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W. G. Spaulding

Publications and source records attributed to W. G. Spaulding.

4 recordsLinked to original sources
USGS2002

Ploidy race distributions since the Last Glacial Maximum in the North American desert shrub, Larrea tridentata

A classic biogeographic pattern is the alignment of diploid, tetraploid and hexaploid races of creosote bush ( Larrea tridentata ) across the Chihuahuan, Sonoran and Mohave Deserts of western North America. We used statistically robust differences in guard cell size of modern plants and fossil leaves from packrat middens to map current and past distributions of these ploidy races since the Last Glacial Maximum (LGM). Glacial/early Holocene (26–10 14 C kyr bp or thousands of radiocarbon years before present) populations included diploids along the lower Rio Grande of west Texas, 650 km removed from sympatric diploids and tetraploids in the lower Colorado River Basin of south-eastern California/south-western Arizona. Diploids migrated slowly from lower Rio Grande refugia with expansion into the northern Chihuahuan Desert sites forestalled until after ~4.0 14 C kyr bp . Tetraploids expanded from the lower Colorado River Basin into the northern limits of the Sonoran Desert in central Arizona by 6.4 14 C kyr bp . Hexaploids appeared by 8.5 14 C kyr bp in the lower Colorado River Basin, reaching their northernmost limits (~37°N) in the Mohave Desert between 5.6 and 3.9 14 C kyr bp . Modern diploid isolates may have resulted from both vicariant and dispersal events. In central Baja California and the lower Colorado River Basin, modern diploids probably originated from relict populations near glacial refugia. Founder events in the middle and late Holocene established diploid outposts on isolated limestone outcrops in areas of central and southern Arizona dominated by tetraploid populations. Geographic alignment of the three ploidy races along the modern gradient of increasingly drier and hotter summers is clearly a postglacial phenomenon, but evolution of both higher ploidy races must have happened before the Holocene. The exact timing and mechanism of polyploidy evolution in creosote bush remains a matter of conjecture.

Arizona, Baja California, Baja California Sur, Cal↗
USGS1984

Preliminary assessment of climatic change during Late Wisconsin time, southern Great Basin and vicinity, Arizona, California, and Nevada

Nine plant macrofossil assemblages from the Eleana Range-2 packrat (Neotoma sp.) midden span 6,500 radiocarbon years and record local vegetational changes in the southern Great Basin of Nevada during the last one-half of the Late Wisconsin glacial age. Climatic reconstructions were developed to account for these changes. During the late full glacial episode (17,000 to 15,000 radiocarbon years before the present), winter precipitation was about 70% greater than present winter precipitation, and summer rainfall was minimal. Average annual precipitation probably exceeded present annual precipitation by less than 40%. Annual temperatures were about 6 to 7 C lower than the present average, and evidence exists for winter temperatures much lower than those of the present. A major warming trend occurred between about 16,000 and 12,000 radiocarbon years before present. By the latest Wisconsin (12 ,000 to 10,000 radiocarbon years before present), annual temperatures were within 2 C of temperatures of the present. During the latest Wisconsin, precipitation was greater during the winter, relative to the present. The climate of this pluvial event was much different from that of the preceding full glacial episode and is consistent with current models of astronomically induced climatic changes. (USGS)

Water-Resources Investigations Report↗
USGS1983

Vegetation and climates of the last 45,000 years in the vicinity of the Nevada Test Site, south-central Nevada

Paleoclimatic reconstructions for the Nevada Test Site, spanning the last 45,000 years, are based on plant macrofossil assemblages from radiocarbonated packrat (Neotoma spp) middens from south-central Nevada. The temperature regime during the Wisconsin glacial age, from before about 45,000 years ago until about 12,000 years ago, was characterized by lower temperatures during all seasons. Wisconsin maximum (about 18,000 years before present) winter temperatures were at least 6 deg. Celsius below those of the present, and the relative decrease in summer temperature was as much as 8 deg. Celsius. The data provide evidence for a precipitation regime drier than that proposed by many studies. The maximum estimated increase in average annual precipitation during the full-glacial period is 40 percent above current precipitation. The increase in temperature signaling the end of the Wisconsin glacial age may have begun as early as about 16,000 years ago. The oldest record of desert scrub vegetation from the Nevada Test Site area dates to about 15,000 years ago. By 10,000 years before present, average annual temperatures may have approximated present values, although seasonal temperature and precipitation regimes probably differed from those of today. Climate changes during the last 10,000 years have been relatively minor variations in a warm, dry climatic regime. Probably future climatic changes include a brief but pronounced warm period within the next 500 years, followed by a protracted transition to the next glacial age during the next 10,000 years. (USGS)

Nevada↗