Owen K Davis

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• Davis, O. K., & Ellis, B. (2010). Early occurrence of sagebrush steppe, Miocene (12 Ma) on the Snake River Plain. Review of Palaeobotany and Palynology, 160(3-4), 172-180.
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  Abstract: Pollen analysis of soils overlain by welded tuffs of the Yellowstone hotspot provides a radiometrically-dated chronology of the vegetation 12-7 Ma for central Snake River Plain. The welded tuffs, produced as the Yellowstone hotspot migrated eastward, overlie soils containing perfectly-preserved pollen, occasionally containing cytoplasm. The pollen assemblage is dominated by Artemisia (sagebrush; ave. 32%, range 11-61%) and Poaceae (grass; ave. 21.3%, range 4-55%). This assemblage is very similar to that found in the area today, except the welded-tuff samples contain low percentages (< 5%) of arboreal taxa not found in the current flora: Podocarpus, Cedrus, Taxus, Aesculus, and Ulmus. The values of Artemisia and Poaceae are much higher than those found in samples of the same age (12-7 Ma) from the Pacific Northwest (which are dominated by tree pollen) and the Great Salt Lake basin (which are dominated by pine [Pinus], and greasewood [Sarcobatus]). Furthermore, the welded-tuff samples from the Snake River Plain contain a diverse herbaceous taxa characteristic of modern sagebrush steppe, and a diverse fungal spore assemblage including the root symbiont Glomus and the dung fungus Sporormiella. These results show that sagebrush steppe was widespread on the western Snake River Plain 12 Ma, at least 5 Ma earlier than previously recognized. © 2010 Elsevier B.V. All rights reserved.
• LeBlanc, B. W., Davis, O. K., Boue, S., DeLucca, A., & Deeby, T. (2009). Antioxidant activity of Sonoran Desert bee pollen. Food Chemistry, 115(4), 1299-1305.
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  Abstract: Bee pollen (pollen collected by honey bees) was collected in the high intensity ultraviolet (UV) Sonoran Desert and analyzed by the DPPH (radical 2,2-diphenyl-1-picryhydrazyl) assay and the FRAP (ferric reducing-antioxidant power) assay on six different pollen samples and in eight different water miscible solvents at 50 mg/ml. The bee pollen taxa were characterized for each pollen type by acetylization of the pollen extracts followed by microscopy and comparison with a library of samples native to the Sonoran Desert. The standards (R-(+)-6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), known as TROLOX, gallic acid and α-tocopherol (vitamin E) were analysed as standards to determine the potency of each pollen sample in the most efficient solvent. The Mimosa pollen sample displayed the highest antioxidant activity. Total polyphenolics, flavanols, flavones were determined, and the results are reported in milligrams of gallic acid, quercetin and naringenin per gram of pollen, respectively. There was good correlation between antioxidant activity and total phenolics. The order of effectiveness of the pollen samples in regard to antioxidant activity was determined and the most effective extraction solvents are discussed. Finally, solid phase micro-extraction, coupled with gas chromatography-mass spectroscopy was utilized to identify and quantify polyphenolic compounds known to have free radical scavenging activity in the pollen samples. © 2009 Elsevier Ltd.
• Minckley, T. A., Bartlein, P. J., Whitlock, C., Shuman, B. N., Williams, J. W., & Davis, O. K. (2008). Associations among modern pollen, vegetation, and climate in western North America. Quaternary Science Reviews, 27(21-22), 1962-1991.
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  Abstract: A compilation of 1884 modern pollen surface samples was analyzed to explore the relationships between spatial distributions of pollen percentage data vs. climate and vegetation in western North America. Modern pollen spectra capture many of the unique traits of regional vegetation patterns and reflect regional patterns of climate diversity. Large-scale vegetation differences were identifiable by their pollen signatures. At the coarsest scale, forested regions were dominated by arboreal pollen and Pinus pollen abundances were typically >30%. In contrast, non-forested regions were dominated by shrub and herbaceous pollen types with Pinus percentages typically
• Davis, O. K. (2006). Feces in the geological record. Palaeogeography, Palaeoclimatology, Palaeoecology, 237(1), 1-3.
• Davis, O. K., & Shafer, D. S. (2006). Sporormiella fungal spores, a palynological means of detecting herbivore density. Palaeogeography, Palaeoclimatology, Palaeoecology, 237(1), 40-50.
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  Abstract: During the historic period, spores of the dung fungus Sporormiella are abundant in lake and cave sediment where livestock are plentiful in the western United States. Sporormiella spores occasionally exceed 50% of the upland pollen sum in samples from corral ponds and bed-grounds, and routinely reach 4% in lake and marsh samples in pastoral areas. Sporormiella spores are comparatively rare in mid-Holocene sedimentary records, but they reach values of 2-4% in Pleistocene samples from lake sediments. Sporormiella spores are directly linked to extinct megaherbivores by their presence in mammoth dung from Bechan Cave, Utah. In several sites in the western United States, a precipitous decline of Sporormiella percentages after ca. 10,800 radiocarbon yr B.P. (12,900 years ago) marks a decline of herbivore density, probably associated with the North American megaherbivore extinction. © 2006 Elsevier B.V. All rights reserved.
