Laurie B. Abbott

Surface soil water loss after summer rainfall in a semidesert grassland

Surface soil water contents were analyzed for bare and litter‐ or gravel‐covered soils for 20 drying periods after summer rainfall in southeastern Arizona. Water contents were measured every minute by fiberglass cells calibrated for the sandy‐loam soil, and 30‐ to 60‐min averages were stored by microloggers. Water loss to equivalent matric potentials of ‐1.5 MPa for bare surface soils (1–3 cm) was fast (1.2 ± 0.5 days), moderate (2.6 ± 0.9 days), or slow (5.9 ± 1.4 days) when the upper 15 cm of soil at the start of the drying period had 13.3, 27.1, and 36.1 cm of water, respectively. Those water contents are near saturation and near field capacity for slow and moderate drying rates, respectively. For fast drying rates, water content was near field capacity at 1–3 cm but dry below 8 cm. Litter or gravel mulches increased the time of surface soil water availability by 0.7 to 1.9 days for fast and moderate drying periods, respectively. Drying from the surface down into the soil profile averaged 3.6 cm day‐1....

Implications of Invasive Plant Variation for Weed Management1

Abstract Genetic variability of invasive plant populations may create significant challenges to weed management through (1) selection for resistant genotypes and (2) differential efficacy of control methods resulting from genotypic variation. Effects of variation on management success may be particularly problematic for native invasive plants because they possess more genetic variation than bottlenecked exotic invasive species. We review the influence of genetic variation among populations and species on efficacy of chemical and biological control of select invasive rangeland plants. Population or genotype variation was more important for successful management when using biological agents than when using herbicides. Long-term success in weed control requires integrating multiple management strategies with attention to specificity of biological control agents to avoid selection for resistant genotypes. Additional index words: Biological control, common garden, genetic variation, metsulfuron, native plants, picloram, rangeland plants.

Cover Pole Design for Easy Transport, Assembly, and Field Use

Abstract Cover poles, also called Robel poles, are used to measure a variety of structural vegetation attributes commonly used in wildlife and livestock management. Although cover pole dimensions, measurement criteria, and interpretation of cover pole data vary depending on measurement objectives, the technical use of cover poles is fairly consistent. Practical use of cover poles requires that they are sturdy, lightweight, and easily transported. We describe a cover pole apparatus that can be easily constructed, transported, and assembled for use in remote locations. This self-supporting cover pole enables one person to take measurements, and can be modified for use in multiple habitats and soil types.

A Comparison of Cover Pole With Standard Vegetation Monitoring Methods

Abstract The ability of resource managers to make informed decisions regarding wildlife habitat could be improved with the use of existing data sets and the use of cost-effective, standardized methods to simultaneously quantify vertical and horizontal cover. We characterized vegetation structure of 3 semiarid plant communities to compare cover pole measurements, standard measurements of vegetation cover, composition, height, and the proportion of the soil surface exposed by large intercanopy gaps. We propose that a more versatile and interpretable description of wildlife habitat can be generated using a line-point intercept method together with measurements of vegetation height and the proportion of the soil surface exposed by large intercanopy gaps.

Physiology and recovery of African rue (Peganum harmala) seedlings under water-deficit stress.

Abstract African rue is an invasive herbaceous perennial that occurs in several states in the western United States. The ability of African rue seedlings to tolerate and recover from progressive drought was examined in greenhouse experiments. Water was withheld for 15 d, and a subset of plants were rewatered after 12 d of water deficit to examine recovery. Conductance rate decreased to 0.1 mol H2O m−2 s−1 and photosynthesis rate decreased to 2 µmol CO2 m−2 s−1 within 6 and 12 d, respectively. Leaf water potential decreased more slowly than gas exchange rates; after 15 d of water deficit plants maintained net carbon gain at −4.8 MPa. Photosynthesis and conductance rates of rewatered plants recovered to levels similar to well-watered controls within 9 and 12 d, respectively. After 9 d of water deficit, seedlings needed only 4 d to recover physiological function similar to well-watered controls. Reduced seedling biomass was observed after 6 d of water deficit, and biomass remained smaller than controls after 15 d of recovery. The rapid change in conductance rate and slower response in leaf water potential indicates that stomatal control is an important component of seedling response to water deficit. The success of African rue in arid environments is due in part to the ability of seedlings to tolerate and recover from water deficit. Nomenclature: African rue; Peganum harmala L. PEGHA.

