Research about Southwest | Geology Reports

USGS2002

Satellite imagery characterizes local animal reservoir populations of Sin Nombre virus in the southwestern United States

The relationship between the risk of hantaviral pulmonary syndrome (HPS), as estimated from satellite imagery, and local rodent populations was examined. HPS risk, predicted before rodent sampling, was highly associated with the abundance of Peromyscus maniculatus , the reservoir of Sin Nombre virus (SNV). P. maniculatus were common in high-risk sites, and populations in high-risk areas were skewed toward adult males, the subclass most frequently infected with SNV. In the year after an El Niño Southern Oscillation (ENSO), captures of P. maniculatus increased only in high-risk areas. During 1998, few sites had infected mice, but by 1999, 18/20 of the high-risk sites contained infected mice and the crude prevalence was 30.8%. Only 1/18 of the low-risk sites contained infected rodents, and the prevalence of infection was lower (8.3%). Satellite imagery identified environmental features associated with SNV transmission within its reservoir population, but at least 2 years of high-risk conditions were needed for SNV to reach high prevalence. Areas with persistently high-risk environmental conditions may serve as refugia for the survival of SNV in local mouse populations.

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USGS1951

Vegetation of Southwestern watersheds in the nineteenth century

The recollections of many old-timers who tell of grass “stirrup high” have given rise to the idea that vegetation in the Southwest was uniformly better in the middle of the last century than it is at present. The change is usually attributed to overgrazing, which timed if it did not cause extensive gullying of the alluvial valleys, I lowering the water table and decreasing the availability of water for plant use. This idea of an originally verdant vegetation, deteriorated as a result of man’s activities, has led to overoptimism concerning the possible results of reduced grazing. Obviously, any decrease in grazing pressure is a step in the right direction, but it is no exaggeration to say that recovery fo vegetation density on depleted ranges, even after protection for years, has been spotty and, in many places, disappointing. We may have allowed ourselves to be deluded by hopes of ‘restoring’ over large areas a level of vegetation density that was originally attained only in selected localities. This conclusion is supported by the published diaries and field notes of members of early American exploring parties. They show that in certain places, particularly in south-central Arizona where grass is now meager, the alluvial valleys formerly supported large expanses of grassland. However, there were also many areas, even alluvial valleys, where grass was so poor that forage for a string of horses could hardly be obtained. Other areas, such as the Rio Puerco Valley, supported good grass in some places but only scattered shrubs, furnishing poor forage, in others, though until well past the middle of the nineteenth century extensive grazing had been prevented by frequent raids of hostile Indians.

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