• Palacios-Fest, M., Homburg, J. A., Brevik, E. C., Orme, A. R., Davis, O. K., & Shelley, S. D. (2006). Late Quaternary palaeoecology of Ballona Lagoon in southern California. Ciencias Marinas, 32(3), 485-504.
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  Abstract: Quaternary coastal environments, including estuaries, are significant to archaeologists, geologists, and palaeoecologists because dramatic changes in geographic settings have strongly affected human land use and adaptation. Estuaries are mainly affected by climate and geologic agents like tectonism, subsidence, and isostatic and eustatic sea level changes. This study of Ballona Lagoon, California, located in the Los Angeles metropolitan area, presents the paleoenvironmental reconstruction of an estuary. Estuaries are characterized by diverse assemblages of fishes, ostracodes, molluscs, foraminifers, siliceous organisms (diatoms and silicoflagellates), and traces of vegetation represented by palynomorphs. Ostracode and pollen analyses were conducted in combination with stratigraphic and geochronometric analyses. A central goal of this study was to delineate the lagoon edge and to document how it migrated through time. The location of the lagoon edge was important in determining how and why prehistoric land-use patterns shifted through time.
• Msaky, E. S., Livingstone, D., & Davis, O. K. (2005). Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika: V. Palynological evidence for deforestation and increased erosion. Journal of Paleolimnology, 34(1), 73-83.
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  Abstract: Pollen spectra from seven short cores taken from deltaic sites in the central and northern parts of Lake Tanganyika provide information about vegetation changes around the lake during the last 5000 years. Pollen analysis was undertaken to understand the history and timing of catchment deforestation and its causal linkage to excess sedimentation and ecosystem change in Lake Tanganyika. The spectra are dominated by grass pollen at all levels in every core. Grass pollen percentage values range between 40 and 80%. Low values of arboreal pollen taxa (1-20%) were documented from most cores except core LT-98-2M. Core LT-98-2M represents the longest duration vegetation record of this study (close to 5000 years BP), and records the onset of increasingly arid conditions in the Late Holocene, especially after ∼ 500 A.D., with the probable replacement of forest by open grassland in the Mahale Mountains region. The pollen/spore content for other cores showed a consistent trend of a decrease in grass pollen and an increase in pteridophyte and forest indicator pollen taxa during the last few centuries, contemporaneous with other indications of increased watershed disturbance from forest clearing (especially isotopes and lake faunal change). The timing or strength of this trend is not tied to specific levels of watershed disturbance. However, increasing fern spore abundance does occur progressively later towards the south, where modern human population densities are lower. Although increasing fern spore abundance is consistent with a land-clearing hypothesis, the rising arboreal pollen percentages are seemingly counterintuitive. One possible explanation is that increasing arboreal pollen proportions reflects the recycling of abundant pollen of this type from rapidly eroding soils. Another likely explanation for this finding is that land clearing involved the replacement of miombo woodland, with its mixture of trees producing little pollen and understory grasses producing large amounts of pollen, by the present day cassava, banana, and legume agricultural systems, all of which are poor pollen producers. This shift in catchment vegetation would increase the relative contribution of Afromontane pollen transported long distances from the surrounding highland regions. This hypothesis is consistent with both the lack of correlation of palynological history with specific watershed deforestation attributes, as well as the broader historical record of human habitation in the Lake Tanganyika region. This study also highlights the need for both modern pollen transect data from the region and comparative cores from low elevation swamps or ponds (wetlands) in the region with smaller catchment areas. © Springer 2005.
• Davis, O. K., Minckley, T., Moutoux, T., Jull, T., & Kalin, B. (2002). The transformation of Sonoran Desert wetlands following the historic decrease of burning. Journal of Arid Environments, 50(3), 393-412.
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  Abstract: The analysis of sediments from six wetlands (cienegas) in the Sonoran Desert of Arizona, U.S.A., and Sonora, Mexico, document a marked expansion of wetland taxa-particularly woody plants-about 200 years ago at the beginning of the historic period, following a decrease in charcoal percentages and increased percentages of the dung fungus Sporormiella. The presence of charred seeds and fruits of wetland plants in prehistoric sediment establishes burning of the cienega itself. The charcoal decline ca. 250 years ago precedes the first occurrence of the pollen exotic plants at several sites, the change of cienega sediment from silt to peat, and the increase of percentages of the decay fungus Tetraploa. We conclude that prior to the historic period, burning was frequent enough to exclude most woody plants (Celtis, Cephalanthus, Populus, Fraxinus, Salix) from the wetlands and suppress the abundance of bulrush (Scirpus). The cienegas were probably burned seasonally as a management tool to harvest animals and promote agriculture. Prehistoric agricultural utilization of the cienegas is demonstrated by the presence of corn (Zea) and pre-Columbian weeds. This study also records postsettlement (ca. 200 years ago) change of upland vegetation; i.e. an increase in the abundance of Juniperus, Quercus, Larrea, and Prosopis pollen. Historic fire suppression may have permitted the expansion of these non-wetland woody species. © 2002 Elsevier Science Ltd.
• Dean, W., Rosenbaum, J., Haskell, B., Kelts, K., Schnurrenberger, D., Blas, V., Cohen, A., Davis, O., Dinter, D., & Nielson, D. (2002). Progress in global lake drilling holds potential for global change research. Eos, 83(9), 85+90-91.
