Activities of American Geographers

Cognitive distance is analyzed in relation to various elements of the built environment. The basis for accepting a power function as the underlying functional relationship between cognitive distance and its objective counterpart is discussed. This counterpart has been assumed to be objective distance. Evidence is presented to indicate that cognition of distance is based upon travel time rather than upon objective distance or upon objective distance modified by other elements of the built environment.     

Downstream hydrologic and geomorphic effects of large dams on American rivers

The hydrology and geomorphology of large rivers in America reflect the pervasive influence of an extensive water control infrastructure including more than 75,000 dams. One hundred thirty-seven of the very large dams, each storing 1.2 km³ (10⁶ acre feet) of water or more, alter the flows of every large river in the country. The hydrologic effects of these very large dams emerge from an analysis of the stream gage records of 72 river reaches organized into 36 pairs. One member of each pair is an unregulated reach above a dam, whereas the other is a regulated reach downstream from the same structure. Comparison of the regulated and unregulated reaches shows that very large dams, on average, reduce annual peak discharges 67% (in some individual cases up to 90%), decrease the ratio of annual maximum/mean flow 60%, decrease the range of daily discharges 64%, increase the number of reversals in discharge by 34%, and reduce the daily rates of ramping as much as 60%. Dams alter the timing of high and low flows and change the timing of the yearly maximum and minimum flows, in some cases by as much as half a year. Regional variation in rivers, dams, and responses are substantial: rivers in the Great Plains and Ozark/Ouachita regions have annual maximum/mean flow ratios that are 7 times greater than ratios for rivers in the Pacific Northwest. At the same time, the ratio of storage capacity/mean annual water yield for dams is greatest for Interior Western, Ozark/Ouachita and Great Plains rivers and least for Pacific Northwest streams. Thus, in many cases those rivers with the highest annual variability have the greatest potential impact from dams because structures can exert substantial control over downstream hydrology. The hydrologic changes by dams have fostered dramatic geomorphic differences between regulated and unregulated reaches. When compared to similar unregulated reaches, regulated reaches have 32% larger low flow channels, 50% smaller high flow channels, 79% less active flood plain area, and 3.6 times more inactive flood plain area. Dams also affect the area of active areas, the functional surfaces that are functionally connected to the present regime of the river. Regulated reaches have active areas that are 72 smaller than the active areas of similar unregulated reaches. The geomorphic complexity (number of separate functional surfaces per unit of channel length) is 37% less in regulated reaches. Reductions in the size of hydrologically active functional surfaces are greatest in rivers in the Great Plains and least in Eastern streams. The largest differences in geomorphic complexity are in interior western rivers. The shrunken, simplified geomorphology of regulated large rivers has had direct effects on riparian ecology, producing spatially smaller, less diverse riparian ecosystems compared to the larger, more complex ecosystems along unregulated reaches of rivers.     

Regional aboveground biomass equations for North American arid and semi-arid forests

Calculations of dry tree, plot and regional aboveground biomass, M, and assessments of complex diverse forests remain key challenges in the implementation of conventional and sustainable projects. This study reports a set of robust regional equations and the application of several allometric tree and plot M equations in Mexican arid and semi-arid forest communities. The data were collected from 1084 tree M fitting models, and 195 arid and semi-arid and 206 mesquite trees and 55 plot datasets were used to validate the models. Theoretical, semi-empirical and empirical models with exogenous variables, as well as wood specific gravity, diameter, top height, and form-factor values, were used to evaluate aboveground biomass. Empirical computer-based equations projected more consistently similar tree M assessments than did semi-empirical or theoretical models. Therefore, empirical models are recommended for assessments of tree and plot M, and future allometry research should properly address independent variables in more theoretical models. The large sample size, model richness, economic and ecological importance, and wide coverage of this dataset make it useful for estimating several biogeochemical and bioenergy density parameters and contribute to the body of knowledge regarding heterogeneity in dry forest stand structures.     

The Three American Wests

In the twenty-first century, there are three American Wests, which cut across cultural, political, physical, and economic boundaries. Parts of the West are booming, building homes, and adding population; others are legally off limits to such development; and much of the West has been bypassed by such development and growth. These are called here the Booming West, Protected West, and Bypassed West. Maps of climate, political boundaries, ethnic and racial identities, or presidential voting patterns do not match these three Wests. Each West has a different relationship to the others and might see them as threats or opportunities, and each West can be expected to grow in different areas at the expense of other Wests. The boundaries between the three Wests could be important locations; sharp transitions can exist between Wests, perhaps nowhere more so than where a fast growing metro area abuts a national park or forest boundary. Finally, the effects of climate change cut across the three Wests and have different implications for their future. Continued population growth will further emphasize the boundaries between each of the three Wests and raise the stakes for their control.     

Activities of American Geographers

BRITAIN-An informal review by L. Dudley Stamp.     

Activities Of American Geographers

Finnish Immigrants in America, 1880–1920. A. William Hoglund.

Geology of the Industrial Rocks and Minerals. Robert L. Bates.

Readings in Culturul Geography. Philip L. Wagner AND Marvin W. Mikesell, eds.

Anglo-America: A Regional Geography of the United States and Canada. P. F. Griffin, R.N. Young, AND R.L. Chatham

Undergraduate Education in Foreign Affirs. Percy W. Bidwell.

Crevecoeur's Eighteenth-Century Travels in Pennsylvania and New York. Michel-Guillaume: Jean DE Crevecoeur. Percy G. Adams, trans. and ed.

Canada and the Canadians: Profile of a Modern Nation. Alistair Horne.

Four Thousund Years Ago: d Panorama of Life in the Second Millennium B.C. Geoffrey Bibby.

Interpretation of Aerial Photographs. T. Eugene Avery.

A Geography of the U.S.S R.: The Background to a Planned Economy. J.P. Cole AND F.C. German.

Report on the Lands of the Arid Region of the United States, with a More Detailed Account of the Lands of Utah. John Wesley Powell. Wallace Stegner, ed.     

South American heartland: the Charcas, Latin American geopolitics and global strategies

Mackinder's 1904 'geographical pivot of history' concept, subsequently developed into his famous 'Eurasian heartland thesis', marginalizes South America, yet his ideas have attracted considerable interest there, including interpretations (and fantasies) of a 'South American heartland'. This paper examines the reception of Mackinder's ideas in Latin American geopolitics and how his heartland thesis was adapted for the South American context. It traces the roots of this adaptation in earlier South American geopolitical writing, and examines these ideas of counter-insurgency policies and global geopolitical strategies, analysing their relationship to military and anticommunist perspectives.     

North American Cartographic Information Society

Multivariate classifications of intra-urban retailing centers have been based almost exclusively on functional variables. This paper advocates, by using a case study, the application of standard multivariate techniques to non-functional and mixed-variable data sets, a procedure that has implications for parsimonious field inventories at a time of accelerated commercial change.