Seeding is a key management tool for arid rangeland. In these systems, however, seeded species of... more Seeding is a key management tool for arid rangeland. In these systems, however, seeded species often fail to establish. A recent study in Wyoming big sagebrush steppe suggested that over 90% of seeded native grass individuals die before seedlings emerged. This current study examines the timing and rate of seed germination, seedling emergence, and seedling death related to this demographic bottleneck. We seeded monocultures of two native perennial bunchgrasses, Pseudoroegenaria spicata (Pursh)Á. Löve and Elymus elymoides (Raf.) Swezey, and one introduced bunchgrass, Agropyron desertorum (Fisch. ex Link) Schult., in 2007, 2008, and 2009 and tracked sown seed and seedling fate. Across the study years and species we found that germination was rapid and high, with species obtaining 50% germination by December, less than 2 mo after planting. Emergence of germinated seed did not occur until late February for A. desertorum and March for the two native grasses. In 2007 the majority of emergence and death was constrained to several weeks, whereas in 2008 and 2009 emergence and death was distributed across several months. The timing of seedling emergence did not influence survival probability or midday plant water potential (probability of exceedance , 0.05). Survival probabilities once seedlings emerged were greater for native species (0.71) than A. desertorum (0.51) in 2 of the 3 study yr (probability of exceedance. 0.98). The early germination of grasses following fall seeding, and the long 2-to 3-mo period that germinated grass seed remain in the soil before emerging, support the hypothesis that seedling recruitment might be limited largely by ecological processes and conditions during winter or early spring (such as soil freeze-thaw events, seed pathogens, or physical crusts). Delaying seeding to early winter or spring and other management tools that mitigate these factors driving this bottleneck might greatly improve restoration outcomes in these systems. Resumen Las resiembras son una herramienta clave de manejo para pastizales á ridos. En estos sistemas, sin embargo, las especies sembradas a menudo no se establecen. En un estudio reciente en un pastizal de Artemisia en Wyoming se sugiere que má s del 90% de los individuos sembrados de pastos nativos mueren antes que la plántula germine. Este estudio examina laépoca y tasa de germinación de las semillas, la aparición de la plá ntula, y la muerte de plá ntula relacionadas con el cuello de botella demográ fico. Se sembraron monocultivos de dos especies nativas de pastos amacollados, Pseudoroegenaria spicata (Pursh)Á. Löve y Elymus elymoides (Raf.) Swezey, y también un pasto amacollado introducido, Agropyron desertorum (Fisch. ex Link) Schult., durante 2007, 2008, y 2009 y se le dio seguimiento a las semillas sembradas así como el destino de las plántulas. A través de los años de estudio y especies se vio que la germinación fue rá pida y alta, con la obtención de la germinación del 50% en diciembre, menos de 2 meses después de la siembra de especies. La aparición de semillas germinadas no ocurrió hasta finales de febrero para A. desertorum y en marzo para las dos especies de pastos nativos. En 2007 la mayoría de aparición y muerte estaba limitada a varias semanas mientras que en 2008 y 2009 el surgimiento y la muerte se distribuyeron a través de varios meses. El tiempo de aparición de las plá ntulas no influyó en la probabilidad de la supervivencia o al potencial de agua de la planta al mediodía o (probabilidad de superación , 0.05). Las probabilidades de supervivencia una vez que surgieron las plá ntulas fueron mayores para las especies nativas (0.71) que A. desertorum (0.51) en dos de los tres años de estudio (probabilidad de superación. 0.98). La germinación temprana de gramíneas después de que cae la semilla y el periodo tardo de dos a tres meses la semilla germinada permanece en el suelo antes de emerger y apoya la hipótesis que el reclutamiento de plá ntulas puede estar altamente limitado por el proceso ecológico y las condiciones durante el invierno o el inicio de la primavera tales (como la descongelación del suelo, los patógenos de la semilla, o las costras físicas). Retrasando la siembra a principios del invierno o primavera y usando otras herramientas de manejo que mitiguen los factores que impulsan este cuello de botella se puede mejorar considerablemente los resultados de la restauración en estos sistemas