• Palacios-Fest, M. R., Mabry, J. B., Nials, F., Holmlund, J. P., Miksa, E., & Davis, O. K. (2001). Early irrigation systems in southeastern Arizona: The ostracode perspective. Journal of South American Earth Sciences, 14(5), 541-555.
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  Abstract: For the first time, the Early Agricultural Period (1200 BC-150 AD) canal irrigation in the Santa Cruz River Valley, southeastern Arizona, is documented through ostracode paleoecology. Interpretations based on ostracode paleoecology and taphonomy are supported by anthropological, sedimentological, geomorphological, and palynological information, and were used to determine the environmental history of the northern Tucson Basin during the time span represented by the sequence of canals at Las Capas (site AZ AA:12:753 ASM). We also attempt to elucidate based on archaeological artifacts if the Hohokam or a previous civilization built the canals. Between 3000 and 2400 radiocarbon years BP, at least three episodes of canal operation are defined by ostracode assemblages and pollen records. Modern (mid-late 20th century) canals supported no ostracodes, probably because of temporally brief canal operation from local wells. Three stages of water management are well defined during prehistoric canal operation. Ostracode faunal associations indicate that prehistoric peoples first operated their irrigation systems in a simple, 'opportunistic' mode (diversion of ephemeral flows following storms), and later in a complex, 'functional' mode (carefully timed diversions of perennial flows). The geomorphological reconstruction indicates that these canals had a minimum length of 1.1 km, and were possibly twice as long. The hydraulic reconstruction of these canals suggests that they had similar gradients (0.05-0.1%) to later prehistoric canals in the same valley. Discharges were also respectable. When flowing at bank-full, the largest canal provided an acre-foot of water in about 2.3 h; when flowing half-full (probably a more realistic assumption), it produced an acre-foot of water in about 8.6 h. Palynological records of the oldest canals (here identified as Features 3 and 4; 3000-2500 years BP) indicate they were used temporarily, since riparian vegetation did not grow consistently in the area. The presence of maize (Zea sp.) pollen in the canals confirms agricultural use of the canal water. However, a low percentage of maize and weed pollen suggests limited agricultural activity in this location, consistent with the lithostratigraphy, granulometry, and ostracode paleoecology. Agricultural fields were probably located downstream of this site. Ostracode assemblages show patterns consistent with the opportunistic or functional water control method, hence providing their value as indicators of human activity and environmental change. The transition from opportunistic to functional modes of canal operation indicates the increasing complexity of the social structure in the Santa Cruz Valley during the San Pedro Phase (1200-800 BC) of the Early Agricultural Period. © 2001 Elsevier Science Ltd. All rights reserved.
• Davis, O. K. (1999). Pollen analysis of Tulare Lake, California: Great Basin-like vegetation in Central California during the full-glacial and early Holocene. Review of Palaeobotany and Palynology, 107(3-4), 249-257.
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  Abstract: Pollen analysis and nine radiocarbon dates of an 853-cm core from historically drained Tulare Lake, south-central California are reported prior to 7000 yr B.P., the vegetation of the southern San Joaquin Valley (central California) resembled that of the contemporary Great Basin, including abundant greasewood (Sarcobatus), which currently does not occur west of the Sierra Nevada. The early-Holocene pollen assemblage is dominated by Cupressaceae (>40%), Pinus (>20%), Quercus (5-20%), Artemisia (> 15%), and Sarcobatus (>5%), suggesting pinyon-juniper-oak woodland in the uplands, with greasewood on the saltflats near the lake. Giant sequoia was widespread along the Sierra Nevada streams draining into Tulare Lake, prior to 9000 yr B.P. as Sequoiadendron pollen is greater than 4%. The pollen assemblages before 18,500 yr B.P. are similar to those of the early Holocene (Cupressaceae, Artemisia, and Sarcobatus), but a gap in sedimentation from ca. 18,500-10,500 yr B.P. prohibits characterization of full-glacial vegetation. The end of Great Basin-like pollen assemblages 7000 yr B.P. (demise of Sarcobatus) coincides with increased frequency of charcoal; i.e., greater fire frequency in the Holocene woodland and grassland. From 7000-4000 yr B.P. the pollen assemblage is dominated by Other Compositae and Chenopodiaceae-Amaranthus pollen, suggesting expansion of xerophytic steppe at the expense of oak woodland. Higher percentages of littoral pollen (Cyperaceae, Typha-Sparganium) and lower percentages of pelagic algae (Botryococcus + Pediastrum) during the middle Holocene indicate lake levels generally lower than during the early Holocene. The late Holocene begins with a cold-wet period 3500-2500 yr B.P. followed by progressive drying of the lake. Climate estimates based on modem pollen analogs confirm the climate implications of the vegetation and lake history. Early Holocene climate was cold and wet, and maximum Holocene temperature and drought occurred between 7000 and 4000 yr B.P. Cool-moist climate from 4000 to 2000 yr B.P. is followed by a return to aridity and high temperature ca. 1000 yr B.P.
• Davis, O. K. (1999). Pollen analysis of a late-glacial and Holocene sediment core from Mono Lake, Mono County, California. Quaternary Research, 52(2), 243-249.
