Experiments on Multiple Factors Affecting Pinaceae Invasions on Isla Victoria, Nahuel Huapi National Park, Argentina

Invasive species are one of the greatest threats to global biodiversity. Therefore, to conserve biodiversity and manage exotic species effectively, it is crucial to determine the factors that regulate biological invasions. Historically, the study of invasions has focused on the dynamics and characteristics of successful invasive species. While studying successful invaders has enhanced our understanding of biological invasions, studying the failures can also illuminate the factors that limit invasions. To further understand the factors limiting the spread of exotic species, I studied invasion dynamics of several species in the family Pinaceae on Isla Victoria, Argentina. Approximately 80 years ago, thousands of trees of at least 135 non-native tree species were planted on Isla Victoria, many of them in the Pinaceae, but few species have escaped the plantation. I tested whether herbivory by exotic deer, seed predation or mycorrhizal facilitation might limit the spread of pine species from plantations. To test whether preferential herbivory by deer on non-native species plays a role, I conducted a cafeteria experiment. Deer browsed more intensively on native species than on exotics, suggesting that deer could potentially facilitate invasion by exotic Pinaceae. To test if seed predation limits exotic conifer establishment, I studied seed predation using field experiments. Seeds of exotics were preferred over seeds of native species, and predation was more intense in areas far from plantations than near plantations, reducing the chances of exotic seed establishment. To test the role of ectomycorrhizal symbiosis on invasion I conducted a series of experiments, in which I found that the lack of proper ectomycorrhizal fungi could limit invasion. Seedling establishment and growth rates were higher near inoculum sources (plantations) than far from such sources. Ectomycorrhizal colonization rates where higher near plantations than far from them, showing that mycorrhizal interactions could be important for understanding plant invasion. Together these studies suggest that pine invasion in Isla Victoria can be controlled by a suite of, to date, underappreciated factors.