Maintaining self-sustaining populations of desired plants is fundamental to rangeland management,... more Maintaining self-sustaining populations of desired plants is fundamental to rangeland management, and understanding the relationships among plant growth, seed production, and seedling recruitment is critical to these efforts. Our objective was to evaluate how changes in maternal plant soil resource environment influences maternal plant biomass and seed production and seedling fitness in three widespread perennial bunchgrass species (Elymus elymoides [Raf.] Sezey, bottlebrush squirreltail; Festuca idahoensis Elmer, Idaho fescue; and Pseudoroegneria spicata [Pursh] A. Löve, bluebunch wheatgrass). We supplied water and nutrients to adult plants growing in the field and measured their productivity and fecundity. Then, in the laboratory, growth chamber, and field we assessed effects of the maternal water and nutrient additions on offspring performance. Across the three study species, vegetative traits were more plastic than reproductive traits, with resource addition measurably increasing plant growth but not seed production. Germination was high in both the laboratory and field across treatments, although seeds from irrigated maternal plants tended to have higher field germination. Seedling relative growth rate, leaf mass ratio, and relative root elongation rate (RRER) were highly variable, although RRER tended to be higher in seedlings derived from irrigated maternal plants. In the field, seedling survivorship was low across all species, but survivorship doubled in seedlings produced by P. spicata plants that received additional water through the growing season. Overall, our results suggest that biomass production and fecundity responses to nutrients are decoupled in the species and environment tested but maternal effects can have significant, although variable, impacts in some grassland species. As a result, biomass responses to natural and anthropogenic changes in resource availability may not be strong predictors of how altered resource supply may ultimately influence plant community dynamics in aridland systems.
... TONY SVEJCAR AND SCOTT CHRISTIANSEN ... In warm-season grasses, stomatal resistance tends to ... more ... TONY SVEJCAR AND SCOTT CHRISTIANSEN ... In warm-season grasses, stomatal resistance tends to domi-nate the total resistance to CO2 flux (Boyer 1970, Ludlow and Wilson 1971, McPherson and Slayter 1973, Gifford 1974), espe-cially at the higher temperatures that are ...
... Scott Christiansen and Tony Svejcar2 ... Caucasian bluestem (Bothriochloa caucasica (Trin.) C... more ... Scott Christiansen and Tony Svejcar2 ... Caucasian bluestem (Bothriochloa caucasica (Trin.) CE Hubb.), an important grass in the Southern Great Plains, is considered grazing tolerant (Sims and De-wald, 1982; Eck and Sims, 1984); however, detailed measures of the response ...
SUMMARY The objective of this study has been to monitor the effects of altered precipitation patt... more SUMMARY The objective of this study has been to monitor the effects of altered precipitation patterns on plant community dynamics in the sagebrush steppe. Plant community response to altered precipitation patterns were assessed by monitoring plant species cover and ...
Restoration efforts in dryland systems are often limited by a complex range of environmental vari... more Restoration efforts in dryland systems are often limited by a complex range of environmental variables and chronically low establishment of seeded native species. Methods for restoring large tracts of degraded drylands in the western United States and southwestern Australia have not advanced substantially since the early 1900s despite continuous efforts to improve success. Historic agricultural practices used in large‐scale restoration efforts are often unsuccessful. A multidisciplinary approach toward problem resolution is necessary for future advancements in restoration applications and methods. Specifically, agricultural technologies such as seed enhancements should be applied to native restoration approaches. Seed enhancement technologies, such as activated carbon coating and extruded pelleting, are novel in the restoration context. However, their use is increasingly recognized as an opportunity to overcome current limitations to restoration efforts. At this early juncture in the development of seed enhancement technologies within restoration, we reflect on the need to tailor current agricultural technologies in light of the differences between agricultural and restoration contexts and reconceptualize our approach to seed enhancement technologies. In this paper, we provide a guide for the development of seed enhancement technologies in ecological restoration.