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  Abstract: Pollen analysis of a 752-cm core from Mono Lake, Mono County, California indicates generally high lake levels 11,600-7000 14C yr B.P., moderate lake levels until ca. 4000 14C yr B.P., and fluctuating levels to the present. Drying events, with lake levels near or below the historic minimum are dated ca. 8800, 4000, 2400, and 1100 14C yr B.P. Chronologic control is provided by six radiocarbon dates and six volcanic ashes. The rate of upland vegetation change is greatest 11,000, 4000, and 1130 14C yr B.P. Juniperus and Sequoaidendron pollen declines 11,000 yr B.P., marking the transition from late-glacial juniper woodland to Holocene steppe. High values (5-20%) of Sequoaidendron pollen are unique to this study and may indicate the presence of these trees east of the Sierra crest. The pollen-based reconstructions of climate are generally cooler and wetter than today, with relatively dry but cool climate during the early Holocene. The contrast between higher lake levels and more arid vegetation during the early Holocene can be explained by insolation-driven seasonality. Greater summer insolation produced summer drought, but lower winter insolation led to greater snowpack, greater spring runoff, and higher lake levels. Increased Artemisia and other Compositae pollen percentages mark the establishment of modern vegetation ca. 2000 14C yr B.P. During the late Holocene, the pollen-based reconstructions of climate generally match the Mono Lake fluctuations proposed by Stine (1990), but fewer fluctuations are recorded.
• Davis, O. K. (1999). Pollen and other microfossils in Pleistocene speleothems, Kartchner Caverns, Arizona. Journal of Cave and Karst Studies, 61(2), 89-92.
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  Abstract: Pollen and other microfossils have been recovered from six carbonate speleothems in three Kartchner Caverns rooms: Grand Central Station (samples T2, T3, T4), the Bathtub Room (T11, T12), and Granite Dells (T16). The carbonate samples were dated from 194-76 Ka. The pollen concentration is greatest (~2 grain/cm3) in sample T11, which has many layers of clastic sediment, and the concentration is least in T4 (~0.05 grain/cm3), which has few mud layers. Therefore, the pollen was probably present in sediments washed into the cave, perhaps during floods. Although the pollen abundance in sample T4 is too low for confident interpretation, modern analogs for the five other samples can be found on the Colorado Plateau in areas that today are wetter and colder than the Kartchner Caverns locality. Agave pollen in samples T2 and T4 indicates that this important source of nectar was in the area during at least the latter part of the Pleistocene. Two orobatid mite exoskeletons recovered in speleothem T4 were probably washed into the cave with the pollen and mud trapped in the speleothems.
• Davis, O. K. (1998). Palynological evidence for vegetation cycles in a 1.5 million year pollen record from the Great Salt Lake, Utah, USA. Palaeogeography, Palaeoclimatology, Palaeoecology, 138(1-4), 175-185.
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  Abstract: Pollen analysis of the mid-lake Indian Cove well in the Great Salt Lake, collected by Amoco Production Co., provides a 1.5 Ma record of climatic change, correlative with the deep-sea oxygen isotope record. Chronologic control for Indian Cove is provided by the Lava Creek B (0.060 Ma). Bishop (0.76 Ma), and Huckleberry Ridge (2.06 Ma) volcanic ashes. The processing of close-interval (3 m. ca. 8 ka) samples is complete for the upper 628 m (1.5 Ma) of the Indian Cove well. During the last 750 ka. interglacial glacial cycles are expressed as the ratio of Juniperus + Ambrosia + Sarcobatus (interglacial) vs. Picea, Abies, and Pseudotsuga (glacial). Correlating the peak abundances of this ratio with the odd-numbered oxygen isotope stage has refined the time control provided by three volcanic tephra. The average Pleistocene sedimentation rate is 0.39 m ka-1 (Huckleberry Ridge, 2057 ka. 797 m). Based on the refined time scale, resulting from correlation with the marine chronology, sedimentation reached maximum values during isotope stages 11.9, and was slow between stages 13 and 11 and stages 9.7. Development of the Bonneville Pluvial cycles, from 759 to 600 ka, is recorded by changes in wetland and aquatic palynomorphs. Increased pollen concentration above 150 m (310 ka) may result from the diversion of the Bear River into the Great Salt Lake Basin.
• Davis, O. K., & Moutoux, T. E. (1998). Tertiary and Quaternary vegetation history of the Great Salt Lake, Utah, USA. Journal of Paleolimnology, 19(4), 417-427.
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  Abstract: Pollen analysis of 5 wells drilled to bedrock in the Great Salt Lake, Utah, USA provide a record vegetation change over the last ca 13.5 Ma. Over 440 pollen samples have been counted. The longest record presented is for the mid-lake Bridge Well. Close-interval (3-10 Ka) sampling is presented for the upper Indian Cove well. Chronologic control is provided by identification volcanic tephra and by K/Ar, Ar/Ar, and fission-track dates. Ash determinations are based on electron microprobe analyses of iron, calcium, and other elements compared to Neogene ash data at the University of Utah. Sedimentation begins 38 Ma, with good pollen preservation is sediments younger than 13.5 Ma, and no obvious gaps in sedimentation after 6 Ma. The upland vegetation is desert from the late Miocene onward, with Sarcobatus and Ephedra pollen dominance during the late Miocene (
• Lund, S. P., Newton, M. S., Hammond, D. E., Davis, O. K., & Bradbury, J. P. (1996). Late quaternary stratigraphy of Owens Lake, California. US Geological Survey Circular, 47-52.
