Invasive annual grasses, such as medusahead, can reduce forage production capacity and interfere with revegetation projects in California rangelands. Because of the taxonomic similarity to other more desirable grasses, achieving selective control of invasive annual grasses can be difficult. In selectivity trials conducted in Yolo and Siskiyou counties, CA, the herbicide imazapic gave control of many nonnative annual grasses yet provided some level of selectivity to specific perennial grasses used in revegetation projects throughout the western United States. The selectivity difference between newly seeded perennial and annual grasses was greater with PRE applications than with POST treatments. Both perennial and annual grasses within the tribe Hordeae were more tolerant to imazapic than other grass species. In addition, field experiments were conducted at three sites in northern California (Yuba, Yolo, and Lassen counties) and one in southern Oregon (Lake County) to test the response of imazapic to varying management conditions. Imazapic was applied PRE in fall (and also spring in Lake County) at rates from 35 to 210 g/ha on undisturbed rangeland, in comparison with rangeland cleared of standing plant material and thatch by either tillage, mowing and raking, or burning. Imazapic generally showed enhanced weed control when applied following disturbance. Rates as low as 70 g/ha, if combined with thatch removal, provided significant suppression of medusahead. In addition, disturbance alone generally reduced medusahead cover in the following year. Although imazapic showed potential for control of medusahead and other annual grasses, its selectivity window was relatively narrow.

No abstract

Native trout species, such as the redband trout (Oncorhynchus mykiss), occupy thermally harsh stream habitats in hot, arid rangeland basins of the western United States. Declines in the distribution and abundance of these species has generated interest in understanding how these cold water species survive in these systems, as well as in identifying opportunities to restore these species to their former ranges. The purpose of this study was to assess the potential for thermal stratification to provide thermal refuge for redband trout in stream pools characterized by warm intermittent flow conditions on arid rangelands. We studied vertical thermal stratification in two pools during three summers on Boles Creek located on the Modoc Plateau in extreme northeastern California. Water and air temperature data were collected on a 0.5 h time step from 15-Jun through 15-Sep during 1996, 1997, and 2000 using commercial temperature data-loggers. Water temperature was measured at the top (0.3 m below pool surface) and bottom (0.3 m above pool substrates) of each pool. Vertical thermal stratification occurred within these pools creating conditions as much as 7.6 C cooler and consistently more constant at the bottom of pools compared to pool surface waters. Thermal stratification was dependent upon air temperature with the magnitude of stratification increasing as air temperature increased. The magnitude of thermal stratification varied significantly from year to year, likely reflecting variation in annual weather conditions. The thermal regime in the study pools was often near the upper lethal limit reported for redband trout, but temperatures at the bottom of these pools did offer refuge from lethal temperatures realized near the pool surface. Temperatures at pool bottom were consistently above optimal levels published for redbands.

Western juniper has been actively invading sagebrush plant communities for about 130 yr. Western juniper canopy cover generally increases as western juniper invades sagebrush steppe communities and succession progresses toward a western juniper woodland. Our goal was to estimate the impact of juniper invasion and canopy increase on understory vegetation structure and productivity on 101 sites in northeastern California. The primary objectives of this study were to: (1) examine the influence of increasing western juniper canopy cover on the composition and productivity of understory vegetation; and (2) assess the effects of western juniper removal on understory vegetation. Sites in early, mid-, and late successional stages and sites on the same soils that had not been invaded were selected. Sites where western juniper had been removed by prescribed fire, mechanical, or chemical methods were compared to adjacent untreated sites. Western juniper canopy cover, understory cover and species composition, productivity, and bare ground were determined at each site during May through July 2005 and 2006. Regression analysis was used to evaluate the relationship between western juniper canopy cover and understory vegetation parameters. Logistic regression was used to detect understory differences between treated (juniper removed) and untreated (juniper not removed) sites. A significant relationship was found between western juniper canopy cover and understory species richness, shrub cover, forb cover, total grass cover, cheatgrass cover, herbaceous productivity, and bare ground. Removal of western juniper increased total grass cover, cheatgrass cover, and productivity, and reduced bare ground. The results of this study support findings by researchers in other states that western juniper influences plant community structure and productivity, and removal of western juniper might reverse these changes in structure, but also might increase opportunities for invasion of cheatgrass.