An increase in the presence and dominance of cheatgrass and red brome has been evident in more ar... more An increase in the presence and dominance of cheatgrass and red brome has been evident in more arid portions of the western Great Basin (Hunter 1990a, 1990b; Young et al. 1987). Beatley (1966) noted the presence of cheatgrass above 5,100 ft and red brome at 3,600-5,100 ft at the Nevada Test Site in southern Nevada. They were primarily found on disturbed areas and red brome did not appear to be aggressive in the region. Recently the presence of these species has expanded to cover most of the Nevada Test Site (Hunter 1 990a, 1990b). These species are now found in undisturbed communities and red brome is more dominant than in previous surveys. In 1988, introduced annuals were 81% of the ephemeral vegetation on disturbed areas and 61% on pristine areas on the Nevada Test Site. A similar increase has been noted for cheatgrass in the Lahontan Basin (Young and Tipton 1990). Similar changes have apparently occurred on Anaho Island in northwestern Nevada. At 750 acres in size, Anaho is the largest island in Pyramid Lake, and rises to about 540 ft above lake level. Pyramid Lake is the rem
The authors thank Scott Conroy for assistance in site selection, and USDA-Forest Service, Plumas ... more The authors thank Scott Conroy for assistance in site selection, and USDA-Forest Service, Plumas National Forest for use of the site. Drs. Edith Allan. Gregg Riegel, and Joe Trlica provided constructive comments on an earlier version of the manuscript.
BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.
Alkali bulrush (Bolboschoenus maritimus) is an emergent plant in Great Salt Lake (GSL) wetlands a... more Alkali bulrush (Bolboschoenus maritimus) is an emergent plant in Great Salt Lake (GSL) wetlands and is a major food source for migratory birds (Evans and Martinson, 2008). GSL managers are interested in restoring alkali bulrush following the removal of the invasive grass Phragmites australis. However, low moisture availability may hinder alkali bulrush germination and establishment, especially in light of continuing water diversions from GSL tributaries and ongoing climate change.
Mycorrhizal fungi are thought to benefit associated plant species via enhanced nutrient uptake an... more Mycorrhizal fungi are thought to benefit associated plant species via enhanced nutrient uptake and/or improved water relations. However, detailed descriptions of the components of mycorrhizal colonization and mycorrhizal hyphal growth are not available for Artemisia tridentata. This species occupies sites characterized by relatively low levels ofboth soil nutrients and moisture. We studied patterns of vesicular, arbuscular, and hyphal mycorrhizal colonization, mycorrhizal hyphal lengths, and soil moisture associated with two subspecies of A. tridentata over a 2-year period. A. tridentata ssp. vaseyana (ATV) is generally associated with more mesic and slightly higher elevation sites compared to A. tridentata ssp. tridentata (ATI). Nearly twice as much precipitation was received the first year compared to the second. In general, there were higher levels of colonization and hyphal lengths associated with ATV than with ATT. The ATV site received slightly more precipitation and was lower in available nutrients than the ATI site. Hyphal lengths and arbuscular colonization appeared more responsive to precipitation than were either vesicular or hyphal colonization. Hyphal colonization did not necessarily follow the same temporal pattern as hyphal lengths. Thus, mycorrhizal activity was greater for the subspecies that received slightly more precipitation and occupied a site lower in available nutrients. Arbuscular colonization and hyphal lengths appeared to be most closely associated with soil moisture and thus plant activity.
Alfalfa was labeled in the field with 99 atom % 13C02 and cut either the same day (C 1) or 30 d a... more Alfalfa was labeled in the field with 99 atom % 13C02 and cut either the same day (C 1) or 30 d after labeling ((330). The C1 alfalfa contained 84% of the 13C label in cell contents, whereas C30 alfalfa contained 47% of the 13C label in cell contents. In two separate trials, C1 and C30 alfalfa were dosed to two or four Suffolk ewes fed natural abundance alfalfa diets. Carbon isotope ratios (13C/12C, expressed as ~5~~C%o[parts per thousand] vs Pee Dee Belemnite standard) were determined for breath, feces, blood, and blood serum from ewes fed C1 alfalfa and blood and feces from ewes fed C30 alfalfa. In the C1 trial, carbon isotope ratios of respired C02 peaked 4 h after feeding, then declined to baseline levels by 40 h after the dose. Fecal samples increased in 13C only slightly from 12 to 40 h after the meal. Blood serum values increased by approximately .5%o from 0 to 4 h after the dose and remained relatively constant thereafter. In both trials, carbon isotope values from whole blood were constant. In the C30 trial, fecal samples peaked in carbon isotope value approximately 30 to 36 h after dosing, then declined; the time of this peak corresponded closely to that from a concurrent study that used a pulse dose of Yb-labeled alfalfa hay. Thus, when incorporated into cell wall material, the excretion pattern of 13C in feces was similar to that of Yblabeled hay, but little 13C enrichment in feces was found when 13C was primarily in cell contents of the labeled forage. When the soluble cell contents were enriched in 13C, the marker was detected in respired C02 soon after feeding, which is consistent with the results of previous marker studies. These results demonstrate the feasibility of using forage labeled with the stable isotope 13C in nutrition and metabolism studies. Carbon-13, not subject to the regulatory constraints associated with 14C, provides a useful alternative when a carbon tracer is desired.