African rue (Peganum harmala) seedling response to herbicides applied under water-deficit stress

Abstract African rue is an exotic, herbaceous perennial established in several western states that tolerates harsh, water-stressed conditions. The influence of water-deficit stress on herbicide response and subsequent herbicide fate within the plant were compared. African rue seedlings were deprived of water for 0 to 7 d to establish a gradient of water-deficit levels before treatment with hexazinone, imazapyr, or metsulfuron. At herbicide application, water-deficit treatments reduced plant water potential values from −1.0 MPa to −4.7 MPa, causing concomitant reductions in photosynthesis. Thirty-five days after treatment, dry weight of imazapyr- and metsulfuron-treated plants was reduced in plants exposed to more than 4 d water-deficit stress before herbicide application. In contrast, hexazinone-treated plants had less dry weight than water-stressed, nonsprayed control plants regardless of water-deficit stress. Seventy-two hours after herbicide application, African rue leaves absorbed from 5 to 42% of her...

Range Education in the 21st Century: Striking the Balance to Maintain a Relevant Profession

Abstract Range science education programs strive to keep pace with the changing needs of the range profession and to ensure that range graduates are knowledgeable, skilled, and able to address contemporary, complex problems unique to rangelands. Today, range education programs face many challenges in our ability to meet the demands and needs of our profession and society. First, our capacity to meet the demands for range science graduates has been diminished by 1) elimination or restructuring of academic rangeland science programs, 2) reduced numbers of range-trained faculty teaching rangeland courses, and 3) limited public awareness of degrees and careers in rangeland science and management. Second, range education programs are challenged to strike a balance between retaining traditional basics and modernizing curriculum to include contemporary concepts and technologies. Third, range science graduates need to understand the current social, political, and economic context of resource management, including global change issues that are of paramount concern to society. We propose multiple approaches to meet these challenges: 1) perform needs assessments with diverse stakeholders to ensure that range education programs are relevant to societys needs and address the future of the profession; 2) find innovative approaches to strike the educational balance between fundamental concepts, practical field experiences, and mastery of technical and interpersonal skills; 3) collaborate across institutional boundaries to share educational resources and incorporate course formats that meet the diverse needs of todays students; 4) examine and align professional qualifications, educational standards, and curriculum by defining learning outcomes and core competencies needed by well-trained range professionals; and 5) communicate the unique features of the rangeland profession that solidify its position among the disciplinary pillars of natural resource science and management. Resumen Programas de educación en la ciencia de pastizales se esfuerzan por mantener el ritmo con el cambio en las necesidades de la profesión del manejo de pastizales, y para asegurarse de que los estudiantes al graduarse cuentan con los conocimientos, habilidades y que sean capaces de abordar problemas contemporáneos y complejos, únicos de los pastizales. Hoy en día, los programas de educación en manejo de pastizales se encuentran ante muchos retos en nuestra habilidad parar cumplir con las demandas de las necesidades de nuestra profesión y sociedad. Primero, nuestra capacidad para cumplir las demandas de los estudiantes graduados de manejo de pastizales han disminuido por: 1) la eliminación o reestructura de los programas académicos del manejo de pastizales, 2) reducción del números de cursos en pastizales enseñados por profesores entrenados en el área de manejo de pastizales, y 3) una conciencia pública limitada de los grados y carreras relacionadas con el manejo y la ciencia de pastizales. Segundo, los programas de educación en manejo de pastizales tienen el reto de alcanzar un balance entre retener la tradición básica y la modernización de la curricula para incluir conceptos y tecnologías contemporáneas. Tercero, graduados de programas de manejo de pastizales necesitan entender el contexto social, político y económico actual del manejo de recursos, incluyendo cuestiones de cambio global que son de suma importancia para la sociedad. Nosotros proponemos múltiples acercamientos para cumplir con estos retos: 1) realizar evaluaciones de las necesidades con las diversas partes interesadas para asegurar la educación de los programas de manejo de pastizales son relevantes para las necesidades de la sociedad y abordar el futuro de la profesión; 2) buscar formas innovadoras para alcanzar un balance educacional entre los conceptos fundamentales, experiencias de prácticas de campo y el dominio de habilidades técnicas e interpersonales; 3) colaborar a través de las fronteras institucionales para compartir recursos educacionales e incorporar cursos con formatos que satisfagan las necesidades de los estudiantes de hoy; 4) examinar y adaptar las credenciales profesionales, estándares de la educación y curricular mediante la definición de los resultados del aprendizaje y competencias básicas necesarias por los profesionales bien entrenados de manejo de pastizales; y 5) comunicar las características únicas de la profesión de manejo de pastizales que solidifiquen su posición entre los pilares de la disciplina de las ciencias naturales y el manejo.