Aspen (Populus tremuloides Michx.) is a disturbance-dependent, fire-resilient, shade-intolerant, clonal species that is in decline throughout western North America. The objective of this study was to examine the effects of intensity and season of browsing on annual height growth of aspen suckers. The goal was to aid development of livestock grazing strategies to restore stands in decline due to excessive livestock browsing. We implemented 33 combinations of intensity and season of browse on aspen suckers in three aspen stands on Eagle Lake Range District, Lassen National Forest, California, USA, during 2003 and 2004. Greatest growth was on suckers with no terminal leader browse and # 25% of biomass removed from branches. Lowest growth occurred when 90% of terminal leader length and 50% of branch biomass was removed. Growth was most negatively affected by browse on terminal leader. Growth was lowest for suckers browsed midseason only and suckers browsed both early and midseason. Occurrence of conifer in the stand overstory significantly reduced sucker growth. Managers should minimize browse on terminal leaders, midseason browse over consecutive years, and repeated browse during a growing season. Resumen Alamo (Populus tremuloides Michx.) es una planta que depende del disturbio, es resistente al fuego, e intolerante a la sombra; clones de estas especies están desapareciendo a trave´s de toda la parte oeste de Norte América. El objetivo de este estudio fue examinar los efectos de intensidad y temporada de ramoneo sobre el aumento anual de la altura de retoñ os de los álamos durante la época de crecimiento. El objetivo fue desarrollar estrategias de pastoreo para restaurar las poblaciones en disminución debido al excesivo ramoneo. Se realizaron 33 combinaciones de intensidad y época de ramoneo sobre los retoñ os de los álamos en tres poblaciones de álamos en Eagle Lake Range District, Lassen National Forest, CA, USA, durante los añ os 2003 y 2004. El mayor crecimiento se obtuvo en retoñ os en que no se ramoneó la hoja terminal y se removió # 25% de la biomasa de las ramas. El menor crecimiento se presentó cuando el 90% de la longitud de la hoja terminal y el 50% de la biomasa de las ramas fue removido. El crecimiento fue negativamente afectado por el ramoneo en hojas terminales. El crecimiento de los retoñ os se afectó mas ligeramente cuando fueron ramoneadas sólo a la mitad de la temporada de crecimiento y los retoñ os ramoneados en al principio y a la mitad de la temporada. La ocurrencia de coníferas en la población en la parte superior redujo significativamente el crecimiento de los retoñ os. Los manejadores deben minimizar el ramoneo en hojas terminales, el ramoneo en la mitad de la temporada en añ os posteriores, y repetir el ramoneo durante una temporada de crecimiento.

No abstract

Riparian meadows occupy a small proportion of the public lands in the western United States but they provide numerous ecosystem services, including the production of high-quality forage for livestock grazing. Modern conservation management strategies (e.g., reductions in livestock stocking rates and adoption of new riparian grazing standards) have been implemented to better balance riparian conservation and livestock production objectives on publicly managed lands. We examined potential relationships between long-term changes in plant community, livestock grazing pressure and environmental conditions at two spatial scales in meadows grazed under conservation management strategies. Changes in plant community were not associated with either livestock stocking rate or precipitation at the grazing allotment (i.e., administrative) scale. Alternatively, both grazing pressure and precipitation had significant, albeit modest, associations with changes in plant community at the meadow (i.e., ecological site) scale. These results suggest that reductions in stocking rate have improved the balance between riparian conservation and livestock production goals. However, associations between elevation, site wetness, precipitation, and changes in plant community suggest that changing climate conditions (e.g., reduced snowpack and changes in timing of snowmelt) could trigger shifts in plant communities, potentially impacting both conservation and agricultural services (e.g., livestock and forage production). Therefore, adaptive, site-specific management strategies are required to meet grazing pressure limits and safeguard ecosystem services within individual meadows, especially under more variable climate conditions.

Feed planning enables ranchers to use feed resources efficiently and increase profits. Feed budgeting requires estimates of expected daily growth rate (DGR) of pasture. The purpose of this study was to estimate DGR and determine if weather variables and herbage mass could be used to predict DGR for an irrigated pasture dominated by tall fescue (Festucu arundinucea Schreb.) and strawberry clover (Trifolium fragiferum L.). A single‐probe capacitance meter was used to estimate herbage mass over 2 yr. Daily growth rate was calculated during the rest periods on 16 rotationally‐grazed paddocks. Maximum and minimum daily air and soil temperature, and solar irradiance were recorded by a California Irrigation Management Information System (CIMIS) weather station located within the pasture. Average daily weather values and the herbage mass at the beginning of the rest period were independent variables in regression with DGR. Solar irradiance was the variable most closely correlated with growth rate, and when combined with beginning herbage mass in multiple regression, predicted DGR with R2 = 0.71 (Sy.x = 9.7) in year 1 and R2 = 0.68 (Sy.x = 5.5) in year 2. Maximum air temperature with beginning herbage mass predicted DGR with R2 = 0.67 (Sy.x × = 10.4) for year 1 and R2 = 0.67 (Sy.x =5.6) for year 2. All weather variables were highly correlated with each other and had similar effects on growth rate. Daily growth rate increased with increasing beginning herbage mass up to 2500 lb dry matter (DM)/acre. While the climatic variables in this study were not strong predictors of DGR, they may be useful for adjusting long term DGR averages to actual weather conditions. Research Question Pasture feed budgeting, as practiced in New Zealand, requires an estimate of expected daily growth rate (DGR) of pasture for each month. This study estimated monthly DGR and the influence of solar irradiance, air temperature, soil temperature, and the amount of herbage per unit area of pasture (herbage mass) on DGR for an irrigated pasture in California's Sacramento Valley. Literature Summary Regional estimates of DGR are readily available to pasture managers in New Zealand but not in California. Daily growth rates will vary as solar irradiance and air temperature change. Herbage mass also influences DGR. Daily growth rates are often greatest within a herbage mass range of 1000 to 2500 lb DM/acre. Below that range leaf area is inadequate to capture solar irradiance efficiently and above that range shading and aging leaf tissue reduces photosynthetic capacity. Study Description Herbage mass was estimated during the rest periods on a rotationally grazed, irrigated pasture. Herbage mass was estimated weekly from May to September, biweekly from mid‐February to April and October to mid‐November, and monthly from mid‐November to mid‐February. Daily growth rate was determined from the change in herbage mass divided by the number of days. Solar irradiance, air temperature, and soil temperature were obtained from a weather station located on the irrigated pa...