Late spring burning response of the dominant big bluestem (Andropogon gerradu) was studied on 8 t... more Late spring burning response of the dominant big bluestem (Andropogon gerradu) was studied on 8 tailgrass site in central Okiaboma (USA) during a dry (1984) and a wet (1985) year. During active gowth (May and June) when temperatures were not limiting, photosynthesis (PS) was higher for burned (25-27 cc moles-2 s-1) relative to unburned plants (20-25 pmoles m-2 s-t); but during summer drought, PS declined to <lO cc moles m-2 s-1 and treatment rank reversed. However, the 2 treatments had simiiar transpiration per unit leaf area, and burned plots had much higher peak big bluestem leaf area indices (6.4 in 1984 and 4.5 in 1985) than unburned plots (2.0 both years). Apparently higher transpirationai demand in burned plots lowered soil moisture, thereby increasing late season moisture stress and lowering PS relative to unburned plots. Burning resulted in a doubling of big bluestem tiller numbers (997-1,034 and 49&600 tillers m-2 for burned and unburned plots, respectively). Peak aboveground biomass of big bluestem was about 3 times higher on burned relative to unburned prairie during both years. During both years burned vs. unburned big bluestem had higher peak values of % leaf nitrogen (N) and more total leaf N (%N* leaf mass). Thus, burning big bluestem increased leaf area during the active growth period and stimulated PS, resulting in higher carbon uptake of burned relative to unburned piants.
The conflicts over management of natural resources, especially on public lands, have resulted in ... more The conflicts over management of natural resources, especially on public lands, have resulted in a high level of frustration among many of the interested parties. There are many underlying causes of the conflicts, but I think several major societal trends must be considered. During the past several decades, there has been increased emphasis on participatory democracy, with the public seeking more involvement in decision making and policy formulation. A related trend is the decline in the public image of science and lack of trust in state and federal agencies. Individual members of society desire to be included in decision making, and may not necessarily view scientists as capable of providing the answers to natural resource issues. One response to natural resource conflicts is to form a group of interested individuals from diverse backgrounds to develop solutions. These groups may also work toward policy development. Coalitions or working groups may take many forms. There are two basic types of groups I will mention: 1) those formed to address a specific issue over a set time period, and 2) those formed to foster communication, interaction, and education. Many working groups have been formed over controversies, but effective use of the groups might also keep controversies from arising. In my opinion, scientists should be active participants in natural resource working groups. Participation provides the opportunity to incorporate science in decision-making and may also guide research efforts insuring that the results are of value to a wider cross-section of society.
Cheatgrass (Bromus tectorum L.) dominates large tracts of rangeland in the western United States.... more Cheatgrass (Bromus tectorum L.) dominates large tracts of rangeland in the western United States. Previous research has demonstrated the competitive nature of this species; however, the mechanisms contributing to its dominance have not been well elucidated. It is often suggested that cheatgrass outcompetes perennial seedlings because it germinates and grows at lower soil temperatures. However, even hr studies where temperatures are not limiting, cheatgrass outcompetes perennial seedlhrgs. Therefore, I conducted a study to compare accumulation of root length, leaf area, and biomass of cheatgrass and crested wheatgrass (Agropyron descrtonrn (Fisch. ex Lhtk) Schult. cv. Nordm) seediings under non-limiting conditions. Seedlings were grown in pots in the greenhouse for 60 days post-sowing. There were 4 seedlhtgs per pot, and sampling was conducted weekly at 24-60 days after sowing. Maximum and minimum temperatures were 280 C and 4" C, respectively, and piants were watered twice a week. Cheatgrass had greater root length density and leaf area than created wheatgrnss, especially during the later samplings. For the last 2 samplings, cheatgrass averaged about 12% more root mass and 56% more shoot mass, yet bad more than twice the root length and leaf area of crested wheatgrass. Cheatgrass was more efficient (per unit of biomass) in producing leaf area and root length, which helps explain its ability to quickly become established and exploit soil nutrient and moisture reserves.
