Date Thesis Awarded
Honors Thesis -- Access Restricted On-Campus Only
Bachelors of Science (BS)
Biodiversity loss is occurring at an unprecedented and alarming rate; we can no longer ignore the effects of humans on the environment and must take action to reduce our impact (Pimm 1995). Restoration of degraded communities and ecosystems can reduce biodiversity loss (Seddon 2007, Armstrong and Seddon 2008). Restoration strategies, sometimes referred to as the “restoration toolbox,” encompass many specific techniques one of which is the reintroduction of individual species (Sodhi and Ehrlich 2010). Re-introductions are the introduction of individuals from a different population of a species to an endemic region of the species, where populations have been eliminated due to natural processes or anthropogenic factors (Sodhi and Ehrlich 2010). Species re-introductions are an important tool in biological conservation; however, they often are unsuccessful or require more resources than expected as it is difficult to predict how a new population will grow (Sarrazin and Barbault 1996, Seddon 2007). California condors (Gymnogyps californianus) and the grey wolf (Canis lupus) are examples of highly successful re-introductions of animal populations (Wilmers 2003, Ralls and Ballou 2004, Ripple 2001). However, there have been few attempts at re-introducing a plant species. Instead plant re-introductions have largely been used only as a part of whole ecosystem restorations. American chestnut (Castanea dentata; chestnut henceforth) offers a potential for intentional plant re-introduction (Jacobs 2007, Jacobs et al. 2013). American chestnut has been called a foundation species in the Eastern United States because it was important for regulating nutrient cycling and decomposition (Ellison 2005), as well as food web dynmaics (Dalgleish & Swihart 2012). Foundation species are unlike keystone species in that they are high in number and widespread, yet similar in that they are important in determining the structure and stability of local ecosystems (Ellison 2005). Trees are often foundation species in forest ecosystems; the presence or absence of specific plant populations have the potential to strongly affect ecosystem structure and health. The American chestnut was a prominent tree in eastern forests from Maine to Georgia in early American history (Jacobs et al. 2013). American chestnut trees impact community and ecosystem processes, such as insect, soil, small mammal, and bird communities, as well as tree composition. In 1905, the fungus Cyphonectria parasitica was accidentally introduced in New York Zoological Garden and quickly spread throughout the range of the American chestnut infecting adult chestnuts of the estimated three to four billion trees in a period of 50 years (Zhang 2013, Welch 2006). The fungus enters chestnut trees through cracks in the bark which are characteristic of older chestnuts or tree wounds, and spreads to the cambium creating cankers that prevents the flow of nutrients (Welch 2006). Restoring American chestnut with a blightresistant chestnut tree has been explored by the American Chestnut Foundation and other researchers since the 1920s. Scientists have experimented with multiple possibilities for creating blight resistance in American chestnut trees including crossbreeding with Asian chestnut trees (primarily Chinese chestnut, Castanea mollissima), infecting trees with a hypovirulent (nonlethal) strains of the blight, C. parasitica, and genetic modification (Jacobs et al. 2013). American chestnut may be important to restoration of forest communities as there is a possibility for the re-introduction of blight resistant chestnut. This is perhaps one of the first opportunities for tree re-introduction and may serve as a model for future plant re-introductions. Monitoring re-introduction projects and modeling the growth of populations are ways to ensure restoration efforts may be achieved. Matrix population models are size structured models that can be used to project population growth rate for re-introduced populations, and offer specific information on what life stages or transitions are the most important for targeting management to enhance population establishment (Morris and Doak 2002). If the population growth rate is declining, it indicates that the population may not be viable without management action or change in environmental factors (Morris and Doak 2002). The rate of decline could be due to many factors. Sensitivity and elasticity values (prospective analysis of matrix models, (Caswell 2001)) can help determine what life stages and transitions are most important to the population growth rate, and thus how to target management strategies. Population models also offer the ability to mathematically experiment with different re-introduction scenarios (Morris and Doak 2002). While significant population monitoring of growth, survival, and reproduction is necessary to create a viable model, population models that advise management can enhance the success of species reintroductions (Morris and Doak 2002). My study creates a matrix population model of a young population of American chestnuts with the goal of informing restoration efforts using blight-resistant, back-crossed American chestnut. My research provides a detailed demographic study for a site just north of the historical range of chestnut experiencing similar annual environmental effects that re-introduced populations in the Northeast may face. The goals of my study are 1) to measure growth, survival, and reproduction of a chestnut population under natural conditions 2) to develop a matrix model that can be used to inform restoration, and 3) to use the model to explore possible restoration scenarios.
Elwood, Elise C., "Population Matrix Model for American Chestnut (Castanea dentata) and the Implications for Re-introduction" (2014). Undergraduate Honors Theses. William & Mary. Paper 88.
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