Treesearch

The Nevada Test Site (NTS) located in south-central Nevada encompasses approximately 3,567 km2 and straddles two major North American deserts, Mojave and Great Basin. Transitional areas between the two desert types have been created by gradients in elevation, precipitation, temperature, and soils. From 1996 to 1998, more than 1,500 ecological landform units were sampled at the NTS for numerous biotic and abiotic parameters. These data provide a basis for spatial evaluations of biodiversity over landscape scales at the NTS. Species diversity maps (species richness versus species abundance)...

Many factors influence species range and diversity, but temperature and temperature variability are always major global determinants, irrespective of local constraints. On a global scale, the ranges of many taxa have been observed to increase and their diversity decrease with increasing latitude. On a local scale, gradients in species distribution are observable with increasing altitude. These gradients in species distribution have not previously been linked to physiology. In this communication, the gradients are proposed to be a consequence of the physical laws governing energy transductio...

The Arrhenius activation energies, and therefore temperature coefficients, for rates of catabolic production of ATP and for anabolic use of ATP differ. Because the intracellular concentration of ATP and the phosphorylation potential must be controlled within a narrow range for cell survival, a mechanism must exist to balance these rates during temperature variation in ectotherms. We hypothesize that much of this control is accomplished via engagement of temperature-dependent reactions that waste ATP or the potential to make ATP in "futile" cycles and that energy-wasting metabolic cycles...

Plants that live in the desert playas of the Great Basin must simultaneously tolerate very high concentrations of salt and high temperature. This study characterizes the respiratory metabolism of one species growing in this environment. An isothermal calorimetric method was used to measure the dark metabolic heat rate (q) and CO2 production rate (RCO2) of stem tissue from Salicornia utahensis grown in the greenhouse or in constant temperature growth chambers at six different concentrations of NaCl solutions ranging from 0 to 1.0 M. Metabolic rates were measured at eight temperatures from 5...

Cheatgrass (Bromus tectorum L.) is a dominant weed that has increased the frequency of wildfire in the Great Basin since its introduction approximately 106 years ago. Characteristics of respiratory metabolism were examined in eleven subpopulations from different habitats. Seeds from each subpopulation were germinated (4mm radicle) and metabolic heat rates (q) and respiration rates (RCO2) determined calorimetrically at 5 °C intervals from 5 to 30 °C or from 5 to 45 °C. From the experimental data, growth rates and ratios of q/RCO2 (a measure of efficiency) were calculated. In general, growth...

Shoots from 4- to 6-day old seedlings of seven ancestral or old cultivars of Zea mays L. were placed in a calorimeter. Dark metabolic heat rate (q) and CO2 production rate (RCO2) were measured at nine temperatures (5, 10, 15, 20, 25, 30, 35, 40, and 45 °C). Temperature dependencies of q and RCO2 were used to model response of both growth and substrate carbon conversion efficiency. Responses at 5 °C were similar, but differences were noted at warmer temperatures. Upper temperature limits for growth were: Minipopcorn (26 °C), Black popcorn (30 °C), Black Mexican Sweet (31 °C), Pula Janku (32...

Vegetation response to various types of disturbances was quantitatively investigated in the Larrea tridentata-Ambrosia dumosa (creosote bush-white bursage) and Coleogyne ramosissima (blackbrush) shrublands of southern Nevada. Between the two control (undisturbed) habitats, the Larrea-Ambrosia vegetation zone had a greater plant species richness, but had a lower percent vegetation cover than the Coleogyne zone. Mean plant species richness and percent vegetation cover were significantly reduced in edge (disturbed) habitats compared to adjacent undisturbed habitats in both vegetation zones. A...

Fire ecology of sagebrush and pinyon-juniper vegetation in the Great Basin has been influenced by human disturbances and exotic plant introductions. Late-seral woody vegetation, which increased following Euro-American settlement, is now decreasing because of wildfire and exotic annuals. Multiple successional pathways following fire have been observed in these vegetation types. Following the 1996 wildfires in west-central Utah, burned and unburned vegetation were compared at four sites. Measures of frequency, cover, and density of vascular plant species were used to show fire effects and to...

Pinyon-juniper woodlands have dramatically increased in both tree density and distribution over the last 150 years. This change led to depleted native herbaceous understory in pinyon-juniper woodlands. One method to increase herbaceous understory is to remove the trees and aerially seed. The objective of this study was to determine how variations of seed mixes used in past revegetation projects have affected residual native species.

The usefulness of measuring community dominance factors and the soil parameters of geometric mean particle size and percent fines as predictors of first-year bare-root establishment of Wyoming big sagebrush seedlings was investigated. The study was conducted on six sandy soils in south-central Washington. Soil parameters that could affect the distribution of Sandberg’s bluegrass and cheatgrass as dominants in seral plant communities were also examined. Plant health was inversely related to increasing geometric mean particle size and directly related to increasing percent fines. Percent...