Owen K. Davis

Spores of the dung fungus Sporormiella: Increased abundance in historic sediments and before Pleistocene megafaunal extinction

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.

Rapid climatic change in coastal southern California inferred from pollen analysis of San Joaquin Marsh

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.

Pollen frequencies reflect vegetation patterns in a Great Basin (U.S.A.) mountain range

Davis, O.K., 1984. Pollen frequencies reflect vegetation patterns in a Great Basin (U.S.A.) mountain range. Rev. Palaeobot. Palynol., 40: 295--315. 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 elevationai 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 fifteenyear interval.

A Holocene climatic record for the Sonoran Desert from pollen analysis of Montezuma Well, Arizona, USA

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 14 C and 10 Be anomalies.

Pollen analysis of Tulare Lake, California: Great Basin-like vegetation in Central California during the full-glacial and early Holocene

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 modern 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.

Dung of Mammuthus in the arid Southwest, North America

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.

Palynological evidence for early Holocene aridity in the southern Sierra Nevada, California

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.

Contrasting climatic histories for the Snake River Plain, Idaho, resulting from multiple thermal maxima

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.

Caves as sources of biotic remains in arid western North America

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 caves 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.

Climate and vegetation patterns in surface samples from arid western U.S.A.: Application to Holocene climatic reconstructions

Abstract Nearly 1,400 samples from over 50 sources have been assembled and analyzed to characterize the contemporary pollen rain of the arid western U.S.A. Of the nearly 300 pollen types recorded, Pinus, Quercus, and Cupressaceae are the most common arboreal types; Chenopodiaceae‐Amaranthus. Gramineae, Artemisia, Ambrosia, and “Other Compositae”; are the most frequent non‐arboreal pollen types. Forest vegetation is represented by 661 samples, steppe by 450 samples, and desert by 116 samples. Ambrosia, Cactaceae, Cruciferae, Leguminosae, Larrea, Malvaceae, Nyctaginaceae, and Prosopis achieve maximum percentages in hot ‐ dry climate (>20°C mean annual temperature and <250 mm mean annual precipitation); Artemisia, Juniperus, Sarcobatus, Caryophyllaceae, Liguliflorae, Other Compositae, and Polygonaceae have minor peaks in cold dry climate (<15°C and <250 mm); Arceuthobium, Abies, Picea, Pinus, Pseudotsuga, Sequoiadendron, Tsuga heterophylla, and T. mertensiana reach maxima in cool moist climate (10–15°C, 500 ...