase the success of both species and strengthen their negative impacts on native species and forest ecosystems. Finally, we tested three buckthorn removal methods (weed-wrenching, cut and paint, and basal bark herbicide application) chosen to differentially affect conditions controlling plant establishment. Removal plots differed in the subsequent cover and diversity of plant regeneration, with methods that disturbed soil and increased available light resulting in the highest species cover and diversity. Non-metric multidimensional scaling ordinations and indicator species analysis demonstrated that the resulting plant communities differed significantly in their species composition, with weed-wrench plots associated with more early-successional community assemblages. Ultimately, removal methods can differentially affect the regeneration of understory vegetation and affect future community succession. Understanding why and how a species invades can encourage a more scientific approach to invasive species management, potentially resulting in improved management outcomes.
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    Tree species effects on decomposition and forest floor dynamics in a common garden
    (Ecological Society of America, 2006) Hobbie, Sarah E; Reich, Peter B; Oleksyn, Jacek; Ogdahl, Megan; Zytkowiak, Roma; Hale, Cynthia; Karolewski, Piotr
    We studied the effects of tree species on leaf litter decomposition and forest floor dynamics in a common garden experiment of 14 tree species (Abies alba, Acer platanoides, Acer pseudoplatanus, Betula pendula, Carpinus betulus, Fagus sylvatica, Larix decidua, Picea abies, Pinus nigra, Pinus sylvestris, Pseudotsuga menziesii, Quercus robur, Quercus rubra, and Tilia cordata) in southwestern Poland. We used three simultaneous litter bag experiments to tease apart species effects on decomposition via leaf litter chemistry vs. effects on the decomposition environment. Decomposition rates of litter in its plot of origin were negatively correlated with litter lignin and positively correlated with mean annual soil temperature (MATsoil) across species. Likewise, decomposition of a common litter type across all plots was positively associated with MATsoil, and decomposition of litter from all plots in a common plot was negatively related to litter lignin but positively related to litter Ca. Taken together, these results indicate that tree species influenced microbial decomposition primarily via differences in litter lignin (and secondarily, via differences in litter Ca), with high-lignin (and low-Ca) species decomposing most slowly, and by affecting MATsoil, with warmer plots exhibiting more rapid decomposition. In addition to litter bag experiments, we examined forest floor dynamics in each plot by mass balance, since earthworms were a known component of these forest stands and their access to litter in litter bags was limited. Forest floor removal rates estimated from mass balance were positively related to leaf litter Ca (and unrelated to decay rates obtained using litter bags). Litter Ca, in turn, was positively related to the abundance of earthworms, particularly Lumbricus terrestris. Thus, while species influence microbially mediated decomposition primarily through differences in litter lignin, differences among species in litter Ca are most important in determining species effects on forest floor leaf litter dynamics among these 14 tree species, apparently because of the influence of litter Ca on earthworm activity. The overall influence of these tree species on leaf litter decomposition via effects on both microbial and faunal processing will only become clear when we can quantify the decay dynamics of litter that is translocated belowground by earthworms.