			Home About us Contact

Southwestern USA (southwestern + usa)

Distribution by Scientific Domains

Life Sciences	50%

Selected Abstracts

Spread and current potential distribution of an alien grass, Eragrostis lehmanniana Nees, in the southwestern USA: comparing historical data and ecological niche models

DIVERSITY AND DISTRIBUTIONS, Issue 5 2006
Heather Schussman
ABSTRACT The potential distribution of alien species in a novel habitat often is difficult to predict because factors limiting species distributions may be unique to the new locale. Eragrostis lehmanniana is a perennial grass purposely introduced from South Africa to Arizona, USA in the 1930s; by the 1980s, it had doubled its extent. Based on environmental characteristics associated with its introduced and native range, researchers believed that E. lehmanniana had reached the limits of its distribution by the early 1990s. We collected data on E. lehmanniana locations from various land management agencies throughout Arizona and western New Mexico and found new records that indicate that E. lehmanniana has continued to spread. Also, we employed two modelling techniques to determine the current potential distribution and to re-investigate several environmental variables related to distribution. Precipitation and temperature regimes similar to those indicated by past research were the most important variables influencing model output. The potential distribution of E. lehmanniana mapped by both models was 71,843 km2 and covers a large portion of southeastern and central Arizona. Logistic regression (LR) predicted a potential distribution of E. lehmanniana more similar to this species current distribution than GARP based on average temperature, precipitation, and grassland species composition and recorded occurrences. Results of a cross-validation assessment and extrinsic testing showed that the LR model performed as well or better than GARP based on sensitivity, specificity, and kappa indices. [source]

Structural biomass partitioning in regrowth and undisturbed mesquite (Prosopis glandulosa): implications for bioenergy uses

GCB BIOENERGY, Issue 1 2010
R. JAMES ANSLEY
Abstract Honey mesquite (Prosopis glandulosa Torr.) which grows on grasslands and rangelands in southwestern USA may have potential as a bioenergy feedstock because of existing standing biomass and regrowth potential. However, regrowth mesquite physiognomy is highly different from undisturbed mesquite physiognomy and little is known regarding growth rates and structural biomass allocation in regrowth mesquite. We compared canopy architecture, aboveground biomass and relative allocation of biomass components in regrowth (RG) trees of different known ages with undisturbed (UD) trees of similar canopy height to each RG age class. RG trees in most age classes (2,12 years old) had greater canopy area, leaf area, basal stem number, twig (<0.5 cm diameter) mass and small stem (0.5,3 cm diameter) mass than UD trees of the same height. Large stem (>3 cm diameter) mass was similar between RG and UD trees in all height classes. Ages of UD trees were determined after harvest and further comparisons were made between age, canopy structure and biomass in RG and UD trees. Relationships between age and total mass, age and height, and age and canopy area indicated a faster growth rate in RG than in UD trees. Large stem mass as a percentage of total tree mass accumulated more rapidly with age in RG than UD trees. Leaf area index and leaf : twig mass ratio were maintained near 1 in all RG and UD trees. Regrowth potential may be one of the most important features of mesquite in consideration as a bioenergy feedstock. [source]

Post-wildfire changes in suspended sediment rating curves: Sabino Canyon, Arizona

HYDROLOGICAL PROCESSES, Issue 11 2007
Sharon L. E. Desilets
Abstract Wildfire has been shown to increase erosion by several orders of magnitude, but knowledge regarding short-term variations in post-fire sediment transport processes has been lacking. We present a detailed analysis of the immediate post-fire sediment dynamics in a semi-arid basin in the southwestern USA based on suspended sediment rating curves. During June and July 2003, the Aspen Fire in the Coronado National Forest of southern Arizona burned an area of 343 km2. Surface water samples were collected in an affected watershed using an event-based sampling strategy. Sediment rating parameters were determined for individual storm events during the first 18 months after the fire. The highest sediment concentrations were observed immediately after the fire. Through the two subsequent monsoon seasons there was a progressive change in rating parameters related to the preferential removal of fine to coarse sediment. During the corresponding winter seasons, there was a lower supply of sediment from the hillslopes, resulting in a time-invariant set of sediment rating parameters. A sediment mass-balance model corroborated the physical interpretations. The temporal variability in the sediment rating parameters demonstrates the importance of storm-based sampling in areas with intense monsoon activity to characterize post-fire sediment transport accurately. In particular, recovery of rating parameters depends on the number of high-intensity rainstorms. These findings can be used to constrain rapid assessment fire-response models for planning mitigation activities. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Ammonia reduction in seawater by Yucca schidigera extract: efficacy analysis and empirical modelling

AQUACULTURE RESEARCH, Issue 8 2010
Roberto A Santacruz-Reyes
Abstract Yucca schidigera is a plant native to southwestern USA and Mexico. Its extract has been used in the livestock industry to control ammonia accumulation in animal holding facilities, and to reduce ammonia concentration in animal excreta. This study investigated the potential and effectiveness of Y. schidigera extract (YUPE) for ammonia reduction in seawater. A dose,response experiment was conducted to determine the effect of different concentrations of YUPE at 0, 18, 36, 72 and 108 mg L,1 on total ammonia nitrogen (TAN) at 1, 3 and 9 mg L,1. At a higher YUPE dosage rate, higher TAN reduction was observed, and TAN reduction was highest during the first 12 h, and decreased thereafter. A stepwise multiple linear regression that included the initial TAN, YUPE concentration and time was developed, which accurately predicted empirical TAN concentrations. Applications of this model for ammonia management strategies were formulated for hypothetical tiger prawn (Penaeus monodon) rearing conditions. YUPE's efficacy for ammonia reduction, natural origin and safety make YUPE a potentially suitable compound for water quality management in mariculture. [source]