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Community Assembly and Dynamics of the Forests of Powdermill Nature Reserve (Rector, PA)

Murphy, Stephen J.
http://orcid.org/0000-0001-8679-2851
http://rave.ohiolink.edu/etdc/view?acc_num=osu153200426920788

Abstract Details

2018, Doctor of Philosophy, Ohio State University, Evolution, Ecology and Organismal Biology.
The Eastern Deciduous Forest (EDF) is one of the most well studied biomes on the planet, yet we still lack an understanding of the fundamental processes influencing the patterns and dynamics of this system. Competition for light in both shaded understories and gaps drives a large portion of the successional dynamics in the EDF, with species shade-tolerance being a key life-history trait. However, this single trait axis alone cannot explain the rich diversity and heterogeneity of this ecosystem, and it is thus necessary to look to other mechanisms that could be influencing the community assembly and dynamics of temperate forests in the Eastern United States. Here, I examine the role of environment, history, chance, and biotic interactions on the assembly and dynamics of a temperate hardwood forest in southwestern Pennsylvania (Powdermill Nature Reserve), with a specific focus on the factors influencing understory seedling demography. I use a large dataset on ~40,000 trees to map compositional heterogeneity across the 900-hectare area of the reserve. I find that a large amount of the variation in species composition is controlled by topographic position and soil type, suggesting the importance of spatial variability in moisture, soil chemical and physical properties, and microclimate. When combined with spatial descriptor variables derived from geographic coordinates, these data accounted for half of the total variation in the site-by-species matrix. Next, I compared patterns in the adult tree community to understory dynamics in the seedling layer. At 51 locations, I established four 1 × 10 m plots to sample seedlings, which I marked and tracked from 2013 to 2016. I found that seedlings tended to be clustered around conspecific adults, likely due to limited dispersal from parents, but that these positive correlations weakened over time as seedlings died. These patterns suggest strong negative conspecific distance and/or density dependent (CNDD) interactions between adults and seedlings. This was particularly true for Acer rubrum, which showed a strong negative exponential relationship between adults and seedlings across all four census years. For most species, mortality was correlated with environmental variables, but these mortality events did not lead to seedling communities becoming more similar to the adult community over time, suggesting contrasting plant~environment relationships across life stages. Next, I explored the issue of conspecific negative density dependence more directly by asking whether an abundant and widespread grazer, Odocoileus virginianus, is capable of mediating CNDD for specific seedling populations. I found strong evidence for CNDD in seedlings, and these effects were dependent on species identity and the specific demographic rate being analyzed. Most interestingly, I observed a weakening of CNDD for two abundant taxa (Prunus serotina and Fraxinus spp.) in plots that were denied access by deer herbivory, suggesting that deer, in combination with other natural enemies, can help to maintain species coexistence in this forest. Together, my results point to the importance of local interactions between trees, the environment, and white-tailed deer, in driving community dynamics in the Eastern Deciduous Forest.
Liza Comita (Advisor)
Peter Curtis (Committee Chair)
Maria Miriti (Committee Member)
Stephen Hovick (Committee Member)
187 p.
Biology; Botany; Ecology; Environmental Science; Experiments; Forestry; Plant Biology

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Citations

  • Murphy, S. J. (2018). Community Assembly and Dynamics of the Forests of Powdermill Nature Reserve (Rector, PA) [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu153200426920788

    APA Style (7th edition)

  • Murphy, Stephen. Community Assembly and Dynamics of the Forests of Powdermill Nature Reserve (Rector, PA). 2018. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu153200426920788.

    MLA Style (8th edition)

  • Murphy, Stephen. "Community Assembly and Dynamics of the Forests of Powdermill Nature Reserve (Rector, PA)." Doctoral dissertation, Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu153200426920788

    Chicago Manual of Style (17th edition)

osu153200426920788
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This open access ETD is published by The Ohio State University and OhioLINK.