• Davis, O. K., Kaimei, D., Dean, J. S., Parks, J., & Kalin, R. M. (1995). Radiocarbon dating of buried trees and climate change in west-central Oklahoma. Radiocarbon, 37(2), 611-614.
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  Abstract: Eleven radiocarbon dates and tree-ring analyses of 3 juniper logs demonstrate the potential for 14C analysis of buried logs in the American Midwest. Three junipers (cf Juniperus virginiana) were recovered from 9.20, 10.50, and 10.60 m in the fill of Carnegie Canyon, west-central Oklahoma. Their 14C ages are calibrated between 3300 and 2800 yr ago. A negative correlation of tree rings and 14C (p = 0.013) supports the findings of Schmidt and Gruhle (1988), who demonstrate the association of global cooliong with reduced solar activity.
• Blinn, D. W., Hevly, R. H., & Davis, O. K. (1994). Continuous Holocene Record of Diatom Stratigraphy, Paleohydrology, and Anthropogenic Activity in a Spring-Mound in Southwestern United States. Quaternary Research, 42(2), 197-205.
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  Abstract: This study presents the first continuous record of fossil diatoms taken from an open spring-mound in southwestern United States. Diatoms were analyzed from a radiocarbon-dated core taken from Montezuma Well, a near thermally constant spring in northcentral Arizona. Fluctuations in total diatom density, oscillations in the relative abundance of Anomoeoneis sphaerophora, and intermittent deposition of calcite suggest that water levels in Montezuma Well underwent dramatic fluctuations to the degree of being intermittently dry, or at least very shallow, during the middle Holocene (∼8000-5000 yr B.P.). The fluctuations in water level probably correspond to oscillations in regional temperature and precipitation, which regulate hydrologic input and evaporation rates. The dramatic fluctuations in water level during the middle Holocene suggest that the endemic biota of Montezuma Well underwent relatively rapid speciation within the past ∼5000 yr. The appearance of endemic species (Gomphonema montezumense and Cyclotella pseudostelligera f. parva ) at ∼5000-3000 yr B.P. supports this hypothesis. Diatom indicators for organic enrichment (Aulacoseira granulata and A. islandica) closely coincide with the prehistoric native occupation of Montezuma Well.
• Davis, O. K. (1994). The correlation of summer precipitation in the southwestern U.S.A. with isotopic records of solar activity during the medieval warm period. Climatic Change, 26(2-3), 271-287.
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  Abstract: Decreased solar activity correlates with positive cosmogenic isotope anomalies, and with cool, wet climate in temperate regions of the world. The relationship of isotope anomalies to climate may be the opposite for areas influenced by monsoonal precipitation, i.e., negative anomalies may be wet and warm. Petersen (1988) has found evidence for increased summer precipitation in the American Southwest that can be shown to be coincident with negative14C anomalies during the Medieval Warm Period. The present study compares palynological indicators of lake level for the Southwest with Petersen's data and with the14C isotope chronology. Percentages of aquatic pollen and algae from three sites within the Arizona Monsoon record greater lake depth or fresher water from A.D. 700-1350, between the Roman IV and Wolf positive isotope anomalies, thereby supporting Petersens's findings. Maximum summer moisture coincides with maximum population density of prehistoric people of the Southwest. However, water depth at a more northern site was low at this time, suggesting a climateisotope relationship similar to that of other temperate regions. Further analysis of latitudinal patterns is hampered by inadequate14C dating. © 1994 Kluwer Academic Publishers.
• Davis, O. K., & Sellers, W. D. (1994). Orbital history and seasonality of regional precipitation. Human Ecology, 22(1), 97-113.
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  Abstract: The Arizona monsoon, a major source of precipitation in the Southwest, shares many features with the monsoons of other continents. Computer modeling and fossil data indicate maximum extent of the African and Asian monsoons 9000 years ago. Fossil data indicate increased summer precipitation 9000 years ago, synchronous with the maxima of the African and Asian monsoons and, paradoxically, with the early-Holocene xerothermic of the Pacific Northwest. Climate model runs for 6000, 9000, 11,500, 13,000, and 18,000 years ago indicate increased summer precipitation 9000 years ago and a reciprocal relationship between precipitation in the Northwest and Southwest, but they relegate insolation to a role secondary to the North American ice sheet in regulating climate, and suggest a non-monsoon source for much of the summer precipitation in the Southwest prior to 9000 years ago. © 1994 Plenum Publishing Corporation.
• Davis, O. K. (1992). Rapid climatic change in coastal southern California inferred from pollen analysis of San Joaquin Marsh. Quaternary Research, 37(1), 89-100.
