Efforts to reintroduce and maintain populations of pronghorn (Antilocapra americana) to the California Central Valley, specifically the Carrizo Plain National Monument (CPNM) and the Mojave Desert (Antelope Valley) portion of Tejon Ranch, have largely been unsuccessful due to dwindling numbers of translocated animals. The objective of this study was to improve upon previous models for the CPNM using aerial survey data and then apply the model to the Tejon Ranch. Aerial survey data collected from 2000-2010 on the CPNM was used to establish “use” and “non-use” areas in the model. Model variables included vegetation type (forest, shrub, grassland, semi-desert scrub, crops, and bare areas), slope, and road density. Vegetation and road density variables were treated categorically and slope as a continuous variable. Kernel density estimation (KDE) was used to estimate utilization distributions and home ranges (Fieberg 2007). An 80% isopleth was used to define “used” and “unused” habitat areas within the study site. Binary logistic regression was used to detect correlations between habitat variables and habitat use by pronghorn. Results of the regression analysis indicated overall significance with a p-value of < 0.0001 (testing that all slopes = 0). Each habitat variable comparison was made after adjusting for the other variables (e.g., slope effects were evaluated after adjusting for road density and vegetation type) and was found to be significant. Each variable coefficient was then included in a predictive equation and entered into GIS to generate a map to predict where pronghorn would likely be observed. Similar layers were created for the Tejon Ranch and the predictive equation was run with the CPNM statistical analysis. Limited conclusions about habitat suitability on the CPNM or the Tejon Ranch can be made based on the habitat data available for this model. While slope, road density, and vegetation type are all significant habitat variables influencing pronghorn habitat use, further study is needed to understand the mechanisms driving these relationships. With additional data expansion of the current habitat suitability model would help to further define pronghorn habitat use, specifically the creation of a focused model of a particular season, life history period, or individual animal use to identify more detailed habitat use patterns.

Les historiens de l’environnement s’attachent à déchiffrer les modes de relation entre l’homme et la nature aux Etats-Unis. La manière dont elle est définie conditionne les politiques environnementales, et donc contribue à la transformation matérielle du continent. Cinq traditions de la pensée environnementale américaine sont décrites : la nature comme ressource transformée par le travail ; le préservationnisme ; le conservationnisme ; l’écologie ; et la justice environnementale. Ces idées perdurent au XXIème siècle dans les discours construits au sujet de la nature : elles se juxtaposent ou se confrontent. L’objectif de ce travail est de savoir si elles se transforment, en évoluant vers une définition de la relation homme/nature comme hybride socionaturel. À cette fin, trois cas sont étudiés, tous situés dans la région de Los Angeles au début des années 2000. Le premier concerne le ranch Tejon, dont l’accord passé en 2008 entre associations de protection de la nature et propriétaires pose la question du sens donné à une préservation qui veut prendre en compte les aspects à la fois écologiques, mythiques et économiques de ce territoire, vestige du passé de l’Ouest. Le second se rapporte à la décision prise en 2007 par la ville de Los Angeles de revitaliser son fleuve et fournit un exemple de l’élargissement de la définition de la nature : celle-ci peut être urbaine. Enfin, troisième cas, la justice environnementale appliquée à la ferme communautaire de South Central Los Angeles, entretenue de 1994 à 2006, est signe de la transition de la pensée de la nature américaine d’un objet délimité dans l’espace vers une problématique mondiale. / Environmental historians have worked at redefining the modes of relationship between man and nature in the United States. The way this relation is defined conditions environmental politics, and therefore contributes to the material transformation of the continent. Five major trends of thought about nature are described: nature as a resource transformed by work ; preservationism ; conservationism ; ecology ; and environmental justice. Those ideas endure to this very day in the discourses constructed about nature: they either juxtapose or confront each other. The goal of this thesis is to understand whether they undergo a transformation, evolving towards a definition of the man/nature relationship as a socionatural hybrid. To this end, three cases are examined here, all of which are connected with the Los Angeles area in the early 2000s. The first concerns Tejon Ranch and the agreement passed in 2008 about Tejon Ranch between environmental associations and the owners : it poses the question of the meaning given to a preservation that would incorporate ecological, mythical and economic aspects of that territory, a remain of the Western past. The second deals with the decision that was made in 2007 by the City of Los Angeles to revitalize its river and offers a good example of the broadening of the definition of nature: it can also be urban. The ecological and cultural preoccupations about the river complicate the conservation problematic in Southern California. Finally, South Central Farm’s environmental justice case (1994-2006) is the sign of a transition in American environmental ideas from a clearly spatially limited object to a world issue.