Seeding is a key management tool for arid rangeland. In these systems, however, seeded species of... more Seeding is a key management tool for arid rangeland. In these systems, however, seeded species often fail to establish. A recent study in Wyoming big sagebrush steppe suggested that over 90% of seeded native grass individuals die before seedlings emerged. This current study examines the timing and rate of seed germination, seedling emergence, and seedling death related to this demographic bottleneck. We seeded monocultures of two native perennial bunchgrasses, Pseudoroegenaria spicata (Pursh)Á. Löve and Elymus elymoides (Raf.) Swezey, and one introduced bunchgrass, Agropyron desertorum (Fisch. ex Link) Schult., in 2007, 2008, and 2009 and tracked sown seed and seedling fate. Across the study years and species we found that germination was rapid and high, with species obtaining 50% germination by December, less than 2 mo after planting. Emergence of germinated seed did not occur until late February for A. desertorum and March for the two native grasses. In 2007 the majority of emergence and death was constrained to several weeks, whereas in 2008 and 2009 emergence and death was distributed across several months. The timing of seedling emergence did not influence survival probability or midday plant water potential (probability of exceedance , 0.05). Survival probabilities once seedlings emerged were greater for native species (0.71) than A. desertorum (0.51) in 2 of the 3 study yr (probability of exceedance. 0.98). The early germination of grasses following fall seeding, and the long 2-to 3-mo period that germinated grass seed remain in the soil before emerging, support the hypothesis that seedling recruitment might be limited largely by ecological processes and conditions during winter or early spring (such as soil freeze-thaw events, seed pathogens, or physical crusts). Delaying seeding to early winter or spring and other management tools that mitigate these factors driving this bottleneck might greatly improve restoration outcomes in these systems. Resumen Las resiembras son una herramienta clave de manejo para pastizales á ridos. En estos sistemas, sin embargo, las especies sembradas a menudo no se establecen. En un estudio reciente en un pastizal de Artemisia en Wyoming se sugiere que má s del 90% de los individuos sembrados de pastos nativos mueren antes que la plántula germine. Este estudio examina laépoca y tasa de germinación de las semillas, la aparición de la plá ntula, y la muerte de plá ntula relacionadas con el cuello de botella demográ fico. Se sembraron monocultivos de dos especies nativas de pastos amacollados, Pseudoroegenaria spicata (Pursh)Á. Löve y Elymus elymoides (Raf.) Swezey, y también un pasto amacollado introducido, Agropyron desertorum (Fisch. ex Link) Schult., durante 2007, 2008, y 2009 y se le dio seguimiento a las semillas sembradas así como el destino de las plántulas. A través de los años de estudio y especies se vio que la germinación fue rá pida y alta, con la obtención de la germinación del 50% en diciembre, menos de 2 meses después de la siembra de especies. La aparición de semillas germinadas no ocurrió hasta finales de febrero para A. desertorum y en marzo para las dos especies de pastos nativos. En 2007 la mayoría de aparición y muerte estaba limitada a varias semanas mientras que en 2008 y 2009 el surgimiento y la muerte se distribuyeron a través de varios meses. El tiempo de aparición de las plá ntulas no influyó en la probabilidad de la supervivencia o al potencial de agua de la planta al mediodía o (probabilidad de superación , 0.05). Las probabilidades de supervivencia una vez que surgieron las plá ntulas fueron mayores para las especies nativas (0.71) que A. desertorum (0.51) en dos de los tres años de estudio (probabilidad de superación. 0.98). La germinación temprana de gramíneas después de que cae la semilla y el periodo tardo de dos a tres meses la semilla germinada permanece en el suelo antes de emerger y apoya la hipótesis que el reclutamiento de plá ntulas puede estar altamente limitado por el proceso ecológico y las condiciones durante el invierno o el inicio de la primavera tales (como la descongelación del suelo, los patógenos de la semilla, o las costras físicas). Retrasando la siembra a principios del invierno o primavera y usando otras herramientas de manejo que mitiguen los factores que impulsan este cuello de botella se puede mejorar considerablemente los resultados de la restauración en estos sistemas