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  Abstract: Pollen analysis and five radiocarbon dates of a 687-cm core provide a detailed chronology of environmental change in a marsh at the head of Newport Bay, Orange County, California. Sediment deposition kept pace with sea-level rise during the early history of the marsh. From ca. 7000 to 4500 yr B.P. the site was a freshwater marsh, trees were more abundant than today, and grassland was the regional vegetation. As sea level rose, salt marsh gradually invaded the site. Brief periods of freshwater marsh 3800, 2800, 2300, and after 560 yr B.P. correlate with episodes of global cooling during the Neoglacial. The historic period is marked by the appearance of exotic species (particularly Erodium cf. cicutarium and Eucalyptus) and the spores of fungi (Sporormiella and Thecaphora). Peak influx of pollen, spores, and charcoal probably reflect greater frequency of flooding and erosion ca. 5000 yr B.P. and during the last 1000 yr. © 1992.
• Davis, O. K., & Shafer, D. S. (1992). A Holocene climatic record for the Sonoran Desert from pollen analysis of Montezuma Well, Arizona, USA. Palaeogeography, Palaeoclimatology, Palaeoecology, 92(1-2), 107-119.
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  Abstract: Pollen and macrofossil analyses of a radiocarbon-dated core, 1125 cm long, from Montezuma Well, elev. 1125 m, Yavapai County, Arizona, provide a record of summer precipitation similar to that of other monsoonal regions of the world. Precipitation was least from 4000 to 5000 yr B.P., and generally was greater than today before 8400 yr B.P. During the early-Holocene moist period, oak and grass pollen are abundant, and the best modern analogs are within the Arizona Monsoon boundary, so increased summer precipitation is indicated. Climatic parameters are estimated with the technique of best modern analogs for fossil samples. Temperature was highest ca. 3400 and 5700 yr B.P., and generally was cooler than today before 6800 yr B.P. Brief cold intervals in the Holocene match periods of global cooling and of positive 14C and 10Be anomalies. © 1992.
• Long, A., Davis, O. K., & Lanois, J. D. (1992). Separation and ¹⁴C dating of pure pollen from lake sediments: nanofossil AMS dating. Radiocarbon, 34(3), 557-560.
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  Abstract: We have developed and tested a practical device for manually separating pollen from pollen concentrates in sufficient quantity for AMS 14C dating. It is a combination of standard, commercially available equipment handled in a clean room by an individual trained to recognize pollen. A typical example requires about 15-20 h of hand-picking under the microscope. We show the usefulness of this procedure with results on a mid-Holocene segment from a core from Mono Lake. -from Authors
• Davis, O. K. (1990). Caves as sources of biotic remains in arid western North America. Palaeogeography, Palaeoclimatology, Palaeoecology, 76(3-4), 331-348.
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  Abstract: Caves have been a valuable source of paleoenvironmental information since the eighteenth century. In arid portions of western North America, caves have replaced small lakes as the primary source of biotic remains of Quaternary age. Packrat middens, dung of extinct animals, pollen, and archeological artifacts are excellently preserved. Aridity of the sediment, which is influenced by the cave's topographic position, internal morphology, and the regional climate, is the primary cause of good preservation. For stratigraphic pollen analysis, the best sites are those without internal moisture sources and without extensive bioturbation. Pollen samples should be taken near the center of the chamber, where eolian deposition is most rapid. Pollen concentrations in cave sediment are lower (2000-355,000 grains g-1) than in lake sediment, and pollen percentages in cave sediment differ from those in packrat middens due to additional transport mechanisms (on plant tissue and on the packrats themselves) for middens. Pollen diagrams for Bechan Cave, Utah, and Organ Pipe Cactus National Monument, Arizona are presented as examples of cave sediment and packrat midden analysis. © 1990.
• Davis, O. K. (1990). Introduction. Palaeogeography, Palaeoclimatology, Palaeoecology, 76(3-4), 187-188.
• Anderson, R. S., & Davis, O. K. (1988). Contemporary pollen rain across the central Sierra Nevada, California, U.S.A.: relationship to modern vegetation types. Arctic & Alpine Research, 20(4), 448-460.
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  Abstract: The relationship between the modern pollen rain and vegetation of alpine areas within the central Sierra Nevada in California is examined. Cluster analysis is used to help designate six major groups, corresponding to modern vegetation units. The results can be applied directly to studies of late Quaternary vegetation and climatic change of the area; most of the changes in past vegetation involved these taxa. -from Authors
• Davis, O. K. (1987). Recent developments in the study of arid lands.. Episodes, 10(1), 41-42.
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  Abstract: Arid lands provide data of immense value in unravelling paleoclimatic history, in assessing the effects of human activities on climate, and in predicting future regional and global changes. Ancient playa deposits in the hyper-arid core of the Sahel, loess and fossil soils, cave deposits, and desert varnish are all proving to be sources of new useful data in establishing paleoclimatic sequences. -Journal summaryDept Geosciences, Univ of Arizona, Tucson, AZ 85721, USA.
• Davis, O. K. (1987). Spores of the dung fungus Sporormiella: Increased abundance in historic sediments and before Pleistocene megafaunal extinction. Quaternary Research, 28(2), 290-294.
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  Abstract: Spores of the dung fungus Sporormiella become abundant following the historic introduction of grazing herbivores at seven sites in the western United States. During the Holocene they are generally rare, but at six sites Sporormiella spores are abundant before the extinction of Pleistocene megaherbivores ca. 11,000 yr B.P. Sporormiella spores are directly linked to extinct megaherbivores by their presence in mammoth dung preserved in Bechan Cave, Southern Utah. Their abundance in late-glacial sediments may reflect the abundance of megaherbivores during Quaternary, thereby indicating the age of Pleistocene extinctions where other indicators are absent. © 1987.
