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A Legacy of Change: Historic Human Impact on Vegetation in the Arizona Borderlands Conrad Joseph Bahre. Tucson: University of Arizona Press, 1991 Reviewed by Ric h a r d w . Reev es Professor, Department of Geography and Regional Development University of Arizona Tucson, AZ 85721 SOUTHEASTERNARIZONAFIGURES prominentlyin the literature on historical ecological change. Successive generations of scholars, including several eminent geographers, have been intrigued by land­ scape alterations that followed the influx of Anglo settlers and livestock in the late nineteenth century. The principal changes— deterioration of grass cover, proliferation of woody species, desicca­ tionofriparianhabitats, arroyocutting—mayappearsubtlecompared to catastrophic landscape transformations that occurred elsewhere following American settlement. Still, modification ofanexotic, wild, sparsely populated region was perceived by many as somehow 239 240 APCG YEARBOOK • VOLUME 53 • 1991 different, lessobviouslyexplained, anddeservingofspecial attention. Bahre’s Legacy of Change concentrates on the region’s vegetation changes and clearly represents the most comprehensive and readable treatment of the subject so far produced. Preoccupationwith southeasternArizonaderivesfromits seminal role in the protracted academic debate over human/nature relation­ ships. Published descriptions ofrapid rangeland deterioration began to appear in the 1890s, when it was still occurring, and these were followed shortly by accounts of increased flooding, active gullying, and widespread erosion of river channels. Explaining these changes was a principal research objective. Two responsible agents, human vs. natural (i.e., climatic), were eventually identified, and their rela­ tive roles have been weighed and argued ever since. Views have moderated overtime, butdistinctelementsofboth environmental and cultural “determinism” are still detectable, even in work published during the past few years. The dialectics of debate in the region are instructive in that they runcountertocommonnotionsofphilosophicalevolutioninAmerican geography. Theinitial“thesis,”subsumingall speculationoncausality published between 1891 and 1914, indicted human actions and often included sermonettes on human folly and/or remedial prescriptions. Changes are attributed to Anglo settlement and its intensified land uses, with particular references to introduction of livestock, overgrazing , trampling of plants and soils, fire suppression, harvesting natural hay, woodcutting, expansion of irrigated agriculture, and formation of trails and roads. It seems that “man’s role in changing the face of the earth,” or atleast parts ofit, was keenly appreciatedby some academics more than sixty years before rediscovery of George Perkins Marsh and at least three decades before Carl Sauer moved to Berkeley. The stream of work asserting humanresponsibilityflowsright up to the present day, and includes some excellent attempts to model, test, or establish aspects of this proposition. The overwhelming majority of investigators who addressed vegetation change in the REEVES: Review ofA Legacy of Change 241 region, andperhaps halfofthoseinterestedprimarily in hydraulic and erosional changes, have favored purely human explanations. The first advocate of the climatic “antithesis” was Ellsworth Huntington (1914), although J.L. Rich had raised and rejected this possibility afew years earlierin his treatmentofarroyo cutting across the border in southwestern New Mexico. Huntington considered causal links between climate and vegetation cover, and between both ofthese phenomena and erosional activity. He applied these ideas to his interpretation of historic arroyo formation and prehistoric cycles oferosion anddepositionthathedetectedfromstratographic evidence alongthe SantaCruzRivernearTucson. Ignoringrecentdeterioration of the region’s grasslands, Huntington hypothesized that “shifts” in climate toward wetter conditions were responsible for increased runoff and thus channel erosion, both past and present, although he concededthatrecentland-usechanges mayhave actedto“trigger”the historical episode. Here, at least for Huntington, was a meaningful example ofongoing climatic change andits effects on prehistoric and contemporary human settlement. Kirk Bryan (1928) revised Huntington’s model to better fit historical facts and erosional mechanics and went on to champion his view—that a change of climate toward drier conditions depleted vegetation andinitiatederosion—in ascoreofpublicationsduring the 1930s, 1940s, and 1950s. Bryan’s model had great appeal for Southwestern archaeologists who employed it repeatedly in inter­ pretations of Southwestern prehistory, especially the decline of the Hohokam and Pueblocultures, although some workers, most notably Antevs (1952), were skeptical of climate’s role in historic events. More sophisticated climatic models have ensued, and some indepen­ dent evidence has been found in the region’s tree-ring records and historical rainfall data to suggest modest secular or long-period climatic variations. In The Changing Mile, until now the most comprehensivestatementonhistoricvegetationchangeinsoutheastern Arizona, Hastings and Turner (1965) assigned the major role to climatic...

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