Maintaining self-sustaining populations of desired plants is fundamental to rangeland management,... more Maintaining self-sustaining populations of desired plants is fundamental to rangeland management, and understanding the relationships among plant growth, seed production, and seedling recruitment is critical to these efforts. Our objective was to evaluate how changes in maternal plant soil resource environment influences maternal plant biomass and seed production and seedling fitness in three widespread perennial bunchgrass species (Elymus elymoides [Raf.] Sezey, bottlebrush squirreltail; Festuca idahoensis Elmer, Idaho fescue; and Pseudoroegneria spicata [Pursh] A. Löve, bluebunch wheatgrass). We supplied water and nutrients to adult plants growing in the field and measured their productivity and fecundity. Then, in the laboratory, growth chamber, and field we assessed effects of the maternal water and nutrient additions on offspring performance. Across the three study species, vegetative traits were more plastic than reproductive traits, with resource addition measurably increasing plant growth but not seed production. Germination was high in both the laboratory and field across treatments, although seeds from irrigated maternal plants tended to have higher field germination. Seedling relative growth rate, leaf mass ratio, and relative root elongation rate (RRER) were highly variable, although RRER tended to be higher in seedlings derived from irrigated maternal plants. In the field, seedling survivorship was low across all species, but survivorship doubled in seedlings produced by P. spicata plants that received additional water through the growing season. Overall, our results suggest that biomass production and fecundity responses to nutrients are decoupled in the species and environment tested but maternal effects can have significant, although variable, impacts in some grassland species. As a result, biomass responses to natural and anthropogenic changes in resource availability may not be strong predictors of how altered resource supply may ultimately influence plant community dynamics in aridland systems.
... TONY SVEJCAR AND SCOTT CHRISTIANSEN ... In warm-season grasses, stomatal resistance tends to ... more ... TONY SVEJCAR AND SCOTT CHRISTIANSEN ... In warm-season grasses, stomatal resistance tends to domi-nate the total resistance to CO2 flux (Boyer 1970, Ludlow and Wilson 1971, McPherson and Slayter 1973, Gifford 1974), espe-cially at the higher temperatures that are ...
... Scott Christiansen and Tony Svejcar2 ... Caucasian bluestem (Bothriochloa caucasica (Trin.) C... more ... Scott Christiansen and Tony Svejcar2 ... Caucasian bluestem (Bothriochloa caucasica (Trin.) CE Hubb.), an important grass in the Southern Great Plains, is considered grazing tolerant (Sims and De-wald, 1982; Eck and Sims, 1984); however, detailed measures of the response ...
SUMMARY The objective of this study has been to monitor the effects of altered precipitation patt... more SUMMARY The objective of this study has been to monitor the effects of altered precipitation patterns on plant community dynamics in the sagebrush steppe. Plant community response to altered precipitation patterns were assessed by monitoring plant species cover and ...
Restoration efforts in dryland systems are often limited by a complex range of environmental vari... more Restoration efforts in dryland systems are often limited by a complex range of environmental variables and chronically low establishment of seeded native species. Methods for restoring large tracts of degraded drylands in the western United States and southwestern Australia have not advanced substantially since the early 1900s despite continuous efforts to improve success. Historic agricultural practices used in large‐scale restoration efforts are often unsuccessful. A multidisciplinary approach toward problem resolution is necessary for future advancements in restoration applications and methods. Specifically, agricultural technologies such as seed enhancements should be applied to native restoration approaches. Seed enhancement technologies, such as activated carbon coating and extruded pelleting, are novel in the restoration context. However, their use is increasingly recognized as an opportunity to overcome current limitations to restoration efforts. At this early juncture in the development of seed enhancement technologies within restoration, we reflect on the need to tailor current agricultural technologies in light of the differences between agricultural and restoration contexts and reconceptualize our approach to seed enhancement technologies. In this paper, we provide a guide for the development of seed enhancement technologies in ecological restoration.