• Davis, O. K., & Turner, R. M. (1986). Palynological evidence for the historic expansion of juniper and desert shrubs in Arizona, U.S.A.. Review of Palaeobotany and Palynology, 49(3-4), 177-193.
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  Abstract: Analysis of the sediment of Pecks Lake, Yavapai County, Arizona, has permitted the first reported palynological evidence for the historic expansion of juniper and desert shrubs in the American Southwest. The palynological evidence is supported by the comparison of modern and historical photographs, which shows the regional expansion of pinyon-juniper woodland, and the local increase of mesquite and creosote bush. A gradual increase in juniper pollen percentages began over 2000 years ago, but the rate of increase abruptly accelerated after the historic introduction of grazing animals. In contrast, juniper percentages did not increase during a prehistoric interval of intense disturbance by humans, about A.D. 1200, and a different weed flora was present. Prehistorically, water depth was greatest at ca. 600 B.C. and was lowest just prior to the arrival of Europeans. Regional climate has gradually cooled since the beginning of the record at 2630 B.P. © 1986.
• Davis, O. K., Sheppard, J. C., & Robertson, S. (1986). Contrasting climatic histories for the Snake River Plain, Idaho, resulting from multiple thermal maxima. Quaternary Research, 26(3), 321-339.
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  Abstract: Ten sites near the Snake River Plain have consistent differences in their climatic histories. Sites at low elevation reflect the "early Holocene xerothermic" of the Pacific Northwest, whereas most climatic chronologies at high elevation indicate maximum warmth or aridity somewhat later, ca. 6000 yr ago. This elevational contrast in climatic histories is duplicated at three sites from the central Snake River Plain. For sites in such close proximity, the different chronologies cannot be explained by changes in atmospheric circulation during the late Quaternary. Rather, the differences are best explained by the autecology of the plants involved and the changing seasonal climate. The seasonal climatic sequence predicted by multiple thermal maxima explains the high- and low-elevation chronologies. During the early Holocene, maximum insolation and intensified summer drought in July forced low-elevation vegetation upward. However, moisture was not a limiting factor at high elevation, where vegetation moved upward in response to increased length of growing season coincident with maximum September insolation 6000 yr ago. © 1986.
• Jackson, S. T., Whitehead, D. R., & Davis, O. K. (1986). Accelerator radiocarbon date indicates mid-Holocene age for hickory nut from Indiana late-glacial sediments. Quaternary Research, 25(2), 257-258.
• mead, J. I., Agenbroad, L. D., Davis, O. K., & Martin, P. S. (1986). Dung of Mammuthus in the arid Southwest, North America. Quaternary Research, 25(1), 121-127.
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  Abstract: The discovery of a unique organic deposit in a dry cave on the Colorado Plateau, southern Utah, permits the first comparison of the physical characteristics and the diet of the dung of the extinct mammoths from the arid Southwest, North America, with that of mammoths from Siberia and northern China, the only other known locations of such remains. The deposit buried beneath sand and rockfall is composed primarily of mammoth dung, estimated at over 300 m3. Radiocarbon dates on dung boluses indicate that the mammoths frequented the cave between approximately 14,700 and 11,000 yr B.P. (the range of ages at 2σ). The desiccated boluses, measuring approximately 230 × 170 × 85 mm, are nearly identical in size to dung from extant elephants. The largest contents in the dung are stalks measuring 60 × 4.5 mm. Grasses and sedges dominated the diet, although woody species were commonly eaten. © 1986.
• Baker, F. A., French, D. W., Kulman, H. M., Davis, O., & Bright, R. C. (1985). Pollination of the eastern dwarf mistletoe.. Canadian Journal of Forest Research, 15(4), 708-714.
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  Abstract: Flowering and pollination of Arceuthobium pusillum growing on Picea mariana were studied in Carlton County, MN. Staminate flowers opened in April and abscission was complete by mid-June. Average number of pistillate flowers per aerial shoot ranged from 4.8-5.1. From the flowering period of seed dispersal (September), 36-59% of pistillate aerial shoots were lost. Based on March flower counts, 0.3-2.4 fruits matured per aerial shoot, ie 5-35% of pistillate flowers developed into mature fruits. Although insect exclusion studies demonstrated that wind pollination did occur, few grains of Arceuthobium pollen were collected with vaseline slides or a Rotorod sampler. Fifty-nine species of insects trapped on sticky-board traps carried pollen of Arceuthobium. Entomophily is the most important pollination mechanism for this dwarf mistletoe. -Authors
• Davis, O. K., Anderson, R. S., Fall, P. L., O'Rourke, M. K., & Thompson, R. S. (1985). Palynological evidence for early Holocene aridity in the southern Sierra Nevada, California. Quaternary Research, 24(3), 322-332.
