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Filters: partyWithName: Ryel, Ronald J (X) > Types: Citation (X)

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Aspen are thought to be declining in this region due to a combination of fire suppression, grazing and wildlife management practices, and potentially cool/wet climates of the past century which favor advancing conifer succession. Many scientists are concerned that aspen?s related species may also be losing habitat, thereby threatening the long-term local and regional viability of this important community. To date, few studies have specifically examined the role of aspen?s epiphytic lichen community. This paper presents basic community research describing the application of Indicator Species Analysis for lichens growing on aspen stems in the central Rocky Mountains of North American. Results show unique lichen assemblages...
Abstract.?We investigated distribution and dispersal patterns of subadult and adult Colorado squawfish Ptychocheilus lucius (recently renamed the Colorado pikeminnow) throughout their range in the upper Colorado River. Annual, river-wide, capture?recapture data were used to document movements during a 5-year period (1991?1995). Average total length of Colorado squawfish progressively increased upstream: juveniles and subadults occurred almost exclusively in the lowermost 105 km of the 298-km study area, whereas most adults were concentrated in the uppermost 98 km. This was most pronounced early in the study and less so later due to the effect of two or three strong year-classes that dispersed through the system....
Juniper species are noted for long-lived foliage, low and persistent gas exchange activity and drought tolerance. Because leaves and roots of the same species are thought to be similar in structure and life history, we hypothesized that Juniperus osteosperma (Torr.) Little (Utah juniper) fine roots would reflect the persistent aboveground foliage characteristic of this species. We monitored fine roots, less than 1 mm in diameter, by minirhizotron imaging to a depth of 150 cm over two growing seasons from April 2002 to December 2003. We measured fine root numbers, lengths and diameters, and noted the time of birth and death of root segments. We correlated our root data with soil water potential measured by thermocouple...
Water conservation is important for plants that maintain physiologically active foliage during prolonged periods of drought. A variety of mechanisms for water conservation exist including stomatal regulation, foliage loss, above- and below-ground allocation patterns, size of xylem vessels and leaf pubescence. Using the results of a field and simulation study with Artemisia tridentata in the Great Basin, USA, we propose an additional mechanism of water conservation that can be used by plants in arid and semi-arid environments following pulses of water availability. Precipitation redistributed more uniformly in the soil column by roots (hydraulic redistribution of water downward) slows the rate at which this water...
Encroachment of pinyon?juniper woodland into rangeland ecosystems is prevalent across the western United States. Mechanisms associated with this successful encroachment are speculative, but probably, in part, involve the effective use of water resources. We explored the ecohydrological characteristics of a two-needle pinyon pine (Pinus edulis Engelm.)?Utah juniper [Juniperus osteosperma (Torr.) Little] woodland on the Colorado Plateau in Utah. We have discovered that a high level of natural soil water repellency or hydrophobicity exists under the canopies of both pinyon and juniper species. We found, following summer precipitation events, that soil water repellency under trees concentrated the soil water below the...
The significance of soil water redistribution facilitated by roots (an extension of "hydraulic lift", here termed hydraulic redistribution) was assessed for a stand of Artemisia tridentata using measurements and a simulation model. The model incorporated water movement within the soil via unsaturated flow and hydraulic redistribution and soil water loss from transpiration. The model used Buckingham-Darcy's law for unsaturated flow while hydraulic redistribution was developed as a function of the distribution of active roots, root conductance for water, and relative soil-root (rhizosphere) conductance for water. Simulations were conducted to compare model predictions with time courses of soil water potential at several...
Eddy covariance measures net ecosystem exchange of CO2 (NEE) at a scale between chamber-based measurements of CO2 exchange processes and large-scale models of CO2 flux dynamics. As the intermediate, it represents a link between small and large-scale estimates of NEE. Accuracy is therefore critical. However, estimates of nighttime ecosystem respiration based on scaled-up measurements of soil and leaf CO2 exchange are most often larger than from eddy covariance. Identifying the source of the discrepancy is difficult due to large measurement uncertainties associated with high variability of fluxes in complex ecosystems. This study compared measurements in a simple system that allowed for minimal uncertainty. We compared...


    map background search result map search result map Hydraulic redistribution in a stand of Artemisia tridentata: evaluation of benefits to transpiration assessed with a simulation model Water conservation in Artemisia tridentata through redistribution of precipitation Root turnover and relocation in the soil profile in response to seasonal soil water variation in a natural stand of Utah juniper (Juniperus osteosperma).