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Leaf area index (LAI) is defined as the one-sided area of leaves above a unit area of ground. It is a fundamental ecosystem parameter that is a required input of process-based plant growth and biogeochemical models. Direct measurement of LAI is the most accurate method, but is destructive, time-consuming, and labor-intensive. LAI is highly variable in time and space on sagebrush-steppe rangelands, and a rapid, nondestructive method is desirable to understand ecosystem processes. The pointintercept method is nondestructive and has been demonstrated to provide accurate LAI estimates, but the method is timeconsuming. LAI measurement with the Accupar ceptometer (Decagon Devices, Pullman, WA) is nondestructive and faster than the point-intercept method, but has not been evaluated on sagebrush-steppe rangelands. The objective of this study was to evaluate the ceptometer for measurement of LAI in sagebrush-steppe rangelands. Ceptometer and point-intercept LAI data were collected at six sites in sagebrush-steppe rangelands and the values were compared. We found that 1) ceptometer LAI data were consistently greater than point-intercept LAI data, 2) ceptometer data were much more variable than the point-intercept data based on standard deviations, and 3) the overall correlation between the two methods was very weak (r 2 5 0.15). The much greater ceptometer LAI values were, at least partly, due to the large woody component of the vegetative cover. We attribute the high variability of ceptometer-measured LAI to high instrument sensitivity of the angle of the instrument relative to the sun. Resumen El índice de área foliar (IAF) se define como el área de hoja verde (un solo lado) por unidad de área de suelo. Este es un parámetro fundamental en los ecosistemas que requiere un proceso basado en el crecimiento de la planta y modelos bio-geoquímicos. Mediciones directas de IAF es el método más preciso pero es destructivo, consume tiempo y mucho trabajo. IAF es muy variable en tiempo y espacio en los pastizales de matorrales de estepa, por lo que se requiere un método no destructivo para entender el proceso del ecosistema. El método del punto de intercepción es no destructivo y ha demostrado en proveer estimaciones de IAF precisas. El Accuper ceptometor (Decagon Devices, Pullman, WA) es un método no destructivo que es más rápido que el punto de intercepción pero no ha sido evaluado en pastizales de estepa con artemisa. El objetivo de este estudio fue evaluar el ceptometro para medir el IAF en pastizales de estepa con artemisa. Se recolectaron datos de IAF del ceptometro y del punto intercepto en seis sitios de pastizal de estepa de artemisa y los valores fueron comparados. Encontramos que 1) los datos de IAF del ceptometro fueron más consistentes que los del punto intercepto, 2) los datos del ceptometro fueron mucho más variables que los del punto intercepto y 3) la correlación general entre los dos métodos fue muy endeble (r 2 5 0.15). Los valores de IAF mayor con el ceptometro el menos en parte se debió a la gran composición de ...

Plant productivity, forage availability and soil carbon dynamics are all strongly controlled by soil water in semi-arid rangelands. Sagebrush steppe ecosystems are among the most extensive in the western USA. We used the soil ecohydrology model (SEM) to simulate soil water dynamics and estimate plant growth at three different sagebrush steppe sites. SEM is a capacitance parameter model that uses a water balance approach to simulate daily changes in soil water and a modification of the de Wit equation to estimate plant yield. Model-simulated soil water results were evaluated using long-term (27-34 years) measured data. We found that SEM accurately simulated soil water dynamics and total soil water storage at all three sites, with R 2 values greater than 0.8, Nash-Sutcliffe efficiencies near 0.8 and mean absolute errors of about 1.5 cm. Model-estimated yield indices indicated a high degree of interannual variability, with values ranging more than fivefold and no long-term trend in plant production due to water availability. We also found that seasonal yield could be estimated with reasonable accuracy at the outset of the growing season (March 1) for about half of the years simulated due to either relatively high or low pre-growing season precipitation. Published 2015.

While the environmental impacts of livestock production, such as greenhouse gas emissions and water usage, have been studied for a variety of US livestock production systems, the environmental impact of US sheep production is still unknown. A cradle-to-farm gate life cycle assessment (LCA) was conducted according to international standards (ISO 14040/44), analyzing the impacts of CS representing five different meat sheep production systems in California, and focusing on carbon footprint (carbon dioxide equivalents, CO 2 e) and irrigated water usage (metric ton, MT). This study is the first to look specifically at the carbon footprint of the California sheep industry and consider both wool and meat production across the diverse sheep production systems within California. This study also explicitly examined the carbon footprint of hair sheep as compared with wooled sheep production. Data were derived from producer interviews and literature values, and California-specific emission factors were used wherever possible. Flock outputs studied included market lamb meat, breeding stock, 2-d-old lambs, cull adult meat, and wool. Four different methane prediction models were examined, including the current IPCC tier 1 and 2 equations, and an additional sensitivity analysis was conducted to examine the effect of a fixed vs. flexible coefficient of gain (k g) in mature ewes on carbon footprint per ewe. Mass, economic, and protein mass allocation were used to examine the impact of allocation method on carbon footprint and water usage, while sensitivity analyses were used to examine the impact of ewe replacement rate (% of ewe flock per year) and lamb crop (lambs born per ewe bred) on carbon footprint per kilogram market lamb. The carbon footprint of market lamb production ranged from 13.9 to 30.6 kg CO 2 e/kg market lamb production on a mass basis, 10.4 to 18.1 kg CO 2 e/kg market lamb on an economic basis, and 6.6 to 10.1 kg CO 2 e/kg market lamb on a protein mass basis. Enteric methane (CH 4) production was the largest single source of emissions for all CS, averaging 72% of total emissions. Emissions from feed production averaged 22% in total, primarily from manure emissions credited to feed. Whole-ranch water usage ranged from 2.1 to 44.8 MT/kg market lamb, almost entirely from feed production. Overall results were in agreement with those from meat-focused sheep systems in the United Kingdom as well as beef raised under similar conditions in California.

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