EXOTIC AND INVASIVE SPECIES IN UNITED STATES URBAN FORESTS

Date of Award

December 2014

Degree Type

Thesis

Degree Name

Master of Arts (MA)

Department

Geography

Advisor(s)

Jacob Bendix

Keywords

exotic species, invasive species, United States, urban forests

Subject Categories

Social and Behavioral Sciences

Abstract

The many benefits provided by urban forests, known as ecosystem services, have been the subject of extensive research. By contrast, exotic and invasive species are often considered detrimental to the natural environment, and there is another large body of work identifying the issues associated with them. However, there is little work identifying the overlap between exotic and invasive species and urban forests. This thesis is an attempt to bring these topics together by identifying how much of the urban forest is comprised of exotic and invasive species. Using data from the United States Forest Service on fourteen cities in the United States, the number of exotic invasive, exotic noninvasive and native noninvasive species and stems within each city was calculated. Species were classified as native or exotic based on range maps, and invasive or noninvasive based on state management plans. The proportion of native noninvasive species in each city ranged from 15.5% to 69.4%, with six of the cities having more than 50% of such species. Exotic noninvasive species comprised as little as 20.8% of urban forests to as much as 75.7%, with an average of 44.5% in each city. Only four cities had more than 10% exotic invasive species, which ranged from 4.6% to 15.2% of urban forest cover. The number of stems classified as native noninvasive ranged from 8.8% to 87.7% in any given city. Exotic noninvasive stems comprised between 3.5% and 67.5% of stems, while exotic invasive made up from as little as 1.7% to as much as 27.8% of stems within a city. This project also uses correlation and regression analyses, to examine which anthropogenic factors of cities may affect the prevalence of these species. The variance of exotic invasive, exotic noninvasive, and native noninvasive species and stem counts from city to city was found to be significantly affected by a number of anthropogenic factors, including population, population density, city area, city age, mean and median income, and percent renter occupied housing.

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