Targeted Grazing of White Locoweed: Short-Term Effects of Herbivory Regime on Vegetation and Sheep

Abstract White locoweed (Oxytropis sericea Nuttall) and nontarget vegetation response to 2 yr of targeted grazing by sheep, one treatment of picloram plus 2, 4-D (HER) or no treatment (CON) were compared. Serum of sheep that grazed locoweed intermittently (IGZ, 5 d on locoweed followed by 3 d off locoweed) vs. counterparts that grazed locoweed continuously for 24 d (CGZ) was also examined. Alkaloid toxicity was inferred by serum levels of thyroxine (T4), triiodothyronine (T3), alkaline phosphatase (ALKP), aspartate aminotransferase (AST), and swainsonine, as well as behavior and body weight gains. Three sites were used in a randomized complete block design. IGZ, CGZ, and HER treatments reduced locoweed density (P < 0.01), canopy cover (P < 0.01), number of flower stalks (IGZ: P = 0.02, CGZ and HER: P = 0.01), and plant size (P < 0.01). White locoweed seed density in the soil seed bank was not reduced with grazing, and nontarget vegetation was mostly unaffected by treatments. Grass canopy cover increased in grazed and herbicide plots throughout the study (IGZ: P = 0.03, CGZ and HER: P < 0.01). Percentage bare ground was unchanged (IGZ: P = 0.46, CGZ: P = 0.44) in grazed plots but decreased (P = 0.03) in HER plots. After 24 d, ewes in the IGZ treatment had lower levels of serum ALKP (P < 0.01) and AST (P = 0.02) and marginally lower swainsonine levels (P < 0.07) than CGZ ewes that tended to exhibit lower serum T3 (P < 0.07) and similar serum T4 (P = 0.25) levels. Time spent feeding on locoweed tended to differ (P = 0.06) between treatments. Body weight gain was the same (P = 0.19) regardless of treatment. IGZ of locoweed-infested rangeland with sheep may be a viable short-term means of reducing locoweed density without detrimentally affecting animal health.

Vegetative and reproductive phenology of african rue (Peganum harmala) in the northern Chihuahuan desert.

Abstract African rue (Peganum harmala) is an herbaceous perennial plant native to arid and semiarid regions of northern Africa and Asian deserts that has spread to parts of the southwestern United States and northern Mexico. Despite its occurrence in many geographic regions, little is known about the biology and ecology of this invasive species. We conducted field studies on 2 populations of African rue in the northern Chihuahuan Desert to describe its vegetative and reproductive phenology. Overwintering, dormant plants in both populations commenced growth in mid March, grew through May and June, and initially senesced during June and July. Shoot development was synchronous between the 2 populations, but was not related to ambient or soil temperatures or precipitation. Onset of senescence was not related to calendar date or accumulated temperature. Flower production commenced at both sites in mid April, and fruit maturation occurred in June and July. Fruit maturation was related to calendar date and ambient temperature. In one population, senescent plants initiated new shoots in August and produced a second cohort of flowers. This renewed growth was not related to temperature, but likely triggered by midsummer precipitation. Therefore, African rue exhibits characteristic “drought evader” growth and reproduction strategies. This fundamental description of African rue phenology provides knowledge needed to manage this invasive species.