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  Abstract: Sediments of Balsam Meadow have produced a 11,000-yr pollen record from the southern Sierra Nevada of California. The Balsam Meadow diagram is divided into three zones. (1) The Artemisia zone (11,000-7000 yr B.P.) is characterized by percentages of sagebrush (Artemisia) and other nonarboreal pollen higher than can be found in the modern local vegetation. Vegetation during this interval was probably similar to the modern vegetation on the east slope of the Sierra Nevada and the climate was drier than that of today. (2) Pinus pollen exceeded 80% from 7000 to 3000 yr B.P. in the Pinus zone. The climate was moister than during the Artemisia zone. (3) Fir (Abies, Cupressaceae, and oak (Quercus) percentages increased after 3000 yr B.P. in the Abies zone as the modern vegetation at the site developed and the present cool-moist climatic regime was established. Decreased fire frequency after 1200 yr B.P. is reflected in decreased abundance of macroscopic charcoal and increased concentration of Abies magnifica and Pinus murrayana needles. © 1985.
• Betancourt, J. L., & Davis, O. K. (1984). Packrat middens from Canyon de Chelly, northeastern Arizona: Paleoecological and archaeological implications. Quaternary Research, 21(1), 56-64.
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  Abstract: In western North America, pollen data from highland lakes are often used to reconstruct vegetation on the adjacent lowlands. Plant macrofossils and pollen from packrat middens now provide a means to evaluate such reconstructions. On the basis of pollen diagrams from the Chuska Mountains, H. E. Wright, Jr., A. M. Bent, B. S. Hansen, and L. J. Maher, Jr., ((1973), Geological Society of America Bulletin, 84, 1155-1180) arrived at conservative estimates for late Pleistocene depression of highland conifers. In their interpretation, a proposed slight depression of 500 m for lower tree line precluded expansion of Pinus ponderosa into elevations now in desertscrub. Instead, it was suggested that pinyon pine and Artemisia occupied the lowland plateaus. Packrat midden records on either side of the Chuskas fail to verify this model. Early Holocene middens from Chaco Canyon, New Mexico, and a terminal Pleistocene midden from Canyon de Chelly, Arizona, show that blue spruce, limber pine, Douglas fir, dwarf juniper, and Rocky Mountain juniper expanded at least down to 1770 m elevation Neither Colorado pinyon nor ponderosa pine was found as macrofossils in the middens. Artemisia pollen percentages are high in the terminal Pleistocene midden, as they are in the Chuska Mountain pollen sequence, suggesting regional dominance by sagebrush steppe. Of 38 taxa identified, only 3 are shared by middens dated 11,900 and 3120 yr B.P. from Canyon de Chelly, indicating a nearly complete turnover in the flora between the late Pleistocene and late Holocene. Although corn was previously thought to have been introduced to the Colorado plateaus after 2200 yr B.P., the midden dated 3120 yr B.P. contains pollen of corn and other indicators of incipient agriculture. © 1984.
• Davis, O. K. (1984). Multiple thermal maxima during the holocene. Science, 225(4662), 617-619.
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  Abstract: The astronomical theory of climatic change provides an alternative to the traditional chronology for Holocene climatic change, which calls for one thermal maximum about 6000 years ago. The theory predicts a series of maxima during the Holocene, one for each season. Because the relation of the perihelion to the spring equinox changes with a 22,000-year period, late summer insolation would have been greatest 5000 years ago, whereas early summer insolation would have been greatest 13,000 years ago. Climatic reconstructions based on the response of ecosystems to late summer climate indicate a later Holocene thermal maximum than paleoclimatic data sensitive to early summer climate. In southern Idaho, three different vegetation types indicate thermal maxima at different times during the Holocene, depending on the climatic variable controlling each type.
• Davis, O. K. (1984). Pollen frequencies reflect vegetation patterns in a great basin (U.S.A.) mountain range. Review of Palaeobotany and Palynology, 40(4), 295-315.
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  Abstract: Five indices are used to quantify the relationship between vegetation and pollen in a mountain range in the arid Great Basin. Computations are based on vegetation coverage and pollen percentages from 63 stands. Association is a measure of whether the presence of the pollen type in a surface sample is an indication of the presence of the parent plant in the local vegetation. Over-representation and under-representation measure tendencies for pollen to occur where the parent plants are absent and vice versa. The correlation coefficient measures the relationship between plant and pollen in stands where both are present. Twenty-nine trees, shrubs, and herbs accurately reflect local vegetation conditions. A percentage diagram shows elevational trends in abundant pollen types. Regional pollen types are used to compute the accumulation rate of pollen in the surface samples. A diagram of pollen accumulation rates shows trends similar to those shown in the percentage diagram. The moss polsters used in this study may collect pollen over a fifteen-year interval. © 1984.
• Bright, R. C., & Davis, O. K. (1982). Quaternary paleoecology of the Idaho National Engineering Laboratory, Snake River Plain, Idaho.. American Midland Naturalist, 108(1), 21-33.
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  Abstract: Based on woodrat middens and pollen from cave sediments, the Holocene vegetation history has been one of sagebrush (Artemisia spp.) steppe that became increasingly similar to shadscale (Atriplex spp.) steppe, culminating 7000 yr BP. A radiocarbon date on snail shells from 'ancient' Lake Terreton shows that the basin was filled as recently as 700 yr BP. Fossils of aquatic organisms were found in aeolian sediments, indicating that lake and stream sediments may be an important source of the aeolian sediment. -from Authors