An increase in the presence and dominance of cheatgrass and red brome has been evident in more ar... more An increase in the presence and dominance of cheatgrass and red brome has been evident in more arid portions of the western Great Basin (Hunter 1990a, 1990b; Young et al. 1987). Beatley (1966) noted the presence of cheatgrass above 5,100 ft and red brome at 3,600-5,100 ft at the Nevada Test Site in southern Nevada. They were primarily found on disturbed areas and red brome did not appear to be aggressive in the region. Recently the presence of these species has expanded to cover most of the Nevada Test Site (Hunter 1 990a, 1990b). These species are now found in undisturbed communities and red brome is more dominant than in previous surveys. In 1988, introduced annuals were 81% of the ephemeral vegetation on disturbed areas and 61% on pristine areas on the Nevada Test Site. A similar increase has been noted for cheatgrass in the Lahontan Basin (Young and Tipton 1990). Similar changes have apparently occurred on Anaho Island in northwestern Nevada. At 750 acres in size, Anaho is the largest island in Pyramid Lake, and rises to about 540 ft above lake level. Pyramid Lake is the rem
The authors thank Scott Conroy for assistance in site selection, and USDA-Forest Service, Plumas ... more The authors thank Scott Conroy for assistance in site selection, and USDA-Forest Service, Plumas National Forest for use of the site. Drs. Edith Allan. Gregg Riegel, and Joe Trlica provided constructive comments on an earlier version of the manuscript.
BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.
Alkali bulrush (Bolboschoenus maritimus) is an emergent plant in Great Salt Lake (GSL) wetlands a... more Alkali bulrush (Bolboschoenus maritimus) is an emergent plant in Great Salt Lake (GSL) wetlands and is a major food source for migratory birds (Evans and Martinson, 2008). GSL managers are interested in restoring alkali bulrush following the removal of the invasive grass Phragmites australis. However, low moisture availability may hinder alkali bulrush germination and establishment, especially in light of continuing water diversions from GSL tributaries and ongoing climate change.
Mycorrhizal fungi are thought to benefit associated plant species via enhanced nutrient uptake an... more Mycorrhizal fungi are thought to benefit associated plant species via enhanced nutrient uptake and/or improved water relations. However, detailed descriptions of the components of mycorrhizal colonization and mycorrhizal hyphal growth are not available for Artemisia tridentata. This species occupies sites characterized by relatively low levels ofboth soil nutrients and moisture. We studied patterns of vesicular, arbuscular, and hyphal mycorrhizal colonization, mycorrhizal hyphal lengths, and soil moisture associated with two subspecies of A. tridentata over a 2-year period. A. tridentata ssp. vaseyana (ATV) is generally associated with more mesic and slightly higher elevation sites compared to A. tridentata ssp. tridentata (ATI). Nearly twice as much precipitation was received the first year compared to the second. In general, there were higher levels of colonization and hyphal lengths associated with ATV than with ATT. The ATV site received slightly more precipitation and was lower in available nutrients than the ATI site. Hyphal lengths and arbuscular colonization appeared more responsive to precipitation than were either vesicular or hyphal colonization. Hyphal colonization did not necessarily follow the same temporal pattern as hyphal lengths. Thus, mycorrhizal activity was greater for the subspecies that received slightly more precipitation and occupied a site lower in available nutrients. Arbuscular colonization and hyphal lengths appeared to be most closely associated with soil moisture and thus plant activity.
Alfalfa was labeled in the field with 99 atom % 13C02 and cut either the same day (C 1) or 30 d a... more Alfalfa was labeled in the field with 99 atom % 13C02 and cut either the same day (C 1) or 30 d after labeling ((330). The C1 alfalfa contained 84% of the 13C label in cell contents, whereas C30 alfalfa contained 47% of the 13C label in cell contents. In two separate trials, C1 and C30 alfalfa were dosed to two or four Suffolk ewes fed natural abundance alfalfa diets. Carbon isotope ratios (13C/12C, expressed as ~5~~C%o[parts per thousand] vs Pee Dee Belemnite standard) were determined for breath, feces, blood, and blood serum from ewes fed C1 alfalfa and blood and feces from ewes fed C30 alfalfa. In the C1 trial, carbon isotope ratios of respired C02 peaked 4 h after feeding, then declined to baseline levels by 40 h after the dose. Fecal samples increased in 13C only slightly from 12 to 40 h after the meal. Blood serum values increased by approximately .5%o from 0 to 4 h after the dose and remained relatively constant thereafter. In both trials, carbon isotope values from whole blood were constant. In the C30 trial, fecal samples peaked in carbon isotope value approximately 30 to 36 h after dosing, then declined; the time of this peak corresponded closely to that from a concurrent study that used a pulse dose of Yb-labeled alfalfa hay. Thus, when incorporated into cell wall material, the excretion pattern of 13C in feces was similar to that of Yblabeled hay, but little 13C enrichment in feces was found when 13C was primarily in cell contents of the labeled forage. When the soluble cell contents were enriched in 13C, the marker was detected in respired C02 soon after feeding, which is consistent with the results of previous marker studies. These results demonstrate the feasibility of using forage labeled with the stable isotope 13C in nutrition and metabolism studies. Carbon-13, not subject to the regulatory constraints associated with 14C, provides a useful alternative when a carbon tracer is desired.
