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A new species of poplar is recognized based on abundant specimens from the early Middle Eocene Parachute Creek Member of the Green River Formation in eastern Utah and western Colorado and compared with two other contemporary species. A rare twig bearing both leaves and fruits serves as a Rosetta stone, linking the vegetative and reproductive structures that formerly were only known from dispersed organs. Fruit and foliage characters distinguish Populus tidwellii sp. n. from Populus cinnamomoides (Lesquereux) MacGinitie (typified on specimens from Green River Station, WY), to which the isolated leaves had formerly been attributed. In addition, new data from fruits and foliage confirm that there were two distinct...
The canopies of woody plants in semiarid ecosystems modify the microclimate beneath and around them, with canopy patches usually having lower soil temperatures than intercanopy patches. However, lacking are studies that have evaluated how heterogeneity in soil temperature, induced by woody plant canopies, influences soil evaporation rates and the consequent effects on plant-available water. Soil temperatures were measured and soil evaporation rates were estimated for canopy and intercanopy patches in a semiarid pinyon-juniper woodland (Pinus edulis and Juniperus monosperma) in northern New Mexico. Soil temperature was measured at 2-cm depths in four canopy and four intercanopy locations during 1994. Maximum soil...
A new genus is described based on fossilized winged fruits from former lake deposits of Wyoming, Utah, Colorado, Oregon, and British Columbia, ranging in age from latest Paleocene to early Middle Eocene. Lagokarpos lacustris McMurran et Manchester gen. et sp. nov. fruits have an elliptical to globose seed body and a conspicuous pair of apical wings with pinnate venation. These wind�dispersed fruits are compared with and distinguished from similar extant winged fruits such as Dipterocarpus Gaertn f. (Dipterocarpaceae), Gyrocarpus Jacq. (Hernandiaceae), and Alberta E. Meyer (Rubiaceae). No modern fruit was found to exhibit the combination of characters seen in Lagokarpos, and we conclude that it represents an extinct...
A new genus is described based on fossilized winged fruits from former lake deposits of Wyoming, Utah, Colorado, Oregon, and British Columbia, ranging in age from latest Paleocene to early Middle Eocene. Lagokarpos lacustris McMurran et Manchester gen. et sp. nov. fruits have an elliptical to globose seed body and a conspicuous pair of apical wings with pinnate venation. These wind?dispersed fruits are compared with and distinguished from similar extant winged fruits such as Dipterocarpus Gaertn f. (Dipterocarpaceae), Gyrocarpus Jacq. (Hernandiaceae), and Alberta E. Meyer (Rubiaceae). No modern fruit was found to exhibit the combination of characters seen in Lagokarpos, and we conclude that it represents an extinct...
Plant and soil resource spatial patterns were measured in pinyon-juniper communities in northern New Mexico over an elevational gradient that also served as a water-availability gradient to examine the role of resource competition and resource availability in determining plant spatial patterns. Total canopy coverage increased with increasing elevation. Percent coverage of juniper declined with elevation and, with the exception of one site, that of pinyon increased. Water appeared to be a strong factor in the maintenance of stand structure and plant distribution in this pinyon-juniper ecosystem. Plant water stress was greater during the dry season at the low-elevation, low-density sites than at the upper-elevation,...
1. Chemical effects of native plants on desert soils were studied. 2. Data are presented which indicate that the pH values of saturated soil pastes and 1: 10 soil-water suspensions, particularly of the surface soil, generally are higher under shadscale and invariably are higher under greasewood than in the adjacent bare areas or under plants such as sagebrush. 3. The pH value of the bare soil is usually highest in greasewood and lowest in sagebrush areas, with shadscale areas either intermediate or similar to those of sagebrush. 4. The exchangeable-sodium percentage of the soil is somewhat higher under shadscale and very much higher under greasewood than in the adjacent bare areas or under other plants such as sagebrush....
U/Pb zircon/titanite geochronology, in situ monazite geochronology, and 40Ar/39Ar thermochronology provide an unusually complete data set for reconstructing the tectonic history of Proterozoic rocks exposed in the Black Canyon, Gunnison, Colorado. These new geochronologic data record three protracted orogenic episodes and an exhumation event between orogenic pulses: (1) Yavapai orogeny (1741–1689 Ma), (2) exhumation marked by an angular unconformity beneath post�Yavapai, pre�Mazatzal quartzites, (3) Mazatzal orogeny (postquartzite deposition), and (4) 1434–1403 Ma intracratonic tectonism. Supracrustal rocks of the Black Canyon succession were deposited or crystallized at or prior to Ma and were intruded...