Late spring burning response of the dominant big bluestem (Andropogon gerradu) was studied on 8 t... more Late spring burning response of the dominant big bluestem (Andropogon gerradu) was studied on 8 tailgrass site in central Okiaboma (USA) during a dry (1984) and a wet (1985) year. During active gowth (May and June) when temperatures were not limiting, photosynthesis (PS) was higher for burned (25-27 cc moles-2 s-1) relative to unburned plants (20-25 pmoles m-2 s-t); but during summer drought, PS declined to <lO cc moles m-2 s-1 and treatment rank reversed. However, the 2 treatments had simiiar transpiration per unit leaf area, and burned plots had much higher peak big bluestem leaf area indices (6.4 in 1984 and 4.5 in 1985) than unburned plots (2.0 both years). Apparently higher transpirationai demand in burned plots lowered soil moisture, thereby increasing late season moisture stress and lowering PS relative to unburned plots. Burning resulted in a doubling of big bluestem tiller numbers (997-1,034 and 49&600 tillers m-2 for burned and unburned plots, respectively). Peak aboveground biomass of big bluestem was about 3 times higher on burned relative to unburned prairie during both years. During both years burned vs. unburned big bluestem had higher peak values of % leaf nitrogen (N) and more total leaf N (%N* leaf mass). Thus, burning big bluestem increased leaf area during the active growth period and stimulated PS, resulting in higher carbon uptake of burned relative to unburned piants.
The conflicts over management of natural resources, especially on public lands, have resulted in ... more The conflicts over management of natural resources, especially on public lands, have resulted in a high level of frustration among many of the interested parties. There are many underlying causes of the conflicts, but I think several major societal trends must be considered. During the past several decades, there has been increased emphasis on participatory democracy, with the public seeking more involvement in decision making and policy formulation. A related trend is the decline in the public image of science and lack of trust in state and federal agencies. Individual members of society desire to be included in decision making, and may not necessarily view scientists as capable of providing the answers to natural resource issues. One response to natural resource conflicts is to form a group of interested individuals from diverse backgrounds to develop solutions. These groups may also work toward policy development. Coalitions or working groups may take many forms. There are two basic types of groups I will mention: 1) those formed to address a specific issue over a set time period, and 2) those formed to foster communication, interaction, and education. Many working groups have been formed over controversies, but effective use of the groups might also keep controversies from arising. In my opinion, scientists should be active participants in natural resource working groups. Participation provides the opportunity to incorporate science in decision-making and may also guide research efforts insuring that the results are of value to a wider cross-section of society.
Cheatgrass (Bromus tectorum L.) dominates large tracts of rangeland in the western United States.... more Cheatgrass (Bromus tectorum L.) dominates large tracts of rangeland in the western United States. Previous research has demonstrated the competitive nature of this species; however, the mechanisms contributing to its dominance have not been well elucidated. It is often suggested that cheatgrass outcompetes perennial seedlings because it germinates and grows at lower soil temperatures. However, even hr studies where temperatures are not limiting, cheatgrass outcompetes perennial seedlhrgs. Therefore, I conducted a study to compare accumulation of root length, leaf area, and biomass of cheatgrass and crested wheatgrass (Agropyron descrtonrn (Fisch. ex Lhtk) Schult. cv. Nordm) seediings under non-limiting conditions. Seedlings were grown in pots in the greenhouse for 60 days post-sowing. There were 4 seedlhtgs per pot, and sampling was conducted weekly at 24-60 days after sowing. Maximum and minimum temperatures were 280 C and 4" C, respectively, and piants were watered twice a week. Cheatgrass had greater root length density and leaf area than created wheatgrnss, especially during the later samplings. For the last 2 samplings, cheatgrass averaged about 12% more root mass and 56% more shoot mass, yet bad more than twice the root length and leaf area of crested wheatgrass. Cheatgrass was more efficient (per unit of biomass) in producing leaf area and root length, which helps explain its ability to quickly become established and exploit soil nutrient and moisture reserves.
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